WO1996013914A2 - Systeme et procedes de transmission sectorisee - Google Patents

Systeme et procedes de transmission sectorisee Download PDF

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Publication number
WO1996013914A2
WO1996013914A2 PCT/US1995/013457 US9513457W WO9613914A2 WO 1996013914 A2 WO1996013914 A2 WO 1996013914A2 US 9513457 W US9513457 W US 9513457W WO 9613914 A2 WO9613914 A2 WO 9613914A2
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WO
WIPO (PCT)
Prior art keywords
signal
station
received
operative
message
Prior art date
Application number
PCT/US1995/013457
Other languages
English (en)
Other versions
WO1996013914A3 (fr
Inventor
Mordechai Ritz
Giora Silbershatz
Samuel Miller
Valentin Lupu
Ran Gozali
Amit Priebatch
Yoav Yaacoby
Julian Dinur
Josef Melamed
David Levy
Yitzhak Meidan
Original Assignee
Power Spectrum Technology Ltd.
Geotek Communications, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from IL11134094A external-priority patent/IL111340A/en
Priority claimed from IL11442595A external-priority patent/IL114425A0/xx
Priority claimed from IL11442995A external-priority patent/IL114429A0/xx
Priority claimed from IL11442295A external-priority patent/IL114422A0/xx
Priority claimed from IL11442495A external-priority patent/IL114424A0/xx
Priority claimed from IL11442895A external-priority patent/IL114428A0/xx
Priority claimed from IL11442695A external-priority patent/IL114426A0/xx
Priority claimed from IL11442795A external-priority patent/IL114427A0/xx
Priority claimed from IL11442095A external-priority patent/IL114420A0/xx
Priority claimed from IL11442195A external-priority patent/IL114421A0/xx
Priority claimed from IL11442395A external-priority patent/IL114423A0/xx
Priority claimed from IL11441995A external-priority patent/IL114419A0/xx
Priority claimed from IL11547595A external-priority patent/IL115475A0/xx
Application filed by Power Spectrum Technology Ltd., Geotek Communications, Inc. filed Critical Power Spectrum Technology Ltd.
Priority to AU40042/95A priority Critical patent/AU4004295A/en
Priority to EP95938799A priority patent/EP0787386A2/fr
Publication of WO1996013914A2 publication Critical patent/WO1996013914A2/fr
Publication of WO1996013914A3 publication Critical patent/WO1996013914A3/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W36/00—Hand-off or reselection arrangements
    • H04W36/06—Reselecting a communication resource in the serving access point
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03G—CONTROL OF AMPLIFICATION
    • H03G3/00—Gain control in amplifiers or frequency changers without distortion of the input signal
    • H03G3/20—Automatic control
    • H03G3/30—Automatic control in amplifiers having semiconductor devices
    • H03G3/3036—Automatic control in amplifiers having semiconductor devices in high-frequency amplifiers or in frequency-changers
    • H03G3/3042—Automatic control in amplifiers having semiconductor devices in high-frequency amplifiers or in frequency-changers in modulators, frequency-changers, transmitters or power amplifiers
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03G—CONTROL OF AMPLIFICATION
    • H03G3/00—Gain control in amplifiers or frequency changers without distortion of the input signal
    • H03G3/20—Automatic control
    • H03G3/30—Automatic control in amplifiers having semiconductor devices
    • H03G3/3036—Automatic control in amplifiers having semiconductor devices in high-frequency amplifiers or in frequency-changers
    • H03G3/3042—Automatic control in amplifiers having semiconductor devices in high-frequency amplifiers or in frequency-changers in modulators, frequency-changers, transmitters or power amplifiers
    • H03G3/3047—Automatic control in amplifiers having semiconductor devices in high-frequency amplifiers or in frequency-changers in modulators, frequency-changers, transmitters or power amplifiers for intermittent signals, e.g. burst signals
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
    • H03M13/00—Coding, decoding or code conversion, for error detection or error correction; Coding theory basic assumptions; Coding bounds; Error probability evaluation methods; Channel models; Simulation or testing of codes
    • H03M13/27—Coding, decoding or code conversion, for error detection or error correction; Coding theory basic assumptions; Coding bounds; Error probability evaluation methods; Channel models; Simulation or testing of codes using interleaving techniques
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
    • H03M13/00—Coding, decoding or code conversion, for error detection or error correction; Coding theory basic assumptions; Coding bounds; Error probability evaluation methods; Channel models; Simulation or testing of codes
    • H03M13/29—Coding, decoding or code conversion, for error detection or error correction; Coding theory basic assumptions; Coding bounds; Error probability evaluation methods; Channel models; Simulation or testing of codes combining two or more codes or code structures, e.g. product codes, generalised product codes, concatenated codes, inner and outer codes
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
    • H04L1/0056—Systems characterized by the type of code used
    • H04L1/0057—Block codes
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
    • H04L1/0056—Systems characterized by the type of code used
    • H04L1/0059—Convolutional codes
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
    • H04L1/0056—Systems characterized by the type of code used
    • H04L1/0064—Concatenated codes
    • H04L1/0065—Serial concatenated codes
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
    • H04L1/0056—Systems characterized by the type of code used
    • H04L1/0067—Rate matching
    • H04L1/0068—Rate matching by puncturing
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
    • H04L1/0056—Systems characterized by the type of code used
    • H04L1/0071—Use of interleaving
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/02—Arrangements for detecting or preventing errors in the information received by diversity reception
    • H04L1/06—Arrangements for detecting or preventing errors in the information received by diversity reception using space diversity
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/08—Arrangements for detecting or preventing errors in the information received by repeating transmission, e.g. Verdan system
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
    • H04W52/04—TPC
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L2001/0098—Unequal error protection
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W16/00—Network planning, e.g. coverage or traffic planning tools; Network deployment, e.g. resource partitioning or cells structures
    • H04W16/24—Cell structures
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W36/00—Hand-off or reselection arrangements
    • H04W36/16—Performing reselection for specific purposes
    • H04W36/18—Performing reselection for specific purposes for allowing seamless reselection, e.g. soft reselection
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W56/00—Synchronisation arrangements

Definitions

  • the present invention relates to apparatus and method for providing voice and data communications. More specifically, it relates to apparatus and method for providing a frequency hopping multiple access communication system.
  • Multiple access communications systems are capable of providing multiple communications at the same time using the same system resources. These systems utilize various communications protocol and various system architectures.
  • One protocol is time division multiple access wherein users communicate on a shared channel at different times.
  • Another protocol is frequency division multiple access wherein separate frequency channels are allocated to mobile radio terminals.
  • the system architecture commonly utilized is a cellular type architecture wherein there are many base stations that provide communication channels to many radio terminals.
  • the existing multiple access communication systems all have various drawbacks. By way of example only, many rely on a hardware intensive architecture that is costly to implement and also costly to operate. These high costs result in a higher cost to customers.
  • the existing multiple access communication systems also have severe limitations on system capacity or, stated differently, require a great deal of spectrum to efficiently operate.
  • the existing multiple access communication systems also have limitations on the quality and the types of the communications services provided, particularly when the system is fully loaded.
  • TDMA time division multiple access
  • FDMA frequency division multiple access
  • FHMA frequency hopping multiple access
  • a system architecture which is typically used is a cellular type architecture in which a plurality of base stations provide communication channels to many radio terminals.
  • Each base station defines a cell and a radio terminal in a cell is capable of communicating with radio terminals in other cells or with radio terminals in the same cell, or with subscriber units in public services telephone networks (PSTN).
  • PSTN public services telephone networks
  • a radio terminal associated with a subscriber unit, receives RF signals and processes them to provide the information required.
  • the terminal When a signal is received at a radio terminal, the terminal has to acquire initial parameters of a control channel which enable it to find the precise frequency and the accurate timing of the control channel.
  • Such procedures have to be performed on initialization only, and then other continuous algorithms are performed to maintain timing and frequency accuracies.
  • FHMA frequency hopping multiple access
  • a timing and frequency synchronization has to be maintained at the base stations and at the subscriber units. Failure to maintain such synchronization may create collisions and misallotment of time slots and frequency slots which affect the quality of cellular communication.
  • the received signal level changes in time for various reasons.
  • Various automatic gain control methods which provide automatic gain control to the receiver amplifiers in order to maintain a constant signal level, are well known in the art.
  • time at which a signal is received the signal changes in time for various reasons, mostly the motion of mobile units. It is desirable in systems where time slots are assigned to particular transmissions to adjust the timing of transmissions so that transmissions fall within their assigned time slots.
  • a base station 11050 serves three sectors 11060, 11070, and 11080.
  • a frequency channel in a wireless communication channel is subject to many sources of degradation. Thus, communication signals will not always be communicated properly on a frequency channel.
  • channel estimators are known in the art, none adequately performs the tasks of determining the state of a frequency hopping channel. Another shortcoming of existing communication systems is found in the usage of channel state information.
  • apparatus and method for determining the state of a frequency channel are needed. Further, apparatus and method for using the channel state information to control the operation of the communication system to achieve improved communication are also needed.
  • Trunked radio services known in the art include the following: Special Mobile Radio (SMR) used in the United States; Public Mobile Radio (PMR) and Public Access Mobile Radio (PAMR) used in Europe and TETRA, described in ETSI standard ETS 300 396 / TETRA Direct Mode.
  • SMR Special Mobile Radio
  • PMR Public Mobile Radio
  • PAMR Public Access Mobile Radio
  • the present invention generally relates to method and apparatus for providing multiple access communications.
  • method and apparatus for handing off communications between a communicating party and a mobile communication radio which is moving from a first sector to an adjacent sector in a communication base station having multiple sectors is provided.
  • a mobile radio detects synchronization information from the first sector and searches for synchronization information from sectors adjacent to the first sector.
  • the mobile radio determines when the synchronization information from the adjacent sector has stronger -reception then the synchronization information from the first sector and then requests a hand off from the base station.
  • the base station enables a three way communication link between the mobile radio in the first sector, the radio in the adjacent sector and the communicating party.
  • voice activity from the base station to the mobile radio is monitored and downlink communications from the base station to the mobile radio are handed off from the first sector to the adjacent sector when voice inactivity is detected. Also, voice activity from the mobile radio to the base station is monitored and uplink communications from the mobile radio to the base station are handed off from the first sector to the adjacent sector when voice inactivity is detected.
  • Another object is to provide apparatus and method for handling subscriber units attempting to communicate in fringe areas.
  • Yet another object is to provide apparatus and method for providing service to subscriber units located at the foot of the base station.
  • Yet a further object is to provide apparatus and method of measuring the quality of service provided by a frequency hopping communication system.
  • Another object of the present invention is to provide method and apparatus for handing off communications between sectors.
  • Another object is to provide apparatus and method for automatic gain control.
  • Another object is to provide apparatus and method for determining and using channel state information.
  • the present invention also seeks to provide a system and methods for acquiring a precise initial frequency and initial timing cf a control channel received at a subscriber unit in a frequency hopping multiple access communication system.
  • the present invention also seeks to provide methods for maintaining synchronization between a timing system in a subscriber unit and a timing system in a base station in a Frequency Hopping Multiple Access communication system (FHMA).
  • FHMA Frequency Hopping Multiple Access communication system
  • the present invention also seeks to provide a Frequency Hopping Multiple Access communication (FHMA) system having, at each subscriber unit, automatic frequency control for measuring and correcting frequency inaccuracies due to inaccuracies in frequency sources and Doppler shift effects at the subscriber units in order to improve detection of information transmitted via the communication systems.
  • FHMA Frequency Hopping Multiple Access communication
  • the present invention also seeks to provide an improved automatic gain control system for use in a slotted radio communication system.
  • the present invention also seeks to provide an improved system for hand-off between sectors and a method for substantially seamless transfer of a mobile subscriber unit between sectors.
  • the present invention also seeks to provide an improved power control system for use in radio communication systems.
  • the present invention also seeks to provide time alignment in a radio communication system.
  • the present invention also seeks to provide an improved method and apparatus for processing received messages in order to reduce repeat transmissions of messages.
  • the present invention also seeks to provide methods for preventing collisions and for coordinating channels between subscriber units in a Frequency Hopping Multiple Access (FHMA) communication system.
  • FHMA Frequency Hopping Multiple Access
  • the present invention also seeks to provide a method for two subscriber units in an FHMA radio system to communicate directly with one another without use of a base station.
  • the present invention seeks to provide improved communication in a vicinity of a base station of a sectorized radio communication system.
  • a frequency offset estimating modem operative to generate an estimated frequency offset value for a signal received by the modem
  • a local oscillator operative to receive the estimated frequency offset value and to generate a frequency converter control signal which is operative to cancel the estimated frequency offset.
  • the system includes a frequency converter operative to receive the frequency converter control signal.
  • the frequency offset estimating modem includes:
  • apparatus for receiving a signal with modulation and for canceling the modulation of the signal, thereby to generate a carrier wave
  • an FFT fast Fourier transform
  • a processor for computing a frequency offset by finding a frequency value which maximizes the final spectrum function.
  • the FFT computing module preferably includes: a converter for converting the waveform of the carrier wave from a time domain to a frequency domain, portion by portion for a plurality of portions of the waveform, thereby to generate a plurality of intermediate spectrum functions; and
  • spectrum function combining unit operative to combine the intermediate spectrum functions to generate the final spectrum function.
  • the spectrum function combining unit includes a summing unit for summing the spectrum function values for each of a multiplicity of frequencies.
  • the carrier wave may include a distorted carrier wave.
  • the detecting includes:
  • the correlating includes:
  • timing information includes an indication of a time at which the optimal correlation appears.
  • the correlating may include:
  • timing information includes an indication of a time at which a predetermined one from among the M optimal correlations appears.
  • the received signal includes a synchronization code period and the synchronization code is embedded in the synchronization code period.
  • the received signal includes a super frame, wherein a plurality of synchronization code periods are embedded in the super frame and at least one synchronization code is embedded within each of the plurality of synchronization code periods.
  • a synchronization code label is associated with each synchronization code, and timing information associated with the super frame is generated and is at least in part based on the plurality of the synchronization code labels.
  • the method includes accumulating a plurality of sequential smooth response signals smaller than a time increment at the number controlled delay generator.
  • the method includes applying the controlled delay correction signal to modify the subscriber synchronization signal by a time increment substantially equal to 3 microseconds.
  • the method includes accumulating a plurality of sequential smooth response signals smaller than a time increment at the number controlled delay generator.
  • the method includes applying the controlled delay correction signal to modify the base station synchronization signal by a time increment substantially equal to 6 microseconds.
  • a delay locked loop method for controlling a local timing system of a receiver by tracking the local timing system of an IF signal generated by the receiver, the method including:
  • step of generating a control signal includes:
  • t1 is a time preceding the estimated time at which the synchronization code embedded in the output signal of the RF/IF converter is maximally correlated with the ideal waveform and t2 is a time following the estimated time;
  • the step of computing and defining includes filtering the difference between the correlations.
  • the method includes one of extracting and inserting at least one clock period to a counter in the timing system according to the control signal.
  • the local timing system may be a timing system at a base station.
  • each subscriber unit includes:
  • a frequency control unit operative to determine and to reduce inaccuracies in each separate frequency of a hopping signal received from at least one base station, to acceptable values.
  • each subscriber unit in the system also includes: two separate antennas for separately receiving signals to achieve space diversity; and
  • each receiver is operable to determine a quality of reception of a corresponding received signal
  • the frequency control unit is selectably operable on one of the corresponding received signal having the best quality reception.
  • the filtering includes:
  • a second closed loop including a limiter for integration and feedback of the preliminary filtered signal between a limited numerical range to provide a smoothed frequency offset signal.
  • the limited numerical range is the numerical range between 0 and 1.
  • a method for controlling a local frequency source of a receiver which supplies a signal of a given frequency to an RF/IF converter in response to a control signal supplied to the local frequency source, the method being operative to maintain a fixed output frequency of the RF/IF converter, the method including:
  • step of generating comprises:
  • the step of generating a control signal includes filtering the control signal.
  • the step of generating a control signal includes compensating for nonlinearity of operation of the local frequency source.
  • a subscriber unit in a frequency hopping multiple access communication system including: at least one antenna for accepting over-the-air RF signals;
  • At least one receiver coupled to the at least one antenna, and operative to receive the RF signals and to provide an IF output of the signals;
  • a local frequency source coupled to the receiver, and operative to provide a signal of a given frequency to the receiver in response to an input signal
  • a memory for storing an ideal waveform of a synchronization code signal
  • a processor coupled to the local frequency source, to the at least one receiver and to the memory, and operative to determine a frequency offset between a synchronization signal embedded in the RF signals and the given frequency of the local frequency source;
  • a frequency control unit operative to maintain a fixed output frequency of the receiver by employing the frequency offset to generate a control signal which controls the local frequency source.
  • an automatic gain control apparatus for use in a receiver of a slotted radio communication system, the apparatus including a sample processor receiving a plurality of samples each indicating a sampled power level of an input signal and operative to produce a processed input power signal indicating a power level of the input signal, and error determining apparatus receiving the processed input power signal and operative to produce a power error signal.
  • the apparatus includes control apparatus receiving the power error signal and producing a gain control signal, and a variable-gain amplifier operative to control gain of the input signal based, at least in part, on the gain control signal.
  • the plurality of samples includes a plurality of samples of a current time slot.
  • the current time slot includes a plurality of symbols and each of the plurality of samples is associated with one of the plurality of symbols.
  • variable-gain amplifier is operative to control gain of the input signal of a time slot succeeding the current time slot.
  • the sample processor includes averaging apparatus operative to compute an average of the plurality of samples.
  • the sample processor includes absolute value computation apparatus operative to compute an average of absolute values of the plurality of samples.
  • the error determining apparatus includes logarithmic scaling apparatus operative to compute a logarithmic function of the processed input power signal.
  • the error determining apparatus includes filtering apparatus.
  • the filtering apparatus includes a lead-lag filter.
  • an automatic gain control method for use in a receiver of a slotted TDMA communication system, the method including receiving a plurality of samples each indicating a sampled power level of an input signal and producing a processed input power signal indicating a power level of the input signal, and receiving the processed input power signal and producing a power error signal.
  • the method includes receiving the power error signal and producing a gain control signal, and controlling the gain of the input signal based, at least in part, on the gain control signal.
  • the plurality of samples includes a plurality of samples of a current time slot.
  • the current time slot includes a plurality of symbols and each of the plurality of samples is associated with one of the plurality of symbols.
  • controlling includes controlling the gain of the input signal of a time slot succeeding the current time slot.
  • receiving a plurality of samples and producing a processed input power signal includes computing an average of the plurality of samples.
  • receiving a plurality of samples and producing a processed input power signal includes computing an average of absolute values of the plurality of samples.
  • receiving the processed input power signal and producing a power error signal includes computing a logarithmic function of the processed input power signal.
  • receiving the processed input power signal and producing a power error signal includes filtering.
  • filtering includes filtering via a lead-lag filtering method.
  • a method for controlling the amplification of a receiver amplifier disposed upstream of a receiver modem, thereby to maintain a fixed modem input amplitude for a wide range of receiver input levels including providing a current demodulator input amplitude value which is related to the amplitude of the current modem input, converting the current demodulator input amplitude value into a logarithmic-like unit, subtracting a desired logarithmic unit level from the converted current modem input amplitude value, thereby to provide a logarithmic- like unit difference value, and providing a control signal to the amplifier based on the logarithmic-like unit difference value.
  • the step of providing a control signal includes filtering the logarithmic-like unit difference value.
  • the step of providing a control signal includes compensating for nonlinearity of operation of the amplifier.
  • an automatic gain control method for use in a receiver of a slotted radio communication system, the method including receiving a plurality of samples each indicating a sampled power level of an input signal and producing a processed input power signal indicating a power level of the input signal, and receiving the processed input power signal and producing a power error signal.
  • an automatic gain control apparatus for use in a receiver of a time slotted TDMA communication system, the apparatus including a sample receiver operative to receive a plurality of samples each indicating a sampled power level of an input signal and operative to produce a processed input power signal indicating a power level of the input signal, and an input power signal receiver operative to receive the processed input power signal and produce a power error signal.
  • apparatus for controlling the amplification of a receiver amplifier disposed upstream of a receiver modem, thereby maintaining a fixed modem input amplitude for a wide range of receiver input levels
  • the apparatus including input value provider operative to provide a current demodulator input amplitude value which is related to the amplitude of the current modem input, an input value converter operative to convert the current demodulator input amplitude value into a logarithmic-like unit, a subtracter operative to subtract a desired logarithmic unit level from the converted current demodulator input amplitude value, thereby providing a logarithmic-like unit difference value, and a control-signal provider operative to provide a control signal to the amplifier based on the logarithmic-like unit difference value.
  • a method for seamlessly transferring a mobile subscriber unit, having an uplink and a downlink, from a first sector served by a first sector radio having a first antenna to a second sector served by a second sector radio having a second antenna including monitoring a mobile subscriber unit in order to detect when the mobile subscriber unit passes from the first sector to the second sector, and switching the uplink and the downlink of the mobile subscriber unit from the first antenna to the second antenna, turning off the uplink and the downlink of the first sector radio and turning on the uplink and the downlink of the second sector radio, all within a time period which is short enough to cause substantially seamless communication.
  • a method for seamlessly transferring a mobile subscriber unit, having an uplink and a downlink, from a first sector served by a first sector radio having a first antenna to a second sector served by a second sector radio having a second antenna including monitoring a mobile subscriber unit in order to detect when the mobile subscriber unit passes from the first sector to the second sector, switching the uplink of the mobile subscriber unit from the first antenna to the second antenna, turning off the uplink of the first sector radio and turning on the uplink of the second sector radio, all while the mobile subscriber unit is not transmitting, and switching the downlink of the mobile subscriber unit from the first antenna to the second antenna, turning off the downlink of the first sector radio and turning on the downlink of the second sector radio while the first sector radio is not transmitting.
  • the method also includes adapting at least one sector radio-subscriber unit control process to the second sector radio.
  • the at least one control process includes time aligning.
  • the at least one control process includes power control.
  • the at least one control process includes AGC (automatic gain control) of the mobile subscriber unit.
  • the at least one control process includes sector radio AGC.
  • the at least one control process includes DLL (delay lock looping) of the mobile subscriber unit.
  • the at least one control process includes sector radio DLL.
  • the at least one control process includes automatic frequency control (AFC) of the mobile subscriber unit.
  • AFC automatic frequency control
  • the switching step includes setting up a 3-way conference between the first and second sector radios and the mobile subscriber unit.
  • apparatus operative to seamlessly transfer a mobile subscriber unit, having an uplink and a downlink, from a first sector served by a first sector radio having a first antenna to a second sector served by a second sector radio having a second antenna
  • the apparatus including a mobile subscriber unit monitor operative to monitor a mobile subscriber unit in order to detect when the mobile subscriber unit passes from the first sector to the second sector, and a link switch operative to switch the uplink and the downlink of the mobile subscriber unit from the first antenna to the second antenna, to turn off the uplink and the downlink of the first sector radio and to turn on the uplink and the downlink of the second sector radio, all within a time period which is short enough to cause substantially seamless communication.
  • apparatus operative to seamlessly transfer a mobile subscriber unit, having an uplink and a downlink, from a first sector served by a first sector radio having a first antenna to a second sector served by a second sector radio having a second antenna
  • the apparatus including a mobile subscriber unit monitor operative to monitor a mobile subscriber unit in order to detect when the mobile subscriber unit passes from the first sector to the second sector, a link switch operative to switch the uplink of the mobile subscriber unit from the first antenna to the second antenna, to turn off the uplink of the first sector radio and to turn on the uplink of the second sector radio, all while the mobile subscriber unit is not transmitting, and a second link switch operative to switch the downlink of the mobile subscriber unit from the first antenna to the second antenna, to turn off the downlink of the first sector radio and to turn on the downlink of the second sector radio while the first sector radio is not transmitting.
  • a power control method for use in a radio communication system including a first station and a second station, the method including choosing an initial transmitted power level for the first station, and performing the following steps iteratively transmitting a first message from the first station to the second station, receiving the first message at the second station, detecting a received power level for the first message at the second station, comparing the received power level to a predetermined value, transmitting a second message from the second station to the first station, the second message including an indication of a difference between the received power level and the predetermined value, receiving the second message at the first station, and modifying the transmitted power level for the first station based, at least in part, on the second message.
  • the initial transmitted power level is a maximum power level.
  • the comparing includes smoothing a signal representing the received power level.
  • the smoothing is based, at least in part, on a value of the indication of difference from at least one previous iteration of the comparing.
  • the modifying includes storing the indication of the difference from the second message, and choosing an increment for modifying the transmitted power level based, at least in part, on the indication of the difference from the second message and based, at least in part, on a stored indication of the difference from a previous iteration.
  • the modifying includes choosing an increment for modifying the transmitted power level based, at least in part, on a stored threshold.
  • choosing an increment is also based, at least in part, on a stored threshold.
  • the stored threshold is between approximately 5dB and approximately 10db.
  • the first station includes a subscriber unit and the second station includes a base station.
  • a power control method for use in a radio communication system including a first station and a second station, the method including determining a desired received power level at the first station, transmitting a signal from the first station to the second station, the signal including an indication of a nominal transmitted power level for the first station, receiving the signal at the second station, detecting a received power level of the signal at the second station, comparing the received power level to the nominal transmitted power level and computing the transmission loss, and determining the transmitted power level of the second station based, at least in part, on the desired received power level at the first station and based, at least in part, on the transmission loss.
  • the signal from the first station to the second station includes a control channel signal, and the control channel signal includes the indication of the nominal transmitted power level.
  • the comparing and computing includes computing the difference between the received power level and the nominal transmitted power level.
  • the determining includes computing the sum of the desired received power level at the first station and the transmission loss.
  • the method includes determining the received power level at the first station, comparing the received power level at the first station to a predetermined value and outputting a signal representing the difference between the received power level at the first station and the predetermined value, transmitting a second signal from the first station to the second station, the second signal including an indication of the difference between the received power level at the first station and the predetermined value, receiving the second signal at the second station, and modifying the transmitted power level for the second station based, at least in part, on the second signal.
  • the first station includes a base station and the second station includes a subscriber unit.
  • the detecting includes computing a signal to noise ratio.
  • the detecting includes computing a bit energy to noise density ratio.
  • the detecting includes computing a carrier to interference ratio.
  • the radio communication system includes a multiple access system.
  • the radio communication system includes a frequency hopping system.
  • apparatus for use in a radio communication system including a first station and a second station, the apparatus including a first station transmitter having an initial transmitted power level for the first station and operative to transmit a first message from the first station to the second station, a second station receiver operative to receive the first message at the second station, a power level detector operative to detect a received power level for the first message at the second station, a power level comparator operative to compare the received power level to a predetermined value, a second station transmitter operative to transmit a second message from the second station to the first station, the second message including an indication of a difference between the received power level and the predetermined value, a first station receiver operative to receive the second message at the first station, and a power level controller operative to modify the transmitted power level for the first station based, at least in part, on the second message.
  • power control apparatus for use in a radio communication system including a first station and a second station, the first station having a desired received power level
  • the apparatus including a first station transmitter operative to transmit a signal from the first station to the second station, the signal including an indication of a nominal transmitted power level for the first station, a second station receiver operative to receive the signal at the second station, a power level detector operative to measure a received power level of the signal at the second station, a power level comparator operative to compare the received power level to the nominal transmitted power level and to compute the transmission loss, and a power level controller operative to determine the transmitted power level for the second station based, at least in part, on the desired received power level at the first station and based, at least in part, on the transmission loss.
  • apparatus includes a multiple access system.
  • the radio communication system includes a frequency hopping system.
  • a method for controlling the transmission power of a local transmitter according to link conditions including determining link conditions by monitoring at least one characteristic of a local receiver associated with the local transmitter, and computing a level of transmission power based on the link conditions.
  • the determining by monitoring step also includes monitoring the transmission power of a remote transmitter which is transmitting to the local receiver and monitoring the noise floor level of a remote receiver which is receiving from the local transmitter and determining link conditions based on the local receiver characteristic, the remote transmitter transmission power, and the remote receiver noise floor level.
  • a method for controlling the transmission power of a local transmitter according to link conditions including determining link conditions based on an indication of a characteristic of a remote receiver which is receiving from the local transmitter, which indication is received from the remote transmitter associated with the remote receiver, and computing a level of transmission power based on the link conditions.
  • the step of link condition determining also includes monitoring a characteristic of a local receiver associated with the local transmitter, initially generating an evaluation of link conditions on the basis of the local receiver characteristic, and improving the evaluation of link conditions upon receipt of the indication of remote receiver indication.
  • the step of computing also includes comparing the initially generated link conditions evaluation to the improved link conditions evaluation and taking into account the result of the comparing step when subsequently performing the initial generating step.
  • the method include storing the result of the comparing step, thereby to take into account the result of the comparing step when performing more than one subsequent initial generating steps.
  • the receiver characteristic includes reception power. Further in accordance with a preferred embodiment of the present invention the receiver characteristic includes the receiver's SNR (signal to noise ratio).
  • the receiver characteristic includes the receiver's SIR (signal interference ratio).
  • the receiver characteristic includes the receiver's voice frame error rate.
  • power control apparatus for use in a radio communication system including a first station and a second station, the apparatus including an initial power level chooser operative to choose an initial transmitted power level for the first station, and an iteration controller operative to control the iterative performance of the following apparatus a first message transmitter operative to transmit a first message from the first station to the second station, a first message receiver operative to receive the first message at the second station, a received power level detector operative to detect a received power level for the first message at the second station, a received power level comparator operative to compare the received power level to a predetermined value, a second message transmitter operative to transmit a second message from the second station to the first station, the second message including an indication of a difference between the received power level and the predetermined value, a second message receiver operative to receive the second message at the first station, and a transmitted power level modifier operative to modify the transmitted power level for the first station based, at least in part, on the second message
  • power control apparatus for use in a radio communication system including a first station and a second station, the apparatus including a desired power level determinator operative to determine a desired received power level at the first station, a signal transmitter operative to transmit a signal from the first station to the second station, the signal including an indication of a nominal transmitted power level for the first station, a signal receiver operative to receive the signal at the second station, a received power level detector operative to detect a received power level of the signal at the second station, a received power level comparator operative to compare the received power level to the nominal transmitted power level and to compute the transmission loss, and a transmitted power level determinator operative to determine the transmitted power level of the second station based, at least in part, on the desired received power level at the first station and based, at least in part, on the transmission loss.
  • a power control method for use in a radio communication system including a first station and a second station, the method including transmitting an initial transmitted power level message from the first station to the second station, receiving the first message at the second station, detecting a received power level for the first message at the second station, comparing the received power level to a predetermined value, transmitting a second message from the second station to the first station, the second message including an indication of a difference between the received power level and the predetermined value, receiving the second message at the first station, and modifying the transmitted power level for the first station based, at least in part, on the second message.
  • a power control method for use in a radio communication system including a first station and a second station, the first station having a desired received power level, the method including transmitting a signal from the first station to the second station, the signal including an indication of a nominal transmitted power level for the first station, receiving the signal at the second station, detecting operative to measure a received power level of the signal at the second station, comparing the received power level to the nominal transmitted power level and to compute the transmission loss, and determining the transmitted power level for the second station based, at least in part, on the desired received power level at the first station and based, at least in part, on the transmission loss.
  • apparatus for controlling the transmission power of a local transmitter according to link conditions, the apparatus including a link condition determinator operative to determine link conditions by monitoring at least one characteristic of a local receiver associated with the local transmitter, and a transmission power level computer operative to compute a level of transmission power based on the link conditions.
  • apparatus for controlling the transmission power of a local transmitter according to link conditions, the apparatus including a link condition determinator operative to determine link conditions based on an indication of a characteristic of a remote receiver which is receiving from the local transmitter, which indication is received from the remote transmitter associated with the remote receiver, and a transmission power level computer operative to compute a level of transmission power based on the link conditions.
  • a method for time alignment of messages in a radio communication system having a first station and a second station, the method including determining a time alignment error of a message sent by the first station and received by the second station, sending a time alignment adjustment message from the second station to the first station, the time alignment adjustment message including a signal indicating the time alignment error of the message sent by the first station, and adjusting the timing of subsequent messages sent by the first station to the second station based, at least in part, on the time alignment adjustment message.
  • determining includes comparing the time alignment error to a minimum error, and the sending and adjusting are performed only if the time alignment error is greater in magnitude than the minimum error.
  • the message sent by the first station includes a station identification
  • determining includes comparing the station identification to a stored station identification of the first station, and sending and adjusting are performed only if the station identification matches the stored station identification.
  • the message sent by the first station includes a message type identification
  • the time alignment adjustment message includes the message type identification
  • adjusting is performed only if the message type identification matches a stored message type identification corresponding to a previous message sent by the first station.
  • adjusting includes incrementally adjusting the timing of the subsequent messages based, at least in part, on a maximum adjustment for each of the subsequent messages.
  • the subsequent messages include messages each having a message type and wherein the maximum adjustment for each one of the subsequent messages is based, at least in part, on the message type of the each one of the subsequent messages.
  • the method also includes determining the distance between the first station and the second station based, at least in part, on the time alignment error.
  • the method includes storing time alignment errors of each of a plurality of messages, and determining the distance between the first station and the second station based, at least in part, on the stored time alignment errors.
  • apparatus for time alignment of messages in a radio communication system having a first station and a second station
  • the apparatus including a time alignment determiner operative to determine a time alignment error of a message sent by the first station and received by the second station, a message transmitter operative to send a time alignment adjustment message from the second station to the first station, the time alignment adjustment message including a signal indicating the time alignment error of the message sent by the first station, and a time alignment adjuster operative to adjust the timing of subsequent messages sent by the first station to the second station based, at least in part, on the time alignment adjustment message.
  • the time alignment determiner includes a time alignment comparator operative to compare the time alignment error to a minimum error, and the message transmitter sends the time alignment adjustment message and the time alignment adjustor adjusts the timing only if the time alignment error is greater in magnitude than the minimum error.
  • the message sent by the first station includes a station identification
  • the time alignment determiner includes a station identification comparator operative to compare the station identification to a stored station identification of the first station, and the message transmitter sends the time alignment adjustment message and the time alignment adjustor adjusts the timing only if the station identification matches the stored station identification.
  • the message sent by the first station includes a message type identification
  • the time alignment adjustment message includes the message type identification
  • the time alignment adjustor adjusts the timing only if the message type identification matches a stored message type identification corresponding to a previous message sent by the first station.
  • the alignment adjustor is operative to adjust the timing of the subsequent messages incrementally based, at least in part, on a maximum adjustment for each of the subsequent messages.
  • the subsequent messages include messages each having a message type and the maximum adjustment for each one of the subsequent messages is based, at least in part, on the message type of the each one of the subsequent messages.
  • a range determiner operative to determine the distance between the first station and the second station based, at least in part, on the time alignment error.
  • the apparatus also includes a time alignment memory operative to store time alignment errors of each of a plurality of messages, and a range determiner operative to determine the distance between the first station and the second station based, at least in part, on the stored time alignment errors.
  • apparatus for time alignment of uplink transmissions including a plurality of time aligning subscriber units, and a time alignment determining base station operative to determine the time at which each uplink transmission arrives at the base station from a corresponding subscriber unit, to compute the timing error of each uplink transmission by comparing the time of arrival thereof to a desired time of arrival, and to transmit each timing error to the corresponding subscriber unit, wherein each time aligning subscriber unit is operative to align its timing in order to reduce its timing error.
  • a method for time alignment of uplink transmissions arriving from a plurality of subscriber units including determining the time at which each uplink transmission arrives at a base station, computing the timing error of each uplink transmission by comparing the time of arrival thereof to a desired time of arrival, transmitting each timing error to the subscriber unit corresponding thereto, and at each subscriber unit, aligning timing of a subsequent uplink transmission in order to reduce its timing error.
  • the timing alignment step includes performing a plurality of partial timing aligning substeps so as to gradually reduce the timing error.
  • a method for processing received messages in order to reduce repeat transmissions of messages including transmitting a message including a plurality of sub-messages, requesting retransmission of at least one incorrectly received sub-message, and if at least one previously incorrectly received sub-message is correctly received by retransmission, replacing at least one previously incorrectly received sub-message with its corresponding correctly received sub-message.
  • the transmitting step includes transmitting via a frequency hopping multiple access (FHMA) communication system.
  • FHMA frequency hopping multiple access
  • the method also includes repeating the retransmission requesting step and the if-replacing step until all sub-messages have been correctly received.
  • the method also includes marking each incorrectly received sub-message.
  • the method also includes the step of, prior to transmitting a sub- message, providing error detection code for the sub- message individually, and wherein the error detection code is decoded upon receipt of the sub-message to determine whether or not the sub-message is received correctly.
  • the retransmission requesting step includes requesting retransmission of the entire message if at least one sub-message is received incorrectly.
  • the step of requesting retransmission includes sending an acknowledgement when retransmission is no longer necessary, thereby to cause retransmission in the absence of an acknowledgement.
  • the method also includes comparing at least first and second correct transmissions of the same sub-message when the sub- message is received correctly more than once.
  • the method if the first and second correct transmissions are different, also includes treating the more than once correctly received sub-message as an incorrectly received sub-message until a predetermined stopping criterion is reached.
  • the predetermined stopping criterion includes receipt of a plurality of correct and identical transmissions of the sub-message.
  • the predetermined stopping criterion includes receipt of a majority of correct and identical transmissions of the sub-message.
  • the method also includes performing a validity check of the message, and if the validity check fails, repeating the validity check on at least one combination of correct transmissions of the sub-messages contained in the message.
  • the if-validity check repeating step includes repeating the validity check on all combinations until one of the combinations yields a successful validity check and requesting retransmission of at least a portion of the message if none of the combinations yields a successful validity check.
  • apparatus operative to process received messages in order to reduce repeat transmissions of messages, the apparatus including a message transmitter operative to transmit a message including a plurality of sub-messages, a retransmission requester operative to request retransmission of at least one incorrectly received sub-message, and a message replacer, operative to, if at least one previously incorrectly received sub-message is correctly received by retransmission, replace at least one previously incorrectly received sub-message with its corresponding correctly received sub-message.
  • a multiplicity of base stations communicate with a multiplicity of subscriber units over a frequency hopping multiple access communication network at a plurality of radio frequencies, the method including:
  • the method also includes:
  • inactive slot to replace the non-transmitted slot, by including in the inactive slot a plurality of inactive symbols having imparted a confidence level zero in at least one of a random sequence and an ordered sequence.
  • the predetermined sequence may be transmitted to each subscriber unit over a control channel.
  • the method includes applying a minimum weight to the inactive symbols during processing of the slots.
  • a transmitter within a first sector is to transmit to a first subscriber within the first sector, the method including:
  • the determining step includes:
  • the determining step includes:
  • the determining step may also include determining whether to transmit with a probability p ⁇ 1 or whether not to transmit.
  • time-slots assigning time-slots to each of a plurality of subsectors within the first sector and to each of a plurality of subsectors within the neighboring sector, each sector including central and peripheral subsectors such that the same time-slot is assigned to a peripheral subsector in the first sector and to a central subsector in the neighboring sector;
  • the method includes allocating an air resource to the transmitters within the first sector so as to reduce the maximum probability, over the transmitters within the first sector, of existence of a problematic subscriber.
  • the air resource may include one of TDMA (time division multiple access) time slots, FDMA (frequency division multiple access) channels frequencies and FHMA (frequency hopping multiple access) time/frequency sequences.
  • each time slot includes an active time slot.
  • the method includes, prior to the determining step, the step of transmitting with a probability 1 if the first subscriber is inside the fringe area.
  • a communication method wherein a first subscriber within a first sector is to transmit to a base station including:
  • the determining step includes:
  • the determining step may also include: for each of a plurality of positions of a sliding time window including n>1 time slots, determining whether or not the number of time slots within the sliding window, as currently positioned, in which transmission did not take place exceeds a threshold number of time slots; and
  • the determining step includes determining whether to transmit with a probability p ⁇ 1 or whether not to transmit.
  • a communications system including apparatus for generating a full-duplex FHMA (frequency hopping multiple access) communication channel between two subscribers, and apparatus for generating a half-duplex FHMA communication channel between two subscribers who are proximate to one another.
  • FHMA frequency hopping multiple access
  • the communications system includes apparatus for determining, for a given pair of subscribers, whether to generate full-duplex or half-duplex communication and for assigning the given pair of subscribers to the full-duplex channel generating apparatus or to the half-duplex channel generating apparatus, accordingly.
  • the apparatus for determining is operative at least partly on a basis of a criterion of the extent of proximity between the given pair of subscribers.
  • the criterion of the extent of proximity includes a criterion of signal quality.
  • the apparatus for determining is operative to assign a given pair of subscribers to the full-duplex channel generating apparatus whenever sufficient air resources are available.
  • the apparatus for determining is operative to store information associating each subscriber with one of a plurality of talk-groups and at least one pair of subscribers associated with the same talk-group are assigned to the half-duplex channel generating apparatus. Still further in accordance with a preferred embodiment of the present invention, the apparatus for full-duplex channel generating and the apparatus for half-duplex channel generating are located within a base station.
  • a method for generating a half-duplex FHMA communication channel between two subscribers who are proximate to one another within a communications system including transmitting a channel request from a first subscriber to a second subscriber, determining a first measure of signal quality of the channel request received at the second subscriber, sending a request acknowledgement from the second subscriber to the first subscriber, determining a second measure of signal quality of the request acknowledgement received by the first subscriber, and generating a half-duplex FHMA communication channel between the first subscriber and the second subscriber only if both the first measure of signal quality and the second measure of signal quality meet a predetermined criterion.
  • the generating step includes reversing use of an uplink channel and a downlink channel in exactly one subscriber from among the first and second subscribers.
  • the generating step includes using exactly one of an uplink channel and a downlink channel for both transmission and reception in both of the first and second subscribers.
  • a communications system including apparatus for generating a mediated FHMA (frequency hopping multiple access) communication channel between two subscribers, and apparatus for generating a direct FHMA communication channel between two subscribers who are proximate to one another.
  • mediated FHMA frequency hopping multiple access
  • the communications system includes apparatus for determining, for a given pair of subscribers, whether to generate mediated or direct communication and for assigning the given pair of subscribers to the mediated channel generating apparatus or to the direct channel generating apparatus, accordingly.
  • the apparatus for determining is operative at least partly on a basis of a criterion of the extent of proximity between the given pair of subscribers.
  • the criterion of the extent of proximity includes a criterion of signal quality.
  • the apparatus for determining is operative to assign a given pair of subscribers to the mediated channel generating apparatus whenever sufficient air resources are available.
  • the apparatus for determining is operative to store information associating each subscriber with one of a plurality of talk-groups and at least one pair of subscribers associated with the same talk-group are assigned to the direct channel generating apparatus.
  • the apparatus for mediated channel generating and the apparatus for direct channel generating are located within a base station.
  • the direct FHMA communication channel includes a full-duplex communication channel.
  • the direct FHMA communication channel includes a half-duplex communication channel.
  • a method for generating a direct FHMA communication channel between two subscribers who are proximate to one another within a communications system including transmitting a channel request from a first subscriber to a second subscriber, determining a first measure of signal quality of the channel request received by the second subscriber, sending a request acknowledgement from the second subscriber to the first subscriber, determining a second measure of signal quality of the request acknowledgement received at the first subscriber, and generating a direct FHMA communication channel between the first subscriber and the second subscriber only if both the first measure of signal quality and the second measure of signal quality meet a predetermined criterion.
  • the generating step includes choosing one of the first subscriber unit and the second subscriber unit, and reversing use of an uplink channel and a downlink channel in the chosen subscriber unit.
  • the generating step includes using exactly one of an uplink channel and a downlink channel for both transmission and reception in both of the first and second subscribers.
  • the direct FHMA communication channel includes a full-duplex communication channel.
  • the direct FHMA communication channel includes a half-duplex communication channel.
  • a communications method including generating a full-duplex FHMA (frequency hopping multiple access) communication channel between two subscribers in a communications system and generating a half-duplex FHMA communication channel between two subscribers who are proximate to one another in a communications system.
  • FHMA frequency hopping multiple access
  • apparatus for generating a half-duplex FHMA communication channel between two subscribers who are proximate to one another within a communications system, and including a channel requester operative to transmit a channel request from a first subscriber to a second subscriber, signal quality determining apparatus operative to determine a first measure of signal quality of the channel request received at the second subscriber, a request acknowledger operative to send a request acknowledgement from the second subscriber to the first subscriber, second signal quality determining apparatus operative to determine a second measure of signal quality of the request acknowledgement received by the first subscriber, and a half-duplex FHMA generator operative to generate a half- duplex FHMA communication channel between the first subscriber and the second subscriber only if both the first measure of signal quality and the second measure of signal quality meet a predetermined criterion.
  • a communications method including generating a mediated FHMA (frequency hopping multiple access) communication channel and a direct FHMA communication channel between two subscribers who are proximate to one another.
  • mediated FHMA frequency hopping multiple access
  • apparatus operative to generate a direct FHMA communication channel between two subscribers who are proximate to one another within a communications system, including a channel requester operative to transmit a channel request from a first subscriber to a second subscriber, signal quality determining apparatus operative to determine a first measure of signal quality of the channel request received by the second subscriber, a request acknowledger operative to send a request acknowledgement from the second subscriber to the first subscriber, second signal quality determining apparatus operative to determine a second measure of signal quality of the request acknowledgement received at the first subscriber, and a FHMA communication channel generator operative to generate a direct FHMA communication channel between the first subscriber and the second subscriber only if both the first measure of signal quality and the second measure of signal quality meet a predetermined criterion.
  • the apparatus for generating a half-duplex FHMA communication channel between two subscribers who are proximate to one another includes apparatus for generating a half-duplex FHMA communication channel between two subscribers who are geographically proximate to one another.
  • a method for reducing interference in a communication system between a plurality of sectors in a vicinity of a base station including a fringe area of at least two of the sectors including assigning a surrounding area which surrounds the base station to an individual one of the plurality of communication system sectors, and allocating air resources to communication system subscriber units within the surrounding area, thereby to allow communication between at least one of the subscriber units and at least one second party.
  • the communication system includes an FHMA (frequency hopping multiple access) communication system.
  • FHMA frequency hopping multiple access
  • base station antenna apparatus including a plurality of sector antennas disposed at a height H relative to the ground, and an auxiliary antenna disposed at a height h ⁇ H relative to the ground having a radiation pattern which includes an entire azimuthal vicinity of the base station.
  • the sector antennas are located directly above the auxiliary antenna.
  • the sector antennas are not located directly above the auxiliary antenna.
  • the auxiliary antenna is fed by a dedicated transmitter.
  • the auxiliary antenna includes an omnidirectional antenna.
  • apparatus operative to reduce interference in a communication system between a plurality of sectors in a vicinity of a base station including a fringe area of at least two of the sectors, the apparatus including a sector assigner operative to assign a surrounding area which surrounds the base station to an individual one of the plurality of sectors, and an air resource allocator operative to allocate air resources to subscriber units within the surrounding area, thereby allowing communication between at least one of the subscriber units and at least one second party.
  • a base station antenna construction method including disposing a plurality of sector antennas at a height H relative to the ground, and disposing at a height h ⁇ H relative to the ground an auxiliary antenna having a radiation pattern which includes an entire azimuthal vicinity of the base station .
  • channel state information is derived from a set of communication symbols received during an individual time slot, although any set of communication signals or even a single communication signal can be used.
  • QPSK modulated symbols are hard detected to determine the actual transmitted signal.
  • the in phase and quadrature components of the received communication symbols in the plane of the modulation points are determined.
  • the sum of the in phase components is determined and the sum of the absolute value of the quadrature components is determined.
  • the channel state is then determined from the ratio of the sum of the in phase components to the sum of the absolute value of the quadrature components.
  • method and apparatus for erasing communication signals in accordance with the channel state are provided.
  • the channel state is determined when the communication signal is received and then signals are erased if the channel state is not better than a predetermined level.
  • method and apparatus for selecting one of two communication signals for processing when diversity signals are received.
  • a first channel state is determined when the first of two diversity communication signals is received and a second channel state is determined when the second of the two diversity communication signals is received. Then, based on the values of the first and the second channel states, one of the two diversity communication signals is selected for further processing.
  • Fig. 1 represents the communication system of the present invention
  • Fig. 2 illustrates the preferred common air interface links between a base station and the subscriber units
  • Fig. 3A illustrates the preferred rules of transmission for traffic, control and access channels in each of the three sectors of the preferred embodiment of the present communication system
  • Fig. 3B shows one way of time and frequency hopping multiple inputs and Fig. 3C illustrates a sequence generator for generating the hopping sequences of the present invention
  • Fig. 4 shows a preferred time slot format
  • Fig. 5 illustrates the preferred timing offset between uplink and downlink transmissions
  • Fig. 6 illustrates a preferred sync-label slot format
  • Fig. 7 illustrates the transmission of the SLS
  • Fig. 8 is a block diagram of a base station
  • Fig. 9 is a block diagram of a sector unit in a base station
  • Fig. 10 illustrates a block diagram of the interconnection of the frame processor and the transmit (Tx) processing unit
  • Fig. 11 illustrates the HDLC interconnections between the frame processing unit, the Tx processing unit, the Rx processing unit and the sector computer;
  • Fig. 12A illustrates a frame processing unit and
  • Fig. 12B illustrates the block diagram of a quad frame board in the frame processing unit;
  • Figs. 13A and 13B illustrate a Rx processing unit and a Tx processing unit, respectively.
  • Fig. 14 is a block diagram of a micro sector unit in a base station
  • Fig. 15 illustrates a preferred embodiment of a subscriber unit
  • Fig. 16 illustrates a preferred embodiment of the RF portion of the subscriber unit
  • Fig. 17 illustrates a preferred method of synthesizing frequencies
  • Fig. 18 illustrates a preferred embodiment of a modem of the subscriber unit
  • Fig. 19 illustrates a preferred embodiment of an ASIC in the modem of the subscriber unit
  • Fig. 20 illustrates a preferred controller in the subscriber unit
  • Fig. 21 illustrates a preferred voice package processor (VPP) in the subscriber unit
  • Figs. 22A and 22B illustrate a preferred service board found in the subscriber unit
  • Figs. 23 and 24 show the preferred signal processing performed when transmitting and receiving signals on traffic channels, respectively;
  • Figs. 25 to 31 show various error coding schemes
  • Figs. 32 to 38 illustrate various steps used in other processes of the present invention
  • Fig. 39 is a simplified block diagram illustrating the overall structure of the software components of the system of Fig. 1;
  • Fig. 40 is a simplified block diagram illustrating the structure of element 700 of Fig. 39 in greater detail
  • Fig. 41 is a simplified block diagram illustrating the structure of element 706 of Fig. 40 in greater detail;
  • Figs. 42A and 42B are simplified block diagrams illustrating the structure of element 708 of Fig. 40 in greater detail;
  • Figs. 43A and 43B are simplified block diagrams illustrating the structure of element 714 of Fig. 42 in greater detail;
  • Fig. 44 is a simplified block diagram illustrating the structure of element 724 of Fig. 42 in greater detail
  • Fig. 45 is a simplified block diagram illustrating the structure of element 718 of Fig. 42 in greater detail
  • Fig. 46 is a simplified block diagram illustrating the structure of element 720 of Fig. 42 in greater detail
  • Fig. 47 is a simplified block diagram illustrating the structure of element 716 of Fig. 42 in greater detail
  • Figs. 48A and 48B are simplified block diagrams illustrating the structure of element 702 of Fig. 39 in greater detail;
  • Figs. 49 - 51 are simplified block diagrams illustrating the structure of a microsite
  • Fig. 52 is a simplified block diagram illustrating the structure of a remote sector
  • Fig. 53 is a generalized block diagram illustration of a portion of a subscriber unit in a frequency hopping multiple access communication system constructed and operative in accordance with a preferred embodiment of the present invention
  • Fig. 54 is a flow chart illustration describing the operation of frequency acquisition in a channel feature acquisition algorithm which is performed at the subscriber unit of Fig. 53 and is operative in accordance with a preferred embodiment of the present invention
  • Fig. 55 is a flow chart illustration describing the operation of timing acquisition in a channel feature acquisition algorithm which is performed at the subscriber unit of Fig. 53 and is operative in accordance with a preferred embodiment of the present invention
  • Fig. 56 is a generalized block diagram illustration of a portion of a subscriber unit in a frequency hopping multiple access communication system constructed and operative in accordance with a preferred embodiment of the present invention
  • Fig. 57 is a simplified illustration of the operation of a delay locked loop in a subscriber unit which forms part of a frequency hopping multiple access communication system constructed and operative in accordance with a preferred embodiment of the present invention
  • Fig. 58 is a generalized block diagram illustration of a portion of a base station in a frequency hopping multiple access communication system constructed and operative in accordance with a preferred embodiment of the present invention
  • Fig. 59 is a simplified illustration of the operation of a delay locked loop in a base station of a frequency hopping multiple access communication system constructed and operative in accordance with a preferred embodiment of the present invention
  • Fig. 60 is a generalized block diagram illustration of a portion of a subscriber unit in a frequency hopping multiple access communication system constructed and operative in accordance with a preferred embodiment of the present invention
  • Fig. 61 is a simplified illustration of the operation of automatic frequency control in a frequency hopping multiple access communication system constructed and operative in accordance with a preferred embodiment of the present invention
  • Fig. 62 is a simplified block diagram of gain control apparatus constructed and operative in accordance with a preferred embodiment of the present invention.
  • Fig. 63 is a simplified flowchart illustrating the operation of a portion of the apparatus of Fig. 62;
  • Fig. 64A is a simplified flowchart illustrating an initialization method for the apparatus of Fig. 62;
  • Figs. 64B and 64C are simplified flowchart illustrations useful in understanding the method of Appendix A;
  • Fig. 65 is a simplified flowchart illustration of subscriber unit operations during a hand-off process provided in accordance with a preferred embodiment of the present invention.
  • Fig. 66 is a simplified flowchart illustration of base station operations during a hand-off process provided in accordance with a preferred embodiment of the present invention.
  • Fig. 67 is a simplified flowchart illustration of subscriber unit operations during a hand-off process provided in accordance with an alternative preferred embodiment of the present invention.
  • Fig. 68 is a simplified flowchart illustration of base station operations during a hand-off process provided in accordance with an alternative preferred embodiment of the present invention.
  • Fig. 69 is a simplified block diagram of a power control system for use in a radio communication system, the power control system being constructed and operative in accordance with a preferred embodiment of the present invention
  • Fig. 70A is a simplified electronic circuit diagram illustrating the operation of the apparatus of Fig. 69;
  • Fig. 70B is a simplified flowchart illustrating the operation of a preferred implementation of step 6203 of Fig. 70A;
  • Fig. 71 is a simplified flowchart illustrating the operation of step 6204 of Fig. 70A according to an alternative embodiment of the present invention
  • Fig. 72 is a simplified block diagram of a power control system for use in a radio communication system, the power control system being constructed and operative in accordance with an alternative preferred embodiment of the present invention
  • Fig. 73 is a simplified flowchart illustrating the operation of the apparatus of Fig. 72;
  • Fig. 74 is a simplified block diagram of a power control system for use in a radio communication system, the power control system being constructed and operative in accordance with another alternative preferred embodiment of the present invention
  • Fig. 75 is a simplified flowchart illustrating a preferred method for operating the apparatus of Fig. 74;
  • Fig. 76 is a simplified partly pictorial, partly block diagram illustration of the time alignment of a radio communication system constructed and operative in accordance with a preferred embodiment of the present invention
  • Fig. 77 is a simplified flowchart illustration of a method for time alignment in the radio communication system of Fig. 76;
  • Fig. 78 is a simplified partly-pictorial, partly block-diagram illustration of a radio communication system constructed and operative in accordance with a preferred embodiment of the present invention
  • Fig. 79 is a simplified block diagram illustration of a preferred method for operating the system of Fig. 78;
  • Fig. 80 is a simplified block diagram illustration of a preferred error detection method useful in conjunction with the method of Fig. 79;
  • Fig. 81 is a simplified block diagram illustration of another preferred error detection method useful in conjunction with the method of Fig. 79;
  • Fig. 82 is a generalized block diagram illustration of a portion of a subscriber unit in a frequency hopping multiple access communication system constructed and operative in accordance with a preferred embodiment of the present invention
  • Fig. 83 is a generalized block diagram illustration of a portion of a base station in a frequency hopping multiple access communication system constructed and operative in accordance with a preferred embodiment of the present invention?
  • Fig. 84 is a flow chart illustration describing the operation of a collision avoidance and channel coordination algorithm employed in the apparatus of Fig. 83;
  • Fig. 85 is a flow chart illustration describing the operation of another collision avoidance and channel coordinating algorithm which is performed at a base station and is operative in accordance with a preferred embodiment of the present invention.
  • Fig. 86 is a flow chart illustration describing the operation of a collision avoidance and channel coordinating algorithm which is performed at a subscriber unit and is operative in accordance with a preferred embodiment of the present invention
  • Fig. 87 is a simplified pictorial illustration of a communication system constructed and operative in accordance with a preferred embodiment of the present invention.
  • Fig. 88A is a simplified flowchart illustration of a preferred method for establishing and maintaining a talk around link between two subscriber units of the system of Fig. 87;
  • Fig. 88B is a simplified flowchart illustration of a preferred implementation of the method of Fig. 88A;
  • Fig. 89 is a simplified flowchart illustration of a preferred method for implementing a link-establishing step of Fig. 88B;
  • Fig. 90 is a simplified flowchart illustration of an alternative preferred method for implementing a link-establishing step of Fig. 88B;
  • Fig. 91 is a simplified flowchart illustration of the base station side of an alternative preferred method for establishing and maintaining a talk around link between two subscriber units of the system of Fig. 87;
  • Fig. 92 is a simplified flowchart illustration of the subscriber unit side of an alternative preferred method for establishing and maintaining a talk around link between two subscriber units of the system of Fig. 87;
  • Fig. 93 is a simplified pictorial illustration of a prior art sectorized communication system
  • Fig. 94 is a simplified pictorial illustration of a sectorized communication system including a region around the foot of a base station, constructed and operative in accordance with a preferred embodiment of the present invention
  • Fig. 95A is a simplified pictorial illustration of the base station 11100 of Fig. 94;
  • Fig. 95B is a simplified pictorial illustration of an antenna coverage pattern of a preferred implementation of the FBS antenna 11125 of Fig. 95A;
  • Fig. 95C is a side view of the antenna coverage pattern of Fig. 95B;
  • Fig. 96 is a simplified pictorial illustration of an alternative embodiment of the present invention, which a region 11115 around the foot of the base station is incorporated into a sector;
  • Fig. 97 is a simplified pictorial illustration of the base station 11100 of Fig. 95A;
  • Fig. 98 illustrates a wireless communication system in which the apparatus and method of the present invention is used
  • Fig. 99 shows the steps used to determine channel state by using the in phase and quadrature components of a received communication signal
  • Fig. 100 illustrate a modulation plane and the determination of channel state by using the in phase and quadrature components of received signals as in Fig. 1;
  • Fig. 101 illustrates the processing apparatus in the subscriber units used to determine channel state
  • Fig. 102 illustrated the process in accordance with another aspect of the present invention wherein communication signals from one of two diversity channels are selected for processing;
  • Fig. 103 illustrates the process in accordance with one aspect of the present invention wherein communication signals are erased
  • Fig. 104 illustrates a metric decision zone.
  • Appendix A is a detailed description of a preferred implementation of the apparatus and method of Figs. 62 and 63;
  • Appendix B is a detailed description of the initialization method of Fig. 64. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
  • Fig. 1 illustrates the system 1 of a preferred embodiment of the present invention.
  • the system 1 includes a base station 10, a plurality of subscriber units 12, three sectors 14, 15 and 16, a microsite 18 and a remote site 20.
  • the base station 10 establishes a communication link between a user on one subscriber unit 12 and one or more other users on other subscriber units 12.
  • the base station 10 can also establish connections between one or more subscriber unit 12 and the Public Switch Telephone Network (PSTN).
  • PSTN Public Switch Telephone Network
  • the communication system 1 is divided into sectors. While Fig. 1 illustrates three sectors 14 to 16, the preferred number of sectors utilized will depend mainly on the geographic location of the communication system 1 and on the number of subscriber units 12 which the system 1 needs to support.
  • the communication links between the base station 10 and subscriber units 12 is referred to as the common air interface.
  • Fig. 2 illustrates a set of preferred communication channels in the common air interface.
  • the communication channels include a plurality of traffic channels (TCHs), one or more control channels (CCHs) and one or more access channels (ACHs). All of these channels are present in each sector 14 to 16.
  • TCHs operate in the uplink (transmissions from subscriber units 12 to the base station 10) and in the downlink (transmissions from the base station 10 to the subscriber units 12).
  • the CCHs and the ACHs operate only in one direction ⁇ the CCHs in the downlink and the ACHs in the uplink.
  • these channels are transmitted over a plurality of carrier frequencies.
  • the number of carrier frequencies (or channels) utilized by the system 1 depends mainly on the available frequency spectrum and on the loading of the system 1.
  • Each carrier frequency is preferably reused in each sector 14 to 16.
  • each sector 14 to 16 uses ten carrier frequencies to define ten uplink channels and uses a different ten carrier frequencies to define ten downlink channels.
  • each uplink and downlink channel ⁇ whether TCH, CCH or ACH ⁇ operates within a channel bandwidth allocation of 25kHz.
  • the uplink band of frequencies is contiguous as is the downlink band of frequencies, although such operation is not necessary to the present invention.
  • nine out of the ten available uplink carrier frequencies are utilized to implement nine uplink TCHs and nine of the ten available downlink carrier frequencies are utilized to implement nine of the ten downlink TCH transmissions.
  • the remaining uplink carrier frequency is utilized to transmit a single ACH while the remaining downlink carrier frequency is utilized to transmit a single CCH.
  • Each of the channels illustrated in Fig. 2 the TCHs, the CCHs and the ACHs ⁇ carries predefined information.
  • the TCHs transmit voice information, data information and inband overhead control signals between the base station 10 and the subscriber units 12.
  • the CCHs transmit timing and control signals from the base station 10 to the subscriber units 12. At least one CCH is preferably transmitted perpetually by each sector unit 14 to 16.
  • the ACHs transmit status and operational requests from the subscriber units 12 to the associated sector unit 14 to 16 in the base station 10.
  • the first rule concerns the transmission of information over the TCHs.
  • the TCHs are defined over nine uplink and nine downlink carrier frequencies. It is appreciated that the number of sectors and number frequencies is given by way of example only and is not meant to be limiting.
  • the transmission of information over a TCH is preferably via frequency hopping so that at a first time, a first block of information is transmitted on a first carrier frequency while at a second time, a second block of information is transmitted on a second carrier frequency, and so on.
  • the transmitted information therefore, is preferably hopped from carrier frequency to carrier frequency.
  • each TCH be constructed of a periodic sequence of fixed, continuous and non-overlapping time slots.
  • FIG. 3B an example of frequency and time hopping of inputs from multiple users by the base station 10 is illustrated.
  • Fig. 3B there are five users, namely users A to E.
  • User A has four blocks of information ⁇ A1, A2 , A3 and A4 ⁇ which are queued for transmission.
  • user B has four blocks of information ⁇ B1, B2 , B3 and B4 ⁇ that are queued for transmission
  • user C has four blocks of information C1, C2 , C3 and C4 ⁇ that are queued for transmission
  • user D has four blocks of information ⁇ D1, D2 , D3 and D4 ⁇ that are queued for transmission
  • user E has four blocks of information ⁇ E1, E2, E3 and E4 ⁇ that are queued for transmission.
  • Each of the ten illustrated channels are constructed of continuous time slots.
  • the queued information on the left side of Fig. 3B is processed by assigning each block of information from each user to a time slot and then to a carrier frequency.
  • user A's information blocks, A1, A2, A3 and A4 are assigned to the time slot IB and to the channel f 3 , to the time slot IIC and to the channel f 6 , to the time slot IIIA and to the channel f 9 , and to the time slot IVB and to the channel f 2 , respectively.
  • the blocks of information to be transmitted therefore, are time hopped between the available time slots. They are also frequency hopped between the available channels.
  • the assignment to time slots and to channels is preferably made in accordance with certain rules which will be discussed later.
  • the queued information blocks for users B, C, D and E are similarly time and frequency hopped, as illustrated.
  • the frequency hopping is preferably done in accordance with a predefined sequence, which can be modified as necessary. It is preferred to select the sets of hopping sequences in an individual sector, for example, sector 14, such that during a selected time slot each of the carrier frequencies f 1 to f 10 , is only being used by a single channel. Stated another way, no two channels within a sector employ the same carrier frequency at the same time. Selection of hopping sequences in accordance with this rule eliminates interference within the sector 14. This preferred transmission rule and the generation of the sequences is more fully described in co-pending United States application number 080,075, filed on 13 June 1993 (and in co-pending Israel application number 103,620, filed 3 November 1992) which is hereby incorporated herein by reference.
  • the second preferred transmission rule also relates to the transmission of TCHs.
  • the set of frequency hopping sequences in one sector are selected such that no channel in that set of sequences employs the same carrier frequency at the same time as more than a predetermined number of channels in another set of frequency hopping sequences in an adjacent sector.
  • the predetermined number of channels is the minimum number of channels possible and in a preferred embodiment is one.
  • a sequence is chosen for the first sector.
  • the sequences for the second sector are generated by a left cyclic shift of each line of the sequences of the first sector by one location.
  • the sequences for the third sector are also generated by a left cyclic shift of each line of the sequences of the second sector by one location.
  • Fig. 3A also describes the preferred transmission rules for CCHs which transmit timing and control signals from the base station 10 to the subscriber units 12.
  • the single CCH is perpetually transmitted over one of the plurality of carrier frequencies. Therefore, the CCH is preferably not frequency hopped.
  • the CCH in each sector 14 to 16 is preferably assigned one of the three time slots and is transmitted only in that time slot. Therefore, in a preferred embodiment, the CCH in sector 14 is transmitted during time slot A, the CCH in sector 15 is transmitted during time slot B and the CCH in sector 16 is transmitted during time slot C.
  • Fig. 3A also describes the preferred transmission rules for ACHs.
  • most of the ACHs are transmitted in a slotted ALOHA format. It is preferred to utilize a variant of the stabilized slotted.
  • a portion of the ACHs is in a format similar to the CCH.
  • each channel is constructed of continuous time slots.
  • Fig. 4 illustrates a preferred format of an active time slot 20.
  • the slot 20 covers 2.22 msec. and includes a total of 41 symbols. Each symbol, therefore, is 54 micro seconds long. Each symbol may consist of two bits of information. Two of the symbols, the first and last ones, are left inactive as guards to protect against time shifted time slots. When the time slot is active, therefore, the middle 39 symbols are active and used to transmit information.
  • the uplink slots 21 from the subscriber unit 12 it is preferred to transmit the uplink slots 21 from the subscriber unit 12 to the base station 10 offset in time from the transmission of downlink slots 22 from the base station 10 to the subscriber units 12, as shown in Fig. 5.
  • the time offset is. preferably 1.11 msec. Offsetting the uplink transmissions from the downlink transmissions allows the system of the present invention to be compatible with either full duplex (receive and transmit simultaneously) or half duplex operation.
  • timing and control information for the system 1 is transmitted over a CCH.
  • One of the CCH messages contains synchronization information and is transmitted in sync/label slots (SLS).
  • Fig. 6 shows a preferred format of a SLS 23.
  • the SLS 23 includes a sync 24 consisting of 20 symbols, a label 25 consisting of 19 symbols and guard symbols 26 and 27 at the front and the end of the SLS 23.
  • the sync 24 is a deterministic synchronization code.
  • the subscriber units 12 detect the sync 24 when it is transmitted and synchronize their operation accordingly.
  • the label 25 is preferably constructed of eight symbols that indicate which communication site transmitted the SLS, four symbols indicating which sector within the site the subscriber unit is located in, six symbols indicating the index of the received SLS 23 within a superframe of information and 1 symbol indicating whether coherent or differential modulation is being utilized.
  • the transmission of the SLS 23 is illustrated in Fig. 7. As illustrated, each sector 14 to 16 is assigned its own time slot. The SLSs are transmitted on the average, every 72 time slots in a staggered manner so as to ensure the reception of at least one SLS in one's own operating time slot. The entire pattern has a period of 216 time slots. Information about the base station 10 is also transmitted on the CCH.
  • the first mode of operation is coherent demodulation and the second mode of operation is differential modulation.
  • Coherent demodulation offers improved performance when the received signal has a stable carrier phase, but requires good synchronization to the phase of the received, yet unmodulated, signal. It is anticipated that some channel conditions ⁇ such as severe fading ⁇ may be such that coherent demodulation may be erratic. It is therefore preferred to utilize differential demodulation as well.
  • the mode of operation will be initially selected for individual communication sites.
  • the base station 10 instructs the subscriber units 12 which mode of operation is being used by setting a bit in the SLS 23.
  • the main task performed by the base station 10 is to connect subscriber unit users 12 with a PSTN or with another subscriber unit 12.
  • the base station 10 provides various voice services to the users, including basic telephony, voice mail, group dispatch calls and individual dispatch.
  • the basic telephony services include incoming phone calls from a PSTN, outgoing phone calls outside the base station 10 area via a PSTN and phone calls between subscribers.
  • the preferred features provided for telephony services includes speed dialing based on a phone number library stored in the subscriber unit 12, fleet phone numbers library, call waiting, call forwarding, emergency call, display of caller phone number, camp-on capability, prescribed telephony privileges per subscribe unit 12 and answering modes that include auto answer and ringing.
  • the features of the group dispatch services includes emergency dispatch and camp-on capability on system resources and on group dispatch. Individual dispatch can be provided via full duplex and via half duplex.
  • the base station 10 also provides data services, including group messaging, individual messaging and virtual circuit. For individual messaging, basic individual messaging services, special delivery and registered delivery are provided. Also provided are: warnings to the sender; guaranteed delivery; unique identification of messages, a dropped message log file; a message receipt time stamp; two levels of message priority; delayed delivery; an address distribution list and an alternate destination address.
  • the virtual circuit provides a connection oriented, packet switched type of service between two users. It is preferred to measure inactivity time for each virtual circuit.
  • the base station 10 also provides fax services. Another basic task performed by the base station 10 is to manage a date base of the subscriber unit 12 users.
  • the base station 10 includes a first sector unit 30, a second sector unit 31, a third sector unit 32, a microsector unit 34, a redundant sector 35, a PABX 36, a voice mail unit 38, a central frequency source unit 40, an administration computer 42, a central controller 44, a data base server 46, a local administrator computer 48, a terminal server 50, an ethernet local area network 52, a power supply 54 and data computers 55.
  • the sector units 30 to 32 establish the previously discussed communication channels within the sectors 14 to 16, respectively.
  • the micro sector unit 34 establishes communication channels with the microsite 18.
  • the redundant sector 35 provides redundant communication channels for the various sector units. Communication with the PSTN is provided via the PABX 36.
  • the sector unit 30 includes antennae 56 and 57, antenna boxes 58 and 59, wideband amplifier units 60 and 61, each of which include an input combiner 62, a preamplifier 63, a power divider 64, amplifiers 65 and an output combiner 66, multicoupler units 67A and 67B, a receive (Rx) processing unit 68, a transmit (Tx) processing unit 70, a frame processing unit 72, a sector controller 74 and a power supply 76.
  • Both antennas 56 and 57 are utilized during a receive cycle and during a transmit cycle.
  • the antenna 57 transmits signals provided by the Tx processing unit 70 through the wideband amplifier 69 and the antenna box 58 into a sector while the antenna 56 transmits signals provided by the Tx processing unit 70 through the wideband amplifier 61 and the antenna box 59.
  • the antennae 56 and 57 both receive signals that are provided to the multicouplers 67A and 67B, respectively, before being sent to the Rx processing unit 68.
  • the antennae 56 and 57 are preferably placed more than several wavelengths from each other. The best received signal is selected from the two and then routed for frame processing.
  • the frame processing unit preferably includes forty (40) FPUs, while the Tx processing unit 70 preferably includes ten (10) TPUs.
  • Each FPU is connected by the sector controller to handle one conversation at a time. Thus, as illustrated, up to forty conversations can be handled by the forty FPUs.
  • the sector controller provides the FPU with a key that specifies the sequence of frequencies to be utilized. The key can also specify the time slot to be utilized.
  • Each FPU is connected to each TPU in the Tx processing unit 70 through a modified HDLC bus.
  • Each TPU provides signals to be transmitted on a predefined frequency (channel).
  • the FPU sends the part of the conversation to be transmitted to the appropriate TPU on the HDLC bus in accordance with the key received from the sector controller.
  • the time slot of transmission is determined in accordance with the time position of the signal to be transmitted on the HDLC bus.
  • the FPU properly places the signal to be transmitted in the proper time sequence on the HDLC bus in accordance with the key provided by the sector controller.
  • Fig. 10 also represents the interconnection between the frame processor unit 72 and the Rx processing unit 68.
  • the Rx processing unit has ten RPUs (represented by the TPUs in Fig. 10), each of which receives signals from the appropriate sector on a predefined frequency (channel).
  • the sector controller instructs the RPU which FPU should receive the signal through a key.
  • the RPU then sends the information received in the proper timing on the HDLC bus to the appropriate RPU where the signal transmitted is reconstructed.
  • Fig. 11 illustrates the HDLC interconnections in greater detail.
  • the frame processing unit 72 includes a bridge interface board 80, a dual T1 board 82 and ten quad frame boards 84.
  • the dual T1 board 82 provides a communication interface to the PABX 36.
  • the bridge interface board 80 provides an interface to the HDLC bus.
  • Each one of the quad frame boards 84 includes four FPUs so that a total of forty FPUs are provided as previously discussed.
  • the quad frame board 84 is illustrated in greater detail in Fig. 12B.
  • Each board 84 includes a host CPU 86.
  • Each board also includes four FPUs, each of which includes a digital signal processor 33, a vocoder 90, buffers 92 and 94, a decoding PAL 96, an oscillator 98, a test buffer 100, a boot ram 102, a viterbi decoder 104, data ram 106 and program ram 108.
  • the host CPU 86 controls the communications on the HDLC bus as well as the overall functioning of each FPU.
  • Each FPU processes the information to be transmitted or received. On the transmit side, the processing includes compressing the information with a vocoder, error correction coding and interleaving the signal. On the receive side, the processing includes the reverse steps.
  • the Rx processing unit 68 preferably includes bridge interface boards 110 and 112, Rx RF/IF boards 114 and 116, digital Rx boards 118 and 120 and reference generator 121.
  • the bridge interface boards 110 and 112 provide an interface to the Tx processing unit 70, where an interface to the frame processing unit 72 is provided.
  • the signals being received are provided to the Rx RF/IF boards 114 and 116 by the multicouplers unit 67A and 67B, respectively, where the signals are converted to digital form. Once in digital form, the signals are provided to the digital Rx boards 118 and 120, where the signals are put in proper form for transmission to the frame processor 72.
  • the Tx processing unit 70 is similar to the Rx processing unit 63, but is configured to send signals in the opposite direction.
  • the Tx processing unit 70 includes bridge interface boards 122 and 124, Tx RF/IF boards 126 and 128, digital Tx boards 130 and 132, and reference generator 133.
  • the bridge interface boards 122 and 124 provide an interface for the Tx RF/IF boards 126 and 128 to the frame processing unit 68.
  • the bridge interface boards 122 and 124 also provide an interface to the Rx processing unit 68, as shown.
  • the digital Tx boards 126 and 128 collect the signals to be transmitted on the various channels and properly format these signals.
  • the Tx RF/IF boards 126 and 128 convert the signals to be transmitted to analog form for transmission.
  • the sector controller 74 provides control of the various functions performed by a sector and is controlled by the central controller 44. Control and data signals are exchanged between the sector controller 74 and the central controller 44 via the LAN 52. In addition to controlling the processing that is performed by the sector 30 to 32, the sector controller 74 also keeps a log book of all the active users under supervision. The sector controller 74 provides this information to the central controller 44 via the LAN 52. Referring back to Fig. 8, the description of the base station 10 will be completed.
  • Each of the sector units 30 to 32 and the micro sector unit 34 is interfaced to the PABX 36.
  • the PABX 36 provides the connection of the system 1 to the public switch telephone network (PSTN). The interface is via a standard 2Txl connection.
  • the PABX 36 also provides three way conferencing, routing, least cost routing of long distance calls, voice mail interfacing, dispatch bridging, user services support and metering functions.
  • the voice mail unit 38 provides voice mail capability.
  • the central frequency source unit 40 provides sector and timing references to the sector units 30 to 32 and to the micro sector unit 34.
  • the frequency source is preferably generated by a rubidium atomic reference.
  • the administrative computer 42 tracks the configuration grouping, tracks administration activities, performs network management, performs bit management and performs the system initialization. It is preferably implemented with a Sun Sparcstation.
  • the central controller 44 provides various functions including call management, dispatch management, control of the PABX 36, voice mail interfacing, operational mode management, subscribers management, call management, billing information and reports generation. It is preferably implemented with a 486 PC compatible computer.
  • the data base server 46 stores user data concerning user rights, status, calls and airtime. It also provides basic data base management and services to all data base clients, such as the local operator, fleet administrators and remote operators.
  • the local administrator computer 48 provides maintenance and operational control of the base station 10.
  • An ethernet local area network (LAN) 52 is provided to enable communications between the various components connected to the network.
  • the micro sector unit 34 is illustrated in greater detail in Fig. 14.
  • the micro sector unit 34 provides communication channels to the microsites 18.
  • the micro sector 34 includes one or more microwave transceivers 134, a video processing unit 136, a micro Tx processing unit 138, a micro Rx processing unit 140, a slot selector unit 142, a frame processing unit 144, a sector controller 146 and a power supply 148.
  • the receive and transmit signal processing is performed by the micro Tx processing unit 138, by the micro Rx processing unit 140, by the slot selector unit 142, by the frame processing unit 144 and by the sector controller 146.
  • the processing steps performed by the micro sector 34 are the same as those performed by the sectors 30 to 32 as previously discussed.
  • Fig. 15 is a block diagram of the subscriber unit (SU) 12 of the present invention.
  • the SU 12 preferably supports the same features supported by the base station 10.
  • these features include, but are not limited to, telephony interconnect, two-way radio, and data communications.
  • the telephony interconnect features include incoming calls, outgoing calls, call waiting, call forwarding, call disconnect, call flip-flop, switching to dispatch and back while on call, dialing while conversing, last number redial and speed dialing.
  • the two-way features include incoming dispatch and dispatch initiation.
  • the SU 12 includes a first antenna 202, a second antenna 204, a radio unit (RU) 206, a baseband unit (BBU) 208, a service board (SB) 210, a GPS interface 211 and a man machine interface (MMI) 212.
  • the RU 206 includes a duplexer 213, a receiver channel 214, a diversity receiver channel 216, a gain and frequency control unit 218, a transmitter 220, a synthe sizer 222 and a gain control unit 224.
  • the BBU 208 includes a modem 226, a controller 228, a voice processing package (VPP) 230 and a MMI interface 232.
  • VPP voice processing package
  • the two antennae 202 and 204 establish the previously discussed communication channels with the base station 10. They are preferably 14 inch, stainless steel, high performance collinear antennae which are magnetically secured to a vehicle. They preferably operate in the frequency range of 890 to 950 MHz, although tuning to any desired frequency is possible.
  • the two antennae 202 and 204 are preferably omnidirectional and have linear vertical polarization, a free space gain of 3 dBi and a maximum VSWR of 1.5:1.
  • the SU 12 when transmitting to the base station 10, transmits only on the first antenna 202.
  • both the first and second antenna 202 and 204 are utilized to achieve space diversity. As with the base station 10, the best signal is selected for processing.
  • the transmitter 220 received I and Q inputs from the modem 226.
  • the I and Q inputs are amplified by amplifiers 234 and 236, respectively, and then filtered by low pass filters 238 and 240, respectively.
  • the filtered I and Q signals are then modulated by. a modulator 242.
  • the modulator 242 is supplied with a hopping oscillator signal, TxLO, from the synthesizer 222A so that the signal transmitted by the transmitter 220 is frequency hopped.
  • the modulated signal is then controllably attenuated by an Up attenuator 244, filtered by a high pass filter 246, amplified by amplifiers 248 and 250, down attenuated by attenuator 252 and filtered by low pass filter 254 before being supplied to the duplexer 213 for transmission by the antenna 202.
  • the gain of the transmitted signal is controlled by the attenuators 244 and 252.
  • the attenuator 244 is controlled by the signal LEVEL CONTROL which is received from the gain control unit 224.
  • the gain control unit 224 receives its inputs (EN5, DATA and CLK) from the modem 226.
  • the antenna 202 in addition to transmitting signals from the transmitter 220 to the base station 10, also receives signals which are transmitted by the base station 10. Those received signals are transmitted through the duplexer 213 to the receive channel 214.
  • the received signal is amplified with a low noise amplifier 256, filtered by a bandpass filter 258 and then downconverted by a mixer 260 to IF.
  • the received signal can be a frequency hopped signal.
  • the mixer 260 downconverts the received signal by mixing the received signal with an oscillating signal from the synthesizer 222B which is also hopping.
  • the downconverted signal is then filtered by a bandpass filter 262 and then amplified by a variable amplifier 264.
  • the variable amplifier 264 is gain controlled in accordance with a signal, AGC, received from the gain & frequency control unit 218.
  • the signal transmitted from the base station 10 to the SU 12 is also received by the second antenna 204.
  • the received signal is then processed by the receiver 216.
  • the received signal is filtered by a band pass filter 272 and then it is processed by a low noise amplifier 274, by a filter 276, by a mixer 278, by a filter 280, by a gain controlled amplifier 282, by a mixer 284, by a filter 286 and by an amplifier 288 in a similar fashion to the processing performed in the receiver 214.
  • gain control of the diversity channel is accomplished by a separate control signal, AGC(D).
  • the synthesizer 222A and 222B generates the signals necessary to modulate the signal transmitted by the transmitter 220 and to downconvert the signal received by the receiver channels 214 and 216.
  • a fixed frequency generator 296 generates a signal having a frequency of 14.4 MHz. This signal is provided to a transmit hopping synthesizer 294.
  • the transmit hopping synthesizer 292 generates an output signal with a frequency that varies from 757.8 MHz to 797 MHz in accordance with control signals, TxHOP CONTROL, which are provided by the modem 226.
  • the output of this synthesizer is output to a divider 294 where the frequency of the synthesized signal is divided by eight. Then the signal is filtered by high pass filter 296 before being supplied to one of the inputs of a mixer 298.
  • the other input to the mixer 298 is supplied by a fixed synthesizer 300 which synthesizes a frequency of 801.29375MHz in accordance with an input from an oscillator (TOXO) 302.
  • the TOXO 302 is controlled by a control signal, AFC, which is generated by the modem 226.
  • the control signal AFC is varied to keep the frequency of transmission constant.
  • the output of the mixer 298 therefore, is a hopped frequency which is filtered by a bandpass filter 304 before being input to the modulator 242 where it is used to modulate the I and Q signals that have been provided by the modem 226.
  • An output from the reference 290 is also supplied to a receive (Rx) hopping synthesizer 306.
  • This synthesizer 306 generates a signal that is hopped in the frequency range of 882.3 MHz to 902.2 MHz.
  • the frequency hopping is controlled by control signal Rx HOP CONTROL generated by the modem 226.
  • the output of the Rx hopping synthesizer 306 is supplied to a divider 308 and then to a high pass filter 310 before being supplied to an input of a mixer 312.
  • the other input of the mixer 312 is supplied by the fixed synthesizer 300.
  • the output of the mixer 312 is filtered by a band pass filter 314 and results in a signal that ranges in frequency from 1021.86875 MHz to 1026.84375 MHz.
  • the signal is then split into two signals by a splitter 316.
  • One of the split signals is supplied to the downconverter 260 in the first receiver channel 214.
  • the other signal from the splitter 316 is supplied to the downconverter 273 in the diversity channel 216.
  • the reference 290 also supplies a reference frequency to an IF synthesizer 313.
  • the IF synthesizer 318 generates a signal having a frequency of 86.33875 MHz. This signal is split by a splitter 320 and then supplied to downconverters 266 and 284 in the receiver channels 214 and 216, respectively.
  • a frequency reference 310 drives a numerical controlled oscillator 311.
  • the two sine and cosine outputs (in quadrature) from the numerical controlled oscillator drive a single sideband (SSB) mixer 312.
  • An additional RF input is provided from a voltage controlled oscillator 313 through a directional coupler 314 at frequency f out
  • the output of the mixer 312 at frequency f out - f NCO is down divided by N using a frequency divider 315.
  • Coarse frequency is set by f R and N and f NCO is used for fine and fast frequency hopping.
  • Fig. 18 illustrates the circuitry of the modem 226.
  • the modem includes a digital to analog converter (DAC) 322, an analog to digital converter (ADC) 324, a converter interface (CNVR) 326, an ASIC 328 and a digital signal processor 330.
  • the DAC 322 during the transmit function, receives I and Q signals from the ASIC 328 and converts those signals to analog form before supplying them to the transmitter 222.
  • the ADC 324 during the receive function, receives a signal IF from the receiver channel 214 and a diversity signal IF-d from the diversity receiver channel 216. It converts these signals to digital form and then supplies them to the ASIC 328 for further processing.
  • the CNVR 326 provides the control signals for automatic gain control of the first receiver channel 214 (AGC), for automatic gain control of the diversity receiver channel 216 (AGC-d) and for automatic frequency control of the TCXO generator 302.
  • the CNVR 326 also received the input from the temperature sensor in the radio unit 206. These signals are either received from or transmitted to the ASIC 328.
  • the ASIC 328 is illustrated in greater detail in Fig. 19.
  • the ASIC 328 includes a transmit (Tx) port interface 332, a receive (Rx) port interface 334, a CNVR interface 336, a Tx control circuit 338, a PLL control 340, a lock indicator 342, a DSP bus interface 344, a Viterbi decoder 346, a timing & interrupt controller 348 and a controller interface 350.
  • the Tx port interface 332 provides digital I and Q signals to the DAC 322.
  • the Rx port interface 334 receives the digital signals from the receiver channels 214 and 216 through the ADC 324.
  • the CNVR interface 336 provides the control signals AGC, AGC-d and AFC to the CNVR 326 and receives the signal OVR from the temperature sensor in the radio unit 206.
  • the Tx control 338 provides control signals for the transmitter 220.
  • the PLL/DDS control 340 provides the control signals to the synthesizer 222 to control the generation of the synthesized frequencies.
  • the DSP bus interface 344 provides an interface between the ASIC 328 and the digital signal processor 330.
  • the Viterbi decoder 346 is utilized to process signals.
  • the timing & interrupt controller 348 provides timing signals.
  • Fig. 20 illustrates the BBU controller 228.
  • the controller 228 includes a microcontroller circuit 352, a MMI interface circuit 354, a car accessories interface circuit 356, a microprocessor supervisor 358, a power supply control circuit 360 and a memory circuit 362.
  • the microcontroller 352 is preferably implemented with a Motorola processor MC68302 or an Intel 386EX.
  • the memory 362 is preferably comprised of 128k ⁇ 8 static RAM and 512k ⁇ 8 flash memory.
  • the memory 362 holds the programs of the microcontroller 352, of the modem 226 and of the VPP 230.
  • the memory 362 will also hold various parameters, user defined telephone numbers and messages that should be kept nonvolatile.
  • the power supply control circuit 360 monitors the state of the subscriber unit 12 and the state of the car and controls the power supply.
  • the supervisor circuit 358 is responsible for the reset mechanism and the power fail indication.
  • the microcontroller 352 is connected to the MMI interface 354 via a single ON/OFF input and via two RS-232 lines, one for each direction.
  • the RS-232 lines carry data, control and test messages.
  • the car accessories interface circuit 356 provides one input from the car's ignition switch and one output to the car's horn.
  • the microcontroller 352 has a two-wire bi-directional RS-232 connection available for GPS interface.
  • VPP voice processing package
  • the VPP 230 performs encoding and decoding of voice signals and consists of a CODEC 364, an analog interface circuit 366 and a digital signal processor 368.
  • the digital signal processor 368 is preferably an Analog Devices' ADSP2115.
  • the program for the digital signal processor 368 is stored in the memory 362 of the BBU controller 228.
  • Figs 22A and 22B illustrate a preferred service board found in the subscriber unit.
  • Figs. 23 and 24 show, respectively, the preferred signal processing performded when transmitting and receiving signals on traffic channels.
  • Figs. 25 to 31 illustrate various coding schemes utilized in the present invention.
  • Fig. 25 shows the preferred transmit processing steps for a voice signal when the system is operating in the differential mode.
  • the bits of the signal to be transmitted are divided into classes in accordance with their importance. Those bits with greater importance then receive greater coding.
  • four classes I, II, III and IV are utilized. The twelve most important bits are assigned to Class I. The next 36 most important bits are assigned to Class II. The next 32 most important bits are assigned to Class III. The least 8 important bits are assigned to Class IV.
  • the bits are then coded with a CRC encoder in step 552 and with a convolutional encoder in step 554 as illustrated.
  • Inband control signals received are also encoded as illustrated.
  • the signal is further coded with a partial repetition encoder by the repetition of 10 symbols.
  • a symbol is replaced with the value PWR_CNT_SYM with a puncture encoder.
  • the symbol that is replaced is preferably one of the lesser important bits.
  • a permutation step can be performed, however, it is presently preferred not to perform this step.
  • the interleaving already discussed is performed.
  • the frame of data is converted into time slots for transmission.
  • Fig. 26 illustrates the steps performed by the Rx processing unit in the differential mode. The steps are essentially the opposite of those described with respect to Fig. 25.
  • step 566 the slot of data is properly framed for processing.
  • step 568 the data is deinterleaved using the reverse process used during the transmit processing.
  • step 570 de-permutation is performed if the permutation step was performed during the transmit processing.
  • step 572 the symbol PWR_CNT_SYM is removed.
  • steps 574 to 576 the signal is decoded as illustrated.
  • step 573 the bit error rate is calculated and, if too high, can disable the voice reception.
  • Figs. 27 and 23 illustrate the steps performed by the Tx processing unit and the Rx processing unit, respectively, during the coherent mode of operation. These steps are very similar to those already discussed with respect to Figs. 25 and 26, except the partial repetition encoder repeats a different number of bits during its encoding.
  • Figs. 29 and 30 illustrate the preferred steps performed when processing data in the differential and in the coherent modes, respectively.
  • the data contains a header and one or more frames of data per message.
  • the data is subdivided into a number of frames, each of which is CRC encoded as illustrated.
  • the header is also CRC encoded, as shown.
  • the remaining encoding steps are selectable, the selection depending on the channel conditions.
  • the coding rate is one.
  • the coding for the coherent mode is very similar to the coding utilized in the differential mode, as illustrated in Fig. 30.
  • Fig. 31 The preferred coding scheme utilized for the ACH and the CCH is illustrated in Fig. 31.
  • the subscriber unit 12 performs several correlations on the signals it receives in order to achieve proper synchronization with the signal transmitted by the base station 10.
  • the complex conjugates of the synchronization signal are formed as follows:
  • the incoming signals are correlated according to the following formulas:
  • One of the processes which the subscriber unit 12 must perform prior to starting communications is the acquisition of the timing of the base station 10. This channel acquisition process is performed when the power to a subscriber unit 12 is first turned on and any time synchronization is lost.
  • a subscriber unit 12 performs acquisition by first accessing a table of communication sites which is maintained in the memory of the subscriber unit controller 228. This table contains a list of sites and the frequency of the associated CCHs. The subscriber unit 12 then sequentially scans the frequencies of channels identified by the site table, trying to lock onto each one in turn. In particular, the subscriber unit 12 attempts to lock onto a channel by searching for the synchronization pattern in a SLS slot in the channel. When the subscriber unit 12 scans a frequency, if there is no CCH at that frequency, there will be no SLS to detect. However, when the subscriber unit 12 scans a control channel (CCH) it will find a SLS.
  • CCH control channel
  • the subscriber unit 12 performs the scanning by performing a sliding correlation based on the mean square of the phase error between the signals on the channel being scanned and the known sync pattern of the SLS slot which the subscriber unit 12 has stored in its memory. When the subscriber unit 12 finds a high correlation, it has found the SLS slot. The subscriber unit 12 can also search all possible frequencies if the search of known sites is not successful.
  • step 600 a counter, SLOT_COUNT, is initialized.
  • step 602 the signals (W1(P)) and the diversity signal W2(P)) being received by the receivers 214 and 216 are first filtered with a digital matched filter and then differentially demodulated.
  • the filter outputs, Z1(p) and Z2(p) and the demodulation outputs U1(p) and U2 (p) are output to step 604.
  • step 604 the average amplitude of these outputs from each receiver channel are compared and the output with the highest average amplitude is selected.
  • step 606 the sliding correlation is performed on the data from the selected channel.
  • the correlation measures the mean square phase error between the phase of the received signals and the phase of the synchronization code which is stored in memory.
  • step 608 a search is performed for the optimum correlation by looking for the minimum error.
  • the process searches for several minimums in a 216 slot window. Generally, approximately five minimums will be found in this window.
  • step 610 the process determines whether the prior steps have been performed the prerequisite number of times. If they have not, then the steps are repeated. If they have, then the process goes on to step 612.
  • the process verifies that it has locked onto the proper synchronization pattern in the SLS slot.
  • the time index of the minimums in the frame of date has been stored. The time between two minimum values must have a legitimate value (generally 72 slots) to be verified.
  • step 614 if it is determined that proper synchronization has not been obtained, the process informs the controller 228 that synchronization has failed. On the other hand, if in step 614, it is determined that proper synchronization has been obtained, then the process continues to step 616.
  • step 616 the timing of the slot is adjusted in accordance with the indices of the minimum received value. In other words, the synchronization timing is known and the slot timing is determined from this knowledge.
  • the subscriber unit 12 performs a delay lock loop process.
  • a delay lock loop process for the subscriber unit 12 is illustrated.
  • the correlation values, RL_COR_EARLY and RL_COR_LATE, are utilized in step 618. The following calculation is performed to determine the delay:
  • step 622 the filtered result is input to a number controlled delay generator where a controlled delay is introduced.
  • a preferred delay lock loop process for the base station 10 is illustrated. Essentially, the same steps 618, 620 and 622 are implemented. However, the base station 10 implements these steps in software so an additional integrating step, step 624, is required.
  • the subscriber unit 12 performs an automatic frequency control process to measure and correct the frequency inaccuracies of its frequency source. Referring to Fig. 35, the steps performed by the subscriber unit 12 during the differential mode are illustrated.
  • the correlations RL_COR_PEAK and IM_COR_PEAK, of the received data are utilized to determine the errors in the frequency being received by the subscriber unit 12.
  • the error is determined, in step 626, by inputting these values into a table to determine the arctangent of the phase difference between RL_COR_PEAK and IM_COR_PEAK. Then the arctangent is filtered in step 628, as illustrated. The result is utilized to correct the frequency source at the subscriber unit 12.
  • This estimation is also utilized as an initial condition at which to start the previously described frequency control process.
  • the first step in the estimation is to select the complex samples of the currently active time slot.
  • the frequency of the slot and nominal value of the slot frequency are determined and, via software, the several frequency values which vary around the nominal value are substituted into the slot. For example, the nominal frequency and six frequencies above the nominal may be selected. The mean square phase error of each of these frequencies is calculated and the frequency with the minimum value is utilized.
  • the receivers in the base station 10 and the subscriber unit 12 all need to receive signals within a certain amplitude range in order to be able to optimally perform demodulation.
  • Gain control therefore, is performed in both the base station 10 and in the subscriber unit 12 to maintain a constant signal level.
  • the gain control process for a receiver channel in the subscriber unit 12 is illustrated.
  • step 632 the average amplitude is compared to a reference level. It is preferred to set the reference level at 0.25, which is 12 dB below the maximum level of 1.
  • the difference between the average amplitude and the reference level is filtered in the next step 634 to smooth the gain control operation to operate on slower variations.
  • step 636 it is preferred to limit the range of the signal being filtered to the range of the input signal. In Fig. 36, the signal is limited to the range of +0.5 to -0.5.
  • the output of the filter is then sent to a look up table in step 638.
  • the look up table is used to account for the nonlinearities found in the amplifiers in the receivers. Accordingly, the values of the look up table will vary according to the amplifiers being used in the receivers. Then the output of the look up table is converted to an analog signal which is, in turn, applied to the amplifiers in the receivers to effect gain control of the received signal.
  • the steps 630 to 636 are performed in the digital signal processor (DSP, Fig. 15) of the modem 226.
  • the value from the filtering step is output to the receiver channels 214 and 216 (Fig. 16) in the subscriber unit 12 through the ASIC 328 (Fig. 13) and through the CNVR INTERFACE 336 (Fig. 19).
  • the processing is performed separately for each channel, that is, one calculation is performed on the signals received from the receiver channel 214 and another calculation is performed on the signals received from the diversity channel 216.
  • the path to the look up table AGC_TBL is through the limiter 636.
  • the path to the look up table AGC_TBL is through the line labeled SGCS_IC and it is preferred to perform a different gain control process.
  • step 640 the initial value of SGCS_IC is set to the middle of the dynamic range of the input signal, in this case 0.
  • step 642 the SGCS_IC is applied to the AGC_IC look up table, as illustrated in FIG. 36.
  • a sliding window preferably of 26 msec, in duration, is established.
  • the average value of 164 symbols is determined.
  • the average value of the next 164 symbols is determined. In a preferred embodiment, this step is repeated a total of 1476 times. The maximum of each of these averages, MAX_W is determined.
  • step 646 If in step 646, MAX_W is determined to be less then W0, then in step 646, the initial value of SGCS_IC is decreased by ⁇ , which is preferably 0.09. Then, in step 648, the value of SGCS_IC is checked. If the value is greater than or equal to -0.5, then the process returns to step 642. However, if the value is less than -0.5, then step 650 is performed. In this step, SGCS_IC is set equal to -0.5, the minimum value of the dynamic range of the signal. Then in step 654, the memory Z -1 (FIG. 36) is set equal to -0.5 and the signal SGCS_IC is applied to the look up table AGC_TBL.
  • step 652 the value of SGCS_IC is incremented by a value which is a function of the value of MAX_W. Then in step 654, if SGCS_IC is greater than 0.5, the process goes to step 652. On the other hand, if SGCS_IC is less than or equal to 0.5 in step 654, then the process goes to step 656. In step 656, if SGCS_IC is less than -0.5, the process goes to step 650. On the other hand, if SGCS_IC is greater than or equal to -0.5, then step 654 is performed. In step 654, the memory Z -1 (FIG. 36) is set equal to SGCS_IC and the signal SGCS_IC is applied to the look up table AGC_TBL.
  • step 654 the memory Z -1 (FIG. 36) is set equal to SGCS_IC and the signal SGCS_IC is applied to the look up table AGC_TBL.
  • the same basic steps are utilized to perform gain control in the base station 10. There are, however, some differences in the implementation details. For example, the averaging step and look up table are implemented in the slot processor while the remaining steps are implemented in the frame processor. Also the initial condition is set via a message on the ACH which set the receiver at the base station 10 at a fixed value.
  • the communication system of the present invention must account for the movement of subscriber units 12 between the sectors 1.4 to 16.
  • the process by which the movement is accounted for is referred to as the "hand off”. It is preferred that the hand off process be seamless, that is, those persons using the system to communicate should not be affected by this process.
  • the hand off process includes first detecting when a situation requiring hand off occurs.
  • hand off situations occur in the sectorized system of the present invention when a subscriber unit 12 relocates from one sector to another, say from sector 14 to sector 15 (FIG. 1) or between any type of site or sector.
  • the next step in the hand off process is to then perform the necessary switching to allow seamless hand off of the communications between the sectors.
  • the hand off situations are detected by the subscriber unit 12.
  • the subscriber unit 12 by virtue of the channel acquisition procedure and the delay lock loop tracking procedure, is already detecting and locked onto the SLS slots of the CCH in the sector in which it is located, say for example, sector 14.
  • the subscriber unit 12 also searches for the SLS slots of the CCH in the sectors which are adjacent to the sector in which it is located, that is the SLS slots of the CCH in sectors 15 and 16 are searched for.
  • the subscriber unit 12 accomplishes this by referring to the label tag embedded in each SLS and determining the frequencies of the CCHs in the adjacent sectors 15 and 16 of the site 1 or, if the CCHs are all on the same frequencies, by looking at that frequency.
  • the subscriber unit 12 will, therefore, have three data streams to process ⁇ i.e., the SLS data from the sector in which it is located (sector 14), the data from a first adjacent sector (sector 15) and the data from the second adjacent sector (sector 16).
  • the digital signal processor 226 in the subscriber unit 12 performs an average correlation of synchronization from each of these data streams as compared to the known synchronization pattern to detect when a hand off situation is occurring.
  • the average correlation of the information from the sector 14 is obtained from the correlation processes previously described.
  • the correlation of the information from the sectors 15 and 16 are somewhat different because the timing of these channels is not known with certainty. Several correlations are performed on the synchronization information from these sectors based on a prediction of the timing of these synchronizations. Then, for each sector, the correlation with the maximum value is selected. Then, the maximum value for several correlations within that sector are selected and averaged.
  • the average correlation of the synchronization information from that sector will be higher than the average correlation of the synchronization information from the adjacent sectors 15 or 16.
  • the average correlation of the synchronization information from the new sector will be increasing.
  • the average correlation of the synchronization information from the new sector 15 will exceed the average correlation of the synchronization information from the old sector 14.
  • the subscriber unit 12 determines that a hand off situation exists.
  • the controller 228 causes a message to be transmitted on the ACH to the base station 10.
  • the message requests the initiation of a hand off procedure by the base station 10.
  • the base station 10 acknowledges the request by the subscriber unit on the CCH.
  • the base station 10 selects a communication link in the new sector 15 and connects it with the communication line in the old sector 14 via a three way conference bridge found in the PABX 36. In this way, a communication link is established between the subscriber unit 12 in the old sector 14, the subscriber unit 12 in the new sector 15 and the other person ( or machine) communicating with the subscriber unit 12, thereby enabling a seamless hand off.
  • the base station 10 and the subscriber unit 12 are both ready to accomplish the hand off.
  • the hand off is accomplished during a time when there is no activity on the channel. This time is detected by the voice activity detector (VAD) in the vocoder in both that the hand off is done independently in the uplink channel and in the downlink channel. Therefore, the VAD in the base station 10 detects the voice inactivity in the down link communications and, upon detection, causes the hand off to occur between the downlink channels. Also, the VAD in the subscriber unit 12 detects the voice inactivity in the uplink communication and that detection, causes the hand off to occur between the uplink channels.
  • VAD voice activity detector
  • the VAD provides a bit upon detecting voice inactivity to the transmitters.
  • the transmitters upon sensing the bit from the VAD, switch the transmission from the old sector to the new sector.
  • the receiver hand off is accomplished by transmitting a STOP RECEIVE marker in the TCH which tells the receiver that a talk spurt has ended ⁇ i.e. that there is voice inactivity ⁇ so that it is time to switch to the new sector.
  • the hand off can be accomplished by another technique.
  • the communications being received by the receiver includes a CRC code, as previously
  • This CRC code is analyzed to determine whether the communications has been properly received. For the hand off process, it is determined how many CRC failures have been detected. When the number of CRC failures exceeds a certain amount during the hand off process (the subscriber unit 12 has requested a hand off), then the hand off is automatically accomplished.
  • the base station 10 and the subscriber unit 12 both perform power control processes whereby each communication link transmits at a minimum power needed for transmission, thereby minimizing the interference in the communication system and saving power. It is preferred to provide power control for the TCH and the ACH, but not for the CCH.
  • the power control for the downlink TCHs will now be described with reference to FIG. 38.
  • the downlink TCH transmissions (from the base station 10 to the subscriber units 12) start at predetermined power, preferably at the maximum power.
  • the subscriber unit 12 detects the received power.
  • the average of the power value (SGCS0 and SGCS1) determined for the two receiver channels 214 and 216 during the automatic gain process are utilized in this process.
  • step 662 the average power from step 660 is compared to a predetermined threshold, REF, and the difference is filtered in step 664 so that power is controlled in a smooth fashion.
  • the output of the filter, FIL_SGCS is then sent to the transmitter in the base station 10 to modify the transmitted power. If there is no activity on the TCH, the information is sent to base station 10 via the ACH. In this case, it is preferred to accumulate the differences between the sensed power and the predetermined threshold so as to modify the transmitted power in increments, for example by 5 dB. If, however, the TCH is active, then the information is preferably sent via the TCH. In this case, it is preferred that the transmitted information be controlled to modify the transmitted power in small increments, for example by 1 dB.
  • the subscriber unit 12 first measures the average received power of the signal being transmitted on the CCH from the base station 10.
  • the CCH transmission power which is constant, is broadcast and received by the subscriber unit 12.
  • the subscriber unit 12 then subtracts the known CCH transmission power from the average received power to determine the transmission losses on the CCH.
  • the desired reception power at the base station 10 of signals transmitted by the subscriber unit 12 by virtue of a broadcast message.
  • the subscriber unit 12 adds the determined transmission losses on the CCH to the desired reception power to determine the power at which the subscriber unit 12 will transmit on the ACH.
  • the control of the power transmission on the uplink TCH transmissions is preferably controlled using a combination of the previously described methods.
  • the power is controlled in the same way as power is controlled on the ACH.
  • the power on the uplink TCH transmissions is controlled using the same process used to control the power on the downlink TCH transmissions.
  • Figs. 39 - 48B are simplified block diagrams illustrating the structure of the software components of the system of Fig. 1.
  • Elements 56 and 57 of Fig. 9 may be any suitable UHF Antenna, such as model DB 874H105, commercially available from Decibel Products, 3184 Quebec Street, POB 569610, Dallas, TX, USA.
  • model DB 874H105 commercially available from Decibel Products, 3184 Quebec Street, POB 569610, Dallas, TX, USA.
  • Element 38 of Fig. 8 may be any suitable voice mail system, such as a Trilog system, commercially available from Comverse, Israel.
  • Element 36 of Fig. 8 may be any suitable PABX system, such as a Coral III or Coral IV system, commercially available from Tadiran, Israel.
  • FIGS. 49 - 51 are simplified block diagrams illustrating the structure of a microsite.
  • microwave antennas in the apparatus of the present application may be any suitable microwave antenna, such as P/N 8838A-24/PCN, commercially available from Alpha Industries, Inc., Massachusetts, USA.
  • the apparatus of Figs. 49 - 51 comprises a UHF antenna, which may be any suitable UHF antenna, such as model DB808-Y, commercially available from Decibel Products, 3184 Quebec Street, POB 569610, Dallas, TX, USA.
  • a UHF antenna such as model DB808-Y, commercially available from Decibel Products, 3184 Quebec Street, POB 569610, Dallas, TX, USA.
  • FIG. 52 is a simplified block diagram illustrating the structure of a remote sector.
  • a remote sector also termed herein a “remote station” functions to enhance the coverage of the system.
  • the system is operative to straighten out the timing of all of the signals received by the base station.
  • subscribers are at different distances. They all downlink and are synchronized. They send uplink on the synchronized timing but due to different distances the communications are not received in synchronized timing.
  • a preferred method to make sure that they are received with synchronize timing is as follows: The base receiver measures the time of arrival on the uplink, and checks if they are within a predefined window. The base station tells the remotes to change their transmission timing so as to have the received signals within the window of the synchronized timing of the base station.
  • the system is operative to reduce the need for large number of multiple retransmissions when long digital messages are being sent.
  • a preferred method for reducing the large number of retransmissions is as follows: Break received message into segments and flag only those segments which are not received correctly. Upon each subsequent transmission only replace those flagged portions; once all flagged portions are received correctly, there is no need for further retransmission even though the retransmission may not have been received totally completely.
  • Fig. 53 is a generalized block diagram illustration of a portion of a subscriber unit in a frequency hopping multiple access communication system constructed and operative in accordance with a preferred embodiment of the present invention.
  • a frequency hopping multiple access communication system utilizes a frequency hopping multiple access communication network and a multiplicity of base stations, at least some of which receive and transmit information at a plurality of radio frequencies over the frequency hopping multiple access communication network.
  • the system also includes a multiplicity of subscriber units, each receiving and transmitting information at a plurality of radio frequencies via the frequency hopping multiple access communication network.
  • a receiving and transmitting unit is operable to receive and transmit radio- frequency (RF) signals.
  • RF radio- frequency
  • Receiving and transmitting unit 1010 preferably includes a first antenna 1012, a second antenna 1014 and a radio unit (RU) 1016.
  • Antennas 1012 and 1014 are operable to establish communication channels with a base station (not shown).
  • antennas 1012 and 1014 operate in the frequency range 890 - 950 MHz.
  • radio unit 1016 RF signals are received at receivers 1018 and 1020, also referred to as RXD and RX respectively.
  • Receiver 1018 is coupled to antenna 1012 and receiver 1020 is coupled to antenna 1014 via a duplexer unit 1022.
  • receivers 1018 and 1020 are RF/IF converters which convert RF signals to intermediate frequency (IF) signals.
  • antenna 1014 In a transmission mode, only antenna 1014 is employed. In a reception mode however, both antenna 1012 and 1014 are employed to achieve space diversity. In that case, receivers RXD and RX determine the quality of reception of the corresponding received signals and the best of the corresponding received signals are selected for processing.
  • receivers 1018 and 1020 are coupled to a combined gain and frequency control unit 1024 which is operable to provide separate automatic gain control (AGC) signals and common automatic frequency control (AFC) signals to receivers 1018 and 1020.
  • AGC automatic gain control
  • AFC common automatic frequency control
  • gain and frequency control unit 1024 is not a combined unit but may rather include a separate gain control unit and a separate frequency control unit.
  • Gain and frequency control unit 1024 is coupled to a synthesizer unit 1026 which is coupled to a transmitter 1028. Transmitter 1028 is coupled to a power control unit 1030. Gain and frequency control unit 1024 provides signals to synthesizer unit 1026 and receives inputs, including a clock signal and data, from a modem 1034 in a baseband unit (BBU) 1032.
  • BBU baseband unit
  • Receivers 1018 and 1020 are also coupled to synthesizer unit 1026 which generates signals necessary to downconvert signals received by receivers 1018 and 1020.
  • Receivers 1018 and 1020 provide the downconverted signals of an intermediate frequency (IF) to modem 1034 in BBU 1032.
  • Synthesizer unit 1026 is also operable to generate signals necessary to modulate signals transmitted by transmitter 1028.
  • Synthesizer unit 1026 also includes a local oscillator 1036 which is operable to supply a signal of a given frequency to the RF/IF converters (receivers 1018 and 1020) in response to a control signal received from modem 1034.
  • the signals generated by synthesizer unit 1026 to frequency downconvert the signals received by receivers 1018 and 1020, and the signals generated by synthesizer unit 1026 to frequency upconvert the signals transmitted by transmitter 1028 are preferably hopping signals which are generated in accordance with control signals communicated to and from modem 1034 in BBU 1032. Different hopping signals may be generated for transmission and for reception.
  • Transmitter 1028 receives control signals from modem 1034 in BBU 1032 and power control signals from power control unit 1030, which also receives inputs from modem 1034 in BBU 1032. Transmitter 1028 is also coupled to a service board (not shown) which provides electric power to transmitter 1028. Transmitter 1028 outputs data for transmission to antenna 1014 via duplexer unit 1022.
  • modem 1034 also includes a DSP (digital signal processing) unit 1038 and an ASIC (Application Specific Integrated Circuit) unit 1040 which is coupled to DSP unit 1038.
  • DSP unit 1038 and ASIC unit 1040 may be separate units which are coupled to modem 1034. It is to be appreciated that DSP unit 1038 is operable to control the operation of ASIC unit 1040.
  • an initialization algorithm for acquiring a precise frequency and a precise timing of a control channel is performed in DSP unit 1038 as described herein after.
  • the initialization algorithm is utilized, as described herein after, in conjunction with an FFT (fast Fourier transform) computing module 1042 which may form part of DSP unit 1038 or may be a separate module coupled to DSP unit 1038.
  • FFT fast Fourier transform
  • Fig. 54 is a flow chart illustration describing the operation of frequency acquisition in a channel feature acquisition algorithm that is performed at the subscriber unit of Fig. 53.
  • the subscriber unit of Fig. 53 when communication is initiated, receives RF signals via antennas 1012 and 1014. The signals are received at receivers 1018 and 1020 and provided to modem 1034. DSP unit 1038 in modem 1034 is operative to generate an estimated frequency offset value for a signal received by modem 1034.
  • the estimated frequency offset value is provided to synthesizer 1026 which generates a frequency converter control signal that changes the frequency of local oscillator 1036.
  • the frequency converter control signal is provided to receivers 1018 and 1020 and is operative to cancel the estimated frequency offset.
  • the signals which are received over the control channel and provided to modem 1034 are modulated signals.
  • modem 1034 is operable to remove the modulation of the signal, to thereby generate a carrier wave.
  • the carrier wave may be a distorted carrier wave.
  • FFT computing module 1042 in DSP unit 1038 is operable to convert the waveform of the carrier wave from a time domain to a frequency domain thus generating a final spectrum function in the frequency domain.
  • FFT computing module 1042 provides the final spectrum function to DSP unit 1038 which computes a frequency offset by finding a frequency value that maximizes the final spectrum function.
  • the conversion of the waveform of the carrier wave from a time domain to a frequency domain is done portion by portion for a plurality of portions of the waveform. Such conversion generates a plurality of intermediate spectrum functions.
  • the intermediate spectrum functions are combined in a spectrum function combining module which forms part of FFT computing module 1042.
  • the intermediate spectrum function values are summed in a summing module for each of a multiplicity of frequencies to form the final spectrum function.
  • Fig. 55 is a flow chart illustration describing timing acquisition in a channel feature acquisition algorithm which is performed at the subscriber unit of Fig. 53.
  • receivers 1018 and 1020 of Fig. 53 provide signals to DSP unit 1038 in modem 1034.
  • DSP unit 1038 a synchronization code embedded in the received signal is detected and timing information associated with the detected synchronization code is generated.
  • the received signal may include a synchronization code period and at least one synchronization code is embedded in the synchronization code period.
  • the timing information is provided to ASIC unit 1040 which includes a local timing system and a local timing system synchronizer which synchronize the local timing system in accordance with the timing information.
  • a representation of the synchronization code is stored in a memory (not shown) at DSP unit 1038.
  • the representation of the synchronization code in the memory is correlated with the received signal.
  • time windows are set and a sliding correlation operation with the stored representation of the synchronization code is performed within a time window in which at least one element of the synchronization code is known to appear.
  • a correlation search over the entire window is performed, and any optimal correlation, if found, is stored in the memory.
  • the timing information associated with the synchronization code includes an indication of a time at which the optimal correlation appears.
  • the sliding correlation operation may be performed within a window in which at least N elements of the synchronization code are known to appear and M optimal correlations within that window may be found.
  • the timing information may include an indication of a time at which a predetermined one from among the M optimal correlations appears.
  • the K optimal correlations are then verified by comparing the K points in time to a known timing pattern of the K optimal correlations.
  • the K optimal correlations may form a subset of the M optimal correlations.
  • timing frame which is larger than a slot.
  • a timing frame is indicated as a super-frame, and it may include a frame of 4.8 seconds.
  • a super-frame includes a plurality of synchronization code periods, such as 10 synchronization code periods. At least one synchronization code is embedded within each of the plurality of synchronization code periods, and each synchronization code is associated with a synchronization code label which includes information indicating the location of the synchronization code in the series of synchronization codes forming part of the super frame.
  • each label includes a constant portion and a variable portion, wherein the variable portion includes a sequence of labels which determine the location of each slot associated with a label in the super frame.
  • a time window which may include several slots is set and the existence of constant portions is checked. Additionally, correspondence of the sequence of labels to a preselected monotonically ordered sequence of numbers is searched.
  • Fig. 56 is a generalized block diagram illustration of a portion of a subscriber unit in a frequency hopping multiple access communication system constructed and operative in accordance with a preferred embodiment of the present invention.
  • the frequency hopping multiple access communication system preferably utilizes a frequency hopping multiple access communication network and a multiplicity of base stations, at least some of which receive and transmit information at a plurality of radio frequencies over the frequency hopping multiple access communication network.
  • the system also includes a multiplicity of subscriber units, each receiving and transmitting information at a plurality of radio frequencies via the frequency hopping multiple access communication network.
  • a receiving and transmitting unit is operable to receive and transmit radio- frequency (RF) signals.
  • RF radio- frequency
  • Receiving and transmitting unit 2010 preferably includes a first antenna 2012, a second antenna 2014 and a radio unit (RU) 2016.
  • Antennas 2012 and 2014 are operable to establish communication channels with a base station (not shown).
  • antennas 2012 and 2014 operate in the frequency range 890 - 950 MHz. However, tuning to other frequency ranges is also possible.
  • RF signals are received at receivers 2018 and 2020, also referred to as RXD and RX respectively.
  • Receiver 2018 is coupled to antenna 2012 and receiver 2020 is coupled to antenna 2014 via a duplexer unit 2022.
  • receivers 2018 and 2020 are converters which convert RF signals to intermediate frequency (IF) signals.
  • receivers RXD and RX determine the quality of reception of the corresponding received signals and the best of the corresponding received signals are selected for processing.
  • Receivers 2018 and 2020 are coupled to a combined gain and frequency control unit 2024 which is operable to provide separate automatic gain control (AGC) signals and common automatic frequency control (AFC) signals to receivers 2018 and 2020.
  • AGC automatic gain control
  • AFC common automatic frequency control
  • gain and frequency control unit 2024 is not a combined unit but may rather include a separate gain control unit and a separate frequency control unit.
  • Gain and frequency control unit 2024 also provides signals to a synthesizer unit 2026, and receives inputs, including a clock signal and data, from a modem 2030 in a baseband unit (BBU) 2028.
  • BBU baseband unit
  • Receivers 2018 and 2020 are also coupled to synthesizer unit 2026 which generates signals necessary to downconvert signals received by receivers 2018 and 2020. Receivers 2018 and 2020 provide the downconverted signals to modem 2030 in BBU 2028.
  • Synthesizer unit 2026 is also operable to generate signals necessary to modulate signals transmitted by a transmitter 2032 which also forms part of radio unit 2016.
  • the signals generated by synthesizer unit 2026 to downconvert the signals received by receivers 2018 and 2020, and the signals generated by synthesizer unit 2026 to modulate the signals transmitted by transmitter 2032, are preferably hopping signals which are generated in accordance with control signals communicated to and from modem 2030. in BBU 2028. Different hopping signals are generated for transmission and for reception.
  • Transmitter 2032 receives control signals from modem 2030 in BBU 2028 and gain control signals from a gain control unit 2024, which also receives inputs from modem 2030. Transmitter 2032 is also coupled to a service board (not shown) which provides electric power to transmitter 2032. Transmitter 2032 outputs data for transmission to antenna 2014 via duplexer unit 2022.
  • a delay locked loop as described with reference to Fig. 57, is operable to maintain the synchronization between the timing signal transmitted by the base station and the timing signal generated in the subscriber unit.
  • the software portion of the delay locked loop is performed and utilized in a DSP (Digital Signal Processing) unit 2036, which forms part of modem 2030, and the hardware operations of the delay locked loop are performed and utilized in a timing unit (not shown) which is part of an ASIC (Application Specific Integrated Circuit) board 2038 in modem 2030 of BBU 2028.
  • DSP unit 2036 and ASIC board 2038 may be separate units which are coupled to modem 2030.
  • Fig. 57 is a simplified illustration of the operation of a delay locked loop in a subscriber unit which forms part of a frequency hopping multiple access communication system constructed and operative in accordance with a preferred embodiment of the present invention.
  • a subscriber unit performs several correlations on a received signal in order to achieve proper synchronization with a signal transmitted by a base station over a control channel.
  • an ideal waveform of a synchronization code signal is stored at DSP unit 2036 of Fig. 56.
  • a synchronization signal portion of incoming RF signals that are received at receivers 2018 and 2020 is detected at the output of receivers 2018' and 2020, and correlated at DSP unit 2036 with the stored ideal waveform of the synchronization code signal.
  • the timing synchronization signal received at the SLS is correlated with the ideal waveform of the synchronization code signal, which is stored at the subscriber unit, to provide an early correlation value RL_COR_ERLY and a late correlation value RL_COR_LATE respectively.
  • the early and late correlation values are a result of the correlations performed at the times tl and t2 , where tl is a time preceding the estimated time at which the synchronization code embedded in the output signal of the RF/IF converter is maximally correlated with the ideal waveform of the synchronization code signal and t2 is a time following that estimated time.
  • the correlation values RL_COR_ERLY and RL_COR_LATE are fed to a delay detector 2050 in which a normalized difference between the early correlation value and the late correlation value is generated. As described hereinafter, the normalized difference is employed to generate a control signal which is monotonically related to the difference.
  • D_ERR (RL_COR_ERLY - RL_COR_LATE) / ( ABS (RL_COR_ERLY) +
  • ABS (RL_COR_LATE) ) (1) where ABS is an absolute value.
  • the output of delay detector 2050 is a time delay value D_ERR that is provided to a loop filter 2052 which is an infinite impulse response filter of a lead-leg type.
  • the output of loop filter 2052 is a smooth response signal DLL_FIL. The following equations are employed to compute DLL_FIL:
  • DLL_FIL D_ERR * C1 + DLL_INTEG ( 3 )
  • Smooth response signal DLL_FIL is provided to a number controlled delay generator 2054 which is operable to generate a hardware delay control signal (HDCS) that is employed to correct timing synchronization.
  • HDCS hardware delay control signal
  • the output of the loop is the hardware delay control signal (HDCS) which is monotonically related to the difference between the timing of the IF signal generated by the receivers 2018 and 2020 and the timing of the ideal waveform of the synchronization signal of the local (subscriber) timing system.
  • HDCS is employed as a hardware instruction to determine the symbol timing by controlling the size of the dividers in counters used for such determination.
  • NCD DLL_FIL + X (4)
  • HDCS ROUND (NCD/R) (5)
  • Fig. 58 is a generalized block diagram illustration of a portion of a base station 2100 in a frequency hopping multiple access communication system constructed and operative in accordance with a preferred embodiment of the present invention.
  • the base station includes a group of receivers 2102, each coupled to an antenna 2104.
  • each receiver in the group of receivers 2102 is operable to receive information signals over one frequency channel.
  • the group of receivers 2102 is coupled to a group of slot processors (SP) 2106. Each receiver in the group of receivers 2102 is coupled to a separate slot processor in the group of SP 2106.
  • SP slot processors
  • the group of SP 2106 is coupled to a communication bus 2108, preferably a modified HDLC communication bus.
  • a group of frame processors (FP) 2110 is also coupled to communication bus 2108.
  • the frame processors in the group 2110 receive inputs from the slot processors in the group 2106 via communication bus 2108.
  • Fig. 59 is a simplified illustration of the operation of a delay locked loop in a base station of a frequency hopping multiple access communication system constructed and operative in accordance with a preferred embodiment of the present invention.
  • the delay locked loop algorithm performed at the base station 2100 is similar to the delay locked loop algorithm performed at the subscriber unit 2010, except that the timing synchronization signal is received and detected at a UTCH_SYNC slot and the calculation of D_ERR is performed in a slot processor and fed as an input to the loop. Furthermore, an additional integration step is applied in the loop due to implementation of the control of the delay in software at the base station.
  • the coefficient C3 has the same value as that of the subscriber unit.
  • the output of loop filter 2140 is a smooth response signal DLL_FIL which is fed to a number controlled delay generator 2142.
  • Number controlled delay generator 2142 is identical with number controlled delay generator 2054 as mentioned previously with reference to Fig. 57.
  • the output of number controlled delay generator 2142 is a DL_OUT value that is fed to an additional integration loop 2144 which is operable to provide a software delay control signal (SDCS), and a hardware delay control signal (HDCS).
  • SDCS software delay control signal
  • HDCS hardware delay control signal
  • the value of SDCS is limited between the values +/- SDCS_LIM, where SDCS_LIM is preferably set to 21.
  • the additional integration loop 2144 is employed at the base station to convert frequency shifts to time shifts.
  • HDCS which is the output of additional integration loop 2144, is employed to correct timing synchronization in software by controlling shift of complex samples in a slot or in a buffer (not shown) in accordance with the time shifts calculated at the additional integration loop 2144.
  • coefficients and correlation values employed in the delay locked loop are real numbers, except for HDCS, SDCS and BACH_DLY which are integers.
  • Fig. 60 is a generalized block diagram illustration of a portion of a subscriber unit in a frequency hopping multiple access communication system constructed and operative in accordance with a preferred embodiment of the present invention.
  • a frequency hopping multiple access communication system utilizes a frequency hopping multiple access communication network and a multiplicity of base stations, at least some of which receive and transmit information at a plurality of radio frequencies over the frequency hopping multiple access communication network.
  • the system also includes a multiplicity of subscriber units, each receiving and transmitting information at a plurality of radio frequencies via the frequency hopping multiple access communication network.
  • a receiving and transmitting unit is operable to receive and transmit radio-frequency (RF) signals.
  • RF radio-frequency
  • Receiving and transmitting unit 3010 preferably includes a first antenna 3012, a second antenna 3014 and a radio unit (RU) 3016.
  • Antennas 3012 and 3014 are operable to establish communication channels with a base station (not shown) .
  • antennas 3012 and 3014 operate in the frequency range 890 - 950 MHz. However, tuning to other frequency ranges is also possible.
  • Radio unit 3016 RF signals are received at receivers 3018 and 3020, also referred to as RXD and RX respectively.
  • Receiver 3018 is coupled to antenna 3012 and receiver 3020 is coupled to antenna 3014 via a duplexer unit 3022.
  • receivers 3018 and 3020 are converters which convert RF signals to intermediate frequency (IF) signals.
  • antenna 3014 In a transmission mode, only antenna 3014 is employed. In a reception mode however, both antenna 3012 and 3014 are employed to achieve space diversity. In that case, receivers RXD and RX determine the quality of reception of the corresponding received signals and the best of the corresponding received signals are selected for processing.
  • Receivers 3018 and 3020 are coupled to a combined gain and frequency control unit 3024 which is operable to provide separate automatic gain control (AGC) signals and common automatic frequency control (AFC) signals to receivers 3018 and 3020.
  • AGC automatic gain control
  • AFC common automatic frequency control
  • gain and frequency control unit 3024 is not a combined unit but may rather include a separate gain control unit and a separate frequency control unit.
  • Gain and frequency control unit 3024 is coupled to a synthesizer unit 3026 which is coupled to a transmitter 3028. Transmitter 3028 is coupled to a power control unit 3030. Gain and frequency control unit 3024 provides signals to synthesizer unit 3026 and receives inputs, including a clock signal and data, from a modem 3034 in a baseband unit (BBU) 3032.
  • BBU baseband unit
  • Receivers 3018 and 3020 are also coupled to synthesizer unit 3026 which generates signals necessary to downconvert signals received by receivers 3018 and 3020.
  • Receivers 3018 and 3020 provide the downconverted signals of the intermediate frequency (IF) to modem 3034 in BBU 3032.
  • IF intermediate frequency
  • Synthesizer unit 3026 is also operable to generate signals necessary to modulate signals transmitted by transmitter 3028.
  • the signals generated by synthesizer unit 3026 to downconvert the signals received by receivers 3018 and 3020, and the signals generated by synthesizer unit 3026 to modulate the signals transmitted by transmitter 3028 are preferably hopping signals which are generated in accordance with control signals communicated to and from modem 3034 in BBU 3032. Different hopping signals may be generated for transmission and for reception.
  • Transmitter 3028 receives control signals from modem 3034 in BBU 3032 and power control signals from power control unit 3030, which also receives inputs from modem 3034 in BBU 3032.
  • Transmitter 3028 is also coupled to a service board (not shown) which provides electric power to transmitter 3028.
  • Transmitter 3028 outputs data for transmission to antenna 3014 via duplexer unit 3022.
  • the gain and frequency control unit 3024 is operable to determine and reduce inaccuracies in each separate frequency of a hopping signal received from at least one base station to acceptable values by employing an AFC algorithm as described with reference to Fig. 61.
  • the AFC algorithm is performed in a DSP (digital signal processing) unit 3036 which may be part of modem 3034.
  • DSP unit 3036 may be a separate unit which is coupled to modem 3034.
  • Fig. 61 is a simplified illustration of the operation of automatic frequency control in a frequency hopping multiple access communication system constructed and operative in accordance with a preferred embodiment of the present invention.
  • a subscriber unit performs several correlations on a received signal in order to achieve proper synchronization with a signal transmitted by a base station.
  • an ideal waveform of a synchronization code signal is stored at DSP unit 3036 of Fig. 60.
  • a synchronization signal portion of incoming RF signals which are received at receivers 3018 and 3020 and are detected and correlated at DSP unit 3036 with the stored ideal waveform of the synchronization code signal to provide complex correlation signals.
  • the correlation provides a frequency difference which is employed to generate a control signal, monotonically related to the frequency difference.
  • the frequency offset is also employed to control the operation of a local frequency source, typically a local oscillator (LO) (not shown) in synthesizer unit 3026, and to compensate for a nonlinearity of operation of the local frequency source.
  • LO local oscillator
  • both antennas of the subscriber unit are employed to achieve space diversity, and the best received signal is selected for processing.
  • correlation signals are obtained at both antennas of the subscriber unit, and diversity selection is performed in DSP unit 3036 on the correlation signals from both antennas to provide a best complex peak correlation signal COR_PEAK, also indicated by (RL_COR_PEAK, IM_COR_PEAK).
  • the frequency offset between the signal received from the base station and the frequency of the LO in the subscriber unit may be obtained by determining the angle between the complex number C0R_PEAK and a positive real axis. The angle obtained is employed to determine an error correction voltage which is applied to a voltage controlled oscillator (not shown), in order to reduce the frequency error.
  • the imaginary part of the complex peak correlation signal IM_COR_PEAK is provided to a first AFC filter 3100 which is performed in DSP unit 3036.
  • first AFC filter 3100 the IM_COR_PEAK signal is filtered to minimize the effects of noise and interference. Filtering of the signal is achieved by performing iterations including integration over time and feed-back operations.
  • C1 and C2 are real numbers whose values are determined in accordance with the number of iterations performed as set forth in Table 1 which is described herein below.
  • the output of the first AFC filter 3100 is a preliminary filtered signal (real number) indicated by FIL_OUT.
  • Signal FIL_OUT is multiplied by a real number coefficient C3 whose values are determined in accordance with the number of iterations performed as set forth in Table 1 which follows:
  • Second AFC filter 3102 receives an input signal SFCS_IC (real number) from DSP unit 3036 which is kept limited between 0 and 1 by a limiter 3104.
  • AFC filter 3102 is operable to perform additional iterations including integration over time using an intermediate value INTEG2 , and feed-back using the SFCS_IC signal.
  • the output of the second AFC filter 3102 is a smoothed frequency offset signal, indicated by SFCS (Software Frequency Control Signal) which has a real number value.
  • SFCS Software Frequency Control Signal
  • the SFCS signal is provided to a frequency to voltage converter 3106, also referred to as CONV, in gain and frequency control unit 3024.
  • the SFCS signal is employed to determine an error correction voltage signal HFCS (Hardware Frequency Control Signal) which is applied to a voltage controlled oscillator (not shown) in gain and frequency control unit 3024, via a D/A converter (not shown) in gain and frequency control unit 3024, in order to reduce the frequency error of the LO.
  • HFCS Hard Frequency Control Signal
  • the HFCS signal is an integer number which is obtained by truncating the function SFCS * (2**12 - 1).
  • variables which exceed +1 or -1 are set to +1 and -1 respectively.
  • Fig. 62 illustrates gain control apparatus which is constructed and operative in accordance with a preferred embodiment of the present invention.
  • the gain control apparatus of Fig. 62 is generally operative to vary the degree of amplification of an amplifier in a radio communications system.
  • the apparatus of Fig. 62 is intended for use in a slotted radio communication system, where received signals are divided into slots.
  • slotted radio communication systems include time-division multiple-access systems. Examples also include certain frequency-division multiple-access systems and cellular communication systems, when those systems also are slotted.
  • the apparatus of Fig. 62 comprises a sample processor 4100.
  • the sample processor 4100 may be any suitable sample processor as, for example, a suitably programmed digital signal processor (DSP), programmed to compute the average of the absolute value of the complex value of incoming samples of each slot.
  • DSP digital signal processor
  • the sample processor 4100 receives gain controlled samples representing the gain level, at different times, of a radio signal received by a radio receiver within a slotted radio communication system.
  • the gain controlled signals received by the sample processor 4100 may be generated, for example, by the RF/IF stage of a radio and an analog to digital converter.
  • the gain controlled samples comprise a plurality of samples for a current slot as, for example, 39 samples per slot.
  • the received signal comprises a plurality of symbols
  • the sample processor 4100 processes the gain controlled samples to produce a processed signal.
  • the apparatus of Fig. 62 further comprises error determination apparatus 4110.
  • the error determination apparatus 4110 may be any suitable error determination apparatus as, for example, a suitably programmed DSP.
  • the error determination apparatus 4110 receives the processed signal from the sample processor 4100. As explained below with reference to Fig. 63, the error determination apparatus 4110 determines the error in the processed signal by comparing the level of the processed signal to a reference level. The error determination apparatus 4110 produces an error signal representing the desired attenuation of the received signal in dB units.
  • the apparatus of Fig. 62 further comprises control apparatus 4120.
  • the control apparatus 4120 may be any suitable control apparatus as, for example, a suitably programmed DSP.
  • the control apparatus 4120 receives the error signal from the error determination apparatus 4110.
  • the control apparatus 4120 converts the error signal, representing attenuation, to a gain control signal and then, through a digital to analog converter, produces an electrical signal of a voltage representing the desired attenuation.
  • the apparatus of Fig. 62 further comprises an attenuator 4130.
  • the attenuator 4130 may be any suitable voltage controlled attenuator, such as, for example, a model TQ9114N commercially available from Triquint Semiconductor, Wireless Communication Division, 3625A W. Murray Blvd, Beaverton, OR 97005.
  • the attenuator 4130 receives the analog electrical signal from the control apparatus 4120 and attenuates the received signal accordingly.
  • Fig. 63 is a simplified flowchart illustrating the operation of a portion of the apparatus of Fig. 62.
  • the flowchart of Fig. 63 illustrates the operation of the sample processor 4100 and the error determination apparatus 4110 of Fig. 62.
  • the method of Fig. 63 preferably comprises the following steps:
  • the plurality of gain controlled samples received by the sample processor 4100, as described above with reference to Fig. 62, are averaged together, typically using an arithmetic average.
  • the samples are grouped together into groups, each group comprising samples for a particular slot.
  • the arithmetic average is computed as the average of the absolute value of the amplitude level over all samples in an active slot.
  • the averaged output of step 4150 is scaled logarithmically to decrease sensitivity to variations.
  • a typical logarithmic scaling would be of the form a log(x) + b , where: x is the averaged output of step 4150; a is a dB scaling factor, typically equal to 20; and b is a threshold level representing the desired level, typically equal to 12.
  • step 4170 The logarithmically scaled output of step 4170 is then filtered, preferably with a finite impulse response - FIR filter.
  • the purpose of step 4170 is to smooth the output, reducing or eliminating the effects of noise and interference.
  • Fig. 64A is a simplified flowchart illustrating an initialization method for the apparatus of Fig. 62, as described in detail in Appendix B. Specifically, steps 4190, 4200, 4210, 4220, 4230, 4240, and 4250 of Fig. 64A are described in Appendix B, paragraphs a - g respectively. Steps 4260, 4270, 4280, and 4290 of Fig. 64A are described in paragraph h of Appendix B.
  • FIGs. 64B and 64C are simplified flowchart illustrations of the method of Appendix A.
  • Fig. 65 is a simplified flowchart illustration of subscriber unit operations during a hand-off process provided in accordance with a preferred embodiment of the present invention.
  • Fig. 66 is a simplified flowchart illustration of base station operations during the hand-off process.
  • the subscriber unit performs a monitoring operation in order to detect a hand-off condition in which the subscriber unit is approaching a fringe area between the old sector through which he is now traveling and a new sector.
  • relative signal strength of control channels in the two sectors is used as a measure of location.
  • the ratio of the signal strengths, or their difference in dB is used.
  • the power of the control channel of a sector neighboring the current sector is at least 4 times as great as the power of the control channel of the current sector, this is taken to indicate presence in a fringe area and is taken to constitute a hand off condition.
  • the subscriber unit When a hand-off condition is detected (process 5020), the subscriber unit sends a hand-off request, identifying the new sector, to a radio servicing the old sector.
  • the hand-off request is forwarded to a radio servicing the new sector via a base station communicating with all sector radios which provides central services to all sectors (process 5030).
  • traffic channel key refers to a packet of information allowing a subscriber unit to transmit and receive, the packet preferably comprising one or more transmission frequencies and one or more reception frequencies.
  • the traffic channel key preferably also comprises a schedule associating each of the plurality of frequencies with one or more slots, such that the subscriber unit is allowed to broadcast and receive on a specified channel in each slot.
  • the new sector will select and transmit a traffic channel key to the subscriber unit. Otherwise (process 5040), the new sector will transmit a "wait signal", also termed herein a "camp-on signal”. If a "camp-on signal" is received (process 5050), the subscriber unit continues using the traffic channel key assigned to him by the old sector radio.
  • a "camp-on signal" continues to be received when the subscriber unit, is already sufficiently deep into the new sector so as to interfere with other subscribers, the subscriber unit preferably disconnects itself.
  • a subscriber unit is taken to be sufficiently deep into the new sector when the received power of the control channel in the new sector is significantly stronger than the received power of the control channel in the old sector as, for example, at least 10 times as strong.
  • the subscriber unit determines the timing and amplitude of the new sector's downlink (process 5060).
  • the subscriber unit sends a new sector synchronization signal to the new sector radio which includes information on uplink timing and amplitude.
  • the new sector radio informs the old sector radio that the old sector traffic channel key is no longer required by the subscriber unit and can be reassigned to another subscriber unit in the old sector (Fig. 66, process 5110).
  • the subscriber unit then switches from the old sector radio to the new sector radio (process 5080), including: terminating use of the old sector traffic channel key; switching the subscriber unit's downlink timing and amplitude from those of the old sector to those of the new sector, as determined in process 5060; and initiating use of the new sector traffic channel key.
  • the base station unit receives the hand-off request sent by the subscriber unit in process 5030 and instructs the new sector radio (process 5090) to try and assign a traffic channel key to the subscriber unit, which is not always possible since traffic channel keys are a limited resource in each sector.
  • the base station which typically includes a switchboard such as a PABX, sets up a 3-way conference call between the subscriber unit, the old sector radio and the new sector radio (process 5100) to "cover" for communication difficulties while the subscriber unit switches from one sector radio to the other.
  • a switchboard such as a PABX
  • the subscriber unit starts operating in the new sector (process 5115).
  • the new sector radio there are typically no special timing considerations for broadcasting to the subscriber unit, and standard methods are therefore employed.
  • For proper reception by the new sector radio it is necessary to utilize correct timing information.
  • the new sector radio has already received a synchronization signal from the subscriber unit (process 5070, above).
  • the synchronization signal is preferably used to provide estimated timing data, and initial reception timing is determined on the basis of the synchronization signal.
  • the base station terminates the 3-way conference (process 5120).
  • the subscriber unit disconnects itself if the subscriber unit is deep into the new sector and has not yet received a traffic channel key from the new sector radio (process 5050).
  • self-disconnection also occurs if a traffic channel key is available however no conference bridge is available at the base station such that no 3-way conference call can be set up between the new and old sector radios, and the subscriber unit which is being handed off.
  • the base station switches the subscriber unit from one sector to another.
  • Fig. 67 is a simplified flowchart illustration of subscriber unit operations during a hand-off process provided in accordance with an alternative preferred embodiment of the present invention.
  • Fig. 68 is a simplified flowchart illustration of base station operations during a hand-off process provided in accordance with an alternative preferred embodiment of the present invention.
  • the method of Fig. 67 is similar to the method of Fig. 65, except that hand-off occurs separately on the uplink channel and on the downlink channel. It is appreciated that the hand-off on the two channels may occur in either order, with the uplink hand-off first or with the downlink hand-off first.
  • the channels are referred to as the first channel and the second channel.
  • process 5080 of Fig. 65 is replaced with processes 5130, 5140, 5150, and 5160.
  • process 5130 the subscriber unit waits until no voice activity is heard on the first channel, preferably by using voice activity detection (VAD), as is well known in the art.
  • VAD voice activity detection
  • process 5140 the subscriber unit switches to the new sector radio for the first channel only, using a process similar to that described above with reference to process 5080, except that the switch occurs on the first channel only.
  • process 5150 the subscriber unit waits until no voice activity is heard on the second channel, preferably by using voice activity detection (VAD), as is well known in the art.
  • VAD voice activity detection
  • process 5160 the subscriber unit switches to the new sector radio for the second channel only, using a process similar to that described above with reference to process 5080, except that the switch occurs on the second channel only.
  • Fig. 68 is similar to Fig. 66, with process 5110 of Fig. 66 replaced with processes 5130, 5170, 5150, and 5180. Processes 5130 and 5150 are described above with reference to Fig. 67.
  • Process 5170 is similar to process 5110, except that process 5170 occurs on the first channel only and with a single channel key, the key associated with the first channel, being freed.
  • Process 5180 is similar to process 5170, except that process 5180 occurs on the second channel and not the first channel.
  • Fig. 69 is a simplified block diagram of a power control system for use in a radio communication system, the power control system being constructed and operative in accordance with a preferred embodiment of the present invention.
  • the power control system of Fig. 69 comprises a first station 6100 and a second station 6110.
  • the present invention may be useful in many different kinds of radio communications systems, including a radio communication system comprising any number of stations.
  • the power control system of the present invention may be used to control and optimize transmission power in any radio communication system, with goals including optimizing reception and minimizing interference between stations while minimizing the power used for transmission.
  • the present invention is described as being used in a mobile radio system.
  • the power control system of the present invention is particularly suited to controlling power in a mobile radio system, since the mobility of stations in a mobile radio system requires relatively frequent power adjustment in order to achieve the goals described above. It is appreciated, however, that the present invention is not limited to use in a mobile radio system, but may be used in any suitable radio communication system.
  • the power control system of the present invention is particularly suited to controlling power in a multiple access radio communication system, and in a frequency hopping system. It is appreciated, however, that the present invention is not limited to use in multiple access and/or frequency hopping radio communication systems, but may be used in any suitable radio communication system.
  • the first station 6100 may comprise a subscriber unit, typically a mobile station, while the second station 6110 may comprise a base station, typically a fixed station. It is appreciated, however, that the first station and second station, as described herein with regard to various embodiments of the present invention, may be any of a number of types of stations.
  • the first station 6100 comprises a first station transmitter 6120, which may be any suitable type of radio transmitter, depending on the type of radio communication supported by the radio communication system. Suitable transmitters include the capability of having their transmission power regulated in response to an external control.
  • Suitable transmitters include transmitters used in SMR (special mobile radio) and cellular systems, including transmitters suitable for TDMA (time division multiple access), FDMA (frequency division multiple access), AMPS (analog FM), and FHMA (frequency hopping multiple access) systems.
  • TDMA time division multiple access
  • FDMA frequency division multiple access
  • AMPS analog FM
  • FHMA frequency hopping multiple access
  • CR-920 Cellular Radio Transmitter Driver commercially available from Frequency Products, Inc., 3475-M Edison Way, Menlo Park, CA 94025.
  • the first station 6100 further comprises a power level controller 6130.
  • the power level controller 6130 is operative to control the transmission power of the first station transmitter 6120.
  • the power level controller 6130 may be any suitable power level controller, such as a gain controlled amplifier or a voltage controlled attenuator operatively associated with a fixed gain amplifier, or a digitally controlled step attenuator operatively associated with an amplifier, typically a fixed gain amplifier.
  • a suitable power controller is the RF2410 UHF Programmable Attenuator, commercially available from RF Micro Devices, 7341-D West Friendly Ave., Greensboro, NC 27410.
  • the first station 6100 also comprises a signal processor 6135, which may be any suitable signal processor as, for example, a DSP 2111, commercially available from Analog Devices.
  • a signal processor 6135 may be any suitable signal processor as, for example, a DSP 2111, commercially available from Analog Devices.
  • the first station 6100 also comprises a first station receiver 6140, which may be any suitable type of radio receiver, depending on the type of radio communication supported by the radio communication system.
  • Suitable receivers include receivers used in SMR (special mobile radio) and cellular systems, including receivers suitable for TDMA (time division multiple access), FDMA (frequency division multiple access), AMPS (analog FM), and FHMA (frequency hopping multiple access) systems.
  • SMR special mobile radio
  • TDMA time division multiple access
  • FDMA frequency division multiple access
  • AMPS analog FM
  • FHMA frequency hopping multiple access
  • CR-910 Cellular Radio Dual Conversion Receiver commercially available from Frequency Products, Inc., 3475-M Edison Way, Menlo Park, CA 94025.
  • the second station 6110 comprises a second station receiver 6150, which may be any radio receiver suitable to receive the transmissions of the first station transmitter 6120. Radio receivers suitable for the first station receiver 6140 are also suitable for the second station receiver 6150.
  • the second station 6110 further comprises a power level detector 6160, suitable for detecting the power level of signals received by the second station receiver 6150.
  • the power level detector 6160 may be any suitable power detector, implemented in hardware, in software, or in a combination of hardware and software. Suitable power level detectors include: an AM detector combined with an automatic gain control current state detector.
  • the power level detector 6160 may alternatively be operative to detect a characteristic other than power, which characteristic provides an alternative measure of signal strength.
  • Examples of such alternative power level detection methods include: computation of signal to noise ratio such as computation of bit energy to noise density ratio in the received signal; computation of carrier to interference ratio; bit error rate performance; channel state performance; frame error rate performance, measured by the rate of bad CRC indications.
  • the second station 6110 further comprises a power level comparator 6170.
  • the power level comparator 6170 may be any suitable analog or digital power level comparator, typically implemented in software. In comparing power levels, the power level comparator 6170 is operative to utilize a threshold value appropriate to the particular power detection method used by the power level detector 6160, based on overall detection and decoding performance of the system as a whole. For example, an appropriate threshold value may be approximately 8 dB.
  • the second station 6110 further comprises a second station transmitter 6180.
  • the second station transmitter 6180 may be any radio transmitter suitable to send transmissions capable of being received by the first station receiver 6140. Radio transmitters suitable for the first station transmitter 6120 are also suitable for the second station transmitter 6180.
  • first station transmitter 6120 and the second station transmitter 6180 may be of different types, including types of transmitters operating on different bands. It is also appreciated that the first station receiver 6140 and the second station receiver 6150 may be of different types, including types of receivers operating on different bands.
  • Fig. 70A is a simplified flowchart illustrating the operation of the apparatus of Fig. 69.
  • the steps of the method of Fig. 70A preferably include the following:
  • STEP 6190 Choose initial transmitted power level for first station.
  • the power level controller 6130 sets an initial transmitted power level for the first station 6100.
  • the initial transmitted power level may be set arbitrarily. Typically, the initial transmitted power level may be the maximum power level.
  • the initial transmitted power level may be based on an open loop estimate of the required power level, relying on the duality of paths between the first station 6100 and the second station 6110. That is, the expected power loss on the path from the first station 6100 to the second station 6110 is approximately equal to the power loss from the second station 6110 to the first station 6100. This principle is called "path loss duality".
  • a nominal initial transmitted power level estimate is made based on the expected power loss and the desired received power at the second station. Then, the initial power level is set accordingly, preferably including a safety margin, typically of lOdB over the nominal estimate.
  • STEP 6192 Transmit first message from first station 6100 to second station 6110.
  • the first station 6100 transmits a first message 6182, shown in Fig. 69, using the first station transmitter 6120 operating at the initial power level, to the second station 6110.
  • STEP 6194 Receive first message at second station.
  • the first message 6182 is received by the second station receiver 6150.
  • STEP 6196 Detect received power level at second station.
  • the power level detector 6160 determines the power level of the first message 6182 as received by the second station 6110. As described above with reference to Fig. 69, any number of different methods may be used by the power level detector 6160 to determine the power level of the first message 6182.
  • STEP 6197 Compare received power level to predetermined value and determine difference.
  • the power level comparator 6170 compares the power level detected by the power level detector 6160 to a predetermined power level.
  • dB scale which is a ratio scale, or as a function of dB level.
  • An arithmetic difference on a dB scale represents a ratio between two power levels.
  • difference refers to any appropriate measure of difference in power as, for example, a difference on the dB scale representing a ratio between two power values.
  • the predetermined power level represents a sufficiently high received power level at the second station 6110 to allow nominal performance.
  • the predetermined power level is thus dependent on the particular characteristics of the second station receiver 6150.
  • the predetermined power level may be between approximately 8 dB and approximately 15 dB.
  • the predetermined power level may typically be determined in advance based on the characteristics of the second station 6110.
  • the power level comparator 6170 determines the difference between the predetermined power level and the detected power level.
  • the received power level at the second station 6110 may vary irregularly from message to message. It is typically not desired to vary the transmitted power level at the first station 6100 more than is necessary to cause the received power level at the second station 6110 to remain within predetermined tolerances.
  • the actual tolerances depend on the particular characteristics of the communication system of which the first station 6100 and the second station 6110 are a part. Typically, the tolerance is approximately 10 dB.
  • comparing the received power level to the predetermined value preferably includes "smoothing" the received power level to remove such irregular variations.
  • smoothing is achieved by low pass filtering of the received power level. Examples of appropriate low pass filters include: an FIR filter ⁇ finite impulse response; an IIR filter infinite impulse response.
  • STEP 6201 Transmit second message from second station to first station, including indication of difference.
  • the second station transmitter 6180 transmits a second message 6184, shown in Fig. 69, to the first station.
  • the second message 6184 includes an indication of the difference between the predetermined power level and the detected power level.
  • the indication of the difference may comprise the difference itself or any function thereof.
  • the second message 6184 preferably also includes other information that would in any case need to be sent from the second station 6110 to the first station 6100, so that no additional message need be sent.
  • the second message 6184 may optionally be sent on the control channel.
  • STEP 6202 Receive second message at first station.
  • the first station receiver 6140 receives the second message 6184 and transmits, within the first station 6100, the indication of the difference between the predetermined power level and the detected power level to the power level controller 6130.
  • STEP 6203 Filter the received message using an appropriate filter, as, for example, a filter implemented in software in signal processor 6135.
  • an appropriate filter as, for example, a filter implemented in software in signal processor 6135.
  • Fig. 70B is a simplified electronic circuit diagram illustrating the operation of a preferred implementation of step 6203 of Fig. 70A.
  • Fig. 70B illustrates in detail the method of operation of one possible example of an appropriate filter. It is appreciated that many other appropriate methods of filtering are also possible.
  • the method of Fig. 70B takes an unfiltered input PWR_CNT_SYM and produces a filtered output HPCS.
  • the unfiltered input PWR_CNT_SYM is a control signal for the method of Fig. 70B.
  • PWR_CNT_SYM is produced by an automatic gain control process.
  • One possible methodL-ior producing PWR_CNT_SYM is as follows: SGCS0 and SCGS1, respectively, be gain control signals from two different reception channels, or diversity channels, 0 and 1.
  • the values of SGCS0 and SGCS1 vary between 0 and 1, with 0 representing minimum signal and maximum gain, and 1 representing maximum signal and minimum gain.
  • a plurality of previous values as, for example, eight values of SGCS0 and SGCS1 from a current slot and the previous 7 slots, are used;
  • T1 and T2 represent threshold values.
  • a typical value of RES, throughout the method of Fig. 70B, is 1/70.
  • delta-T has the value 6160 msec for the first 40 iterations and 480 msec afterwards.
  • the method of producing PWR_CNT_SYM uses a non-smooth function. It is appreciated that many other methods of producing PWR_CNT_SYM are also possible, such as using a linear function or a non-linear but smooth function.
  • Fig. 70B The method of Fig. 70B is self-explanatory, except as follows:
  • DZ 6198 is a dead zone, whose output Y depends on its input X according to the relationship:
  • Limiter 6199 limits the signal input between 0 and 1 ;
  • dB_to_V 6200 produces the filtered output signal HPCS and, in one preferred embodiment of the present invention, typically operates as follows:
  • IC_SPCS near 0 indicates transmission of a transmitted signal at the lower end of the dynamic range.
  • IC_SPCS near 1 indicates transmission of a transmitted signal at the higher end of the dynamic range.
  • STEP 6204 Modify transmitted power level for first station.
  • the power level controller 6130 modifies the current power level based on the initial power level and the difference. Typically, the new power level is set to be the initial power level plus the filtered difference, within a predetermined maximum and minimum power level.
  • the difference typically a difference on a dB scale representing a ratio between power levels
  • the modification to the current power level may be based partly on the stored difference.
  • the difference may be compared to a stored minimum or threshold value and the current power level may be modified only if the difference exceeds the stored threshold value.
  • the stored threshold value may be a predetermined value such as, for example, 5dB or lOdB.
  • the method of Fig. 70A may be performed iteratively, although the method of Fig. 70A may be performed only once.
  • the power level is modified repeatedly over time in order to adapt to changing needs. Iteratively modifying the power level is particularly preferred in the case where at least either the first station 6100 or the second station 6110 is a mobile station, so that the positions of the first station 6100 and the second station vary over time, as do the distance between the first station 6100 and the second station 6110, and the locations of the first station 6100 and the second station 6110 relative to sources of interference and of shadowing.
  • Fig. 71 is a simplified flowchart illustrating the operation of step 6204 of Fig. 70A according to an alternative embodiment of the present invention.
  • Fig. 71 illustrates the alternative wherein the difference between the predetermined power level and the detected power level is stored and the modification to the current power level is based partly on the stored difference.
  • the method of Fig. 71 preferably includes the following steps:
  • STEP 6206 Store indication of filtered difference.
  • the indication of the filtered difference between the predetermined power level and the detected power level is stored for future retrieval.
  • the filtered difference may be stored along with an indication of when the difference occurred, such as, for example, the time or a message identification.
  • some function based on the filtered difference may be stored, such as, for example, the sum of all filtered differences until the current filtered difference.
  • STEP 6208 Choose increment based on both current difference and stored difference.
  • the increment to be used in modifying the current power level is chosen based on both the current filtered difference and on one or more stored filtered differences.
  • Typical methods for choosing an increment include: computing an average of the current difference and the stored difference and using the average as the increment; computing a trend of stored differences and the current difference and choosing the sign of the increment based on the trend; and computing the magnitude of the increment as a function of the current difference and the stored differences and also applying a stored threshold difference and choosing a non-zero increment only if the computed function exceeds the stored threshold difference.
  • the stored threshold difference may be a predetermined value such as, for example 5dB or 10dB.
  • Fig. 72 is a simplified block diagram of a power control system for use in a radio communication system, the power control system being constructed and operative in accordance with an alternative preferred embodiment of the present invention.
  • the power control system of Fig. 72 comprises a first station 6210. Except as described below, the first station 6210 is similar to the first station 6100 of Fig. 69.
  • the power control system of Fig. 72 also comprises a second station 6220. Except as described below, the second station 6220 is similar to the second station 6110 of Fig. 69.
  • the present invention may be useful in many different kinds of radio communication system, including a radio communication system comprising any number of stations.
  • the power control system of the present invention may be used to control and optimize transmission power in any radio communication system, with goals including optimizing reception and minimizing interference between stations while minimizing the power used for transmission.
  • the first station 6210 comprises a first station transmitter 6120, a first station receiver 6140, and a signal processor 6135, each as described above with reference to Fig. 69.
  • the first station 6210 need not comprise other elements of the first station 6100 as described above with reference to Fig. 69.
  • the second station 6220 comprises a second station receiver 6150, a power level detector 6160, and a second station transmitter 6180, each as described above with reference to Fig. 69.
  • the second station 6220 further comprises a power level comparator 6230.
  • the power level comparator 6230 may be similar to the power level comparator 6170 of Fig. 69.
  • the second station 6220 further comprises a power level controller 6240.
  • the power level controller 6240 is operative to control the transmission power of the second station transmitter 6180.
  • the power level controller 6240 may be similar to the power level controller 6130 of Fig. 69.
  • Fig. 73 is a simplified flowchart illustrating the operation of the apparatus of Fig. 72.
  • the steps of the method of Fig. 73 include the following:
  • STEP 6243 Determine desired received power level at first station 6210.
  • the desired received power level represents the optimum received power level at the first station 6210.
  • the desired received power level may typically be determined in advance based on the characteristics of the first station receiver 6140.
  • the desired received power level may be a predetermined parameter known to the second station 6220, or may alternatively be communicated to the second station 6220, either before the operation of the method of Fig. 72 or as part of a message transmitted from the first station 6210 to the second station 6220.
  • STEP 6244 Transmit signal from first station 6210 to second station 6220, including indication of first station 6210 transmitted power level.
  • the first station 6210 transmits a signal comprising a first message 6241, shown in Fig. 72, using the first station transmitter 6120 operating at a transmitted power level, to the second station 6220.
  • the first message 6241 includes an indication of the transmitted power level and an indication of the noise level received by the first station 6210 in previous transmissions from the second station 6220.
  • the portion of the first message 6241 comprising an indication of the transmitted power level and the received noise level may be transmitted on a different channel than the remaining portion of the first message 6241.
  • Such a different channel is typically called a control channel.
  • the transmissions on the control channel may typically comprise other signals useful for control of the radio communication system.
  • STEP 6246 Receive signal at second station.
  • the signal comprising the first message 6241 is received by the second station receiver 6150.
  • STEP 6248 Measure received power level of signal at second station 6220.
  • the power level detector 6160 determines the power level of the first message 6241 as received by the second station 6220, as described above with reference to Figs. 69 and 70.
  • STEP 6250 Compare received power level to transmitted power level and compute transmission loss.
  • the power level comparator 6230 compares the power level detected by the power level detector 6160 to the transmitted power level.
  • the transmission loss is computed by computing the difference between the received power level and the transmitted power level.
  • the transmitted power level was received by the second station 6220 as part of the first message 6241.
  • the power level comparator 6230 computes the difference between the transmitted power level and the detected power level and thus determines the transmission loss between the first station 6210 and the second station 6220.
  • the method of Fig. 73 relies on the assumption of path loss duality, as explained above with reference to Fig. 70A.
  • the computed path loss of the first message 6241 sent from the first station 6210 to the second station 6220 is taken, according to path loss duality, to be the expected value of transmission loss for a second message 6242 sent from the second station 6220 to the first station 6210.
  • the received power levels at the second station 6220 and at the first station 6210 may vary irregularly from message to message. It is typically not desired to vary the transmitted power level at the second station 6220 more than is necessary to cause the received power level at the first station 6210 to remain within acceptable limits. Depending on the characteristics of the first station receiver 6140, the limits may typically be between 10dB and 70dB. Therefore, comparing the received power level to the transmitted power level preferably includes smoothing the received power level to remove such irregular variations. Alternatively, smoothing may be done in the first station 6210, typically in the power level controller 6130, as described above with reference to Fig. 70A.
  • STEP 6252 Determine transmitted power level for second station 6220 based on desired received power level, on transmission loss, and on received noise level at the first station 6210.
  • the transmitted power level for the second station 6220 is computed based on the desired received power level, determined in advance; the expected transmission loss in the direction from the second station 6220 to the first station 6210, determined in step 6250; and the received noise level at the second station, also determined in step 6250.
  • the transmitted power level for the second station 6220 is the sum in dB of the desired received power level, the expected transmission loss, and the received noise level at the second station.
  • the second message 6242 is then sent with the transmitted power level.
  • the transmitted power level is computed by signal processor 6135 by computing the sum of the desired received power level and the expected transmission loss.
  • Fig. 74 is a simplified block diagram of a power control system for use in a radio communication system, the power control system being constructed and operative in accordance with another alternative preferred embodiment of the present invention.
  • the apparatus of Fig. 74 comprises the components of station 6110 of Fig. 69 and of station 6220 of Fig. 72.
  • Message 6254 comprises message 6184 of Fig. 69 and message 6241 of Fig. 72
  • message 6256 comprises message 6182 of Fig. 69 and message 6242 of Fig. 72.
  • Fig. 75 is a simplified flowchart illustrating a preferred method for operating the apparatus of Fig. 74.
  • the method of Fig. 75 combines the methods of Figs. 70A and 73.
  • the open loop control method of Fig. 73 is taken as the master, while the closed loop control method of Fig. 70A is used to adjust the results of the open loop method. This is done because, typically, the closed loop method is slower but more accurate.
  • Fig. 74 is symmetrical, that is, either station 6110 or station 6220 of Fig. 74 may take the role of first station or second station in the methods of Figs. 70A and 73.
  • the open loop power control method of Fig. 73 is performed (step 6270).
  • the closed loop power control method of Fig. 70A is performed (step 6280).
  • the results of the open loop method are adjusted based on the results of the closed loop method (step 6290).
  • Fig. 76 is a simplified partly pictorial, partly block diagram illustration of a radio communication system constructed and operative in accordance with a preferred embodiment of the present invention.
  • the system of Fig. 76 comprises a base station (BS) 7010 and a subscriber unit (SU) 7020.
  • BS base station
  • SU subscriber unit
  • the SU 7020 is a mobile subscriber unit.
  • a regular transmission 7030 is sent from the SU 7020 to the BS 7010.
  • the BS 7010 determines the time alignment error of the regular transmission 7030 and sends a timing alignment message 7040 to the SU 7020.
  • the SU 7020 then corrects its timing for subsequent transmissions based on the timing alignment message 7040.
  • time alignment of messages sent from the SU 7020 generally varies over time due to a number of factors as, for example, movement of the SU 7020 relative to the BS 7010.
  • Fig. 77 is a simplified flowchart illustration of a method for time alignment in the radio communication system of Fig. 76.
  • the SU 7020 when the SU 7020 first receives a control channel signal sent by the BS 7010, as, for example, when the SU 7020 is first switched on or, for example, when the SU 7020 moves into the range of another base station and first receives a control signal therefrom, the SU 7020 resets any time alignment data which it may have accumulated.
  • the reason for resetting the time alignment data in those circumstances is that time alignment relates to alignment with a particular base station, so that being switched on or coming into the range of a new base station implies that the old time alignment data is invalid.
  • the SU 7020 transmits an uplink transmission (process 7100), which may comprise, for example, an access channel transmission (ACH) or an uplink traffic channel transmission (UTCH).
  • An ACH is a uplink control/information transmission sent from the SU 7020 to the BS 7010.
  • An uplink traffic channel transmission is a regular uplink message, such as a message carrying voice or data. The uplink transmission is transmitted via an air interface to the BS 7010.
  • the uplink transmission is detected and decoded (process 7120).
  • Detection and decoding comprises determining the timing offset (D) of the uplink transmission, that is, the difference between the time at which the uplink transmission is received and the assigned time for that uplink transmission.
  • the absolute value of the timing offset D is compared to a threshold offset D 0 (process 7130).
  • the threshold offset D 0 is set at 1/2 of the time necessary to transmit a single symbol.
  • a timing alignment command TA_COM(D) indicating the time offset value D is transmitted (process 7135) from the BS 7010 to the SU 7020 via the air interface.
  • the timing alignment command TA_COM(D) is received at the SU 7020.
  • the SU 7020 immediately acknowledges the receipt of the timing alignment command to the BS 7010 (acknowledgement not shown in Fig. 77).
  • the SU 7020 corrects its time alignment in accordance with the information received in the timing alignment command TA_COM(D) (process 7140).
  • the timing alignment command TA_COM(D) comprises a unique sequence number
  • the SU 7020 checks the sequence number and does not perform a time alignment correction if a message with a duplicate sequence number is received.
  • a preferred implementation of correction of time alignment in process 7140 is as follows.
  • T_SLT local transmitter timing
  • a second timing alignment message is not sent until a predetermined delay after acknowledgment of the first timing message.
  • the predetermined delay is approximately 60 seconds.
  • certain messages from the SU 7020 which, if acted upon, might interfere with system operations, are ignored if the SU 7020 is found not to be time aligned.
  • Examples of such messages preferably include messages requesting allocation of a channel, such as, for example, traffic and access channel allocation.
  • the BS 7010 will ignore messages associated with the SU 7020 if the SU 7020 is not operating in the sector of the BS 7010, or containing a code not suited to be sent by a subscriber unit.
  • the timing alignment command TA_COM(D) comprises an indication of whether the timing alignment is based on an access channel transmission or a traffic channel transmission.
  • the SU 7020 compares the message type, access or traffic, to the message most recently sent by the SU 7020 and corrects its time alignment only if the message type contained in the timing alignment message is identical to the type of the most recent transmission.
  • step 7120 A preferred method for determining the timing offset D in step 7120 is now described.
  • BACH_DLY BACH Delay
  • TCH_FP Traffic Channel Frame Processor
  • TCHM Traffic Channel Message
  • D_ERR Current Delay Control Signal
  • TA_CMD(D) For each new D, check whether D > D 0 . If the answer is affirmative, than a TA_CMD(D) with the D parameter and sequence number is sent to SU 7010. D is given a range compatible with the number of bits available. The TA_CMD(D) is then acknowledged.
  • the SU 7020 transmits a periodic status message to the BS 7010.
  • a periodic status message to the BS 7010.
  • the SU 7020 accumulates the set of all time alignment performed since the last reset was done upon receipt of an initial time alignment command.
  • a detailed implementation of the handling of accumulated time alignment is as follows. After each timing reset (SU 7020 resets its transmitter timing (T_SLT) after completing time acquisition) or sector switching (Handoff and/or reserved sector) SU 7020 should transmit its Tx Timing Status (During regular operation (IDLE, VOICE, etc.)), the Subscriber accumulates the net Tx Timing Shift and subtracts it from the current Rx timing, i.e. the sum of all Tx shifts minus the sum of all Rx shifts since the last reset. The current accumulation result is noted by Tx Timing Status.
  • the shifting operations are limited so that the Tx Timing Status does not exceed +/- 96 shifting increments of 1/16 symbol) to the new sector and wait for an acknowledgement.
  • the transmission has up to 1024 possible values and thus the message should include 10 bits CACH (Composite Access Channel) transmission or UTCH_IBOH (Uplink Traffic Channel Inband Overhead) .
  • any SU_STATUS signals are transmitted during a time interval, described hereinabove, (i.e. from receiving a TA_CMD(D) command until the end of the time shifting) then the SU_STATUS transmission is delayed until after the end of this interval.
  • the BS 7010 may optionally compute the range of the SU 7020.
  • a preferred method for computing the range of an individual subscriber unit is as follows:
  • BS 7010 needs the range of any eligible Subscriber Unit, the range is evaluated by the following:
  • R ⁇ D + SUM(D i ) + D 0 /2 ) *C *T-/2 + R- where R is Range of the Subscriber Unit;
  • D is the last BACH_DLY or the current SDCS (Software Delay Control Signal) if within a UTCH receiving;
  • D i is the BACH_DLY or the SDCS parameter of the TA_CMD(D) number i;
  • TA_NUM is the number of TA_CMD(D) which were sent and acknowledged to this Subscriber Unit, since the last "Tx Timing Status";
  • D 0 is the last "TX Timing Status" of the Subscriber
  • R 0 is a calibration parameter (sector dependent). and the SUM(D i ) is taken from 1 to TA_NUM.
  • Fig. 78 is a simplified partly-pictorial, partly block-diagram illustration of a radio communication system constructed and operative in accordance with a preferred embodiment of the present invention.
  • the system of Fig. 78 comprises a transmitting station 8050 and a receiving station 8060, both of which may be any appropriate type of radio communication station, including stations of types which are well-known in the prior art.
  • the stations are part of a frequency hopping multiple access (FHMA) communication system.
  • FHMA frequency hopping multiple access
  • the transmitting station 8050 breaks a message into a plurality of sub-messages and transmits the sub-messages to the receiving station 8060 in sub- message transmission 8070.
  • the receiving station receives each sub-message, checks the sub-message for errors and, if the sub-message contains an error, adds the sub-message to a list of bad sub-messages.
  • the receiving station 8060 When all of the sub-messages are received by the receiving station 8060, the receiving station 8060 preferably transmits a retransmission request 8080 to the transmitting station 8050, comprising a list of sub-messages which were not received correctly. The transmitting station 8050 then retransmits the requested sub-messages in a retransmission 8090 to the receiving station 8060.
  • the receiving station 8060 may transmit an acknowledgement message to the transmitting station 8050, comprising an acknowledgement that all sub-messages were received correctly.
  • the absence of such an acknowledgement is typically taken as the equivalent of a retransmission request for all sub-messages.
  • Fig. 79 is a simplified block diagram illustration of a preferred method for operating the system of Fig. 78.
  • the method of Fig. 79 preferably includes the following steps:
  • STEP 8100 Break message into sub-messages.
  • the message is broken into sub-messages at the transmitting station 8050.
  • the sub-messages may be of any appropriate size.
  • the size of sub- messages is chosen in order to minimize, in practice, the mean or average number of retransmissions.
  • STEP 8110 Add error detection code to each sub-message. Any appropriate error detection code, as is well known in the art, is added to each sub-message. Preferably, CRC code is used. Alternatively, in place of error detection code other means for detecting errors, such as checking received messages for internal consistency, may be used.
  • STEP 8120 Transmit sub-message. The current sub-message is transmitted from the transmitting station 8050 to the receiving station 8060.
  • STEP 8130 Receive, detect, and decode sub-message.
  • the receiving station 8060 receives the sub-message and decodes the sub-message so that the data portion and the error detection code can be examined.
  • STEP 8140 Check error detection code of sub-message .
  • the error detection code of the sub-message is checked to see whether any errors are indicated.
  • STEP 8150 Was sub-message received correctly? Check, preferably based on the error detection code, whether the sub-message was received correctly.
  • STEP 8160 Mark sub-message bad. If the sub-message was not received correctly, the sub-message is marked bad in an internal list maintained by the receiving station 8060.
  • STEP 8170 Was last sub-message received? Check whether the sub-message just processed was the last sub-message in the message. If not, processing continues at step 8120, described above.
  • STEP 8190 Acknowledge message. If no sub-message was marked bad, the receipt of the entire message is acknowledged by the receiving station 8060 to the transmitting station 8050. Alternatively, the receiving station 8060 may notify the transmitting station 8050 that certain messages were not received correctly by sending a message comprising a list of sub-messages which were not received correctly.
  • STEP 8200 Request retransmission. If any sub-message was marked bad, the receiving station 8060 requests the transmitting station 8050 to retransmit those sub-messages which were marked bad. Preferably, only the sub-messages marked bad are retransmitted. Processing then continues at step 8120, described above.
  • Fig. 80 is a simplified block diagram illustration of a preferred error detection method useful in conjunction with the method of Fig. 79.
  • the method of Fig. 80 is preferably performed at the completion of the method of Fig. 79.
  • the transmitting station 8050 may typically retransmit a plurality of sub-messages comprising both sub-messages which were not received correctly and sub-messages which were already received correctly.
  • the sub-messages retransmitted may comprise sub-messages which were already received correctly. Thus, a given sub-message may be received correctly more than once.
  • the receiving station 8060 preferably determines which sub-message contents to use based on a decision criterion as, for example, based on taking the majority of the different instances of the sub-message or based on taking the most prevalent of the different instances of the sub-message (step 8220).
  • Fig. 81 is a simplified block diagram illustration of another preferred error detection method useful in conjunction with the method of Fig. 79.
  • the method of Fig. 81 is preferably performed at the completion of the method of Fig. 79.
  • an additional error detection code is assigned to the message as a whole and is transmitted from the transmitting station 8050 to the receiving station 8060 either as part of one or more of the sub-messages or as a separate message (step 8230).
  • the additional whole message error detection code is more reliable than the error detection codes of each sub-message.
  • the CRC code of the whole message is computed using more bits than the CRC codes of the individual sub-messages.
  • the receiving station 8060 checks the whole message error detection code (step 8240). If the whole message error detection code is erroneous, the receiving station 8060 checks each possible combination of sub-messages received, for all sub-messages where more than one instance of the sub-message was received, looking for a combination of sub-message instances which yields correct error detection code (step 8250). If such a correct combination is found, that combination as a whole is taken to be the correct message.
  • the receiving station 8060 requests retransmission of sub-messages for which no clear majority or other indication of definitely correct reception is found (step 8260).
  • the steps of the method of Fig. 81 are preferably repeated until correct whole message error detection code is found (step 8245).
  • the steps are only repeated until some predetermined repetition limit is reached as, for example, a maximum number of retransmission requests or a maximum time to receive a single message.
  • MARQ memory automatic repeat request
  • the receiver tests the validity of all frames received based on CRC (cyclic redundancy checking). A frame is considered valid if one of the following conditions apply:
  • the receiver computes the CS ("check sum").
  • N3 is the number of Triple_Ambiguous_Frames, then every possible permutation is tried and the validity of CS tested for each.
  • Fig. 82 is a generalized block diagram illustration of a portion of a subscriber unit in a frequency hopping multiple access communication system constructed and operative in accordance with a preferred embodiment of the present invention.
  • a frequency hopping multiple access communication system utilizes a frequency hopping multiple access communication network and a multiplicity of base stations, at least some of which receive and transmit information at a plurality of radio frequencies over the frequency hopping multiple access communication network.
  • the system also includes a multiplicity of subscriber units, each receiving and transmitting information at a plurality of radio frequencies via the frequency hopping multiple access communication network.
  • a receiving and transmitting unit is operable to receive and transmit radio-frequency (RF) signals.
  • RF radio-frequency
  • Receiving and transmitting unit 9010 preferably includes a first antenna 9012, a second antenna 9014 and a radio unit (RU) 9016.
  • Antennas 9012 and 9014 are operable to establish communication channels with a base station (not shown).
  • antennas 9012 and 9014 operate in the frequency range 890 - 950 MHz.
  • Radio unit 9016 RF signals are received at receivers 9018 and 9020, also referred to as RXD and RX respectively.
  • Receiver 9018 is coupled to antenna 9012 and receiver 9020 is coupled to antenna 9014 via a duplexer unit 9022.
  • receivers 9018 and 9020 are converters which convert RF signals to intermediate frequency (IF) signals.
  • antenna 9014 In a transmission mode, only antenna 9014 is employed. In a reception mode however, both antenna 9012 and 9014 are employed to achieve space diversity. In that case, receivers RXD and RX determine the quality of reception of the corresponding received signals and the best of the corresponding received signals are selected for processing.
  • receivers 9018 and 9020 are coupled to a combined gain and frequency control unit 9024 which is operable to provide separate automatic gain control (AGC) signals and common automatic frequency control (AFC) signals to receivers 9018 and 9020.
  • AGC automatic gain control
  • AFC common automatic frequency control
  • gain and frequency control unit 9024 is not a combined unit but may rather include a separate gain control unit and a separate frequency control unit.
  • Gain and frequency control unit 9024 is coupled to a synthesizer unit 9026 which is coupled to a transmitter 9028. Transmitter 9028 is coupled to a power control unit 9030. Gain and frequency control unit 9024 provides signals to synthesizer unit 9026 and receives inputs, including a clock signal and data, from a modem 9034 in a baseband unit (BBU) 9032.
  • BBU baseband unit
  • Receivers 9018 and 9020 are also coupled to synthesizer unit 9026 which generates signals necessary to downconvert signals received by receivers 9018 and 9020.
  • Receivers 9018 and 9020 provide the downconverted signals of the intermediate frequency (IF) to modem 9034 in BBU 9032.
  • IF intermediate frequency
  • Synthesizer unit 9026 is also operable to generate signals necessary to modulate signals transmitted by transmitter 9028.
  • the signals generated by synthesizer unit 9026 to downconvert the signals received by receivers 9018 and 9020, and the signals generated by synthesizer unit 9026 to upconvert the signals modulated at modem 9034 and which are transmitted by transmitter 9028 are preferably hopping signals that are generated in accordance with control signals communicated to and from modem 9034 in BBU 9032. Different hopping signals may be generated for transmission and for reception.
  • Transmitter 9028 receives control signals from modem 9034 in BBU 9032 and power control signals from power control unit 9030, which also receives inputs from modem 9034 in BBU 9032. Transmitter 9028 is also coupled to a service board (not shown) which provides electric power to transmitter 9028. Transmitter 9028 outputs data for transmission to antenna 9014 via duplexer unit 9022.
  • modem 9034 includes a DSP (digital signal processing) unit 9038 in which a collision avoiding and channel coordinating algorithm is performed as described herein after.
  • DSP unit 9038 may be a separate unit which is coupled to modem 9034.
  • Fig. 83 is a generalized block diagram illustration of a portion of a base station 9100 in a frequency hopping multiple access communication system constructed and operative in accordance with a preferred embodiment of the present invention.
  • the base station includes a group of receivers 9102, each coupled to an antenna 9104.
  • each receiver in the group of receivers 9102 is operable to receive information signals over one frequency channel.
  • the group of receivers 9102 is coupled to a group of slot processors (SP) 9106. Each receiver in the group of receivers 9102 is coupled to a separate slot processor in the group of SP 9106.
  • SP slot processor
  • the group of SP 9106 is coupled to a communication bus 9108, preferably a modified HDLC communication bus.
  • a group of frame processors (FP) 9110 is also coupled to communication bus 9103.
  • the frame processors in the group 9110 receive inputs from the slot processors in the group 9106 via communication bus 9108.
  • Disconnection in a case of collision may occur since slot receivers, in a first subscriber unit, may receive signals which are transmitted to a second subscriber unit and vice versa. Such collisions may be avoided by employing methods as described herein after with reference to Figs. 84 - 86.
  • Fig. 84 is a flow chart illustration describing the operation of a collision avoidance and channel coordinating algorithm employed in the apparatus of Fig. 83.
  • a plurality of frequency hopping channels for transmitting and receiving information signals are provided to a plurality of subscriber units. At each channel the information is transmitted over slots which are defined in a time domain and in a frequency domain.
  • collisions are prevented by allowing each subscriber unit to skip transmission of at least one slot selected in accordance with a predetermined sequence during transmission of information.
  • the predetermined sequence may be transmitted to each subscriber unit over a control channel.
  • BER Bit-Error-Rate
  • a receiver at a receiving end recognizes a non-transmitted slot and builds an inactive slot to replace the non-transmitted slot by including in the inactive slot a plurality of inactive symbols having imparted a confidence level zero (0) .
  • a slot includes 38 symbols and the confidence level zero is imparted in an ordered or random sequence.
  • the system includes a module of error correction which is typically performed by a dedicated ASIC (Application Specific Integrated Circuit) module (not shown).
  • ASIC Application Specific Integrated Circuit
  • the module of error correction is operable to apply a minimum weight to the inactive symbols during processing of the slots so as to minimize information disruption.
  • Forced disconnection of subscribers is performed at a base station in accordance with their location in a fringe area.
  • the location of a subscriber in a fringe area is determined by monitoring the control channels. If the subscriber unit receives signals having similar magnitude from the control channels of two adjacent sectors then the subscriber unit determines that it is in a fringe area. Magnitudes of the two control channels are considered to be similar if the difference between the magnitudes is of the order of 6 dB or less.
  • collisions may be prevented by using another algorithm which employs a preselected probability to determine whether to transmit over a time slot or not.
  • Fig. 85 is a flow chart illustration describing the operation of another collision avoidance and channel coordinating algorithm which is performed at a base station including a transmitter which transmits to a subscriber unit in a frequency hopping multiple access communication system.
  • a transmitter within a first sector transmits to a first subscriber within the first sector. If the first subscriber is located within a fringe area then the transmitter transmits the information to the first subscriber sequentially over all the slots (with a probability 1) . If the first subscriber is not in a fringe area then the base station determines, for each of at least one time slot, whether or not to transmit from the transmitter to the first subscriber during each of the at least one time slot.
  • the determination if the first subscriber unit or a second subscriber unit or both are in the fringe area may be achieved by monitoring the control channels at the first subscriber unit and at the second subscriber unit respectively as mentioned before with reference to Fig. 84.
  • the transmitter transmits in the time slot.
  • the base station defines, for each of a plurality of time segments, a partition of the time during which the transmission occurs.
  • the base station also determines, for each time segment including at least one time slot, whether or not the number of time slots within the time segment in which transmission did not take place exceeds a threshold number of time slots, for example 2. If the threshold is exceeded, then the transmitter transmits over each time slot at which the determination is currently performed.
  • a sliding time window is defined and determination is made, for each of a plurality of positions of the sliding time window including n>1 time slots, whether or not the number of time slots within the sliding window, as currently positioned, in which transmission did not take place exceeds a threshold number of time slots. If the threshold is exceeded, the transmitter transmits over each time slot which is currently determined.
  • the determination whether to transmit or not is performed by preselecting a fixed probability p ⁇ 1. Each time a determination whether to transmit or not is required, a random number between 0 and 1 is selected and compared to the preselected probability p. If the selected random number is equal to p or exceeds p then the transmitter transmits over the currently determined time slot.
  • an average number AVE_SS of skipped transmittals over a time period T is computed. If AVE_SS exceeds a preselected allowable constant number X of skipped transmittals, the transmitter transmits over the current time slot. Otherwise, transmittal over the time slot is skipped.
  • the base station may assign time-slots to each of a plurality of subsectors within a first sector at which the subscriber unit is located, and to each of a plurality of subsectors within a neighboring sector.
  • Each sector may be divided to central and peripheral subsectors such that the same time-slot is assigned to a peripheral subsector in the first sector and to a central subsector in the neighboring sector.
  • the base station may assign more power to downlink transmissions to subscribers within the peripheral subsectors than to downlink transmissions to subscribers within the central subsectors.
  • the power differences between the subsectors may be employed to prevent collision.
  • an air resource may be allocated to the subscribers within the first sector so as to reduce the maximum probability, over the subscribers within the first sector, of existence of a problematic subscriber.
  • the transmitter may transmit with a probability 1 if the first subscriber is inside the fringe area even if there is a problematic subscriber in a neighboring sector.
  • the air resource may include one of TDMA (time division multiple access) time slots, FDMA (frequency division multiple access) channels frequencies and FHMA (frequency hopping multiple access) time/frequency sequences.
  • TDMA time division multiple access
  • FDMA frequency division multiple access
  • FHMA frequency hopping multiple access
  • Fig. 86 is a flow chart illustration describing the operation of a collision avoidance and channel coordinating algorithm which is performed at a subscriber unit and is operative in accordance with a preferred embodiment of the present invention. It is to be appreciated that the collision avoidance and channel coordinating algorithm performed at the subscriber unit is substantially similar to the algorithm performed at the base station.
  • a subscriber within a first sector is operable to transmit to a base station. If the subscriber is not located within a fringe area, then the subscriber transmits to the base station. Otherwise, the subscriber determines, for each of at least one time slot, whether or not to transmit during the time slot.
  • the subscriber unit definition is made, for each of a plurality of time segments, of a partition of the time during which the transmission occurs, each time segment including at least one time slot, and determination is made whether or not the number of time slots within the time segment in which transmission did not take place exceeds a threshold number of time slots, for example 2. If the threshold is exceeded, the subscriber unit transmits in a current time slot.
  • a threshold number of time slots for example 2. If the threshold is exceeded, the subscriber unit transmits in a current time slot.
  • a sliding time window is defined and determination is made, for each of a plurality of positions of the sliding time window including n>1 time slots, whether or not the number of time slots within the sliding window, as currently positioned, in which transmission did not take place exceeds a threshold number of time slots. If the threshold is exceeded, the subscriber unit transmits over each time slot which is currently determined.
  • the determination whether to transmit or not is performed by preselecting a fixed probability p ⁇ 1. Each time a determination whether to transmit or not is required, a random number between 0 and 1 is selected and compared to the preselected probability p. If the selected random number is equal to p or exceeds p then the subscriber unit transmits over the currently determined time slot.
  • an average number AVE_SS of skipped transmittals over a time period T is computed. If AVE_SS exceeds a preselected allowable constant number X of skipped transmittals, the subscriber unit transmits over the current time slot. Otherwise, transmittal over the time slot is skipped.
  • Fig. 87 is a simplified pictorial illustration of a communication system constructed and operative in accordance with a preferred embodiment of the present invention, in which proximate subscriber units can communicate without base station intervention.
  • the system of Fig. 87 comprises a base station 10100 and a plurality of subscriber units, depicted in Fig. 87 as four subscriber units 10110, 10120, 10130, and 10140. It is appreciated that the system of Fig. 87 may comprise any number of subscriber units. It is also appreciated that functions generally assigned to the base station may be otherwise assigned.
  • the subscriber units 10110, 10120, 10130, and 10140 are equipped with the ability to identify their location at any given time.
  • One example of such a system is a GPS system 10142, whereby the subscriber units are in communication with a global positioning satellite system.
  • Other methods of identifying location known in the prior art, may also be used.
  • subscriber units 10110 and 10120 are shown in communication with each other via the base station 10100.
  • the base station mediated communication between subscriber units 10110 and 10120 may be established and maintained by any of a number of means, including means which are well-known in the prior art of mobile radio and cellular telephone systems.
  • subscriber units 10130 and 10140 are shown as being located proximate to one another, and are shown in direct communication with each other without the intervention of the base station 10100.
  • Fig. 88A is a simplified flowchart illustration of a preferred method of establishing and maintaining a talk around link between two subscriber units of the system of Fig. 87.
  • a first subscriber unit, 10130 requests a conversation with a second subscriber unit 10140 (step 10144).
  • a decision is then made, typically at the base station 10100, as to whether to establish a mediated communication channel via the base station 10100 between the first subscriber unit 10130 and the second subscriber unit 10140, or whether to establish a direct communication channel bypassing the base station 10100 (step 10146).
  • a direct communication channel is also termed herein a "talk around channel” or a "talk around link”, while communication using such a channel is called "talk around”.
  • the base station 10100 is operative to decide whether a requested conversation between a given pair of subscriber units is to be established via a mediated channel or via a direct channel as described above. Alternatively, the subscriber units may make this decision between themselves, as described below with reference to Fig. 83B.
  • the decision on whether to establish mediated or direct communication is based, at least partly, on information identifying the location of each subscriber unit and on a predetermined criterion, such as, for example, a criterion of proximity.
  • the position of each subscriber unit may be known based on position information supplied by a GPS system associated with the subscriber unit; alternatively, the position information may be derived from other means.
  • adjacency may be determined based on the signal quality of direct communication between the subscriber units.
  • the signal quality may be measured by any appropriate measure of signal quality, as, for example, signal strength or signal to noise ratio.
  • Establishing a mediated communication channel via the base station uses more air resources than establishing a direct communication channel between the subscriber units.
  • the base station 10100 decides to establish a mediated communication channel whenever sufficient air resources are available, and decides to establish a direct communication channel only when sufficient air resources for a mediated communication channel are not available.
  • a plurality of subscriber units may be assigned to one or more groups termed herein "talk groups". For example, if there are 10,000 subscriber units, 1,200 of the subscriber units might be divided into 30 talk groups, the talk groups having varying numbers of subscriber units as members. The remaining 8,800 subscriber units might not be members of any talk group.
  • a direct communication between the two member subscriber units is preferably established even when sufficient air resources are available for a mediated connection.
  • the connection request is handled as described above, for the case where there are no talk groups, with preference being given to a mediated over a direct connection.
  • a direct or a mediated connection is established (step 10148).
  • the quality of a direct link depends on many factors, including the distance between the two subscriber units, which distance may change with time, thus causing a possible degradation in quality.
  • a direct channel is maintained and monitored and, if necessary, it is switched automatically to a mediated channel (step 10150).
  • Fig. 88B is a simplified flowchart illustration of a preferred implementation of the method of Fig. 88A.
  • the method of Fig. 88B preferably includes the following steps:
  • STEP 10155 A first subscriber requests a talk around connection with a second subscriber or, even without requesting talk around, requests a conversation with second subscriber who is another member of subscriber's own talk group. Alternatively, as described above, the base station may decide whether a regular conversation request is to be handled by talk around.
  • STEP 10160 The second subscriber receives the talk around request and compares the quality of the received talk around request signal to a minimum signal quality threshold.
  • the signal quality may be measured by any appropriate measure of signal quality, as, for example, signal strength or signal to noise ratio.
  • the minimum signal threshold may, for example, be determined based on operational characteristics of the system, on subjective factors affecting users of the system, or on other criteria.
  • a typical signal to noise ratio threshold may be, for example, approximately 15 dB.
  • STEP 10170 Is the signal quality of the talk around request above the minimum signal quality threshold?
  • STEP 10180 Reject the talk around request. If the quality of the received signal is below the minimum threshold, the talk around request is rejected because a signal quality below the threshold is taken to be inadequate to allow a direct conversation of acceptable quality. Typically, a mediated communication channel is then established (not shown).
  • STEP 10190 The second subscriber sends a talk around request acknowledgement signal to the first subscriber.
  • STEP 10200 The first subscriber receives the talk around request acknowledgement and compares the quality thereof to a minimum threshold.
  • the signal quality and the minimum threshold are typically similar to those described above with reference to step 10160.
  • STEP 10210 Is the signal quality of the talk around request acknowledgement signal above the minimum? Check to see whether the quality of the received signal is above the minimum threshold. If the quality is below the minimum, processing of the talk around request continues at step 10180, described above.
  • STEP 10220 Talk around link is established. A direct link is now established between the two subscriber units.
  • STEP 10230 During talk around conversation, continue to monitor quality and switch to regular link via base station if quality is below minimum threshold.
  • the subscriber units in the system of Fig. 87 are mobile subscriber units. As the subscriber units move, the signal quality may change. Other factors, such as, for example, atmospheric conditions and the presence of large buildings or geographical features may also lead to a change in signal conditions. Typically, signal quality is monitored throughout the duration of the talk around link and, should signal quality fall below a second minimum threshold, the communication link is switched to a direct link via the base station 10100.
  • the second minimum threshold of step 10230 may be different in value, typically lower than the first minimum threshold described above. In other words, signal quality is allowed to degrade somewhat during the talk around conversation without causing a switch to a mediated link.
  • Fig. 89 is a simplified flowchart illustration of a preferred method for implementing step 10220 of Fig. 88B.
  • the method of Fig. 89 preferably includes the following steps:
  • STEP 10260 Choose one of the subscriber units to play the role of the base station during the talk around conversation.
  • the subscriber unit so chosen is termed herein the base station subscriber unit, or BS-SU.
  • the BS-SU may be chosen by any appropriate means, including randomly.
  • the decision must be known to both subscriber units, so that one and only one subscriber unit becomes the BS-SU.
  • the decision is typically made arbitrarily, and is preferably made by the base station 10100.
  • STEP 10270 The BS-SU reverses the use of its uplink and downlink channels during the talk around conversation.
  • the uplink channel is used to transmit from the subscriber unit to the base station 10100, and the downlink channel is used to receive, at the subscriber unit, transmissions originating in the base station 10100.
  • the uplink and downlink channels are now reversed; that is, the BS-SU transmits on the channel normally used for downlink reception, and receives on the channel normally used for uplink transmission.
  • the BS-SU thus mimics the behavior of the base station 10100 in a normal conversation. In this way, the subscriber unit which was not selected as the BS-SU in step 10260 may transmit and receive normally.
  • STEP 10280 At the conclusion of the talk around conversation, the BS-SU reverts to normal operation. In other words, the BS-SU reverts to using its uplink and downlink channels in the normal fashion, for uplink and downlink communication respectively, and thus resumes normal subscriber unit operation.
  • a link established using the method of Fig. 89 is a full-duplex direct link.
  • the link may be a half-duplex direct link.
  • Fig. 90 is a simplified flowchart illustration of an alternative preferred method for implementing the link-establishing step of Fig. 88B.
  • the method of Fig. 90 is particularly suitable for establishing a half-duplex direct link.
  • both subscribers use a single channel for both talking and listening.
  • the subscriber units in cooperation with each other or based upon instructions received externally as, for example, instructions received from the base station 10100, choose one of the available channels, either the uplink channel or the downlink channel for use during the talk around conversation (step 10290).
  • the choice of uplink versus downlink channel may be predetermined for all subscriber units, or may be agreed upon in a communication between the two subscriber units.
  • both subscriber units use the chosen channel for both talking and listening (step 10300).
  • the use of the single chosen channel may be controlled by any appropriate means of controlling the use of a single channel for both talking and listening, as is well known in the art.
  • both of the subscriber units return to normal operation, that is, both talk on the uplink and listen on the downlink (step 10310).
  • Fig. 91 is a simplified flowchart illustration of the base station side of an alternative preferred method for establishing and maintaining a talk around link between two subscriber units of the system of Fig. 87.
  • Fig. 92 is a simplified flowchart illustration of the subscriber unit side of an alternative preferred method for establishing and maintaining a talk around link between two subscriber units of the system of Fig. 87.
  • the methods of Figs. 91 and 92 typically are performed in conjunction with each other.
  • the base station 10100 extracts information describing the situation of both subscriber units, preferably including the location of the two subscriber units, whether or not the two subscriber units are members of the same talk around group, whether or not the subscriber units are subscribed to use talk around, and whether the subscriber units are located within a microsite (step 10350).
  • a microsite is a generally small geographical area served by a transponder, and not directly from a base station. Microsites are described in US Patent 5,408,496 to Ritz et al., and in copending Israel Application Nos. 111339, 111340, 111341, and 111342, referred to above.
  • a predetermined maximum distance such as, for example, several hundred meters (step 10380); or if the distance is not precisely known from the GPS 10142 or otherwise (step 10390).
  • step 10400 a check is made to see whether the microsite is high powered or low powered.
  • the geographical area defined by a high powered microsite is larger than the geographical area defined by a low powered microsite.
  • both subscribers are located in a regular microsite.
  • the base station 10100 assigns call keys, containing all of the information necessary to establish a direct talk around communication link, typically including channel frequencies allocated and frequency hopping sequences, to both subscriber units.
  • call keys containing all of the information necessary to establish a direct talk around communication link, typically including channel frequencies allocated and frequency hopping sequences.
  • each subscriber unit is assigned two keys, with the transmission key of the first subscriber unit being identical to the reception key of the second subscriber unit, and vice versa.
  • half duplex communication a single identical key is assigned to each subscriber unit, and the single key is used for both transmission and reception.
  • the base station 10100 assigns one of the two subscriber units the role of the BS (step 10420). Typically, the choice of which subscriber unit plays the role of the base station 10100 is made randomly, but any other appropriate means may also be used to choose the subscriber unit.
  • the call is monitored and maintained (step 10430).
  • the base station 10100 checks the control channels, switching the connection from a talk around connection to a regular call if necessary based on an indication of signal quality provided by the subscriber unit, or another appropriate criterion.
  • the keys are deallocated so that they may be reassigned as necessary (step 10440).
  • a subscriber unit monitors control channels until receiving a message indicating available talk around resources (step 10445).
  • step 10450 the subscriber unit attempts to establish a talk around connection using a predetermined channel assigned in advance (step 10460).
  • the subscriber unit checks to see whether a talk around instruction was received from the base station 10100 (step 10470). If no talk around instruction was received, a regular connection is established (step 10480).
  • the subscriber unit receives and uses a key assignment from the base station 10100 (step 10490).
  • the subscriber unit checks signal quality to see whether it is sufficient according to a predetermined criterion of signal quality as, for example, any of the criteria described above with reference to step 10160. (step 10500). If signal quality is insufficient, the subscriber unit, via request to the base station 10100, deallocates the talk around keys (step 10510) and establishes a regular connection (step 10480, described above).
  • the subscriber unit During the talk around connection, the subscriber unit, according to instructions received from the base station 10100, operates a half duplex connection on an uplink traffic channel only, or operates a full duplex connection in accordance with keys allocated to the subscriber unit by the base station 10100 (step 10520).
  • the talk around connection is terminated and the key or keys are deallocated (step 10540).

Abstract

L'invention concerne un appareil de transmission voix-données dans un système de transmission à accès multiples (1) à saut de fréquence, comportant de préférence des fonctions de commande automatique de gain, de réglage temporel, de commande de puissance, de coordination des concordances et des effacements forcés, de commande automatique de fréquence, de boucle à retard de phase, de traitement des zones périphériques, d'acquisition et de poursuite des caractéristiques des canaux, de transfert, de conversation à plusieurs, et de retransmission.
PCT/US1995/013457 1994-10-19 1995-10-19 Systeme et procedes de transmission sectorisee WO1996013914A2 (fr)

Priority Applications (2)

Application Number Priority Date Filing Date Title
AU40042/95A AU4004295A (en) 1994-10-19 1995-10-19 Sectorized communication system and methods useful therefor
EP95938799A EP0787386A2 (fr) 1994-10-19 1995-10-19 Systeme et procedes de transmission sectorisee

Applications Claiming Priority (26)

Application Number Priority Date Filing Date Title
IL11134094A IL111340A (en) 1994-10-19 1994-10-19 Frequency hopping multiple access communication system
IL111,340 1994-10-19
IL11442695A IL114426A0 (en) 1995-06-30 1995-06-30 Apparatus and method for retransmitting messages
IL11442795A IL114427A0 (en) 1995-06-30 1995-06-30 Communication system with two communication channels and method for communicating therewith
IL11441995A IL114419A0 (en) 1995-06-30 1995-06-30 Apparatus and method for time alignment of messages in a communication system
IL114,425 1995-06-30
IL11442295A IL114422A0 (en) 1995-06-30 1995-06-30 Apparatus and method for power control in a radio communication system
IL114,428 1995-06-30
IL11442895A IL114428A0 (en) 1995-06-30 1995-06-30 Apparatus and method for reducing communication system base station vicinity interference
IL114,423 1995-06-30
IL11442095A IL114420A0 (en) 1995-06-30 1995-06-30 Apparatus and method for transferring a subscriber from one communication system sector to another
IL11442595A IL114425A0 (en) 1995-06-30 1995-06-30 Channel feature acquisition
IL114,426 1995-06-30
IL11442395A IL114423A0 (en) 1995-06-30 1995-06-30 Automatic frequency control
IL114,419 1995-06-30
IL114,429 1995-06-30
IL11442995A IL114429A0 (en) 1995-06-30 1995-06-30 Apparatus and method for automatic gain control
IL114,420 1995-06-30
IL114,424 1995-06-30
IL114,427 1995-06-30
IL114,422 1995-06-30
IL114,421 1995-06-30
IL11442195A IL114421A0 (en) 1995-06-30 1995-06-30 Coordinated hits and forced erasures
IL11442495A IL114424A0 (en) 1995-06-30 1995-06-30 Delay locked loop
IL115,475 1995-10-01
IL11547595A IL115475A0 (en) 1995-10-01 1995-10-01 Apparatus and method for determining and using channel state information

Publications (2)

Publication Number Publication Date
WO1996013914A2 true WO1996013914A2 (fr) 1996-05-09
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EP0911993A2 (fr) * 1997-10-22 1999-04-28 Matsushita Electric Industrial Co., Ltd. Synchronisation de l'émission d'un terminal TDMA par mesure du delais de transmission
EP0986280A2 (fr) * 1998-09-07 2000-03-15 Matsushita Electric Industrial Co., Ltd. Station mobile et station de base à méthode de diffusion améliorée
WO2000052831A2 (fr) * 1999-03-05 2000-09-08 Tantivy Communications, Inc. Correction d'erreur automatique sur des canaux multiplexes a acces multiple par code de repartition permettant un codage haut debit
WO2000057572A1 (fr) * 1999-03-18 2000-09-28 Siemens Aktiengesellschaft Procede pour reguler la puissance d'emission dans un systeme radiotelephonique mobile, et systeme radiotelephonique mobile correspondant
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EP1389025A1 (fr) * 2002-08-10 2004-02-11 Motorola, Inc. Système de communication portable sans fil, unite de communications et procédé
WO2004068750A1 (fr) * 2003-01-30 2004-08-12 Samsung Electronics Co., Ltd. Dispositif et procede permettant de mesurer et de corriger le temps de propagation entre une station de base principale et une station de base distante interconnectees par un cable optique
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US6973140B2 (en) 1999-03-05 2005-12-06 Ipr Licensing, Inc. Maximizing data rate by adjusting codes and code rates in CDMA system
US6999440B2 (en) 1997-10-22 2006-02-14 Matsushita Electric Industrial Co., Ltd. TDMA radio terminal capable of adjusting transmit timing by using measured delay time
AU2004208744B2 (en) * 2003-01-30 2007-02-01 Samsung Electronics Co., Ltd. Apparatus and method for measuring and compensating delay between main base station and remote base station interconnected by an optical cable
US7368824B2 (en) * 2002-02-28 2008-05-06 Infineon Technologies Ag Diffusion solder position, and process for producing it
WO2009002232A1 (fr) * 2007-06-25 2008-12-31 Telefonaktiebolaget Lm Ericsson (Publ) Télécommunication ininterrompue avec des liens faibles
US7796563B2 (en) * 2001-10-16 2010-09-14 Qualcomm Incorporated Method and system for selecting a best serving sector in a CDMA data communication system
US9240210B2 (en) 2013-11-26 2016-01-19 Seagate Technology Llc Physical subsector error marking
CN112865893A (zh) * 2021-01-20 2021-05-28 重庆邮电大学 智能反射面辅助的sm-noma系统资源分配方法
CN113189627A (zh) * 2021-04-29 2021-07-30 中国电子科技集团公司第五十四研究所 一种基于北斗卫星的通信定位一体化双模机载系统
US20220069885A1 (en) * 2018-12-11 2022-03-03 Nordic Semiconductor Asa Radio devices with switchable antennas
US11984963B2 (en) * 2018-12-11 2024-05-14 Nordic Semiconductor Asa Radio devices with switchable antennas

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Cited By (47)

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WO1998042106A3 (fr) * 1997-03-20 1998-12-17 Ericsson Telefon Ab L M Modulateur en phase et en quadrature de phase et procede associe
WO1998042106A2 (fr) * 1997-03-20 1998-09-24 Telefonaktiebolaget Lm Ericsson (Publ) Modulateur en phase et en quadrature de phase et procede associe
US6693883B2 (en) 1997-10-22 2004-02-17 Matsushita Electric Industrial Co., Ltd. TDMA radio terminal capable of adjusting transmit timing by using measured delay time
EP0911993A2 (fr) * 1997-10-22 1999-04-28 Matsushita Electric Industrial Co., Ltd. Synchronisation de l'émission d'un terminal TDMA par mesure du delais de transmission
US6999440B2 (en) 1997-10-22 2006-02-14 Matsushita Electric Industrial Co., Ltd. TDMA radio terminal capable of adjusting transmit timing by using measured delay time
EP1515458A1 (fr) * 1997-10-22 2005-03-16 Matsushita Electric Industrial Co., Ltd. Synchronisation de l'émission d'un terminal TDMA par mesure du delais de transmission
EP0911993A3 (fr) * 1997-10-22 2003-08-13 Matsushita Electric Industrial Co., Ltd. Synchronisation de l'émission d'un terminal TDMA par mesure du delais de transmission
EP0986280A2 (fr) * 1998-09-07 2000-03-15 Matsushita Electric Industrial Co., Ltd. Station mobile et station de base à méthode de diffusion améliorée
EP0986280A3 (fr) * 1998-09-07 2001-01-24 Matsushita Electric Industrial Co., Ltd. Station mobile et station de base à méthode de diffusion améliorée
US6614770B1 (en) 1998-09-07 2003-09-02 Matsushita Electric Industrial Co., Ltd. Mobile station apparatus and base station apparatus
US6973140B2 (en) 1999-03-05 2005-12-06 Ipr Licensing, Inc. Maximizing data rate by adjusting codes and code rates in CDMA system
US7502424B2 (en) 1999-03-05 2009-03-10 Ipr Licensing, Inc. Maximizing data rate by adjusting codes and code rates
US8068474B2 (en) 1999-03-05 2011-11-29 Ipr Licensing, Inc. Variable rate coding for enabling high performance communication
US9369235B2 (en) 1999-03-05 2016-06-14 Intel Corporation Maximizing data rate by adjusting codes and code rates
US7826437B2 (en) 1999-03-05 2010-11-02 Ipr Licensing, Inc. Variable rate coding for enabling high performance communication
WO2000052831A3 (fr) * 1999-03-05 2000-12-21 Tantivy Comm Inc Correction d'erreur automatique sur des canaux multiplexes a acces multiple par code de repartition permettant un codage haut debit
US8204140B2 (en) 1999-03-05 2012-06-19 Ipr Licensing, Inc. Subscriber unit and method for variable forward error correction (FEC) decoding
US7593380B1 (en) 1999-03-05 2009-09-22 Ipr Licensing, Inc. Variable rate forward error correction for enabling high performance communication
US7145964B2 (en) 1999-03-05 2006-12-05 Ipr Licensing, Inc. Maximizing data rate by adjusting codes and code rates in CDMA system
US9306703B2 (en) 1999-03-05 2016-04-05 Intel Corporation Variable rate coding for enabling high performance communication
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WO2000052831A2 (fr) * 1999-03-05 2000-09-08 Tantivy Communications, Inc. Correction d'erreur automatique sur des canaux multiplexes a acces multiple par code de repartition permettant un codage haut debit
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WO2000057572A1 (fr) * 1999-03-18 2000-09-28 Siemens Aktiengesellschaft Procede pour reguler la puissance d'emission dans un systeme radiotelephonique mobile, et systeme radiotelephonique mobile correspondant
US7366154B2 (en) 1999-04-28 2008-04-29 Interdigital Technology Corporation Forward error correction scheme for high rate data exchange in a wireless system
US8045536B2 (en) 1999-04-28 2011-10-25 Ipr Licensing, Inc. Forward error correction scheme for high rate data exchange in a wireless system
US6614776B1 (en) 1999-04-28 2003-09-02 Tantivy Communications, Inc. Forward error correction scheme for high rate data exchange in a wireless system
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US6785323B1 (en) 1999-11-22 2004-08-31 Ipr Licensing, Inc. Variable rate coding for forward link
US8194783B2 (en) 1999-11-22 2012-06-05 Ipr Licensing, Inc. Variable rate coding for a forward and reverse link
US7796563B2 (en) * 2001-10-16 2010-09-14 Qualcomm Incorporated Method and system for selecting a best serving sector in a CDMA data communication system
US7368824B2 (en) * 2002-02-28 2008-05-06 Infineon Technologies Ag Diffusion solder position, and process for producing it
EP1389025A1 (fr) * 2002-08-10 2004-02-11 Motorola, Inc. Système de communication portable sans fil, unite de communications et procédé
AU2004208744B8 (en) * 2003-01-30 2008-08-21 Samsung Electronics Co., Ltd. Apparatus and method for measuring and compensating delay between main base station and remote base station interconnected by an optical cable
US7359408B2 (en) 2003-01-30 2008-04-15 Samsung Electronics Co., Ltd. Apparatus and method for measuring and compensating delay between main base station and remote base station interconnected by an optical cable
AU2004208744B2 (en) * 2003-01-30 2007-02-01 Samsung Electronics Co., Ltd. Apparatus and method for measuring and compensating delay between main base station and remote base station interconnected by an optical cable
WO2004068750A1 (fr) * 2003-01-30 2004-08-12 Samsung Electronics Co., Ltd. Dispositif et procede permettant de mesurer et de corriger le temps de propagation entre une station de base principale et une station de base distante interconnectees par un cable optique
WO2009002232A1 (fr) * 2007-06-25 2008-12-31 Telefonaktiebolaget Lm Ericsson (Publ) Télécommunication ininterrompue avec des liens faibles
US8380525B2 (en) 2007-06-25 2013-02-19 Telefonaktiebolaget Lm Ericsson (Publ) Continued telecommunication with weak links
US9240210B2 (en) 2013-11-26 2016-01-19 Seagate Technology Llc Physical subsector error marking
US20220069885A1 (en) * 2018-12-11 2022-03-03 Nordic Semiconductor Asa Radio devices with switchable antennas
US11984963B2 (en) * 2018-12-11 2024-05-14 Nordic Semiconductor Asa Radio devices with switchable antennas
CN112865893A (zh) * 2021-01-20 2021-05-28 重庆邮电大学 智能反射面辅助的sm-noma系统资源分配方法
CN112865893B (zh) * 2021-01-20 2022-06-03 重庆邮电大学 智能反射面辅助的sm-noma系统资源分配方法
CN113189627A (zh) * 2021-04-29 2021-07-30 中国电子科技集团公司第五十四研究所 一种基于北斗卫星的通信定位一体化双模机载系统

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