MXPA95004037A - Method and apparatus for increasing spec efficiency - Google Patents

Abstract

The present invention relates to a method for increasing the efficiency of the spectrum in a digital multiple access wireless communication system having a base station and a portable device adapted to communicate with said wireless base station, said method comprises the steps of maintaining the radio frequency (RF) in silence at the base station, establishing said portable device as a synchronization pattern until a call originates from said portable device, and establishing a communication link between said portable device and said radio station;

Description

METHOD AND APPARATUS FOR INCREASING SPECTRUM EFFICIENCY ASSIGNEE: MOTOROLA, INC., SOCIEDAD DE NACIONALIDAD NORTEAMERICANA, WITH ADDRESS AT: 1303 EAST ALGONQUIN ROAD, SCHAUMBURG, ILLINOIS 60196 - E. U. A.

INVENTORS: CHARLES J. MALEK, OF NACIONALIDADIDAD NORTEAMERI CANA, WITH ADDRESS AT: 915 CAMELOT DRIVE, CRYSTAL LAKE, ILLINOIS 60014, E.U.A.

DAVID L. WEIGAND, OF NACIONALIDAD NORTEAMERI CANA, WITH ADDRESS AT: 1035 ÁSTER AVENUE, # 3115, SUNNYVALE, CALIFORNIA 94086, E.U.A.

Summary A method and apparatus that increases the efficiency of the spectrum in a wireless communication system having base stations that can be positioned to operate within the range of one another. The method and apparatus eliminate the requirements for a base station to periodically transmit to maintain synchronism with an associated telephone 504. The telephone actually assumes the role of a base station when it makes the 508 call. The telephone will be synchronized with other traffic. telephone or another base station within the range 506. The telephone will then send a search signal to the base station 510. The elimination of the requirement that the base station repeatedly transmits a signal to maintain synchronism with a base station. Telephone significantly increases the location of the available spectrum to provide the possibility of a communication. Reversing the paper of the telephone also allows a communication from one telephone to another telephone independent from the base station 808. the Field of Invention This invention relates to radio frequency (RF) radiocommunication systems, and more particularly to a method and apparatus for increasing the efficient use of the spectrum.

Background of the Invention In communications systems, great efforts have been made to increase the use of spectrum for allow it to be used by a large number of subscribers in a given frequency band.

An example of a technique to increase spectrum efficiency is the so-called frequency division multiple access (FDMA) technique. In a conventional FDMA system, a given frequency is divided into a certain number of channels, where each of said channels is not occupied by a subscriber.

An FDMA system can also be a time division duplex (TDD) system, where a given RF channel is used to transmit frames in both forward and backward communications directions that are separated in time.

Other techniques include digital multiple access communications systems. One of such conventional digital multiple access techniques to increase the efficient use of the spectrum is the so-called time division multiple access (TDMA) technique. In a TDMA system, each channel is divided into a plurality of time segments for signal trans- mission.

Each time segment can be located for a different call. A TDMA system can also employ TDD techniques. Accordingly, a certain number of calls can be transmitted simultaneously on a single channel, or on a single frequency.

Finally, the increased spectrum efficiency can be achieved by means of extended spectrum techniques, in the form of both a slow frequency jump system and a direct sequence CDMA system. In a slow-skip frequency system, the carrier frequency of the signal is changed to a predetermined value over a wide range of possible frequencies in a pseudo-random sequence known in advance by the receiver.

Generally, broad-spectrum techniques reduce both intentional and unintended effects of interference. Direct sequence CDMA systems allow multiple subscribers to share the same spectrum where each user or subscriber receives the assignment of a pseudo noise code sequence.

The signal is spread by means of the pseudo-noise sequence of the broad bandwidth in advance by the receiver. In a conventional multi-access communication system, a base station periodically transmits a beacon signal or synchronization signal to maintain synchronization with an associated telephone.

For example, in a time division duplex multiple access system, a time segment in a time frame must be occupied even if the base station is not busy with a call. Depending on the communication system, the resources available to provide communication between the devices are used to maintain synchronization between those devices that are not in communication.

In keeping with what has been said, there is a need for a method and an apparatus for increasing the spectrum efficiency to allow a greater number of users to occupy a given frequency band.

Brief Description of the Drawings FIGURE 1 is a plan view of a wireless communication system having multiple base stations connected to the public system of the telephone network.

FIGURE 2 is a block diagram of the circuit for a conventional wireless base station or a telephone.

FIGURE 3 is a flow diagram to illustrate the preferred steps for determining an index available in a low frequency system.

FIGURE 4 is a frame diagram of an air interface protocol for synchronizing the telephone with the base station.

FIGURE 5 is a flow chart illustrating a method for increasing spectrum occupancy according to the present invention.

FIGURE 6 is a flow diagram illustrating a method for receiving a call generated on a landline in accordance with the present invention.

FIGURE 7 is a timing diagram illustrating the transmission of signals between a standard or praster system and a dependent one operating in a co-location system according to the present invention.

FIGURE 8 is a flow diagram illustrating an alternative use of telephones operating in a wireless communication system in accordance with the present invention.

FIGURE 9 is a flow chart illustrating the steps for synchronizing telephones according to the present invention.

Description of the Preferred Configuration In a communication system, the spectrum is scarce and must be used efficiently to allow a large number of subscribers to communicate in a given frequency band. The method and apparatus of the present invention provide the facilities to obtain a spectrum with increased efficiency by eliminating the requirements for base stations to maintain synchronization with telephones.

In particular, a base station will not continuously transmit a synchronization signal, but transmits a telephone code and search signal when a call is received by the base station.

In the event that there is a call generated on a telephone, the telephone will effectively function as a base station (eg, as a standard device) and call its associated base station.

The phone will revert back to the conventional telephone operation (for example, a dependent device). In a low frequency system that has 83 channels for example, a maximum of 83 base stations can operate in the system at the same time.

However, the apparatus of the present invention can support 83 calls in progress at the same time. Accordingly, the number of base stations positioned within the range of one another can be increased considerably, assuming that, in the average case, not all base stations will be used at the same time.

Returning in principle to FIGURE 1, a conventional wireless communication system 102 is illustrated. The wireless communication system has a plurality of base stations 104, each of which provides RF coverage over an area 108.

Each base station can be connected to the public telephone network 106. However, it should be understood that the circuit and the method of the present invention can be implemented in a wireless communication system having base stations that are not connected to the network of public communications.

The base stations can be connected together in an independent network, or they could be left as single units that can operate in the same frequency bands. Each base station is also adapted so that it can communicate with one or more telephones 110.

Finally, each base station can communicate with another base station that is within the radius by means of the RF signals.

Preferably, the control signals, including the synchronized signals, can be transmitted by means of the RF signals between the base stations.

Turning now to FIGURE 2, a block diagram illustrates a conventional base or a telephone circuit. In the preferred configuration, an ASIC (Specific Application Integrated Circuit) 201, such as the CMOS ASIC in the MDA08 or H4C technology, of Motorola, Inc., and the microprocessor 203, such as is the case of the 68HC11 microprocessor also of Motorola, Inc., combine to generate the communications protocol illustrated in FIGURE 4.

The ASIC 201 preferably includes a separate search engine for detecting a second source of synchronization according to the present invention. The second search engine could be a separate digital phase loop (DPLL) or an oversampled cross correlator. The digital phase loops are well known in the art.

An example of a digital phase loop or loop can be found in U.S. Pat. of North America Number 3,983,498 titled: "Loop of Traba de Fase Digital" that was granted on September 28, 1976 to Male.

All the contents of the aforementioned Patent are incorporated herein by reference. An example of an oversampled cross correlator can be found in U.S. Patent No. 5,117,441 entitled "Method and Apparatus for Real-time Demodulation of a GMSK Signal by a Non-Receiver. -Coherent "granted on May 26, 1992 to Weigand.

All the contents of the aforementioned patent are incorporated herein by reference. The microprocessor 203 uses a RAM 205, an EEPROM 207 and a ROM 209, consolidated in a packet 211 in the preferred configuration, to execute the steps necessary to generate the protocol and to carry out other functions for the communications unit, such as the writing on a data display screen 213, accepting the information from the keyboard 215, and controlling the frequency of the frequency synthesizer 225.

The ASIC 201 processes the audio transformed by the audio circuit 219 from a microphone 217 and to a speaker 221. Certain message fields are constructed by means of the ASIC 201 and are generalized by means of the audio circuit 219, the microprocessor 203, and others are constructed by means of ASIC 201, which generates the frame of the message and transfers it to a transmitter 223.

The transmitter 223 transmits through an antenna 229 using carrier frequencies produced by the frequency synthesizer 225 in the manner chosen by the system and directed by the processor 203. The information received by the antenna of the communications unit 229 enters the receiver 227 that demodulates the symbols comprising the message frame using the carrier frequencies of frequency synthesizer 225, in accordance with the manner chosen by the system.

The ASIC 203 then analyzes the message received in its constituent parts. If the circuit of FIGURE 2 is incorporated into a residential base station, the audio circuit of the base station can be connected to a TELCO network 233.

Turning now to FIGURE 3, the preferred steps for following the sequence in a conventional system form can be seen therein. In step 302, the index (eg, an outstanding voltage in a predetermined sequence of channels starting with the first channel) is set equal to zero.

In step 304, the base station sweeps the next index (the same sequence of channels beginning with the second channel in the sequence) and determines whether the receiver signal energy injector (RSSI) of all channels is lower than the predetermined threshold in step 306.

If the RSSI of all the channels is less than the predetermined threshold, the base station stores an indication that the index N has channels occupied in step 308. If the RSSI of all the channels is not less than the threshold in step 306, the base station indicates the number of channels occupied in step 310.

In step 312, the base station determines if three indices are available without busy channels. If three indices are available, the base station selects the first index in step 314 and assumes normal operation in step 316. However, if all three indices are not available, the base station determines whether all indices have been swept in step 318. If all the indices have not been swept, the base station sweeps the next index in step 304.

If all the indexes have been swept, the base station uses the most available index depending on the minimum number of occupied channels that have an RSSI value greater than the predetermined threshold. The three indexes are used to form a better next list.

If the index fails during a call, a request can be sent to change the index. The next best list can be updated periodically depending on radio resources and other limitations. The RSSI is determined according to how it was previously indicated; the evaluation of the quality of the channel by means of the RSSI is given merely by way of the example. Any other method for determining the quality of the signal can be used within the scope of the present invention.

Returning in principle to FIGURE 4, an air interface protocol for the synchronization of the base stations is illustrated. Preferably, both the primary and redundant frames 402 and 404 are transmitted between the base stations illustrated in FIGURE 7. A method and apparatus for maintaining the frequency and synchronization of the bit having the primary and redundant frames are described in the patent. from the USA No. 5,212,715 to Pickert et al. entitled "Digital Communications Signaling System" which was granted on May 18, 1993. Referring to the specific segments, frame 402 includes a segment 406 for the synthesizer lock time.

The next four segments are for the primary data fields forward and redundant forward, and for the primary data fields in reverse and redundant in reverse. In particular, segment 408 is for a primary data segment forward (base to the telephone).

Segment 410 is a redundant data field ahead. Segment 412 is a primary data field in reverse (from the telephone to the base station), while segment 414 is a redundant data field in reverse. Segment 416 is a time segment of the synthesizer. The next two segments are a beacon signal segment (beacon in English) 418 and a blank segment 420.

The beacon segment is used to transmit a base synchronization field that is used to synchronize the base stations. A beacon message would comprise a plurality of beacon signals transmitted in the beacon segment. The blank segment can be used to detect the telephone traffic of another base station.

Alternatively, the beacon segment can be used to detect a beacon signal to synchronize with another base station.

As illustrated in FIGURE 4, the primary forward time segment 408 of the primary frame 402 is also transmitted in the forward redundant segment 426 of the redundant frame 404. That is, the redundant segment contains: the redundant segment containing the information that matches with the previous segment or the previous quarter. In order, the reverse primary segment 412 of the primary frame 402 is transmitted in the redundant reverse segment 430 of the redundant time frame 404. The operation of transmitting the redundant and primary data fields is well known in the art and it will not be described in detail.

However, it will be understood that a system that transmits a redundant segment does not need to be employed in accordance with the present invention, and a frame can only be transmitted.

FIGURE 4 also shows the structure of the preferred segment for a data segment both towards the forward and backward direction, or a primary segment or a redundant segment in any direction. The preferred fields for a digital control channel (DCCH in English) 450 are illustrated. Each DCCH data segment comprises a ramp / guard field (ramp / guard, R / G in English) 454, a preamble field 456, a synchronization field 458, a data field 460, a cyclic redundancy check field (CRC in English) 462 yu field R / G 464.

Qn digital traffic field 452 is also illustrated. The preamble field represents a marker signal to identify the base station. The telephone can be synchronized with respect to the base station based on the preamble transmitted in the digital control channel.

In the reverse channel, the marking signal would identify the telephone. The data segment of the digital traffic channel comprises an R / G field 466, a synchronization field 468, an associated slow channel (SACCH in English) 470, a CRC field 472, a vocoder load field 474 and a field R / G 476. The preferred data field protocol is described in FIGURE 4; the minor or additional fields may be transmitted within the range covered by the present invention.

Turning now to FIGURE 5, a flow chart shows the method for increasing the spectrum occupancy according to the present invention. The conventional designation of the synchronism pattern is a baee and the synchronism dependent is a telephone. This conventional allocation is inverted according to the present invention to maintain a calm spectrum in a frequency-leap system. As will be described later in detail with reference to FIGURE 8, the role reverser will also allow a telephone-to-telephone intercom in a mobile communications environment having a personal base station (such as a residential or office base station) adapted to communicate with multiple phones.

Referring to FIGURE 5, both the base and telephone base pair / telephone are not in communication, and therefore, they do not transmit any signal in step 504. When the telephone initiates a call, the telephone synchronizes with any another base station by detecting telephone traffic in a free segment in step 506.

The telephone then assumes a major role in step 508. As a standard synchronizing device, the telephone calls the base station in step 510. The call can be transmitted in data block 460 in the digital control channel (telephone to base) in reverse (DCCH in English) block 450.

In step 512, the telephone reverses the normal telephone operation as a dependent synchronization device. Similarly, the base reverts to the normal base operation as the pattern synchronizing device in step 514. If an activation response is received from the base in step 516, normal base / telephone pair operation is assumed in step 518. If the answer is not received, the telephone attempts to synchronize with other telephone traffic in step 506.

Turning now to FIGURE 6, the method for receiving a call shown in accordance with the present invention is illustrated. The base station and the telephone remain silent at step 604. In order to receive the call, the telephone must detect a search call from the base station. If the telephone is in the battery save mode, the telephone is periodically activated and listens to the base station in step 606.

After the detection of the call, for example, a call of a land line network, the base transmits a search call and a telephone code in repetition of step 608. The base station preferably transmits the search signal and the telephone code for an extended period to solve the telephone rest work cycle and the accumulated time base disparity while resting.

If the search and telephone codes are received, the telephone transmits an acknowledgment to the base station in step 610. If the base station receives an acknowledgment in step 612, the base station picks up, the process begins of call and normal operation in step 614. the base is not rec ected and acknowledged by the base, the base again transmits a search signal and a telephone code in step 608.

Turning now to FIGURE 7, a call flow diagram illustrates the operation of the synchronization pattern and the synchronization dependent, and particularly the configuration of the telephone as a synchronization pattern and, both a telephone and a base station as a dependent of synchronism. The usual role of a base station is to be a synchronization pattern, while the usual role of a telephone is to be a dependent synchronization device.

Conventionally, in a slow frequency hopping system, a beacon signal in the DCCH segment format is transmitted by the sync pattern at least once per hopping revolution to provide the phone's synchronism and also to indicate that none call or search signal has taken place.

As illustrated in FIGURE 7, the synchronization pattern always transmits in a fixed phase (-T-1). The dependent then adjusts its frame manager to the phase -ßl + the phase delay - &d; d of the channel. Then, the dependent synchronization device transmits in alignment with its received phase, plus a delay -? - offset, in a TDD system.

The synchronism pattern then adjusts its second box director to the traffic received from the dependent synchronism, receiving a phase of -? - l + 2 'ßd + ß offset.

This synchronization protocol prevents the transmitted phase of the synchronism pattern from advancing with each transmission, as would occur in both entities would behave as a dependent synchronization device.

Turning now to FIGURE 8, an alternative use of telephones is illustrated which is based on the inverse role of a telephone in a communication system. By reversing the phone's role to function as a base, a pair of phones can communicate independently of the base. In step 804 an intercommunication mode is selected. The intercom mode can be selected in the base or by means of the telephone.

One of the telephones is set to act as the sync pattern in step 808. The second telephone remains as a dependent synchronization device in step 810. The two telephones then communicate in a manner similar to a pair of telephones in a base normal in step 812.

If the communication is made in step, the first telephone inverts the dependent synchronization device in step 816. This alternative use of the telephones provides great functionality to a communications system adapted to operate with multiple telephones.

Turning now to FIGURE 9, a preferred method for achieving or maintaining synchronization between the master and dependent entities by means of the use of DPLL 231 is described (e.g., by synchronizing a telephone with a base station as a source of synchronism in step 904).

The base station will determine if a valid marker signal is received in step 906. If a valid marker signal is received, the base station will then determine if the dialing will be received earlier in step 908. If the beacon signal is received earlier, the station The base will adjust the frame counter before in step 910. However, if the beacon signal is not received beforehand, the base station will adjust the frame counter later in step 912. It will be understood, however, that the other known methods in art they could be used to maintain synchronism.

In summary, the present invention describes a method and apparatus for increasing the efficiency of the spectrum in a wireless communication system having base stations that can be positioned to operate within the range of one another.

The method and apparatus eliminate the requirements for a base station to transmit signals to maintain synchronism with the associated telephone. In accordance with the present invention, the telephone effectively assumes the role of a base station when making a call. The base station will synchronize with other telephone traffic or another base station that is within the specific range.

The phone will then call the base station. Eliminating the requirement that the base station repeatedly call transmitting a signal to maintain synchronism with a telephone significantly increases the location of the available spectrum to establish a communication.

Reversing the role of a telephone also allows a telephone-to-telephone communication independent of the base station.

Despite the specific configurations described above, the variations and modifications of the Requesters will fall within the spirit and scope of the invention. The invention of the Applicants will be limited only to that claimed in the appended Claims.

Claims (10)

1. A method for increasing the spectrum efficiency in a digital multiple access wireless communications system having a base station and a portable device adapted to communicate with said wireless base station; said method is CHARACTERIZED BY the following steps: maintain 504 radio frequency (RF) silence at said base station; setting 508 that said portable device be considered as if it were a standard synchronization device until a call originates from said portable device; Y establishing 510 a communication link between said portable device and said base station.

2. The method for increasing the spectrum efficiency according to claim 1 further characterized by a step of establishing 508 the base station as a dependent synchronization device.

3. The method for increasing the spectrum efficiency according to claim 2 further being CHARACTERIZED BY a step of re-establishing the base station as a synchronous pattern device or after said communication link has been established.

4. The method for increasing the spectrum efficiency according to claim 1 which is further CHARACTERIZED BY a step of re-establishing the telephone as a dependent synchronization device.

5. The method for increasing the spectrum efficiency according to claim 1 which is further CHARACTERIZED BY a step of periodically monitoring 516, in said portable device, to locate a search signal transmitted by said base station.

6. The method for increasing the spectrum efficiency according to claim 1 wherein said step of establishing a communication link between the portable device and a base station is CHARACTERIZED BY establishing a communication link between a portable device and a wireless base station personal .

7. The method for increasing the spectrum efficiency according to claim 1 wherein said step of establishing a communication link is CHARACTERIZED BY the signal transmission in a Time Division Multiple Access (TDMA) communication system.

8. The method for increasing the spectrum efficiency according to claim 7 wherein said step for transmitting the signals in a communication system df Multiple Time Division Access (TDMA) is also CHARACTERIZED BY transmitting data in a system of communications Duplex Division by Time (TDD).

9. The method for increasing the spectrum efficiency according to claim wherein the step of establishing a communication link is CHARACTERIZED BY transmitting signals in a low frequency hopping communications system of Time Division Multiple Access (TDMA).

10. A method for increasing the efficiency of the spectrum in a time division multiple access (TDMA) slow frequency hopping communications system having a base station and a portable device adapted to communicate with said wireless base station; said method is CHARACTERIZED BY the following steps: maintaining 502 radio frequency (RF) silence at said base station and said portable device; periodically monitoring 506, on said portable device, to locate a search signal transmitted by said base station; setting 508 said portable device as a syncing pattern device until a call originates from said portable device; 510 transmitting a signal from said portable device to said base station to establish a communication link; establishing that the base station is a dependent synchronism device until receiving said signal from the portable device; establishing a communication link between said portable device and said base station; transmitting 516 an acknowledgment signal from said base station to said portable device;