Definitions

• frequency usage implemented in such a system is ultimately driven by customer demand as well as legal and practical constraints. While a first customer may request a time-division multiple access / time-division duplex system for a particular business wireless application, a second customer may thereafter demand a time-division multiple access / frequency-division duplex system for a wireless local loop application.
• the present invention fulfills the above-described and other needs by providing a flexible division duplex mechanism in a time-division multiple-access communications system. More specifically, the disclosed system utilizes a mixed, or hybrid, division duplex mechanism such that uplink and downlink transmissions are separated in frequency while time slots associated with transmission and reception are also separated in time.
• the hybrid duplex scheme referred to herein as frequency-time division duplex (FTDD)
• FTDD frequency-time division duplex
• the disclosed system can utilize a single hardware platform for applications where either time-division duplex or frequency-division duplex is preferred.
• the disclosed system is neither a pure time-division duplex system, in which the same frequency band is used for both uplink and downlink transmissions, nor a pure frequency-division duplex system in which both uplink and downlink transmissions occur simultaneously. Rather, the disclosed system utilizes separate frequency bands as well as separate time slots for uplink and downlink communications.
• a hardware platform initially designed for use in a time-division multiple access / time-division duplex system can be readily adapted for use in a time-division multiple access / frequency-division duplex system, and vice versa, without significant hardware modification. This feature of the present invention results in lower non-recurring engineering costs and shorter system development time.
• a wireless communications system includes a plurality of mobile stations and a base station.
• the base station is configured to transmit downlink communications signals to the mobile stations via a first carrier frequency and to receive uplink communications signals from the mobile stations via a second carrier frequency, the downlink and uplink communications signals being transmitted and received via successive time division multiple access frames, each frame including a plurality of time slots.
• a first time slot within each frame is allocated for downlink communications and a second time slot within each frame is allocated for uplink communications, the first and second allocated time slots being separated in time by a fixed time offset.
• a first partition of the time slots within each frame is reserved for downlink communications from the base station to the mobile stations and a second partition of the time slots within each frame is reserved for uplink communications from the mobile stations to the base station.
• the communications system can also include an additional base station co- located with the first base station and similarly configured to transmit downlink communications signals to the mobile stations via the first carrier frequency and to receive uplink communications signals from said mobile stations via the second carrier frequency, the downlink and uplink communications signals of each of said additional base stations being transmitted and received via successive time division multiple access frames, each frame including a plurality of time slots.
• an additional base station co- located with the first base station and similarly configured to transmit downlink communications signals to the mobile stations via the first carrier frequency and to receive uplink communications signals from said mobile stations via the second carrier frequency, the downlink and uplink communications signals of each of said additional base stations being transmitted and received via successive time division multiple access frames, each frame including a plurality of time slots.
• a first time slot within each frame of the additional base station is allocated for downlink communications from the additional base station and a second time slot within each frame of the additional base station is allocated for uplink communications to the additional base station, the first and second allocated time slots being separated in time by a fixed time offset.
• a first partition of the time slots within each frame of the additional base station is reserved for uplink -5- communications and a second partition of the time slots within each frame of the additional base station is reserved for downlink communications.
• the first and second partitions of the frames of each of the base stations are structured such that, for each time slot in each frame, only one of the base stations is permitted to transmit on the first carrier frequency and only one of the base stations is permitted to receive on the second carrier frequency.
• Figure 1 depicts an exemplary wireless communications system in which the teachings of the invention can be implemented.
• Figure 2A depicts a base station and a terminal communicating in accordance with a conventional time-division multiple-access / time-division duplex scheme.
• Figure 2B depicts an exemplary time slot arrangement in a conventional time-division multiple-access / time-division duplex system.
• Figure 3 A depicts a base station and a terminal communicating in accordance with a conventional time-division multiple-access / frequency-division duplex scheme.
• Figure 3B depicts an exemplary time slot arrangement in a conventional time-division multiple-access / frequenc -division duplex system. -6-
• Figure 4A depicts a base station and a terminal communicating in accordance with a time-division multiple-access / frequency-time division duplex scheme taught by the present invention.
• Figure 4B depicts an exemplary time slot arrangement in a time-division multiple-access / frequency-time division duplex system according to the invention.
• Figure 4C depicts an alternative and complimentary time slot arrangement in a time-division multiple access / frequency-time division duplex system according to the invention.
• Figure 5 depicts reference timing among two groups of base stations in an exemplary time-division multiple-access / frequency-time division duplex system according to the invention.
• Figure 6 depicts an exemplary base station transceiver constructed in accordance with the present invention.
• Figure 1 depicts a wireless communications system 100 in which the teachings of the present invention can be implemented.
• the exemplary wireless system includes ten cells or coverage areas C1-C10, ten base stations Bl- B10, a timing master TM and ten mobile stations M1-M10.
• Such a wireless system can be constructed, for example, in accordance with the Personal Wireless Telecommunication (PWT) standard, and can therefore be used, for example, to provide mobile communications within a building or throughout a campus including many buildings and open areas.
• PWT Personal Wireless Telecommunication
• a wireless system can include far more than ten cells, ten base stations and ten mobile stations; however, ten of each is sufficient for illustrative purposes.
• one or more base stations can be situated in each of the cells.
• Figure 1 shows the base stations located toward the cell centers, each base station can instead be located anywhere within a cell. Base stations located toward a cell center typically employ omni-directional antennas, while base stations located toward a cell boundary typically employ directional antennas.
• the timing master TM or radio exchange, maintains timing synchronization between the base stations as is known in the art.
• the timing master can be connected to the base stations by cable, radio links, or both.
• Each base station and each mobile station includes a transceiver for transmitting and receiving communications signals over the air interface.
• the base and mobile stations communicate using a form of time, frequency or code division multiple access (i.e., TDMA, FDMA or CDMA) as is known in the art.
• TDMA time, frequency or code division multiple access
• CDMA code division multiple access
• FIG. 2A depicts uplink and downlink communication according to a conventional TDD scheme. As shown, signals transmitted from a TDD base station B20 to a TDD handset M20, and those transmitted from the TDD handset -8-
• a predetermined time interval T represents the duration of a single TDMA / TDD frame T20
• the separation between uplink and downlink transmissions is typically one half of the predetermined time interval T, or T/2.
• each frame is 10 milliseconds in duration and includes twenty-four data slots. Within a data frame, twelve time slots are used for transmission (from the TDD base station B20 to the TDD handset M20), and the remaining twelve time slots are used for reception (i.e., transmission from the TDD handset M20 to the TDD base station B20). Though transmissions and receptions are separated by certain fixed (or variable) time, they share a common frequency band. The channel of such a system is therefore defined by a predetermined frequency and time reference pair.
• Such TDMA / TDD systems are widely adopted in various wireless communications applications.
• An advantage of these systems is that of frequency efficiency, as both uplink and downlink transmissions use a common frequency carrier. Additionally, since transmissions and receptions are separated in time, a single hardware path (including filters, local oscillators, etc.) can be used for both functions. As a result, TDD systems are relatively low cost. Also, since receiving hardware can be turned off during transmission (and transmitting hardware can be turned off during reception), TDD systems consume relatively little power.
• FDD frequency-division duplex
• Figure 3A depicts uplink and downlink communications between a conventional FDD base station B30 and a conventional FDD handset M30
• Figure 3B shows an exemplary TDMA / FDD frame T30. Since both transmit and receive are accomplished simultaneously, separate hardware paths are required in both base stations and terminals.
• FDD systems are typically higher cost and consume more power as compared to conventional TDD systems.
• FDD systems provide relatively little cross-channel interference and are sometimes preferred from an inter-system perspective.
• a FDD scheme may be required to make a system compatible with proximate systems using an adjacent portion of the frequency spectrum.
• FDD systems have also been widely adopted in wireless communications applications.
• the present invention provides a hybrid, frequency-time division duplex (FTDD) scheme which provides certain of the advantages of both types of conventional system and which further allows a single hardware configuration to be readily adapted to suit virtually any wireless communications application.
• FTDD frequency-time division duplex
• signals transmitted from the FTDD base station B40 to the FTDD handset M40, and those transmitted from the FTDD handset M40 to the FTDD base station B40, are separated in both time and frequency.
• a general channel definition for such a TDMA / FTDD scheme is described in co-pending U.S. Patent Application Serial No. , entitled
• a data frame for the channel defimtions of Figures 4B and 4C is defined to include 2N time slots (N an integer).
• N an integer
• One half of the slots i.e., a first N slots
• the remaining half of the slots i.e., a second N slots
• T the duration of a single frame in the frequency-time division duplex scheme
• an upper frequency band is reserved for base station to handset transmission, and a lower frequency is reserved for handset to base station transmission.
• the first N time slots in a frame are dedicated for downlink communication
• the second N time slots are dedicated for uplink communication.
• the second N time slots are reserved for downlink communication
• the first N time slots are reserved for uplink communication.
• one half of the frame T, or T/2 is reserved for downlink signals and the remaining half is reserved for uplink signals.
• Figure 4B with a second base station operating in accordance with the channel definition of Figure 4C, complete time and spectral efficiency can be provided for a particular coverage area. In other words, both frequencies in each TDMA time slot can be used for uplink or downlink transmission.
• timing alignment among base stations is maintained. Specifically, individual base stations are time shifted with respect to a base reference. For example, a first group of base stations can employ zero offset so that they operate according to the channel definition of Figure 4B, and another group of base stations can employ a half-frame offset (i.e., T/2) so that they operate according to the channel definition of Figure 4C.
• T/2 half-frame offset
• uplink and downlink transmissions for the second group of base stations are offset by T/2 with respect to those of base stations in the first group.
• a system according to the invention can achieve efficiency in frequency and time while maintaining full capacity for individual base stations.
• any number of base station groups can be used with appropriate fixed time-slot offsets between groups.
• four groups of base stations can be implemented using quarter-frame offsets between groups.
• each group reserves one quarter of the time slots in each TDMA frame for uplink transmission and another one quarter of the time slots in each TDMA frame for downlink transmission.
• the frames are reserved for each group so that, at any moment in time, at most one group of base stations can transmit on the downlink frequency and at most one group of base stations can receive on the uplink frequency.
• four co-located -13- base stations, one from each of the four groups can provide full time and spectral efficiency for a particular coverage area.
• time slots reserved for uplink and downlink transmission for a particular type of base station need not be consecutive time slots within a TDMA frame.
• time slots reserved for uplink and downlink transmission for a particular type of base station need not be consecutive time slots within a TDMA frame.
• the first group of base stations can reserve even numbered time slots for downlink communication and odd numbered time slots for uplink communication, while the second complimentary group of base stations reserves odd numbered time slots for downlink communication and even numbered time slots for uplink communications.
• the time slots in that particular partition cannot be also be used for the same type of transmission by another group of base stations. Indeed, the time slots reserved for uplink and downlink transmission for each base station group can be randomly distributed throughout the TDMA frames.
• an exemplary base station transceiver 600 includes a transmit signal processing path and a receive signal processing path.
• the transmit processing path includes first and second transmit blocks 610, 620, first -14- and second transmit / receive blocks 630, 640, a local oscillator 650, a duplexor 660 and an antenna 670.
• the receive signal processing path includes the local oscillator 650, the duplexor 660 and the antenna 670, as well as first and second receive blocks 680, 690.
• the first transmit block 610 can include, for example, a conventional upconverter
• the second transmit block 620 can include, for example, power amplifiers and mixers.
• the first receive block 680 can include, for example, low noise amplifiers (LNAs) and mixers
• the second receive block 690 can include, for example, a conventional downcoverter and limiter.
• the first transmit / receive block 630 can include, for example, a modem
• the second transmit / receive block 640 can include, for example, bandpass filters.
• the duplexor 660 can be, for example, a two-way filter or a switch.
• the duplexor 660 couples the antenna 670 to the second transmit block 620 and isolates the antenna 670 from the first receive block 680.
• Baseband transmit signals are processed by the first transmit / receive block 630 and are then upconverted, filtered and amplified in blocks 610, 640, 620, respectively, prior to transmission via the antenna 670.
• the duplexor 660 couples the antenna 670 to the first receive block 680 and isolates the antenna 670 from the second transmit block 620. Radio frequency signals are received at the antenna 670 and then amplified, filtered and downconverted in blocks 680, 640 and 690, respectively, prior to being processed by the first transmit / receive block 630.
• a base station transceiver constructed in accordance with the invention can be made smaller and less costly as compared to conventional TDMA / FDD transceivers.
• the disclosed frequency-time division duplex scheme is not a true frequency-division duplex system, in that transmission and reception are not conducted simultaneously, the frequency-time division duplex scheme nonetheless appears to proximate systems as a frequency-division duplex scheme from the perspective of intersystem interference.
• a system utilizing the frequency- time division duplex scheme can be implemented in contexts where a frequency- division duplex scheme is preferred.
• hardware configured to implement the frequency-time division scheme can also be utilized where time- division duplex is preferred.
• a simple software change can be used to shift one or both of the uplink and downlink frequencies (i.e. , by changing the frequencies of the local oscillators used to generate the corresponding carriers) so that the uplink and downlink frequencies are the same and the system operates as a true time-division duplex system.
• a time-division multiple-access system constructed according to the present invention can be easily configured to use either a time-division duplex scheme or a pseudo frequency-division duplex scheme. Furthermore, a system originally configured to use time-division duplex can be easily converted to use frequency-division duplex, and vice versa, as needs change. Advantageously, such conversions can be accomplished quickly and inexpensively without architecture modification.
• the present invention provides a time-division multiple access system with a flexible frequency-time division duplex mechanism.
• existing time-division multiple access / time-division duplex hardware can be utilized for applications where frequency-division duplex is preferred or required.
• the disclosed system allows either a common frequency band or dual frequency bands to be used for uplink and downlink communications.
• time-division duplex capability is maintained, -16- as are the benefits of low hardware cost and low power consumption.
• a system can be repeatedly converted for both time-division duplex and frequency-division duplex without requiring significant hardware modification.
• a base station for use in a wireless communications system including a plurality of mobile stations, said base station comprising: a transceiver configured to transmit downlink communications signals to said mobile stations via a first carrier frequency and to receive uplink communications signals from said mobile stations via a second carrier frequency, the downlink and uplink communications signals being transmitted and received via successive time division multiple access frames, each frame including a plurality of time slots, wherein, for each active communications link between said base station and a particular mobile station, a first time slot in each frame is allocated for downlink communication to the particular mobile station and a second time slot in each frame is allocated for uplink communication from the particular mobile station, the first and second allocated time slots being separated in time by a fixed time offset, and wherein a first partition of the time slots within each frame is reserved for downlink communications from said base station to the mobile stations and a second partition of the time slots within each frame is reserved for uplink communications from the mobile stations to said base station.
• a base station wherein a first half of the time slots within each frame are reserved for downlink communications and a second half of the time slots within each frame are reserved for uplink communications.

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• 1998
  • 1998-11-13 EP EP98957929A patent/EP1031194A1/de not_active Withdrawn
  • 1998-11-13 CN CN 98813104 patent/CN1290432A/zh active Pending
  • 1998-11-13 JP JP2000521605A patent/JP2004500724A/ja not_active Withdrawn
  • 1998-11-13 ID IDW20000919A patent/ID25841A/id unknown
  • 1998-11-13 CA CA002309713A patent/CA2309713A1/en not_active Abandoned
  • 1998-11-13 BR BR9814962-8A patent/BR9814962A/pt not_active IP Right Cessation

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