GB2448757A - Frame structure for use with half frequency division duplex mobile terminals on Wimax networks - Google Patents

Abstract

Wimax (IEEE 802.16e) networks are capable of handling full frequency division duplexing, however for economic and other reasons it may be desirable to operate half frequency division duplex (HFDD) terminals on the network. The invention proposes a frame structure with an initial downlink broadcast period 1005, followed by a half duplex downlink period1007 followed by a half duplex uplink period 1013. At the very end of the frame special transmission can be sent 1015/1017, with full duplex units going last 1017 so that half duplex units can use the time to switch back to downlink/receive mode. Uplinks from full duplex units, and possibly half duplex units not scheduled to receive downloads, are scheduled into the half duplex download period 1011. Similarly full duplex downloads are preferably scheduled during the half duplex download period 1009. All of the periods have variable durations which are advised along with terminal allocations in a map broadcast by the base station.

Description

I

METHOD AND APPARATUS FOR WIRELESS COMMUNICATIONS

Field of the Invention

100011 The present invention relates generally to a method and apparatus for wireless communications. In particular, the present invention relates to scheduling of resource allocations for wireless communication in a frequency division duplex system.

BackEround 100021 WiMAX (Worldwide Interoperability for Microwave Access) is a standards-based technology enabling the delivery of last mile wireless broadband access as an alternative to wired broadband such as cable and DSL (Digital Subscriber Line). WiMAX provides fixed, nomadic, portable and, currently being developed, mobile wireless broadband connectivity without the need for direct line-of-sight with a base station.

10003! Mobile WiMax is a broadband wireless solution that enables convergence of mobile and fixed broadband networks through a common wide area radio access technology and flexible network architecture. The new technology is proposed to provide wireless communication in accordance with the 802.16e standard of the IEEE (Institute of Electrical and Electronic Engineers). The 802.16e standard of the IEEE, herein referred to as the 802.16e standard', is an amendment to the 802.16 standard of the IEEE, herein referred to as the 802.16 standard' to extend its applicability. The 802.16 standard entitled Air Interface for Fixed Broadband Wireless Access Systems' is the standard which was published by the IEEE on April 8th, 2002. It was developed by the 802.16 Working Group of the IEEE working on fixed broadband wireless access in Wireless Metropolitan Area Networks (WMAN). The 802.16 standard defines fixed terminal, point-to-multipoint, communications by BWA (Broadband Wireless Access). The 802.16e standard is the standard which was published by the IEEE on February 28th 2006 entitled Physical and Medium Access Control Layers for Combined Fixed and Mobile Operation in Licensed Bands'. It extends operation of the 802.16 standard to wireless broadband connectivity by mobile terminals. The expression 802.16e standard' as used herein includes this published standard and any future amendments or successions to the 802. 16e standard published by the IEEE (or any successor standards authority).

100041 Operation according to the 802.16e standard involves use of a form of OFDM modulation to communicate information. OFDM (Orthogonal Frequency Division Multiplexing) is a spread spectrum technology which allows high speed transmission of data via multiple lower speed sub-channels provided by division of the allocated frequency spectrum into sets of modulated sub-carriers.

[00051 The form of OFDM used in the protocol defined in the 802.16e standard is OFDMA (Orthogonal Frequency Division Multiple Access'). An OFDMA system is one in which different user terminals may operate in the same frequency spectrum and each of these terminals may occupy a separate channel.

10006J In OFDMA communications, the available communication resource can be considered as a two dimensional set of communication resource slots and can be represented graphically by a two dimensional map. One dimension of the map represents time and the other dimension represents frequency. Referring to the frequency dimension, the OFDMA sub-carriers are pseudo-randomly spread on the entire available frequency spectrum for achieving frequency diversity. A designated group of spread sub-carriers is known as a frequency sub-channel. The time dimension is numbered (counted) in units of symbols, known as OFDMA symbols.

A given number of frequency sub-channels in the frequency dimension and a given number of symbols in the time dimension make up a frame.

100071 In an OFDMA system the communication resource available is divided between user terminals by assigning a specified set of multiple sub-channels and multiple symbols per user terminal. Thus, the channel occupied by each user terminal is defined in terms of a specified time in which the user terminal occupies a specified set of the sub-carriers defining a specified sub-channel for the specified time.

100081 Generally, the 802.16e standard allows two possible modes of duplexing between downlink and uplink communications. These are respectively a Time Division Duplex (TDD) mode and a Frequency Division Duplex (FDD) mode.

100091 The TDD mode uses the same carrier frequency for both uplink and downlink transmissions and each successive frame occurring in time consists of a downlink sub-frame, in which communication from the base station to each given mobile station takes place, followed by an uplink sub-frame within the same frame in which communication from each given mobile station to the base station takes place.

[00101 The FDD mode uses different carrier frequencies for downlink and uplink transmissions. In this case, uplink transmissions and downlink transmissions are divided into frames having a fixed duration. The uplink and downlink frames are coincident in time.

100111 It is generally assumed that when in the FDD mode mobile stations will be operating in a full duplex manner in which such stations are able to transmit and receive at the same time. However, the FDD mode of operation in accordance with the 802.1 6e standard and other wireless communications divided into a sequence of frames each providing a two dimensional set of communication resource slots can also be used by mobile stations operating in a half duplex manner. In this case, uplink and downlink transmissions have to be sent separately, since the mobile stations cannot receive when they are transmitting, and vice versa.

Brief description of the drawings

[00121 The accompanying drawings, in which like reference numerals refer to identical or functionally similar elements throughout the separate figures and which together with the detailed description below are incorporated in and form part of the description of this specification, serve to further illustrate various embodiments and to explain various principles and advantages all in accordance with embodiments of the present invention. In the accompanying drawings: [00131 FIG. 1 is a block schematic diagram of a communication system which is for operation in accordance with embodiments of the invention.

[00141 FIG. 2 is a block schematic diagram of an illustrative layout of a mobile station of the system 100.

[00151 FIG. 3 is a block schematic diagram of an illustrative layout of a base station of the system 100.

6] FIG. 4 is an illustrative graph of frequency plotted against time showing illustrative sequences of communication frames which may be adapted for use in the system of FIG. 1 in accordance with embodiments of the present invention.

100171 FIG. 5 shows more detail of an illustrative downlink frame of sequences of FIG. 4.

100181 FIG. 6 shows more detail of illustrative downlink and uplink frames of the sequences of FIG. 4 in accordance with an embodiment of the present invention.

[00191 FIG. 7 shows more detail of illustrative downlink and uplink frames of the sequences of FIG. 4 in accordance with another embodiment of the present invention.

0] FIG. 8 shows more detail of illustrative downlink and uplink frames of the sequences of FIG. 4 in accordance with another embodiment of the present invention.

[00211 The present invention relates generally to a method and apparatus for wireless communications. In particular, the present invention relates to scheduling of resource allocations for wireless communication in a frequency division duplex system.

[00221 FIG. 9 shows sequences of OFDMA symbols in parts of illustrative downlink and uplink frames of the frame sequences of FIG. 4 and shows how frame section boundaries are arranged in accordance with an embodiment of the present invention.

[0023) FIG. 10 shows more detail of illustrative downlink and uplink frames in communication frame sequences in accordance with another embodiment of the present invention.

[00241 Persons of ordinary skill in the art will appreciate that elements in the drawings are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the drawings may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.

Detailed descriDtion 100251 Before describing in detail embodiments that are in accordance with the present invention, it should be observed that the embodiments reside primarily in combinations of method steps and apparatus components related to wireless communication, particularly the scheduling of resource allocations in wireless communication. Accordingly, the apparatus components and method steps have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the

benefit of the description herein.

100261 In this document, relational terms such as first' and second', top' and bottom', and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element preceded by "comprises. . .a" does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element.

100271 It will be appreciated that embodiments of the invention described herein may be comprised of one or more conventional processors and unique or non-unique stored program instructions that control the one or more processors to implement, in conjunction with certain nonprocessor circuits, some, most, or all of the functions of wireless communication, particularly the scheduling of resource allocations in wireless communication, and operation in accordance with such scheduling, as described herein. The non-processor circuits may include, but are not limited to, a radio receiver, a radio transmitter, signal drivers, clock circuits, power source circuits, and user input devices. As such, these functions may be interpreted as steps of a method to perform wireless communication, particularly the scheduling of resource allocations in wireless communication. Alternatively, some or all functions could be implemented by a state machine that has no stored program instructions, or in one or more application specific integrated circuits (ASICs), in which each function or some combinations of certain of the functions are implemented as custom logic. Of course, a combination of the two approaches could be used. Thus, methods and means for these functions have been described herein. Further, it is expected that one of ordinary skill, notwithstanding possibly significant effort and many design choices motivated by, for example, available time, current technology, and economic considerations, when guided by the concepts and principles disclosed herein will be readily capable of generating such software instructions and programs and ICs with minimal experimentation.

100281 FIG. 1 is a block schematic diagram of an illustrative simplified communication system 100 for operation in accordance with embodiments of the present invention. The system 100 operates using a protocol in which wireless communications are divided into a sequence of frames each providing a two dimensional set of communication resource slots. In the following description it is assumed that the system 100 is to operate in accordance with the 802.16e standard as referred to earlier, although the system 100 could operate using another protocol in which wireless conununicaijons are divided into a sequence of frames each providing a two dimensional set of communication resource slots. The system 100 operates in a Frequency Division Duplex (FDD) mode as referred to earlier.

[00291 The system 100 includes a first base station (BS) 101 having wireless links with a plurality of user terminals in a service cell or site defined by the position of the BS 101. The user terminals include mobile stations and may also include at least one fixed terminal (not shown), e.g. used by a dispatcher or other operator sending and receiving operational control messages. Four of many possible mobile stations are shown linked to the BS 101, namely mobile stations (MSs) 104, 105, 107 and 109 having wireless links 110, 111, 113 and 115 respectively with the BS 101. The BS 101 thereby serves user terminals including the MSs 104, 105, 107 and 109 with wireless communications to and from other mobile stations either served by the BS 101 or by other base stations of the system 100 operably linked to the BS 101 or in other systems (not shown) operably linked to the system 100.

100301 The system 100 also includes a second base station (BS) 103. This is shown having a wireless link 117 with the first BS 101. The wireless link 117 is optional. The BS 103 has wireless links with a plurality of user terminals in a service cell or site defined by the position of the BS 103. The user terminals include mobile stations and may also include at least one fixed terminal (not shown), e.g. used by a dispatcher or other operator sending and receiving operational control messages. Four of many possible mobile stations are shown linked to the BS 103, namely mobile stations (MSs) 124, 125, 127 and 129 having wireless links 130, 131, 133 and 135 respectively with the BS 103. The BS 103 thereby serves user terminals including the MSs 130, 125, 127 and 129 with wireless communications to and from other mobile stations either served by the BS 103 or by other base stations of the system 100 operably linked to the BS 103, e.g. the BS 101, or in other systems (not shown) operably linked to the system 100.

(0031) Communications between the BS 101 and each of the MSs it serves, including the MSs 104, 105, 107 and 109 via the links 110, 111, 113 and 115 respectively, are made using an OFDMA Frequency Division Duplex (FDD) protocol in accordance with the 802. 16e standard. Similarly, communications between the BS 103 and each of the MSs it serves, including the MSs 124, 125, 127 and 129 via the links 130, 131, 133 and 135 respectively, are made by the same OFDMA FDD protocol.

100321 Each of the BSs 101 and 103 operates in a full duplex manner, that is it is capable of transmitting and receiving at the same time. The MSs of the system 100 form a first set which are half duplex MSs, that is they are MSs which cannot transmit and receive at the same time, and a second set which are full duplex MSs.

It is assumed for the purposes of illustration in the following description that the MSs 104, 105, 124 and 125 are half duplex MSs and the MSs 107, 109, 127 and 129 are full duplex MSs.

100331 FIG. 2 shows an illustrative block diagram 200 of operational components in each mobile station (MS) of the system 100, including the MSs 104, 105, 107, 109, 124, 125, 127 and 129. As will be apparent to those skilled in the art, the layout of each of the mobile stations may take one of many possible forms, and the block diagram 200 is therefore to be regarded as illustrative rather than definitive.

In the block diagram 200, a controller 201 controls functional operations of the MS.

A processor 202 operably connected to the controller 201 processes infonnat ion sent to and from the MS. The controller 201 and the processor 202 are operably connected to a timer 205 which provides operational synchronization and timing and to a memory 206 which stores data and programs needed in operation by the controller 201 and the processor 202.

100341 The processor 202, which may for example comprise a digital processor, which may be included with the controller 201 in a common digital signal processing unit, is operably connected to a radio frequency (RF) transceiver 203 which transmits and receives RF signals including signals carrying information sent to and from the mobile station. The signals are delivered over-the-air to and from an antenna 217 connected to the RF transceiver 203.

(0035J When the RF transceiver 203 via the antenna 217 receives an RF signal including information representing communicated speech, the processor 202 extracts the speech information and delivers a signal including the extracted speech information to an audio output 210 which comprises a transducer such as a speaker which converts the signal to audio form to reconstruct the communicated speech for a user of the mobile station having the layout 200. The MS also includes an audio input 211 which comprises a transducer such as a microphone which converts speech of the user into the form of an electrical signal and delivers the signal to the processor 202 which processes the signal into a form suitable for inclusion in an RF signal for transmission by the RF transceiver 203 via the antenna 217.

[0036J When the RF transceiver 203 receives via the antenna 217 a signal representing communicated (non-speech) data, e.g. alphanumeric characters representing words or numerals or picture or video information, the processor 202 extracts infonnation relating to the communicated data and delivers a signal including the extracted data to a data output 212. The data output may for example comprise a connection to an external data processing terminal (not shown), e.g. a personal computer.

10037] A data input 213 provides an input signal from a user including data to be communicated. The data input 213 may for example comprise a connection to a data source, e.g. a personal computer (not shown). The signal provided by the data input 213 is delivered to the processor 202 which processes information included in the signal into a form suitable for inclusion in an RF signal to be transmitted by the RF transceiver 203 via the antenna 217.

100381 The MS illustrated by the block diagram 200 in FIG. 2 also includes a user interface 214, e.g. a keypad and control buttons, which allows a user to enter instructions and data into the mobile station. The user interface 214 is operably connected to the controller 201 to receive signals representing instructions entered by a user at the user interface 214. The user interface 214 is also operably connected to the processor 202 to enable a signal representing data entered by the user at the user interface 214 to be delivered to the processor 202. The processor 202 processes data included in the signal into a form suitable for inclusion in an RF signal to be transmitted by the RF transceiver 203 via the antenna 217.

[0039J The MS includes an electro-optical display 209 operable to display information to a user in a known manner. The display 209 is driven by a display driver 207 under control of the controller 201.

100401 The MS includes a battery 216 which provides a source of electrical energy for all active components of the mobile station.

100411 The MS illustrated in FIG. 2 also includes a resource acceptor 220 operably coupled to the controller 201. The resource acceptor 220 may be incorporated within the controller 201. The resource acceptor 220 is a processor or part of a processor, e.g. a digital signal processor, which operates a programmed algorithm. The resource acceptor 220 carries out functions within the MS relating to scheduling of communications between the MS and the BS serving the MS in accordance with the defined protocol by which the MS and BS operate. In particular, the resource acceptor 220 ensures that downlink transmissions from the BS are received, and uplink transmissions to the BS are sent, at times which have been notified to the resource acceptor 220 by a resource scheduler 320 (FIG. 3) in accordance with the defined protocol, such as in one of the ways described later with reference to FIGS. 4 to 10.

100421 As noted earlier, in some cases, the MS represented by the block diagram may be a half duplex MS, that is it may operate in only one of a receive mode or a transmit mode. Switching between the two modes may be controlled by the controller 201 operating in conjunction with the timer 205 and the resource acceptor 220.

100431 In other cases, the MS may be a full duplex MS, that is it may operate independently in a receive mode and in a transmit mode at the same time. In this case, the RF transceiver 203 and the antenna 217 (e.g. a multiple antenna configuration) provide independent transmission and reception paths in a known manner.

100441 FIG. 3 shows an illustrative block diagram 300 of operational components in each of the BS 101 and the BS 103. As will be apparent to those skilled in the art, the layout of each of the BSs 101 and 103 may take one of many possible forms, and the block diagram 300 is therefore to be regarded as illustrative rather than definitive. In the block diagram 300, a controller 301 controls functional operations of the BS. A processor 302, e.g. a digital signal processor, operably connected to the controller 301 processes information sent in RF signals to and from the base station.

The controller 301 and the processor 302 are operably connected to a timer 305, which provides operational synchronization and timing, and to a memory 306 which stores data and programs needed in operation by the controller 301 and the processor 302.

[0045J The processor 302 is operably connected to a plurality of RF transceivers two of which are shown, namely an RF transceiver 303 and an RF transceiver 307.

Each of the RF transceivers 303 and 307 transmits and receives RF signals including signals carrying information sent to and from user terminals including mobile stations served by the BS. The signals are delivered over-the-air to and from an antenna 304 connected to the RF transceiver 303 and to and from an antenna 308 connected to the RF transceiver 307.

100461 When the RF transceiver 303 receives via the antenna 304 an RF signal including information representing communicated speech or data, the signal is passed to the processor 302. Similarly, when the RF transceiver 307 receives via the antenna 308 an RF signal including information representing communicated speech or data, the signal is passed to the processor 302. The processor 302 converts each signal including communicated information from the RF transceiver 303 or the RF transceiver 304 into an electronic signal including communicated information. The communicated information includes system control information and user communicated information for onward delivery. Where the communicated information comprises system control information the electronic signal produced by the processor 302 is passed to the controller 301. Where the electronic signal produced by the processor 302 comprises user communicated information for onward delivery it is delivered to a router 312 which routes the electronic signal toward its destination, e.g. via a wired or wireless link to another base station (such as via the link 117) or to a mobile station (other than the originator of the information) served by the BS via the processor 302. Similarly, each incoming electronic signal received at the router 312 from a source other than the processor 302 which includes communicated user information to be sent to one of the user terminals including mobile stations served by the BS having the layout shown in the block diagram 300, is routed by the router 312 to the processor 302. The processor 302 processes each electronic signal which it receives from the router 312 into a form suitable for inclusion in an RF signal for transmission by the RF transceiver 303 via the antenna 304 or for transmission by the RF transceiver 307 via the antenna 308.

100471 The processor 302 also prepares and receives system control messages and data received from the controller 301 to be sent to the mobile terminals served by theBS.

10048] The BS of the block diagram 300 includes a power supply 311, e.g. from the main (mains) electricity supply, which provides a source of electrical energy for all active components of the BS.

100491 Although the BS of the block diagram 300 is shown in FIG. 3 as having two RF transceivers connected respectivcly to two antennas 304 and 308, it could have one combination or alternatively more than two combinations of RF transceivers and antennas. In any event, the BS operates in a full duplex manner.

100501 The BS of the block diagram 300 also includes a resource scheduler 320 operably coupled to the controller 301. The resource scheduler 320 may be incorporated within the controller 301. The resource scheduler 320 is a processor, e.g. a digital signal processor, which operates a programmed algorithm to carry out functions within the BS relating to scheduling of communications between the BS and MSs, both half and full duplex, and other terminals (if any) served by the BS. In particular, the resource scheduler 320 computes, organises and specifies the structure of communication frames according to a protocol and in one of the ways to be described later with reference to FIGS. 4 to 10. The resource scheduler 320 sends to MSs served by the BS notifications of the structure of frames it has specified including the positions in such frames when MSs are to receive downlink data transmissions and are to make uplink data transmissions. The manner and fonn of these scheduling notifications are illustrated later with reference to FIGS. 4 to 10.

100511 FIG. 4 shows illustrative communication frames which may be adapted (as described later) for wireless communications in the communication system 100 between one of the base stations of the system 100, e.g. the BS 101, and the mobile stations served by the base station, e.g. the MSs 104, 105, 107 and 109. FIG. 4 shows a sequence 401 of consecutive downlink frames in which transmission by the BS 101 may take place, and a corresponding sequence 403 of the same downlink frames in which reception by one of the served MSs 104, 105, 107 and 109 may take place. FIG. 4 also shows a sequence 405 of consecutive uplink frames in which transmissions by the MSs 104, 105, 107 and 109 may take place. The downlink frames of the sequence 401 and of the sequence 403 coincide with the uplink frames of the sequence 405, and the frames in each of these sequences may be considered to have a common frame numbering system. In FIG. 4, three frames, namely Frame n-I, Frame n and Frame n+I, are shown in each of the sequences 401, 403 and 405, where n indicates an arbitrary numbering integer. As will be familiar to those of ordinary skill in the art, and as illustrated in FIG. 4, each of the frames of the sequences 401,403 and 405 is equivalent to an area of a graph of OFDMA frequency (plotted in units of numbers of sub-channels) versus time (plotted in units of OFDMA symbols). Further, each frame is logically considered to be made up of a grid of rectangular portions. The frames in FIG. 4 for clarity are not shown resolved into these known rectangular portions. The minimum size of a rectangular portion is one OFDMA symbol measured along the horizontal or time axis and one frequency sub-channel measured along the vertical or frequency axis. A minimum unit of area in each of the frames employed for a particular resource allocation, that is for allocation for a particular data transmission, is known in the art as a slot'. In downlink frames of the downlink sequences 401 and 403, a slot consists of a rectangle having dimensions of two OFDM symbols in length by one sub-channel in height. In frames of the uplink sequence 405, a slot consists of a rectangle having dimensions of three OFDM symbols (an OFDM triplet') in length by one sub-channel in height. 100521 The OFDMA frequency scale for the frames of the downlink

sequences 401 and 403 shown in FIG. 4 is in a different part of the frequency spectrum from the OFDMA frequency scale for the uplink sequence 405, since the downlink sequences 401, 403 of consecutive downlink frames have a different carrier frequency from that of the uplink sequence 405 of consecutive uplink frames, in view of the FDD mode of operation.

100531 Each of the frames in the sequences shown in FIG.4 includes two sections, namely a first section followed by a second section. Thus, in the sequences 401, 403 and 405, the Frame n-I has first sections 407, 419 and 431 followed by second sections 409, 421 and 433 respectively. In the sequences 401, 403 and 405 the Frame n has first sections 411, 423 and 435 followed by second sections 413, 425 and 437 respectively. In the sequences 401, 403 and 405 the Frame n+1 has first sections 415, 427 and 439 followed by second sections 417, 429 and 441 respectively.

100541 The first section and the second section of each frame in each sequence have a common boundary which extends as a straight vertical line between the top of the frame and the bottom of the frame, as illustrated by a boundary 443 in the Frame n between the sections 411 and 413, between the sections 423 and 425 and between the sections 435 and 437. Alignment between the sections of the uplink and downlink frames in this way is not essential for full duplex MSs but is essential for half duplex MSs and so is employed in the frame structuring in methods embodying the invention to be described.

100551 Data for broadcast to all MSs served by the BS 101 is sent by the BS 101 in the first section of each downlink frame in the sequence 401, e.g. the section 411 of the Frame n. The receiver of each of the served MSs receives the broadcast data in the first section of each frame of the sequence 403, e.g. in the first section 423 for the Frame n.

100561 The data broadcast in each first section of each frame of the downlink sequences 401 and 403 includes (amongst other things) a downlink map, known in the art as the DL MAY', and an uplink map, known in the art as the UL_MAP'.

The downlink map defines the portions of the frame, herein also called resource allocations', that are scheduled to be taken up by one or more downlink data transmissions, known in the art as data bursts', addressed to individual or multiple targeted MSs served by the BS 101 (as distinct from all served terminals when addressed by broadcast). The downlink map has been computed, arranged and specified by the resource scheduler 320 of the BS 101 and is understood and acted upon when received by the resource acceptor 220 of the relevant receiving MS. The uplink map defines the portions of the frame in the uplink sequence 405 that are scheduled to be taken up by one or more uplink data transmissions from individual MSs. The uplink map has also been computed, arranged and specified by the resource scheduler 320 of the BS 101 and is understood and acted upon when received by the resource acceptor 220 of the relevant MS. Any other data that has to be broadcast to served MSs is sent in the first section of each frame of the downlink sequence 401. Such broadcast data includes for example the Downlink Channel Descriptor (DCD), the Uplink Channel Descriptor (UCD) and more.

100571 Each half duplex MS served by the BS 101 has to be in its transmit mode or in its receive mode at appropriate times according to the timing information it receives in the downlink map and in the uplink map sent by the BS 101 in the first section of each downlink frame. In order to receive the downlink map and the uplink map in the first section of a given frame, each half duplex MS is not able to transmit during the first section of the frame. Therefore, the resource scheduler 320 of the BS 101 does not allow any uplink data transmission to take place from any half duplex MS during the first section of any frame, e.g. the first section 435 of the Frame n, when the MS has to receive broadcast data.

100581 Each half duplex MS served by the BS 101 potentially may receive any downlink transmission from the BS 101 targeted to that MS by unicast or multicast transmission (rather than by broadcast) or may transmit in the uplink direction during the second section of each appropriate frame. The portions of the second section allocated for such downlink and uplink transmissions to be made are computed, arranged and specified by the resource scheduler 320 of the BS 101 and are indicated to served BSs in the downlink map and uplink map sent in the first section of a frame which may for example be the same frame. These allocated portions are understood and acted upon by the resource acceptor 220 of each relevant MS.

100591 The resource scheduler 320 of the BS 101 does not schedule any uplink transmission to take place for a specific half duplex MS, for example the MS 104 in FIG. 1, during the period of time(s) when that MS is scheduled to receive a downlink data transmission. This is illustrated in FIG. 5 in which a data burst 501 is sent from the BS 101 in the second section 413 of the Frame n of the sequence 401.

The data burst 501 is received by the half duplex MS 104 as indicated by a received data burst 503 in the sequence 403. During the period of time when the data burst 503 is to be received (the horizontal width of the data burst 503), the MS 104 has to be in receive mode and cannot therefore be scheduled to make any uplink transmission.

100601 Similarly, during each period of time in each second section in which the resource scheduler 320 has allocated an uplink data transmission from a specific half duplex MS, e.g. the MS 105, to the BS 101 to take place, the same MS is not be allowed to receive data sent in a downi ink transmission.

100611 The scheduled uplink transmissions that have to be made in each uplink frame in the sequence 405 include data transmissions known in the art as special data transmissions. These special uplink data transmissions include ranging data sent in Ranging Regions' to allow the BS 101 to perform a known synchronization procedure. The timing of Ranging Regions is common for all MSs, both full duplex and half duplex. Additional special uplink data transmissions are the Fast Feedback Region', also known by the name Channel Quality Indication Channel (CQICH') and the Acknowledgement Channel' (ACKCH). The scheduling of these special uplink transmissions is arranged by the resource scheduler 320 not to coincide with any downlink transmission to a half duplex MS.

100621 Thus, there are restrictions as described above on the time periods when half duplex MSs of the system 100 may transmit or receive data. In contrast, full duplex MSs such as the MS 107 may make uplink data transmissions at any time. In the following description, further in accordance with embodiments of the invention, methods are described in which the sequences of frames illustrated in FIG. 4 are further adapted to permit efficient use of resources for communication between the BS 101 and half duplex MSs as well as full duplex MSs served by the BS 101.

100631 In the following description, the Frame n refers to an individual frame and could be any given frame in a sequence of frames. The Frame n-I and the Frame n+1 are the frames that precede and follow the given frame.

4] In a first method, frames of the sequences 401, 403 and 405 are designated alternately as even numbered frames and odd numbered frames. Thus, for example, the Frames n-I and n+1 are designated as odd numbered frames and the Frame n is designated as an even numbered frame. Downlink data transmissions from the BS 101 to targeted half duplex MSs such as the MSs 104 and 105 are scheduled by the resource scheduler 320 to take place in the second section of only even numbered frames, and uplink transmissions from the half duplex MSs to the BS 101 are scheduled to take place in the second section of only odd numbered frames (or vice versa). Half duplex MSs are thus required to be in their receive mode during all even numbered frames and during the first section only of all odd numbered frames.

Half duplex MSs are required to be in their transmit mode during the second section of all odd numbered frames. Downlink data transmissions to Full duplex MSs, such as the MS 107, may be scheduled by the resource scheduler 320 to take place during the second section of any frame, and uplink data transmissions from full duplex MSs may be scheduled to take place at any time during uplink frames.

100651 In a first method, the uplink map broadcast in the first section of each given frame may advantageously specify a region being allocated in the second section of an uplink frame two frames later for an uplink data transmission. This is illustrated in FIG. 6, in which an uplink map 601 is broadcast by the BS 101 in the first section 407 of the Frame n-1 sent in the downlink sequence 401. The uplink map 601 specifies a region 603 in the second section 441 of the Frame n+1 of the sequence 405 in which the next uplink data transmission from the MS 107 to the BS 101 is scheduled to take place. The MS 107 makes the required uplink data transmission in the allocated region 603 of the second section 441 of the Frame n+ 1.

100661 The first method described herein is effective in combining communication between the BS 101 and full duplex and half duplex MSs in the same FDD system 100. The following implementation procedures are preferably applied in that method: [0067J (i) When in the first method broadcast or multicast data transmissions from the BS 101 are to be sent to targeted half duplex MSs as well as full duplex MSs, these transmissions should preferably be made in the second section of even frames only, such as the Frame n depicted in FIG. 4. For this purpose, the BS 101 may have prior stored knowledge, e.g. in the memory 306, or may gain knowledge in data received from each MS, indicating for each MS served by the BS 101 whether the MS is a half duplex MS or a full duplex MS.

100681 (ii) Special uplink data transmissions such as those specified earlier, which are required to be received by the BS 101 in transmissions from all MSs, should preferably be scheduled only in the second section of odd numbered frames, such as the Frame n-I, since the half duplex MSs are not allowed to transmit during even numbered frames.

[0069J In a second method, frames of the sequences 401, 403 and 405 are again designated as alternate even numbered frames and odd numbered frames as in the first method embodying the invention. Half duplex MSs are again in the receive mode during all odd numbered frames but they can be in transmit mode during the whole of each of the even numbered frames (or vice versa). Full duplex MSs again have no restrictions and can be in simultaneous transmit and receive mode in all odd and even numbered frames.

10070i In the second method, the downlink map for half duplex MSs such as the MS 104 may be given in the first section of only odd numbered frames, e.g. the Frame n-I. The downlink map may define for the second section in the same odd numbered frame one or more regions of the second section in which downlink data transmissions to the half duplex MSs are due to take place. The uplink map for half duplex MSs may also be given in the first section of only the odd numbered frames, e.g. Frame n-I. However, the uplink map for half duplex MSs may advantageously specify a region being allocated in the second section of the next even numbered frame, e.g. Frame n, for an uplink data transmission. This is illustrated in FIG.7. An uplink map 701 is broadcast by the BS 101 in the first section 407 of the Frame n-i in the sequence 401. The uplink map 701 specifies a region 703 in the next Frame n of the uplink sequence 405 in which an uplink data transmission from the half duplex MS 104 to the BS 101 is to take place. The Frame n of the sequence 405 is shown as a complete uplink frame 705 which combines the first section 435 and the second section 437 of FIG. 4.

100711 It is to be noted that the half duplex MSs such as the MS 104 and the MS need to switch between their transmit mode and their receive mode at the end of each whole frame in the second method embodying the invention. These MSs do not have to listen to the broadcast data in the first section of the even numbered frames, e.g. the data in the first section 411 of the Frame n, since there is no data for them in that section. The data broadcast in even numbered frames is directed only to full duplex MSs such as the MS 105.

100721 Furthermore, although not indicated specifically in the drawings, the frame timing protocol of the system 100 has to allow a finite time for half duplex MSs to switch between their transmit and receive modes. As the switching in the second method is to be carried out in the boundary region between successive frames, allowance may easily be made for the time required for the switching to be made.

For example, the time period occupied by the last OFDMA symbol in each frame may be employed to allow the switching to be made. A typical required switching time is 50 ts (fifty microseconds), whereas the time period of one OFDMA symbol in accordance with the 802.1 6e standard is always greater than 90 j.ts (ninety microseconds). Thus, the switching time can be easily accommodated in a time allowance of one OFDMA symbol immediately before the boundary between frames.

100731 The second method is effective in efficiently combining communication between the BS 101 and full duplex and half duplex MSs in the same FDD system 100. The following implementation procedures are preferably applied in that method: 100741 (i) Broadcast and multicast data transmissions that are addressed to a combination of half duplex and full duplex MSs should preferably be transmitted in odd numbered frames only, since half duplex MSs can receive only in such frames; 100751 (ii) Special uplink data transmissions such as those defined earlier that need to be sent by all MSs, including full duplex MSs as well as full duplex MSs, should desirably be scheduled to be sent only in even numbered frames, since half duplex MSs can transmit only in such frames.

100761 In a third method, half duplex MSs may transmit and receive in each frame by further dividing each frame in the sequences shown in FIG. 4 according to the following procedure. The second section of each frame is divided into two zones, namely a first zone and a second zone. (These could alternatively be considered as two sections or sub-sections formed by dividing the second section). The first sect ion of each frame is employed for broadcast transmissions as described earlier with reference to FIG. 1. Downlink unicast and multicast data transmissions to targeted half duplex MSs are scheduled by the resource scheduler 320 to be made only in the first zone of the second section of each downlink frame. Uplink data transmissions from half duplex MSs that have to receive downlink transmissions in the first zone are scheduled by the resource scheduler 320 to be made only in the second zone of the second section of each uplink frame.

100771 This is illustrated in FIG. 8 for the Frame n. The first sections 411, 423 and 435 in FIG. 8 are the same as shown in and described with reference to FIG. 4.

The second section 413 of the Frame n in the downlink sequence 401 is divided into a first zone 801 and a second zone 802. The second section 425 of the Frame n in the downlink sequence 403 is divided into a first zone 805 and a second zone 804.

The second section 437 of the Frame n in the uplink sequence 405 is divided into a first zone 806 and a second zone 809. A data burst 803 targeted to a particular half duplex MS, e.g. the half duplex MS 104, is transmitted by the BS 101 in the first zone 801 of the second section 413, and a corresponding data burst 807 is received by the MS 104 in the first zone 805 of the second section 425. Thus, the MS 104 has to be in receive mode during the first zone 805, particularly during the period when the data burst 807 is due to be received, and, in consequence, no uplink data transmission is scheduled by the resource scheduler 320 to be made by the MS 104 during the corresponding first zone 806 of the uplink sequence 405. Uplink transmissions from lI.ill duplex MSs may be scheduled by the resource scheduler 320 to be made at any time during the Frame n.

10078J It is to be noted that each half duplex MS that does not need to receive a downljnjc data transmission in the first zone 805, that is a downlinlc unicast or multicast transmission targeted to that MS, may be in transmit mode during the corresponding first zone 806 of the second section 437 of the uplink sequence 405.

Such half duplex MSs, may therefore be allocated resource by the resource scheduler 320 to make an uplink data transmission in the first zone 806 (as well as in the second zone 809, if required) of the second section 437 of the uplink sequence 405. However, to simplifr operation in the system 100, all half duplex MSs may be required to be in receive mode during all of the first zone 806 of the second section 437, and the resource scheduler 320 may operate to schedule no uplink transmissions from half duplex MSs during the first zone 806.

100791 FIG. 8 shows a common boundary 81 1 between the first and second sections of the Frame n for each of the sequences 401, 403 and 405 and also a common boundary 813 between the first zone and the second zone of the second section of the Frame n for each of the sequences 401, 403 and 405. The position of the boundary 811 may be dynamically varied by the scheduler 320 from frame-to-frame depending on the amount of data to be broadcast in the first section 411. The position of the boundary 811 could alternatively be fixed and known by the BS 101 and the MSs it serves for all frames. The position of the boundary 813 may also be dynamically varied depending on the resource allocations (number of slots) required for downlink unicast and multicast data transmissions required to be made in the first zone of the Frame n to targeted MSs, especially half duplex MSs.

[00801 The positions of the boundary 811 (if required to be notified to MSs) and of the boundary 813 for the Frame n may beneficially be computed by the resource scheduler 320 and notified to all MSs in a frame earlier than that in which they are relevant. Thus, the position of the boundaries 811 and 813 for the Frame n may be sent in the uplink map broadcast to MSs in the first section 407 of the Frame n-i (FIG. 4). The position of the boundary 811 and of the boundary 813 for a given frame are thereby known by MSs before the uplink map is sent by the BS 101 for that frame. This procedure may be applied because there may be difficulty in the scheduler 320 becoming aware during a given frame of the number and sizes of downlink transmissions required to be allocated for that given frame. However, it is easier for the scheduler 320 to know before the start of a given frame the exact sizes of downlink transmissions required for the given frame. So the position of the boundaries 811 and 813 for a given Frame n is desirably scheduled by the scheduler 320 and notified to MSs in a previous frame, e.g. the Frame n-i. Thus, the uplink map for a given frame may be for a succeeding frame, e.g. the next frame downlink map. On the other hand, the downlink map sent in a given frame may be for the current frame.

100811 If the size of the downlink map for the Frame n is not known by the scheduler 320 at the time the position of the boundaries 811 and 813 have to be broadcast by the BS 101, an estimated value of the size of the downlink map may be computed by the scheduler 320 and employed by the scheduler 320 to compute the position of the boundary 811. Where such a size estimation is used, the downlink scheduling for the Frame n as indicated in the downlink map for the Frame n is constrained by the estimation. This means that the allocations for downlink transmissions to targeted half duplex MSs by the BS 101 in the first zone 801 of the second section 413 of the Frame n should be cut off when the estimated size for the downlink map has been reached even if there are more available slots for downlink transmissions in the Frame n.

100821 Similarly, an estimated size of the uplink map transmitted by the BS 101 in a given downlink frame in the sequence 401 may also be computed by the scheduler 320 in a previous frame, e.g. the frame immediately preceding that in which the uplink map is sent. Where such an estimation is used, the uplink transmissions for the given frame are constrained by the estimation. In order to prevent over-estimation, the scheduler 320 does not allow further scheduling of any data transmission when the scheduling for the relevant frame or frame zone is already full.

100831 If the exact size of the allocations required in the first zone 801 for the Frame n is not known when the downlink map and/or the uplink map for such allocations and the position of the boundary 811 and the boundary 813 have to be broadcast, an estimation of the size and position may be made by the scheduler 320 according to some suitable estimation criterion, e.g. a recent or total (maximum allowed) rate of traffic loading. The BS 101 can control the number of active MSs which it is to serve. For each active MS allowed to be served, the resource scheduler 320 knows the recent average traffic rate and also the maximum rate traffic rate which can be permitted.

[00841 The boundaries 811 and 813 in the Frame n are desirably aligned with OFDMA symbol boundaries. This is illustrated in FIG. 9, in which part of the Frame n is shown as a downlink sequence 901 of OFDMA symbols 902 making up part of the first section 411 and second section 413 of the downlink sequence 901.

These slots include consecutive symbol pairs 905, 907, 909, 911, 913 and 915 for downlink transmissions. Each of these pairs constitutes a downlink slot according to the 8O2.16(e) standard. Part of the corresponding uplink sequence of the Frame n making up part of the first section 423 and the second section 425 of the sequence 403 is also shown as a sequence 903 of OFDMA symbols 904. These symbols include consecutive triplets 917, 919, 921 and 923. Each of these triplets constitutes an uplink slot according to the 802.16(e) standard. The boundary 811 for the Frame n in this illustration is arranged by the resource scheduler 320 to be co-incident with the boundary between the downlink slots 905 and 907 and between adjacent symbols 904 inside the uplink slot 917. The boundary 813 for the Frame n is arranged by the resource scheduler 320 to be co-incident with the boundary between the triplet 921 and the triplet 923 and co-incident with the boundary between adjacent symbols 902 inside the downlink slot 913.

100851 It is to be noted that the boundaries between downlink slots and the boundaries between uplink slots are fixed according to the 802.16(e) standard. Also, in selection of the position of the boundary 811 by the resource scheduler 320, no switching between receive mode and transmit mode has to be allowed. Thus, the position of the boundary 811 may conveniently be selected as shown in FIG. 9 to be between downlink slots but not between uplink slots. However, in selection of the position of the boundary 813 by the resource scheduler 320, switching between receive mode and transmit mode of half duplex MSs has to be allowed as discussed earlier, and the boundary 813 should be at the start of an uplink triplet. The illustrative position of the boundary 813 as shown in FIG. 9 suitably fulfils these requirements. Although the first symbol of the downlink slot 913 may not be used for transmission of downlink data, it serves for half duplex MSs to switch from their receive mode to their transmit mode. A similar allowance has to be made at the end of each frame to allow half duplex MSs to switch back to their receive mode after being in transmit mode, e.g. at the end of the second zone 809 of the Frame n. This allowance is implicitly provided for by the 802.16(e) standard.

[00861 As noted earlier, the position of the boundary 813 in Frame n between the first and second zones of the second section of the Frame n is dynamically variable by the scheduler 320. The position depends on the load balance required between the downlink and uplink data traffic required in the Frame n to and from all MSs served by the BS 101, particularly half duplex MSs served by the BS 101. As noted earlier, the positions of the boundaries 811 and 813 in a given frame are notified to MSs in the first section of the preceding frame, so the half duplex MSs are able to store these positions, e.g. in the memory 206, and to use the stored position of the boundary 813 to begin switching from receive mode to transmit mode one OFDMA symbol before the boundary 813 is reached.

100871 The specification of the boundary 813 between the first and second zones of the second section of each frame, serves an additional purpose in the third method. As is well known in the art, the allocation of uplink resource for data transmission by MSs in a given frame is normally applied in the form of a raster scan in the time direction within the boundaries of the frame, i.e. along a given row along the time axis then along the next row below, and so on. Normally, when an uplink resource allocation is being made and the allocation reaches the end of a row at the end of the frame, the allocation continues at the beginning of the frame on the next row. This is acceptable for full duplex MSs but not for half duplex MSs, since the beginning of the frame is dedicated for downlink broadcast transmissions in the first section of the frame as described earlier. Defining the position of the boundary 813 by the scheduler 320 ensures that the raster scan of the uplink resource allocation stays within the second zone of the second section, so that when one row is completed at the end of the frame the next row is begun at the start of the second zone of the second section, that is the start of the second zone 809 in FIG. 8.

100881 It should be noted that the first zone 806 of the second section 437 may be absent in some selected frames, in that case, the second zone 809 will follow immediately after the first section 435. In other words, the boundaries 811 and 813 will be combined in such frames, 100891 In the third method, uplink resource allocations for special uplink data transmissions by half duplex MSs, such as those specified earlier, are made in the second zone 809 in the Frame n.

(0090J The partitioning of the frames into sections and zones in the manner of the third method embodying the invention provides an efficient way of managing the communication resources available in an FDD system including both full duplex and half duplex MSs. The partitioning introduces certain restrictions in the scheduling of the corresponding downlink frames for downlink transmissions to half duplex MSs. The following implementation procedures are preferably applied in that method: 100911 (i) All broadcast transmissions including those to full duplex MSs should preferably be scheduled to be made in the first section of each frame.

[0092J (ii) Downlink data transmissions to specific (but not all) half duplex MSs should preferably be scheduled to be made during the first zone of the second section of each frame (e.g. the section 809 in FIG. 8). If for some reason this is not possible in a given frame and a downlink data transmission to a particular half duplex MS has to be made during the second zone of the second section of a particular frame this specific MS should preferably not have an uplink scheduling in this particular second zone.

100931 A fourth method is illustrated in FIG. 10, which shows a single frame, Frame n, of a downlink frame sequence 1001 and a corresponding uplink frame sequence 1003. Other frames in the sequences 1001 and 1003 have a format similar to that shown in FIG. 10. In the downlink sequence 1001, the Frame n has three frame sections 1005, 1007 and 1009. In theuplink sequence 1003, the Frame n has four frame sections 1011, 1013, 1015 and 1017. A boundary 1019 is formed between the frame sections 1007 and 1009 of the downlink sequence 1001 and between the frame sections 1011 and 1013 of the uplink sequence 1003. Resource allocations in the frame sections of the Frame n of the sequences 1001 and 1003 are made by the scheduler 320 and used in the following manner.

100941 In the frame section 1005 of the Frame n of the downlink sequence 1001, downlink broadcasts of data such as the downlink map and the uplink map are made (as in the first section 411 of the Frame n shown in FIG. 4). In the frame section 1007 which follows the frame section 1005, unicast and multicast data transmissions are made to specific targeted MSs but only those that are half duplex MSs, e.g. the MS 104 and the MS 105. Thus, half duplex MSs need to be in their receive mode during the frame section 1007. In the frame section 1009 which follows the frame section 1007, unicast and multicast data transmissions are made to specific targeted MSs but only those that are full duplex MSs, e.g. the MS 107 and the MS 109. Thus, half duplex MSs do not need to be in their receive mode during the frame section 1009 and can switch to their transmit mode at the end of the section 1007.

100951 In the frame section 1011 of the Frame n of the uplink sequence 1003, uplink data transmissions may be scheduled by the scheduler 320 to take place but only from full duplex MSs. Half duplex MSs need to be in their receive mode in the frame sect ion 1011 to receive downi ink transmissions sent in the frame sections 1005 and 1007 and so cannot transmit during the frame section 1011 of the uplink sequence 1003. In the frame section 1013 which follows the frame section 1011 in Frame n of the uplink sequence 1003, uplink data transmissions are scheduled to take place from half duplex MSs as well as from full duplex MSs. The half duplex MSs are able to transmit during the frame section 1013 since the frame section 1013 occurs during a period of time coinciding with part of the frame section 1009 when no downlinjc transmissions are made to half duplex MSs.

100961 The frame sections 1015 and 1017 are two short optional sections following the frame section 1013 in the Frame n of the uplink sequence 1003. The frame section 1015 is allocated for uplink transmissions of special data, such as referred to earlier, from half duplex MSs. Similarly, the frame section 1017 is allocated for uplink transmissions of special data, such as referred to earlier, from full duplex MSs. Alternatively, the sections 1015 and 1017 may be encompassed within the frame section 1013.

(0097J The uplink resource available in each frame is limited and is therefore valuable. The provision of the frame section 1017 following the frame section 1015 as shown in FIG. 10 for special uplink data transmissions from full duplex MSs makes good use of the uplink resource in the time period at the end of the Frame n, because the same time period may be used for half duplex MSs to switch from their transmit mode to their receive mode to be ready to receive at the start of the section 1005 of the next frame.

100981 The fourth method simplifies scheduling operations by the scheduler 320 by grouping together the data transmissions to targeted full duplex MSs in the frame section 1009 and by grouping together the data transmissions to targeted half duplex MSs in the frame section 1007.

100991 In the foregoing specification, specific embodiments of the present invention have been described. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the present invention as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of present invention. The benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential features or elements of any or all the claims. The invention is defined solely by the appended claims including any amendments made during the pendency of this application and all equivalents of those claims as issued.

Claims (33)

1. Claims 1. A method of scheduling wireless communications between a

   first terminal which is a full duplex terminal and each of a plurality of second terminals which are half duplex terminals, the wireless communications being divided into a sequence of frames each providing a two dimensional set of communication resource slots, wherein downlink transmissions from the first terminal are in downlink frames on a first carrier frequency and uplink transmissions from the second terminals are in uplink frames on a second carrier frequency, the downlink and uplink frames being coincident in time, the method comprising: allocating selected frames or sections of frames for sending only one of: (i) uplink transmissions from the second terminals; and (ii) downlink transmissions, other than broadcast transmissions, targeted to the second terminals.
2. 2. A method according to claim 1 wherein the first terminal is a base station and the second terminals are mobile stations.
3. 3. A method according to claim 1 or claim 2 wherein the scheduling of uplink and downlink transmissions is carried out by a scheduler associated with the first terminal.
4. 4. A method according to any one of the preceding claims including at least one third terminal which is a full duplex terminal which communicates with the first terminal, wherein downlink transmissions from the first terminal to the third terminal are in the same downlink frames on the first carrier frequency as those sent to the second terminals and uplink transmissions from the at least one third terminal to the first terminal are in the same uplink frames on the second carrier frequency as those sent from the second terminals.
5. 5. A method according to any one of the preceding claims wherein the downlink and uplink transmissions allocated for a given frame are announced respectively in a downlink map and in an uplink map in a broadcast section of each downlink frame.
6. 6. A method according to any one of the preceding claims including allocating for the second terminals to make uplink transmissions selected frames which are interspersed by at least one frame in which uplink transmissions from the second terminals are not allowed.
7. 7. A method according to claim 6 wherein each of the second terminals is allowed to make uplink transmissions only in each alternate frame of the sequence of uplink frames.
8. 8. A method according to claim 7 wherein downlink transmissions to the second terminals are allocated to be made only in alternate downlink frames between the alternate uplink frames in which the uplink transmissions are allocated to be made.
9. 9. A method according to any one of claims 1 to 4 wherein the uplink frames and the downlink frames are divided into mutually exclusive sections or zones, and the uplink transmissions from the second terminals are allocated to be made in a selected section or zone of each uplink frame.
10. 10. A method according to claim 9 wherein the downlink transmissions, other than broadcast transmissions, to the second terminals are allocated to be made only in a selected section or zone of each downlink frame which does not coincide with the selected section or zone of the up link frame.
11. 11. A method according to claim 9 or claim 10 wherein the selected section or zone of each uplink frame follows the selected section or zone of a corresponding downlink frame.
12. 12. A method according to any one of claims 9 to 11 wherein the selected sect ion or zone of each downl ink frame follows a section or zone of the downi ink frame in which data is broadcast.
13. 13. A method according to any one of claims 9 to 12 wherein at least one of the sections or zones has a boundary whose position is dynamically variable from frame-to-frame.
14. 14. A method according to any one of the preceding claims wherein at least one boundary between the sections or zones coincides with a boundary between uplink data symbols and a boundary between downlink data symbols.
15. 15. A method according to claim any one of claims 9 to 14 wherein the second terminals are not allowed to make uplink transmissions during the selected section or zone of each downlink frame.
16. 16. A method according to any one of claims 9 to 14 wherein each of the second terminals is allowed to make an uplink transmission during the selected section or zone of each downlink frame if it is not a terminal targeted by unicast or multicast downlink transmission during that selected section or zone.
17. 17. A method according to any one of claims 9 to 16 wherein uplink and downj ink frames are divided into a first section and a second section which is divided into at least two zones, wherein downlink broadcast Iransmissions are scheduled to be made in the first section, downlink transmissions other than broadcast transmissions are scheduled to be made to the second terminals in the first zone of the second section and uplink transmissions by the second terminals are scheduled to be made in the second zone of the second section.
18. 18. A method according to claim 17 wherein a boundary between the first and second sections coincides with a boundary between downlink resource slots.
19. 19. A method according to claim 17 or claim 18 wherein a boundary between the first and second zones of the second section coincides with a boundary between uplink resource slots.
20. 20. A method according to claim 4 or claim 5 wherein in each consecutive frame downlinlc transmissions which are broadcast transmissions are scheduled to be made in a first downlink frame section, downlink transmissions which are other than broadcast transmissions are scheduled to be made to the second terminals but not the at least one third terminal in a second downljnk frame section, downlink transmissions which are other than broadcast transmissions are scheduled to be made to the at least one third terminal but not the second terminals in a third downlink frame section and uplink transmissions from the second terminals are scheduled to be made in a second uplink frame section coinciding with the third downlink frame section.
21. 21. A method according to claim 4, claim 5 or claim 19 wherein uplink special data transmissions from the second terminals but not from the at least one third terminal are scheduled to be made in a separate section of each up link frame and uplink special data transmissions from the at least one third tenninal but not from the second terminals are scheduled to be made sent in a further separate section of each uplink frame, the further separate section immediately preceding a frame boundary.
22. 22. A method according to any one of the preceding claims wherein resource allocations for at least one of uplink and downlink transmissions for a given frame are made during an earlier frame.
23. 23. A method according to claim 22 wherein resource allocations for at least one of uplink and downlink transmissions for a given frame are made during a frame which is followed by at least one other frame before the given frame.
24. 24. A method according to claim 22 or claim 23 wherein resource allocations for at least one of uplink and downlink transmissions for a given frame are notified to the second terminals during an earlier frame.
25. 25. A method according to any one of the preceding claims wherein an estimate is made for a given frame of the number of slots required for uplink transmissions to or downlink transmissions from the first terminal during the given frame.
26. 26. A method of operation in a wireless communication system in which scheduling of resource allocations is carried out by the method according to any one of the preceding claims and communications between the first terminal and the second terminals are carried out in accordance with the scheduled allocations.
27. 27. A method according to any one of the preceding claims wherein the first terminal communicates with each of the second terminals using a multiple access protocoL
28. 28. A method according to claim 27 wherein the multiple access protocol is an orthogonal frequency division multiple access communication protocol.
29. 29. A method according to claim 28 wherein the protocol is in accordance with the 802.16e standard defmed by the Institute of Electrical and Electronics Engineers.
30. 30. A method according to any one of the preceding claims 26 to 29 wherein the second terminals switch between their receive mode and their transmit mode in a section or zone of a downlink frame corresponding to a symbol immediately preceding a slot of an uplink frame in a section or zone of the uplink frame in which the second terminals are scheduled to send uplink transmissions.
31. 31. A method according to any one of the preceding claims and substantially as herein described with reference to any one or more of the accompanying drawings.
32. 32. A conmiunicat ion system including a first terminal which is a fill duplex terminal and a plurality of second terminals which are half duplex terminals, wherein the first terminal and each of the second terminals are operable to communicate with one another using the method according to any one of the preceding claims.
33. 33. A scheduler for a communication system including a first terminal which is a full duplex terminal and a plurality of second terminals which are half duplex terminals, the scheduler being operable to schedule between the first terminal and each of the plurality of second terminals wireless communications divided into a sequence of frames each providing a two dimensional set of communication resource slots, wherein downlink transmissions from the first terminal are in downlink frames on a first carrier frequency and uplink transmissions from the second terminals are in uplink frames on a second carrier frequency, the downlink and uplink frames being co-incident in time, the scheduler being operable to allocate selected frames or sections of frames for sending only one of: (i) uplink transmissions from the second terminals; and (ii) downlink transmissions, other than broadcast transmissions, targeted to the second terminals.