HK1172187A - Apparatus and method for signalling active assignments to a group of wireless stations - Google Patents

Description

Apparatus and method for signaling active assignments to groups of wireless stations

RELATED APPLICATIONS

This application claims priority to U.S. provisional patent application No. 61/222,947 filed on U.S. patent office at 7/3/2009, the contents of which are incorporated herein by reference.

Technical Field

The present invention relates to wireless communication systems. More particularly, the present invention relates to an apparatus and method for signaling active assignments to a group of wireless stations in a wireless communication system.

Background

Wireless communication systems are widely deployed to provide various types of communication content such as voice, data, and other content. These systems may be multiple-access systems capable of supporting communication for multiple wireless terminals simultaneously by sharing the available transmission resources (e.g., frequency channels and/or time intervals). Since the transmission resources are shared, efficient allocation of the transmission resources is important as it affects the utilization of the transmission resources and the quality of service perceived by the individual end users. One such wireless communication system is an Orthogonal Frequency Division Multiple Access (OFDMA) system in which a plurality of wireless terminals perform multiple access using Orthogonal Frequency Division Multiplexing (OFDM).

OFDM is a multi-carrier modulation technique that partitions the overall system bandwidth into multiple orthogonal frequency channels, each associated with a respective subcarrier that may be modulated with data. In OFDMA, the transmission resources extend over two latitudes: frequency channels and time intervals. The resources of a given frequency channel may relate to contiguous and/or non-contiguous groups of subcarriers.

Examples of OFDM communication systems include, but are not limited to, wireless local area network ("WLAN") protocols such as those defined in accordance with the institute of electrical and electronics engineers ("IEEE") radio standards 802.11a, b, g, and n (hereinafter "Wi-Fi"), wireless MAN/fixed broadband wireless access ("BWA") standards defined in accordance with IEEE 802.16 (hereinafter "WiMAX"), mobile broadband 3GPP long term evolution ("LTE") protocols with air interface high speed OFDMA packet access ("HSOPA") or evolved UMTS terrestrial radio access ("E-UTRA"), 3GPP2 ultra mobile broadband ("UMB") protocol, digital radio system digital audio broadcasting ("DAB") protocol, hybrid digital ("HD") radio, terrestrial digital TV system digital video broadcasting-terrestrial ("DVB-T"), cellular communication system flash-OFDM, and the like. Wired protocols using OFDM technology include asymmetric digital subscriber line ("ADSL") and very high bit rate digital subscriber line ("VDSL") broadband access, power line communications ("PLC") including broadband over power line ("BPL"), and multimedia alliance over coax ("MoCA") home networking.

There are several proposals for 3GPP2 for OFDMA VoIP implementations, one of which defines numerology such that OFDMA resources consisting of a set of 340 subcarriers in frequency over an OFDM symbol duration in time are divided into 20ms VoIP frames each containing 24 slots, each slot containing 10 OFDM symbols. The resources of each slot are further subdivided into Distributed Resource Channels (DRCHs), each DRCH comprising 81 subcarrier locations distributed across the 10 symbols of the slot for a total of 40 DRCHs per slot, allowing for pilot and other overhead that may be present. Transmissions for a given user occur at different rates or frame sizes. For example, an EVRC (enhanced variable rate codec) codec generates speech frames having four different rates or frame sizes: with probabilities 29%, 4%, 7%, and 60% full, 1/2, 1/4, and 1/8, respectively. The particular rate is typically determined based on voice activity factors. For a given user, a single packet is nominally expected to be delivered within one VoIP frame. The current definition allows an initial attempt to deliver a packet and three subsequent attempts. Including any initial or subsequent attempts, are referred to herein as sub-packets.

Generally, there are a large number of terminals that can access a multiple access system at any one time. Each of these terminals needs to be scheduled and transmission resources allocated. Scheduling involves allocating transmission resources to specific terminals and performing any signaling that the terminals need to know when and where to schedule their resources.

The allocation of transmission resources to groups of radio terminals is typically controlled by the base station through conventional bitmap signaling (bitmap signaling). In an exemplary conventional bitmap signaling scheme, terminals are grouped into groups according to predefined metrics — for example, terminals with about the same arrival time and/or similar channel conditions and/or the same or similar MCS (modulation and coding scheme) levels may be grouped and identified by a group ID. Wireless terminals may join and leave groups, typically under the control of a base station. The terminal may leave the group, for example, if the VoIP call to the terminal has ended or if the terminal no longer meets the requirements in the group according to predefined metrics (e.g., it leaves the cell). For example, a terminal may join a group if it has started a VoIP call (or has a call in progress) and it meets a predefined metric.

During a scheduling interval, a respective Ordered Assignment Bitmap (OAB) is transmitted for each group, wherein each wireless terminal in a group is associated with a respective bit position of a corresponding OAB. The OAB is used to indicate which terminal(s) in the group are active. If the terminal's corresponding bit is set to "1", it is active (i.e., assigned a resource). If the terminal's corresponding bit is set to "0," it is inactive (i.e., not assigned resources). Other parameters, such as a Resource Allocation Bitmap (RAB), may also be used to indicate the amount of transmission resources allocated to each active terminal.

The scheduling interval may be any period of time that has been assigned for a particular task (e.g., transmission of control information and/or user data bursts). For example, in a VoIP implementation, the scheduling interval may be used by all users in the VoIP group, and it may contain control information (e.g., OAB, etc.) and associated VoIP packet(s). Alternatively, the scheduling interval for the control information and associated VoIP packet(s) may be separate-e.g., the OAB may be in a different scheduling interval than the interval (patch) scheduled for the user VoIP packet(s). According to OAB, the indicated VoIP users will know that they have packet(s) to decode. Each VoIP user checks the scheduling interval associated with the OAB and if it has a "1" in its assigned position, the terminal decodes the relevant VoIP packet in the data burst associated with the scheduling interval for its group ID.

In many cases, scheduling also involves reserving future capabilities for performing retransmissions that may occur, for example, according to conventional transmission error control schemes, such as hybrid automatic repeat request (HARQ).

There are several variations of the HARQ scheme. One variation is unicast HARQ, where each coded packet includes data from one user. This can be fully asynchronous, in which case the modulation and coding rate (MCS-modulation and coding scheme), transmission time (slots/frames) and resource allocation are independent for each transmission (first and all retransmissions) of the coded packet. Assignment signaling is used to describe the resource allocation, MCS and user ID for each transmission and retransmission. Although this approach allows adaptation to real-time channel conditions, it incurs a large amount of signaling overhead. Unicast HARQ may alternatively be fully synchronous. In this case, the MCS scheme for the transmission (first and all retransmissions) is the same, and the resource allocation (location) remains the same for the first and all retransmissions (the transmission location must be the same as for the first transmission). The transmission interval is fixed and only the first transmission requires assignment signaling. This enables a lower signaling overhead for retransmissions, but may cause significant scheduling complexity and signaling overhead for the first transmission due to irregular resource vacancies (which occur because some resources need to be reserved for retransmissions which may not be necessary).

Another HARQ variant is multicast HARQ, where each coded packet includes data for multiple users. The worst CQI (channel quality indicator) among the plurality of users is considered for selecting the MCS. If one or more users cannot successfully decode the entire packet, the entire packet is retransmitted even though some users may have successfully decoded the packet. Multicast HARQ may be implemented using fully asynchronous and fully synchronous schemes.

In the case of a large number of terminals, especially in allocation schemes where each transmission and/or retransmission of a packet needs to be scheduled, a large amount of transmission resources need to be dedicated to the control signaling related to the scheduling.

There is thus still a need for new signaling schemes for resource allocation in wireless communication systems.

Disclosure of Invention

In general, a method of signaling active assignments to an ordered group of wireless terminals in communication with a base station in a wireless communication system, each wireless terminal of the ordered group having a corresponding position within the ordered group, the method comprising: at a base station: determining an allocation of active assignments for the ordered group, the allocation corresponding to an active assignment number; determining an index value that identifies an allocation in a set of possible allocations for a number of active assignments for an ordered group; and transmitting the index value to at least one wireless terminal of the ordered group of wireless terminals.

In some embodiments, the method further comprises transmitting an indication of the size of the ordered group to at least one wireless terminal.

In some embodiments, the method further comprises transmitting to each of the at least one wireless terminal an indication of its corresponding position within the ordered group.

In some embodiments, the method further comprises: assigning each wireless terminal in the ordered group a position within a bitmap, the position within the bitmap corresponding to a position within the ordered group, wherein a bit set to "1" in the bitmap indicates an active assignment and a bit set to "0" in the bitmap indicates an inactive assignment, such that the bitmap indicates an allocation; creating a table associating the indices with corresponding sets of values for the bitmap, the sets of values corresponding to a set of possible allocations of the number of active assignments for the ordered group; and wherein determining the index value comprises using a table to identify the index value in the index using a bitmap.

In some embodiments, the active assignments indicate which of the wireless terminals have been allocated transmission resources, and wherein the method further comprises allocating a plurality of transmission resource units to each active assignment.

In some embodiments, the active assignments indicate which of the wireless terminals have been allocated resources for retransmitting the packet, and wherein the method further comprises allocating a plurality of transmission resource units to each active assignment. The retransmission may be a HARQ retransmission.

In some embodiments, the method further comprises transmitting an indication of the number of active assignments to at least one wireless terminal.

In some embodiments, the method further comprises transmitting an indication of the number of active resource units (a) and the number of resource units per active assignment (U) to at least one wireless terminal.

In yet another aspect of the present application, a base station forming part of a communication system, the base station in communication with an ordered set of wireless terminals, each wireless terminal of the ordered set having a corresponding location within the ordered set, the base station comprising logic operable to: determining an allocation of active assignments for the ordered group, the allocation corresponding to an active assignment number; determining an index value that identifies an allocation in a set of possible allocations for a number of active assignments for an ordered group; and transmitting the index value to at least one wireless terminal of the ordered group of wireless terminals.

In some embodiments, the logic is further operable to transmit an indication of the size of the ordered group to at least one terminal.

In some embodiments, the logic is further operable to transmit to each of the at least one wireless terminal an indication of its corresponding position within the ordered group.

In some embodiments, the logic is further operable to: assigning each wireless terminal in the ordered group a position within a bitmap, the position within the bitmap corresponding to a position within the ordered group, wherein a bit set to "1" in the bitmap indicates an active assignment and a bit set to "0" in the bitmap indicates an inactive assignment, such that the bitmap indicates an allocation; creating a table associating the indices with corresponding sets of values for the bitmap, the sets of values corresponding to possible sets of allocations for the number of active assignments for the ordered group; and wherein determining the index value comprises using a table to identify the index value in the index using a bitmap.

In some embodiments, the active assignments indicate which of the wireless terminals have been allocated transmission resources, and wherein the logic is further operable to allocate a plurality of transmission resource units to each active assignment.

In some embodiments, the active assignments indicate which of the wireless terminals have been allocated resources for retransmitting the packet, and wherein the logic is further operable to allocate a plurality of transmission resource units to each active assignment. In some embodiments, the retransmission may be a HARQ retransmission.

In some embodiments, the logic is further operable to transmit an indication of the number of active assignments to at least one wireless terminal.

In some embodiments, the logic is further operable to transmit an indication of the number of active resource units and the number of resource units per active assignment to at least one wireless terminal

In yet another aspect of the present application, a wireless terminal comprises logic operable to: receiving, from a base station, an indication that a wireless terminal has been added to an ordered group of wireless terminals; receiving a Terminal Assignment Index (TAI) from a base station; and deriving an Ordered Assignment Bitmap (OAB) using the TAI, wherein each wireless terminal in the ordered group is associated with a position of a respective bit of the OAB.

In some embodiments, the logic is further operable to receive an indication of a size of the ordered group from the base station.

In some embodiments, the logic is further operable to determine a number of active assignments for the ordered group.

In some embodiments, deriving the OAB using the TAI comprises: building a TAI table when the size of the ordered group and the number of active assignments for the ordered group are given; and uses the TAI to look up the OAB in the TAI table.

In some embodiments, determining the number of active assignments comprises receiving an indication of the number of active assignments from a base station.

In some embodiments, determining the number of active assignments comprises: receiving an indication of a number of assigned resource units for the ordered group from a base station; receiving an indication of a number of resource units per active assignment from a base station; and dividing the number of assigned resource units by the number of resource units per active assignment.

In some embodiments, the logic is further operable to receive an indication of a location for the wireless terminal within the ordered group from the base station.

Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.

Drawings

In the drawings which illustrate embodiments of the invention by way of example only,

fig. 1 is a block diagram of a cellular communication system;

FIG. 2 is a block diagram of an example base station that may be used to implement some embodiments of the present application;

FIG. 3 is a block diagram of an example wireless terminal that may be used to implement some embodiments of the present application;

FIG. 4 is a block diagram of an example relay station that may be used to implement some embodiments of the present application;

FIG. 5 is a block diagram of a logical decomposition of an example OFDM transmitter architecture that may be used to implement some embodiments of the present application;

FIG. 6 is a block diagram of a logical decomposition of an example OFDM receiver architecture that may be used to implement some embodiments of the present application; and is

Fig. 7 is a terminal assignment index table for a set of four wireless terminals with two active assignments.

Detailed Description

Referring to the drawings, FIG. 1 shows a Base Station Controller (BSC) 10 that controls wireless communications within a plurality of cells 12, which are served by corresponding Base Stations (BS) 14. In some configurations, each cell is further divided into a plurality of sectors 13 or areas (not shown). In general, each base station 14 facilitates communication using OFDM with wireless terminals 16, which wireless terminals 16 are within the cell 12 associated with the corresponding base station 14. Movement of the wireless terminal 16 relative to the base station 14 causes significant fluctuations in channel conditions. As shown, the base station 14 and wireless terminals 16 may include multiple antennas to provide spatial diversity for communications. In some configurations, the relay station 15 may assist in communications between the base station 14 and the wireless terminals 16. A wireless terminal 16 may be handed off from any cell 12, sector 13, region (not shown), base station 14, or relay 15 to other cells 12, sectors 13, regions (not shown), base stations 14, or relays 15. In some configurations, the base stations 14 communicate with each other and with another network, such as a core network or the internet (neither shown), through the backhaul network 11. In some configurations, the base station controller 10 is not required.

Referring to fig. 2, an example of a base station 14 is illustrated. The base station 14 generally includes a control system 20, a baseband processor 22, transmit circuitry 24, receive circuitry 26, an antenna 28, and a network interface 30. Receive circuitry 26 receives radio frequency signals carrying information from one or more remote transmitters provided by wireless terminals 16 (shown in fig. 3) and relay stations 15 (shown in fig. 4). A low noise amplifier and filter (not shown) may cooperate to amplify the signal and remove broadband interference from the signal for processing. Downconversion and digitization circuitry (not shown) will then downconvert the filtered, received signal to an intermediate or baseband frequency signal, which is then digitized into one or more digital streams.

The baseband processor 22 processes the digitized received signal to extract the information or data bits conveyed in the received signal. This processing typically includes demodulation, decoding, and error correction operations. As such, the baseband processor 22 is typically implemented in one or more Digital Signal Processors (DSPs) or Application Specific Integrated Circuits (ASICs). The received information is then sent across the wireless network via the network interface 30 or sent to another wireless terminal 16 served by the base station 14, either directly or via a relay 15.

On the transmit side, the baseband processor 22 receives digitized data, which may represent voice, data, or control information, from the network interface 30 under the control of the control system 20 and encodes the data for transmission. The encoded data is output to the transmission circuit 24 where it is modulated by one or more carrier signals having one or more desired transmission frequencies. A power amplifier (not shown) will amplify the modulated carrier signal to a level suitable for transmission and deliver the modulated carrier signal to the antenna 28 through a matching network (not shown). Modulation and processing details are described in more detail below.

Referring to fig. 3, an example of a wireless terminal 16 is illustrated. Similar to the base station 14, the wireless terminal 16 will include a control system 32, a baseband processor 34, transmit circuitry 36, receive circuitry 38, an antenna 40, and user interface circuitry 42. The receive circuitry 38 receives radio frequency signals carrying information from one or more base stations 14 and relays 15. A low noise amplifier and filter (not shown) may cooperate to amplify the signal and remove broadband interference from the signal for processing. Downconversion and digitization circuitry (not shown) would then downconvert the filtered, received signal to an intermediate or baseband frequency signal, which would then be digitized into one or more data streams.

The baseband processor 34 processes the digitized received signal to extract the information or data bits conveyed in the received signal. This processing typically includes demodulation, decoding, and error correction operations. The baseband processor 34 is typically implemented in one or more Digital Signal Processors (DSPs) and Application Specific Integrated Circuits (ASICs).

For transmission, the baseband processor 34 receives digitized data from the control system 32 that it encodes for transmission, which may represent voice, video, data, or control information. The encoded data is output to the transmission circuitry 36 where it is used by the modulator to modulate one or more carrier signals at one or more desired transmission frequencies. A power amplifier (not shown) will amplify the modulated carrier signal to a level suitable for transmission and deliver the modulated carrier signal to the antenna 40 through a matching network (not shown). Various modulation and processing techniques are available to those skilled in the art for signal transmission between wireless terminals and base stations, either directly or via relay stations.

In OFDM modulation, the transmission band is divided into a plurality of orthogonal carriers. Each carrier is modulated according to the digital data to be transmitted. Since OFDM divides a transmission band into a plurality of carriers, the bandwidth of each carrier decreases and the modulation time of each carrier increases. Since multiple carriers are transmitted in parallel, the transmission rate for digital data or symbols on any given carrier is lower than when a single carrier is used.

OFDM modulation utilizes an Inverse Fast Fourier Transform (IFFT) performed on the information to be transmitted. For demodulation, a Fast Fourier Transform (FFT) is performed on the received signal to recover the transmitted information. In practice, the IFFT and FFT are provided by digital signal processing that performs an Inverse Discrete Fourier Transform (IDFT) and a Discrete Fourier Transform (DFT), respectively. OFDM modulation is thus characterized by the generation of orthogonal carriers for multiple frequency bands within the transmission channel. Modulated signals are digital signals that have a relatively low transmission rate and can remain within their respective frequency bands. The individual carriers are not directly modulated by the digital signal. Instead, all carriers are modulated at once by the IFFT process.

In one embodiment, OFDM is preferably used for at least downlink transmissions from the base stations 14 to the wireless terminals 16. Each base station 14 is equipped with "n" transmission antennas 28 (n > = 1), and each wireless terminal 16 is equipped with "m" reception antennas 40 (m > = 1). Note that the respective antennas may be used for reception and transmission using appropriate duplexers or switches and are so labeled only for clarity.

When using a relay station 15, OFDM is preferably used for downlink transmissions from the base station 14 to the relay 15 and from the relay station 15 to the wireless terminals 16.

Referring to fig. 4, an example of the relay station 15 is illustrated. Similar to the base station 14 and the wireless terminal 16, the relay station 15 includes a control system 132, a baseband processor 134, transmission circuitry 136, reception circuitry 138, an antenna 130, and a relay circuit 142. The relay circuitry 142 enables the relay 14 to assist in communications between the base station 16 and the wireless terminals 16. The receive circuitry 138 receives radio frequency signals carrying information from one or more base stations 14 and wireless terminals 16. A low noise amplifier and filter (not shown) may cooperate to amplify the signal and remove broadband interference from the signal for processing. Downconversion and digitization circuitry (not shown) will then downconvert the filtered, received signal to an intermediate or baseband frequency signal, which is then digitized into one or more digital streams.

The baseband processor 134 processes the digitized received signal to extract the information or data bits conveyed in the received signal. This processing typically includes demodulation, decoding, and error correction operations. The baseband processor 134 is typically implemented in one or more Digital Signal Processors (DSPs) and Application Specific Integrated Circuits (ASICs).

For transmission, the baseband processor 134 receives digitized data from the control system 132 that it encodes for transmission, which may represent voice, video, data, or control information. The encoded data is output to the transmit circuitry 136 where it is used by a modulator to modulate one or more carrier signals at one or more desired transmit frequencies. A power amplifier (not shown) will amplify the modulated carrier signal to a level suitable for transmission and deliver the modulated carrier signal to the antenna 130 through a matching network (not shown). As described above, the various modulation and processing techniques available to those skilled in the art are used for signal transmission between a wireless terminal and a base station, either directly or indirectly via a relay station.

Referring to fig. 5, a logical OEDM transmission architecture will be described. Initially, the base station controller 10 will send data to the base station 14 to be transmitted to the various wireless terminals 16, either directly or via the relay station 15. The base station 14 may use Channel Quality Indicators (CQIs) associated with the wireless terminals to schedule data for transmission and to select appropriate coding and modulation for transmitting the scheduled data. The CQI may be directly from the wireless terminal 16 or determined at the base station 14 based on information provided by the wireless terminal 16. In either case, the CQI for each wireless terminal 16 is a function of the degree to which the channel amplitude (or response) varies across the OFDM frequency band.

Data scrambling logic 46 is used to scramble the data in a manner that reduces the peak-to-average power ratio associated with the scheduled data 44 as a bit stream. A Cyclic Redundancy Check (CRC) for the scrambled data is determined and the CRC is appended to the scrambled data using CRC addition logic 48. Channel coding is then performed using channel encoder logic 50 to effectively add redundancy to the data to facilitate recovery and error correction at the wireless terminal 16. The channel coding that is also used for a particular wireless channel 16 is based on CQI. In some implementations, the channel encoder logic 50 uses known Turbo encoding techniques. The encoded data is then processed by rate matching logic 52 to compensate for the data spreading associated with the encoding.

The bit interleaver logic 54 systematically records the bits in the encoded data to minimize the loss of consecutive data bits. Mapping logic 56 systematically maps the resulting data bits to corresponding symbols according to the selected baseband. Preferably using Quadrature Amplitude Modulation (QAM) or Quadrature Phase Shift Keying (QPSK) modulation. The degree of modulation is preferably selected based on the CQI for a particular wireless terminal. The symbols may be systematically recorded using symbol interleaver logic 58 to further enhance the immunity of the transmitted signal to periodic data loss caused by frequency selective fading.

At this point, groups of bits have been mapped into symbols representing positions in the amplitude and phase constellation. When spatial diversity is required, the block of symbols is then processed by space-time block code (STC) encoder logic 60, which STC encoder logic 60 modifies the symbols in a manner that makes the transmitted signal more resistant to interference and easier to decode at the wireless terminal 16. The STC encoder logic 60 will process the incoming symbols and provide "n" outputs corresponding to the number of transmit antennas 28 for the base station 14. The control system 20 and/or baseband processor 22 as described above with respect to fig. 5 will provide a mapping control signal for controlling STC encoding. At this point, it is assumed that the symbols for the "n" outputs represent data to be transmitted and can be recovered by the wireless terminal 16.

For the present example, assume that the base station 14 has two antennas 28 (n = 2) and that the STC encoder logic 60 provides two symbol output streams. Each symbol stream output by SIC encoder logic 60 is thus sent to a corresponding IFFT processor 62 (illustrated separately for ease of understanding). Those skilled in the art will recognize that one or more processors may be used to provide such digital signal processing, either alone or in combination with other processing described herein. The IFFT processors 62 will preferably operate on the respective symbols to provide an inverse fourier transform. The output of the TUFT processor 62 provides symbols in the time domain. The time domain symbols are grouped into frames that prefix insertion logic 64 associates with the prefixes. Each resulting signal is up-converted to an intermediate frequency in the digital domain and converted to an analog signal via corresponding digital up-conversion (DUG) and digital-to-analog (DIA) conversion circuitry 66. The resulting (analog) signal is then simultaneously modulated, amplified, and transmitted at the desired RF frequency via RF circuitry 68 and antenna 28. Note that the pilot signal known to a given wireless terminal 16 is scattered among the subcarriers. The wireless terminal 16, discussed in detail below, will use the pilot signal for channel estimation.

Reference is now made to fig. 6 to illustrate that the wireless terminal 16 receives the transmitted signal from the base station 14, either directly or via the relay station 15. As the transmitted signals reach each antenna 40 of the wireless terminal 16, the respective signals are demodulated and amplified by the corresponding RF circuitry 70. For brevity and clarity, only one of the two receive paths is described and illustrated in detail. Analog-to-digital (AID) converter and down-conversion circuitry 72 digitizes and down-converts the analog signal for digital processing. The resulting digitized signal may be used by an automatic gain control circuit (AGC) 74 to control the gain of the amplifiers in the RF circuitry 70 based on the received signal level.

The digitized signal is initially provided to synchronization logic 76, which includes coarse synchronization logic 78 that buffers a number of OFDM symbols and calculates an autocorrelation between two successive OFDM symbols. The resulting time index corresponding to the maximum value of the correlation result determines the fine synchronization search window that is used by the fine synchronization logic 80 to determine the fine framing starting position based on the header. The output of the fine synchronization logic 80 facilitates frame acquisition by the frame alignment logic 84. Proper framing alignment is important so that subsequent PET processing provides an accurate conversion from the time domain to the frequency domain. The fine synchronization algorithm is based on a correlation between the received pilot signal carried by the preamble and a local copy of the known pilot data. Once frame alignment acquisition occurs, the OFDM symbol is prefixed with prefix removal logic 86 and the resulting samples are sent to frequency offset correction logic 88, which frequency offset correction logic 88 compensates for the system frequency offset caused by the unmatched logical oscillators in the transmitter and receiver. Preferably, the synchronization logic 76 includes frequency offset and clock estimation logic 82, the logic 82 helping to estimate such effects on the transmitted signal based on the preamble and providing those estimates to the correction logic 88 to properly process the OFDM symbols.

At this point, the OFDM symbols in the time domain are ready to be converted to the frequency domain using the EFT processing logic 90. The result is a frequency domain symbol that is sent to processing logic 92. The processing logic 92 extracts scattered pilot signals using scattered pilot extraction logic 94, determines channel estimates based on the extracted pilot signals using channel estimation logic 96, and provides channel responses for all subcarriers using channel reconstruction logic 98. To determine the channel response for each subcarrier, the pilot signal is essentially a plurality of pilot symbols scattered in a known pattern in both time and frequency in data symbols throughout the OFDM subcarrier. Continuing with fig. 6, processing logic compares the received pilot symbols with pilot symbols expected in certain subcarriers at certain times to determine the channel response for the subcarrier in which the pilot symbol was transmitted. The results are interpolated to estimate the channel response for most, if not all, of the remaining subcarriers for which pilot symbols are not provided. The actual and interpolated channel responses are used to estimate the total channel response, which includes the channel responses for most, if not all, of the subcarriers in the OFDM channel.

The frequency domain symbols derived from the channel response for each receive path and the channel reconstruction information are provided to an STC decoder 100. the STC decoder 100 provides STC decoding of the two receive paths to recover the transmitted signal. The channel reconstruction information provides equalization information to the STC decoder 100 sufficient to remove the effects of the transmission channel when processing the corresponding frequency domain symbols.

The recovered symbols are put back in turn using symbol deinterleaver logic 102 corresponding to the symbol interleaver logic 58 of the transmitter. The de-interleaved symbols are then demodulated or de-mapped into a corresponding bit stream using de-mapping logic 104. The bits are then deinterleaved using bit deinterleaver logic 106 corresponding to the bit deinterleaver logic 54 of the transmitter architecture. The deinterleaved bits are then processed by rate dematching logic 108 and presented to channel decoder logic 110 to recover the original scrambled data and CRC checksum. The CRC logic 112 thus removes the CRC checksum, checks the scrambled data in a conventional manner and provides it to the de-scrambling logic 114 for de-scrambling using the known base station de-scrambling code to recover the originally transmitted data 116.

In parallel with recovering the data 116, a CQI, or at least information sufficient to create a CQI at the base station 14, is determined and transmitted to the base station 114. As noted above, the CQI may be a function of the carrier-to-interference ratio (CR) and the degree to which the channel response varies across the various subcarriers in the OFDM band. For this embodiment, the channel gains for each subcarrier in the OFDM band used to transmit information are compared with respect to each other to determine the degree to which the channel gains vary across the OFDM band. While a number of techniques may be used to measure the degree of variation, one technique is to calculate the standard deviation of the channel gain for each subcarrier used to transmit data throughout the OFDM band.

In some embodiments, the relay station may operate in a time division manner using only one radio or instead include multiple radios.

Fig. 1-6 provide one specific example of a communication system that may be used to implement embodiments of the present application. It will be appreciated that embodiments may be implemented with a communication system having an architecture that differs from the specific examples but operates in a manner consistent with the implementation of the embodiments as described herein.

Referring to fig. 2, the control system 20 of the base station 14 may contain logic for performing the exemplary methods of the present application. Similarly, referring to FIG. 3, the control system 32 of the wireless terminal 16 may contain logic for performing the exemplary methods of aspects of the present application.

As described in more detail below, the base station 14 is configured to signal an active assignment to the wireless terminal 16 by transmitting a Terminal Assignment Index (TAI) to the wireless station 16. More specifically, the base station 14 classifies the wireless terminals 16 into groups according to predefined metrics. For example, wireless terminals 16 having approximately the same arrival time and/or similar channel conditions and/or the same or similar MCS levels may be grouped and identified by a group ID. A particular wireless terminal 16 may belong to more than one group. Wireless terminals 16 may be added to or removed from the group. Wireless terminals 16 within a group are ordered such that the assignment of a particular wireless terminal may be designated by a "1" for an active assignment at the appropriate position of a given ordered assignment bitmap for the group. An active assignment may be associated with one or more transmission resource units (e.g., frequency channels and/or time intervals).

As previously noted, the base station 14 signals the ordered assignments to the terminals within the group by transmitting TAIs to the group. The TAI is an index with a one-to-one correspondence to a set of possible ordered terminal assignments (active and inactive) for a given group size (i.e. the total number of terminals in the group) and a given number of active assignments in the group.

The ordered assignment indicates which terminals 16 are active ("1") and which terminals 16 are inactive ("0"). As noted above, the terminal 16 may be assigned a predetermined position in the ordered set. This assignment may be indicated when the terminal 16 joins the group. For example, for a group of four terminals 16, the ordered assignment of "1010" means that the second and fourth terminals of the group are inactive and the first and third terminals of the group are active.

The TAI signal may be used in allocating uplink resources for transmission by the wireless terminal 16 to the base station 14 or in allocating downlink resources for transmission by the base station 14 to the wireless terminal 16. The TAI may also be used for one or more (possibly all) transmissions/retransmissions of a packet.

In operation, the control system 20 of the base station 14 may use the TAI table for different possible combinations of: (1) group size (i.e., the total number of terminals in the group) and (2) the number of active assignments in the group. Each entry in a given TAI table contains a TAI number, a TAI field, and a corresponding ordered assignment. In some embodiments, the TAI table may be replaced with a process or function for deriving the TAI from an ordered assignment given the appropriate parameters.

An example TAI table is provided below for the following four combinations: (1) a group size of two terminals with two active assignments, (2) a group size of three terminals with two active assignments, (3) a group size of four terminals with two active assignments, and (4) a group size of four terminals with one active assignment. In these examples, the number of resource units assigned per user is one.

It will be appreciated that other tables, formulas, and/or relationships are possible, as long as given a TAI, it is possible to derive a set of assignments for a group of terminals, and vice versa.

Note that in the following example the "ordered assignment" column is equal to the Ordered Assignment Bitmap (OAB) for the group in conventional systems.

For the case of a group of two terminals with two active assignments, there is only one case, such that a single bit is required for TAI indication. Since only a single case exists, other values of the bits may be used to indicate another characteristic or condition (reserved).

Table 1: a group of two terminals with two active assignments.

For the case of three terminals with two active assignments, there are three cases, such that two bits are required for TAI indication for all possible cases. The fourth value of the field may be used for an indication of another feature or condition (reserved).

Table 2: a group of three terminals with two active assignments.

For the case of a group of four terminals with two active assignments, there are six cases, so that three bits are needed for TAI indication for all possible cases. The seventh and eighth values of the field may be used for indication of other features or conditions (reserved 1 and 2).

Table 3: a group of four terminals with two active assignments (reproduction of its copy is fig. 7).

For the case of a group of four terminals with one active assignment, there are four cases, so that two bits are needed for TAI indication for all possible cases.

Table 4: group of four terminals with one active assignment.

During a given terminal assignment (active and inactive) set for a group, the base station 14 transmits to the terminals 16 within the group TAI entries corresponding to ordered assignments from the appropriate TAI table. As described in more detail below, the terminals 16 know or are able to determine the number of terminals in a group and the number of active assignments for the group. Knowing these two parameters, the terminal 16 can determine the correct bit length of the TAI field in order to detect and decode the TAI received from the base station 14 and determine the appropriate TAI table to use to look up the ordered assignment indicated by the received TAI. In some embodiments, the TAI table may be replaced with a procedure or function for deriving ordered assignments from the TAI and two known parameters (i.e., the number of terminals in the group and the number of active assignments for the group). If a terminal 16 is assigned a position in the group (ordered position), it can observe whether it has been given an active assignment (assigned resources) or set to inactive (unassigned resources) by checking its position in the ordered assignment.

In some embodiments, the terminals 16 assigned to a group will know the number of terminals in the group. For example, the base station 14 may indicate the number of terminals in a group by sending a control message (e.g., DL _ MAP in WiMAX) to the terminals 16. The message may contain an indication that the terminal 16 is a member of the group identified by the group ID, and it may contain an indication of the group size, the location of the terminal in the group, and the number of active assignments allowed for the group. With the group size and number of active assignments, the terminal 16 can build an appropriate TAI table so that when it receives the TAI from the base station 14 it can derive the OAB and determine from the OAB which terminals in the group are active, and since it knows its location, it will know whether it is one of the active terminals.

In some embodiments, the base station 14 may instead indicate the number of resource units assigned to the group (R) instead of indicating the number of active assignments to the terminal 16 (a), and the terminal 16 may derive the number of active assignments (a) from the value R. That is, if the number of active resource units (R) and the number of resource units per active assignment (U) are known, R divided by U can derive the number of active assignments (a) (i.e., a = R/U). It is assumed that the terminal 16 knows U (e.g. that it is indicated by the base station 14 or that it is a standard value).

Advantageously, by transmitting the TAI instead of the OAB, the number of bits required to signal active and inactive assignments to the terminal 16 may be reduced. TAI uses fewer bits than the conventional approach (i.e., OAB) because it assumes that the number of active assignments for a group is known. Note that in the conventional manner it has been assumed that the group size is known, since the terminal 16 needs to know the correct bit length of the OAB in order to detect and decode the OAB. As noted above, the group size may be indicated by the base station 14, for example, in a control region (e.g., DL _ MAP in WiMAX) or it may be a standard value.

A scenario will now be described in which the terminal 16 uses knowledge of the group size, the number of assigned resource units (R) and the number of resource units per active assignment (U) to derive the number of active assignments (a), and thereby determine the appropriate TAI table to use. Although this scenario describes the use of a TAI table, it will be understood that appropriate procedures or functions may instead be used to derive TAIs from ordered assignments at the base station 14, and that appropriate procedures or functions may similarly be used to derive ordered assignments from TAIs at the terminal 16. In this scenario, two transmission resource units (R) are assigned to a group having the size of four terminals 16. The number of resource units (U) per active assignment is one. The first and fourth terminals 16 of the group are active (i.e. assigned resources). The conventional OAB for this scenario is "1001". At the base station 14, the ordered assignment "1001" matches in the appropriate TAI table (table 3 above) with the corresponding TAI number "3" and TAI field "011". The TAI of "011" (3 bits) is then transmitted to the terminals 16 in the group.

At terminal 16, the terminal knows that a group is assigned two transmission resource units (R = 2) and that the number of resource units per active assignment is one (U = 1). Thus, the terminal 16 is able to determine that there are two active assignments (a) in the group (a = R/U). The size of the group is also already known to the terminal 16 and in this case it is four. The terminal 16 is thus able to determine the correct length (3 bits) of the TAI field in order to detect and decode the TAI field received from the base station 14, and to determine the appropriate TAI table (table 3 above) to use to look up the ordered assignment indicated by the received TAI. Thus, upon decoding the TAI field "011", the terminal 16 derives the ordered assignment bitmap "1001" by performing a lookup in the appropriate TAI table. The terminal 16 can then determine its resource assignment based on its assigned position in the group.

Although embodiments have been described in which the number of resource units per active assignment is a predefined number (U), it will be appreciated that embodiments may be implemented in which the number of resource units per active assignment may be dynamically assigned in a manner known in the art. For example, in addition to transmitting the TAI to the terminal 16, the base station 14 may also transmit a Resource Allocation Bitmap (RAB) to indicate the amount of transmission resources allocated to each active terminal in the set. For example, the first bit of the RAB may correspond to a first active terminal, the second bit of the RAB may correspond to a second active terminal, the third bit of the RAB may correspond to a third active terminal, and so on. A "1" in the RAB may indicate X units of transmission resources to be assigned, while a "0" may indicate Y units of transmission resources to be assigned, where X is greater than Y, for example. It will be appreciated that other conventional methods of dynamically assigning variable amounts of transmission resources for each active assignment in the group of terminals 16 may be used.

As previously noted, the TAI field may be used to efficiently signal some or all of the packet transmissions. In some embodiments, the TAI field may signal HARQ retransmissions for a group of terminals 16, where the group of terminals 16 has a first HARQ transmission opportunity assigned persistently. In particular, when the first HARQ transmission is assigned continuously, no signaling is required for this transmission. The resource availability bitmap may be used to indicate to other terminals/groups which resources are "in use". For retransmissions, terminals that have been allocated resources for HARQ packet retransmission are indicated by the TAI. Since the number of terminals in a group that need retransmission may be small in some cases, there is a potential overhead savings over explicitly signaling an ordered assignment bitmap. It may also be advantageous to configure the group of terminals such that each terminal in the group has its first transmission opportunity in the same subframe (or frame or scheduling event).

For example, consider a group having a size of four terminals. All four terminals are allocated predefined or persistent resources for their first HARQ transmission. All four terminals have the first HARQ packet transmission sent on persistent resources at a specific scheduling interval. The group is not signaled in this scheduling interval. At a later time, the group is scheduled for the first retransmission opportunity. The packet for terminal 2 requires a second transmission, while the packets for terminals 1, 3 and 4 have been successfully received and do not require retransmission. The ordered assignment may be expressed as "0100" and an appropriate TAI may be sent to indicate the assignment. Using the example table 4 described above, a TAI of "10" may be sent to represent an active/inactive assignment for a terminal of a group. This process may be repeated for more retransmissions.

Other modifications will be apparent to those skilled in the art and the invention is therefore defined in the claims.

Claims (25)

1. A method of signaling an active assignment to an ordered group of wireless terminals communicating with a base station in a wireless communication system, each wireless terminal of the ordered group having a corresponding position within the ordered group, the method comprising:

at the base station:

determining an allocation of active assignments for the ordered group, the allocation corresponding to an active assignment number;

determining an index value that identifies the allocation in a set of possible allocations for the number of active assignments for the ordered group; and is

Transmitting the index value to at least one wireless terminal of the ordered group of wireless terminals.

2. The method of claim 1, further comprising transmitting an indication of the size of the ordered group to the at least one wireless terminal.

3. The method of claim 2, further comprising transmitting to each of the at least one wireless terminal an indication of its corresponding position within the ordered group.

4. The method of claim 1 or 2, further comprising:

assigning each wireless terminal in the ordered group a position within a bitmap, the position within the bitmap corresponding to the position within the ordered group, wherein a bit set to "1" in the bitmap indicates an active assignment and a bit set to "0" in the bitmap indicates an inactive assignment, such that the bitmap indicates the allocation;

creating a table associating indices with corresponding sets of values for the bitmap, the sets of values corresponding to the set of possible allocations of the number of active assignments for the ordered group; and is

Wherein the determining the index value comprises using the table to identify the index value in the index using the bitmap.

5. The method according to any of claims 1 to 4, wherein the active assignments indicate which of the wireless terminals have been allocated transmission resources, and wherein the method further comprises allocating a plurality of transmission resource units to each of the active assignments.

6. The method according to any of claims 1 to 4, wherein the active assignments indicate which of the wireless terminals have been allocated resources for packet retransmission, and wherein the method further comprises allocating a plurality of transmission resource units to each of the active assignments.

7. The method of claim 6, wherein the retransmission is a HARQ retransmission.

8. The method according to any of claims 1 to 7, further comprising transmitting an indication of the number of active assignments to the at least one wireless terminal.

9. The method of any of claims 5 to 7, further comprising transmitting an indication of the number of active resource units and the number of resource units per active assignment to the at least one wireless terminal.

10. A base station forming part of a communication system, the base station in communication with an ordered set of wireless terminals, each wireless terminal of the ordered set having a corresponding position within the ordered set, the base station comprising logic operable to:

determining an allocation of active assignments for the ordered group, the allocation corresponding to an active assignment number;

determining an index value that identifies the allocation in a set of possible allocations for the number of active assignments for the ordered group; and is

Transmitting the index value to at least one wireless terminal of the ordered group of wireless terminals.

11. The base station of claim 10, wherein the logic is further operable to transmit an indication of the size of the ordered group to the at least one terminal.

12. The base station of claim 10 or 11, wherein the logic is further operable to transmit to each of the at least one wireless terminal an indication of its corresponding position within the ordered group.

13. The base station of any of claims 10 to 12, wherein the logic is further operable to:

assigning each wireless terminal in the ordered group a position within a bitmap, the position within the bitmap corresponding to the position within the ordered group, wherein a bit set to "1" in the bitmap indicates an active assignment and a bit set to "0" in the bitmap indicates an inactive assignment, such that the bitmap indicates the allocation;

creating a table associating indices with corresponding sets of values for the bitmap, the sets of values corresponding to the set of possible allocations of the number of active assignments for the ordered group; and is

Wherein the determining the index value comprises using the table to identify the index value in the index using the bitmap.

14. The base station of any of claims 10 to 13, wherein the active assignments indicate which of the wireless terminals have been allocated transmission resources, and wherein the logic is further operable to allocate a plurality of transmission resource units to each of the active assignments.

15. The base station of any of claims 10 to 13, wherein the active assignments indicate which of the wireless terminals have been allocated resources for packet retransmission, and wherein the logic is further operable to allocate a plurality of transmission resource units to each of the active assignments.

16. The base station of claim 15, wherein the retransmission is a HARQ retransmission.

17. The base station of any of claims 10 to 16, wherein the logic is further operable to transmit an indication of the number of active assignments to the at least one wireless terminal.

18. The base station of any of claims 14 to 16, wherein the logic is further operable to transmit an indication of the number of active resource units and the number of resource units per active assignment to the at least one wireless terminal.

19. A wireless terminal comprising logic operable to:

receiving an indication from a base station that the wireless terminal has been added to an ordered group of wireless terminals;

receiving a Terminal Assignment Index (TAI) from the base station; and is

Deriving an Ordered Assignment Bitmap (OAB) using the TAI, wherein each wireless terminal in the ordered set is associated with a position of a respective bit of the OAB.

20. The wireless terminal of claim 19, wherein the logic is further operable to receive an indication of a size of the ordered group from the base station.

21. The wireless terminal of claim 19 or 20, wherein the logic is further operable to determine a number of active assignments for the ordered group.

22. The wireless terminal of claim 21, wherein said deriving the OAB using the TAI comprises:

building a TAI table when the size of the ordered group and the number of active assignments for the ordered group are given; and is

Using the TAI to look up the OAB in the TAI table.

23. The wireless terminal of claim 21 or 22, wherein said determining said number of active assignments comprises receiving an indication of said number of active assignments from said base station.

24. The wireless terminal of claim 21 or 22, wherein said determining said number of active assignments comprises:

receiving, from the base station, an indication of a number of assigned resource units for the ordered group;

receiving, from the base station, an indication of a number of resource units for each active assignment; and is

Dividing the number of assigned resource units by the number of resource units per active assignment.

25. The wireless terminal of claim 19 or 24, wherein the logic is further operable to receive an indication of a location for the wireless terminal within the ordered group from the base station.