HK1135258A - Diversity transmission modes for mimo ofdm communication systems - Google Patents

Description

Diversity transmission mode for MIMO OFDM communication systems

The present application is a divisional application of a patent application having an application date of 2003, month 6 and 20, and an application number of 038197189, entitled "diversity transmission mode for MIMO OFDM communication system".

The present invention relates generally to communication communications, and more specifically to techniques for transmitting data using multiple diversity transmission modes in a MIMO OFDM system.

Background

Wireless communication systems are widely deployed to provide various types of communication such as voice, packet, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users in sequence or simultaneously. This may be achieved by sharing the available system resources, which may be quantified by the total available operating bandwidth and transmit power.

A multiple access system may include multiple access points (i.e., base stations) that communicate with multiple user terminals. Each access point may be equipped with one or more antennas for transmitting and receiving data. Similarly, each terminal may be equipped with one or more antennas.

The transmission characteristics between a given access point and a given terminal may be described by multiple antennas for data transmission and reception. In particular, an access point and a terminal pair may be viewed as (1) if multiple (N) are used for data transmission_T) Transmitting antenna and a plurality of (N)_R) Receive antennas, a multiple-input (MIMO) system, (2) if so, a multiple-input multiple-output (MIMO) systemA multiple-input single-output (MISO) system using multiple transmit antennas and a single receive antenna, (3) a single-input multiple-output (SIMO) system if a single transmit antenna and multiple receive antennas are used, or (4) a single-input single-output (SISO) system if a single transmit antenna and a single receive antenna are used.

For MIMO systems, N_TA transmission sum N_RThe MIMO channel formed by the receiving antennas can be decomposed into N_SA separate channel of which N_S≤min{N_T，N_R}。N_SEach of the individual channels is referred to as a spatial subchannel of the MIMO channel and corresponds to a dimension. MIMO systems may provide improved performance (e.g., increased transmission capacity and/or greater reliability) if the additional dimensionalities created by the multiple transmit and receive antennas are utilized. For a MISO system, only one spatial subchannel is available for data transmission. However, multiple transmit antennas may be used to transmit data in a manner that improves the likelihood of correct reception by the receiver.

The wideband system spatial subchannels may encounter different channel conditions due to various factors such as fading and multipath. Each spatial subchannel may thus experience frequency selective fading, which is characterized by different channel gains at different frequencies of the overall system bandwidth. Frequency selective fading is known to cause inter-symbol interference (ISI), a phenomenon in which symbols in a received signal are distorted as successive symbols in the received signal. ISI distortion degrades performance by affecting the ability to correctly detect the received symbol.

To combat frequency selective fading, Orthogonal Frequency Division Multiplexing (OFDM) can be used to effectively divide the overall system bandwidth into multiple (N)_F) A subband, also referred to as an OFDM subband, frequency bin, or frequency subchannel. Each subband is associated with a respective subcarrier on which data may be modulated. The symbols may be at N for each time slot that may depend on one subband bandwidth_FIs transmitted on each of the sub-bands.

For a multiple-access system, a given access point may communicate with terminals having different numbers of antennas at different times. Moreover, the characteristics of the communication channel between the access point and the terminals typically vary from terminal to terminal, and may further vary over time, particularly for mobile terminals. Different transmission schemes may be required for different terminals depending on their capacity and requirements.

There is therefore a need in the art for techniques for transmitting data using multiple diversity transmission modes depending on receiver device capacity and channel conditions.

SUMMARY

Techniques are provided herein for transmitting data in a manner that improves the reliability of data transmission. MIMO OFDM systems may be designed to support multiple modes for data transmission. These transmission modes may include diversity transmission modes, which may be used to obtain higher reliability for some data transmissions (e.g., for overhead channels, poor channel conditions, etc.). The diversity transmission mode attempts to achieve transmit diversity by establishing orthogonality between multiple signals transmitted from multiple transmit antennas. Orthogonality between the transmitted signals may be achieved by frequency, time, space, or any combination thereof. The transmission modes may also include spatial multiplexing modes and beam steering transmission modes, which may be used to achieve higher bit rates under some more favorable channel conditions.

In one embodiment, a method of processing data for transmission in a wireless (e.g., MIMO OFDM) communication system is provided. According to the method, a particular diversity transmission mode is selected for each of one or more data streams from a plurality of possible transmission modes. Each diversity transmission mode redundantly transmits data in time, frequency, space, or a combination thereof. Each data stream is coded and modulated based on a coding and modulation scheme selected for that data stream to provide modulation symbols. The modulation symbols for each data stream are then further processed based on the selected diversity transmission mode to provide transmit symbols. For OFDM, the transmit symbols for all data streams are further OFDM modulated to provide a stream of transmit symbols for each of one or more transmit antennas used for data transmission. The pilot symbols may also be multiplexed with the modulation symbols using Frequency Division Multiplexing (FDM), Time Division Multiplexing (TDM), Code Division Multiplexing (CDM), or any combination thereof.

The transmission modes may include, for example, (1) transmitting modulation symbols redundantly on multiple OFDM subbands, (2) on N_TWalsh diversity transmission mode with each modulation symbol transmitted over one OFDM symbol period, where N_TIs the number of transmit antennas used for data transmission, (3) a space-time transmit diversity (STTD) transmission mode in which modulation symbols are transmitted over multiple OFDM symbol periods and multiple transmit antennas, and (4) a Walsh-STTD transmission mode in which modulation symbols are transmitted using a combination of Walsh diversity and STTD. For Walsh diversity and Walsh-STTD transmission modes, the same modulation symbols may be sent redundantly on all transmit antennas, or different modulation symbols may be sent on different transmit antennas.

Each data stream may be for an overhead channel or destined for a particular receiver device. The data rate of each user-specific data stream may be adjusted based on the transmission capacity of the receiver device. The transmit symbols for each data stream are transmitted on a respective set of one or more subbands.

In another embodiment, a method is provided for processing a data transmission at a receiver of a wireless communication system. According to the method, a particular diversity transmission mode to be used for each of the one or more data streams to be recovered is initially determined. The received symbols for each data stream are then processed based on the diversity transmission mode used for the data stream to provide recovered symbols, which are estimates of the modulation symbols transmitted for the data stream from the transmitter. The recovered symbols for each data stream are further demodulated and decoded to provide decoded data for the data stream.

Various aspects and embodiments of the invention are further described in detail below. The present invention also provides methods, transmitter units, receiver units, terminals, access points, systems, and other apparatuses and elements that implement various aspects, embodiments, and features of the invention, as described in detail below.

Brief description of the drawings

The features, nature, and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings in which like reference characters identify correspondingly throughout and wherein:

FIG. 1 is a diagram of a multiple access system supporting multiple users;

fig. 2 is a block diagram of an embodiment of an access point and two terminals;

FIG. 3 is a block diagram of a transmitter unit;

FIG. 4 is a block diagram of a TX diversity processor for implementing a frequency diversity scheme;

fig. 5 is a block diagram of a TX diversity processor for implementing a Walsh diversity scheme;

FIG. 6 is a block diagram of a TX diversity processor for implementing the STTD scheme;

FIG. 7 is a block diagram of a TX diversity processor for implementing a duplicate Walsh-STTD scheme;

FIG. 8 is a block diagram of a TX diversity processor for implementing a non-duplicate Walsh-STTD scheme;

FIG. 9 is a block diagram of a receiver unit;

FIG. 10 is a block diagram of an RX diversity processor;

FIG. 11 is a block diagram of an RX antenna processor within an RX diversity processor and that may be used for a Walsh diversity scheme; and

fig. 12 is a block diagram of an RX subband processor within an RX antenna processor and may be used for duplicate and non-duplicate Walsh-STTD schemes.

Detailed Description

Fig. 1 is a diagram of a multiple access system 100 supporting multiple users. The system 100 includes one or more Access Points (APs) 104 (only one access point is shown in fig. 1 for simplicity) that communicate with a plurality of terminals (T) 106. An access point may also be referred to as a base station, UTRAN, or some other terminology. A terminal may also be called a handset, mobile station, remote station, User Equipment (UE), or some other terminology. Each terminal 106 may concurrently communicate with multiple access points 014 during soft handoff (if the system supports soft handoff).

In an embodiment, each access point 104 uses multiple antennas and represents (1) Multiple Inputs (MI) for downlink transmissions from the access point to the terminal, and (2) Multiple Outputs (MO) for uplink transmissions from the terminal to the access point. The set of one or more terminals 106 communicating with a given access point together represent the multiple-output for downlink transmissions and the multiple-input for uplink transmissions.

Each access point 104 may concurrently or sequentially communicate with one or more terminals 106 via multiple antennas available at the access point and one or more available antennas at each terminal. Terminals that are not in active communication may receive pilot and/or other signaling information from the access point, as shown by the dotted lines for terminals 106e through 106h in fig. 1.

For the downlink, the access point uses N_TAn antenna, and each terminal uses 1 or N_RThe multiple antennas are used to receive one or more data streams from the access point. General formula N_RDifferent for different multi-antenna terminals and may be any integer. N is a radical of_TA transmitting antenna and N_RThe MIMO channel formed by the receiving antennas can be decomposed into N_SA separate channel of which N_S≤min{N_T，N_R}. Each such independent channel is also referred to as a spatial subchannel of the MIMO channel. Terminals that concurrently receive downlink data transmissions need not be equipped with an equal number of receive antennas.

For the downlink, the number of receive antennas at a given terminal may be equal to or greater than the number of transmit antennas at the access point (i.e., N)_R≥N_T). For such terminals, the space letterThe number of lanes is limited by the number of transmit antennas at the access point. Each multi-antenna terminal communicates with the access point via a respective MIMO channel, which is defined by N of the access point_TA transmitting antenna and its own N_RA plurality of receiving antennas. However, even if multiple multi-antenna terminals are selected for a concurrent downlink data transmission, only N, regardless of the number of terminals receiving the downlink transmission_SOne spatial subchannel is available.

For the downlink, the number of receive antennas at a given terminal may be less than the number of transmit antennas at the access point (i.e., N)_R＜N_T). For example, MISO terminals are equipped with a single receiving antenna (N) for downlink data transmission_R1). The access point may use diversity, beam steering, Spatial Division Multiple Access (SDMA), or some other transmission technique to communicate with one or more MISO terminals simultaneously.

For the uplink, each terminal uses a single antenna or multiple antennas for uplink data transmission. Each terminal may also utilize all or a subset of the antennas for uplink transmission. N of uplink at a given time_TThe multiple transmit antennas are formed by all antennas used for one or more active terminals. The MIMO channel is then formed by N from all active terminals and access points_RA plurality of receiving antennas. The number of spatial subchannels is limited by the number of transmit antennas, which is typically limited by the number of receive antennas of the access point (i.e., N)_S≤min{N_T，N_R})。

Fig. 2 is a block diagram of an embodiment of an access point 104 and two terminals 106. On the downlink, at access point 104, various types of traffic data, such as user-specific data from a data source 208, signaling, and so forth, are provided to a Transmit (TX) data processor 210. Processor 210 then formats and encodes the traffic data based on one or more coding schemes to provide coded data. The encoded data is then interleaved and further modulated (i.e., symbol mapped) based on one or more modulation schemes to provide modulation symbols (modulated data). The data rate, coding, interleaving, and symbol mapping may be determined by controls provided by controller 230 and scheduler 234. The processing by TX data processor 210 is described in detail below.

A transmit processor 220 then receives and processes the modulation symbols and pilot data to provide transmission symbols. The pilot data is typically known data, if any, that is processed in a known manner. In particular embodiments, the processing by transmit processor 220 includes (1) processing the modulation symbols based on one or more transmission modes selected for data transmission to the terminals to provide transmit symbols and (2) OFDM processing the transmit symbols to provide transmit symbols. The processing of transmit processor 220 is discussed in detail below.

Transmit processor 220 to N_TA plurality of transmitters (TMTR)222a through 222t provide N_TOne for each antenna used for data transmission. Each transmitter 222 converts its stream of transmission symbols into one or more analog signals and further conditions (e.g., amplifies, filters, and frequency upconverts) the analog signals to generate a downlink modulated signal suitable for transmission over the wireless communication channel. Each downlink modulated signal is transmitted through a respective antenna 224 to the terminals.

At each terminal 106, the downlink modulated signals from the multiple transmit antennas of the access point are received by an antenna 252 available at one or more terminals. The received signal from each antenna 252 is provided to a respective receiver (RCVR) 254. Each receiver 254 conditions (e.g., filters, amplifies, and downconverts) its received signal and further digitizes the conditioned signal to provide a corresponding sample stream.

A receive processor 260 then receives and processes the sample streams from all receivers 254 to provide recovered symbols (i.e., demodulated data). In particular embodiments, the processing by receive processor 260 includes (1) OFDM processing the received transmission symbols to provide received symbols, and (2) processing the received symbols based on the selected transmission mode to obtain recovered symbols. The recovered symbols are estimates of the modulation symbols transmitted by the access point. The processing of receive processor 260 is described in detail below.

A Receive (RX) data processor 262 then demaps, deinterleaves, and decodes the recovered symbol symbols to obtain user-specific data and signaling for transmission on the downlink to the terminals. The processing by receive processor 260 and RX data processor 262 is complementary to the processing by transmit processor 220 and TX data processor 210, respectively, at the access point.

On the uplink, at terminal 106, various types of traffic data, such as user-specific data and signaling from a data source 276 are provided to a TX data processor 278. The processor 278 encodes different types of traffic data according to their respective coding schemes and further interleaves the encoded data. Modulator 280 then maps the interleaved data symbols to provide modulated data, which is provided to one or more transmitters 254. OFDM may or may not be used for uplink data transmission, depending on system design. Each transmitter 54 conditions the received modulated data to generate a corresponding uplink modulated signal, which is then transmitted via an associated antenna 252 to the access point.

At access point 104, the uplink modulated signals from one or more terminals are received by antennas 224. The received signal from each antenna 224 is provided to a receiver 222, which conditions and digitizes the received signal to provide a corresponding sample stream. The sample streams from all receivers 222 are then processed by a demodulator 240 and further decoded (if necessary) by a RX data processor 242 to recover the data transmitted by the terminals.

Controllers 230 and 270 direct the corresponding operations at the access point and the terminal. Memories 232 and 272 provide storage for program codes and data used by controllers 230 and 270, respectively. A scheduler 234 schedules data transmission on the downlink (and possibly uplink) for the terminals.

For clarity, various transmit diversity schemes for downlink transmission are described in detail below. These schemes may also be used for uplink transmission and this is within the scope of the invention. Also for clarity, in the following description, subscript "i" is used as an epitome for the receive antennas, subscript "j" is used as an index for the transmit antennas, and subscript "k" is used as an index for the subbands in the MIMO OFDM system.

Transmitter unit

Fig. 3 is a block diagram of a transmitter unit 300, which is an embodiment of the transmitter portion of the access point 104. Transmitter unit 300 includes (1) a TX data processor 210a, which receives and processes traffic and pilot data to provide modulation symbols, and (2) a transmit processor 220a, which further processes the modulation symbols to N_TOne transmitting antenna provides N_TA stream of transmission symbols. TX data processor 210a and transmit processor 220a are respective embodiments of TX data processor 210 and transmit processor 220 in fig. 2.

In the particular embodiment shown in fig. 3, TX data processor 210a includes an encoder 312, a channel interleaver 314, and a symbol mapping element 316. Encoder 312 receives and encodes traffic data (i.e., information bits) based on one or more coding schemes to provide coded bits. The encoding increases the reliability of the data transmission.

In one embodiment, the user-specific data for each terminal and the data for each overhead channel may be considered different data streams. Overhead channels may include broadcast, paging, and other common channels to be received by all terminals. Multiple data streams may also be sent to a given terminal. Each data stream may be independently encoded based on a particular coding scheme selected for that data stream. Thus, multiple independently encoded data streams may be provided by encoder 312 for different overhead channels and terminals.

The particular coding scheme used for each data stream is determined by coding control from controller 230. The coding scheme for each terminal may be selected based on, for example, feedback information received from the terminal. Each coding scheme may include any combination of Forward Error Detection (FED) codes (e.g., Cyclic Redundancy Check (CRC) codes) and Forward Error Correction (FEC) codes (e.g., convolutional codes, Turbo codes, block codes, etc.). The coding scheme may also not specify any coding. Binary or trellis-based coding can also be used for each data stream. Also, in the case of convolutional and Turbo coding, puncturing may be used to adjust the coding rate. In particular, puncturing may be used to increase the coding rate above the base coding rate.

In particular embodiments, the data of each data stream is initially divided into frames (or packets). For each frame, the data may be used to generate a set of CRC bits for the frame, which are then appended to the data. The data and CRC bits for each frame are then encoded with either a convolutional code or a Turbo code to generate encoded data for the frame.

Channel interleaver 314 receives and interleaves the coded bits based on one or more interleaving schemes. In general, each coding scheme is associated with a corresponding interleaving scheme. In this case, each independently encoded data stream would be separately interleaved. The interleaving provides time diversity for the coded bits such that each data stream is transmitted based on the average SNR for the subbands and spatial subchannels used for the data stream, is resistant to fading, and further removes correlation between the coded bits used to form each modulation symbol.

In OFDM, a channel interleaver may be designed to allocate the encoded data for each data stream over multiple subbands in a single OFDM symbol or possibly over multiple OFDM symbols. The purpose of the channel interleaver is to randomize the encoded data to reduce the likelihood of corruption of successive coded bits by the communication channel. When the interleaving interval for a given data stream covers a single OFDM symbol, the coded bits for the data stream are randomly distributed across the subbands used for the data stream to exploit frequency diversity. When the interleaving interval covers multiple OFDM symbols, the coded bits are randomly distributed across the subbands carrying the data and the multi-symbol interleaving interval to exploit frequency and time diversity. For Wireless Local Area Networks (WLANs), the time diversity achieved by interleaving over multiple OFDM symbols may not be important if the minimum expected coherence time of the communication channel is many times greater than the interleaving interval.

Symbol mapping component 316 receives and maps according to one or more modulation schemesThe interleaved data is transmitted to provide modulation symbols. A particular modulation scheme may be used for each data stream. Symbol mapping for each data stream may be achieved by grouping q_mThe encoded and interleaved sets of bits form data symbols (each of which may be a non-binary value) and each data symbol is mapped to a point within a signal constellation corresponding to the modulation scheme selected for use with the data stream. The selected modulation scheme may be QPSK, M-PSK, M-QAM, or some other modulation scheme. Each mapped signal point is complex-valued and corresponds to M_mMeta-modulation symbols of where M_mCorresponds to a particular modulation scheme selected for data stream m, andsymbol mapping element 316 provides a stream of modulation symbols for each data stream. The modulation symbol streams for all data streams are shown together in fig. 3 as modulation symbol stream s (n).

Table 1 lists various coding and modulation schemes that may be used to obtain a spectral efficiency range (or bit rate) using convolutional and Turbo coding. Each bit rate (in bits per second per hertz or bps/Hz) can be achieved using a particular combination of code rate and modulation scheme. For example, half the bit rate can be obtained using 1/2 rate and BPSK modulation, one bit rate can be obtained using 1/2 rate and QPSK modulation, etc.

In Table 1, BPSK, QPSK, 16-QAM and 64-QAM may be used for the listed bit rates. Other modulation schemes such as DPSK, 8-PSK, 32-QAM, 128-QAM, etc. may also be used and are within the scope of the present invention. DPSK (differential phase shift keying) can be used when the communication channel is difficult to track because a coherent reference is not required at the receiver to demodulate the DPSK modulated signal. For OFDM, modulation may be achieved on a per-subband basis, and the modulation scheme for each subband may be independently selected.

Table 1

Other combinations of code rate and modulation scheme may also be used to achieve various bit rates and this is within the scope of the invention.

In the particular embodiment shown in FIG. 3, transmit processor 220a includes TX diversity processor 320 and N_TAn OFDM modulator. Each OFDM modulator includes an Inverse Fast Fourier Transform (IFFT) unit 330 and a cyclic prefix generator 332. TX diversity processor 320 receives and processes the modulation symbols from TX data processor 210a according to one or more selected transmission modes to provide transmit symbols.

In one embodiment, TX diversity processor 320 also receives and multiplexes the transmit symbols and pilot symbols (i.e., pilot data) within a subset of the available subbands using frequency division multiplexing. An example implementation of the FDM pilot transmission scheme is shown in table 2. In this implementation, there are 64 subbands available for the MIMO OFDM system, and subband indices of + -7 and + -21 are used for pilot transmission. In other embodiments, pilot symbols may be multiplexed with the transmit symbols, e.g., using Time Division Multiplexing (TDM), Code Division Multiplexing (CDM), or any combination of FDM, TDM, and CDM.

TX diversity processor 320 provides one transmit symbol stream to each OFDM modulator. The processing by TX diversity processor 320 is detailed below.

Each OFDM modulator receives a respective transmit symbol stream x_j(n) of (a). Within each OFDM modulator, IFFT unit 330 divides N_FCombining a set of transmitted symbols in stream x_j(n) to form a corresponding symbol vector and convert the symbol vector into its time domain representation using an inverse fast fourier transform (this is also referred to as an OFDM symbol).

For each OFDM symbol, cyclic prefix generator 332 repeats a portion of the OFDM symbol to form a corresponding transmission symbol. The cyclic prefix ensures that the transmission symbol retains its orthogonal properties in the presence of multipath delay spread, thereby improving performance against deleterious path effects such as channel dispersion caused by frequency selective fading. A fixed or adjustable cyclic prefix may be used for each OFDM symbol. As a specific example of an adjustable cyclic prefix, the system has a bandwidth of 20MHz, a chip period of 50nsec, and 64 subbands. For this system, each OFDM symbol has a duration of 3.2 microseconds (μ sec) (or 64 × 50 nsec). The cyclic prefix for each OFDM symbol has a minimum length of 4 chips (200nsec), a maximum length of 16 chips (800nsec), and increments of 4 chips (200 nsec). Each transmission symbol is 3.4 microseconds to 4.0 microseconds for a duration range of 200nsec to 800nsec cyclic prefix, respectively.

A cyclic prefix generator 332 within each OFDM modulator provides a stream of transmission symbols to an associated transmitter 222. Each transmitter 222 receives and processes a respective stream of transmission symbols to generate a downlink modulated signal, which is then transmitted from an associated antenna 224.

The coding and modulation of MIMO OFDM systems is described in detail in the following U.S. patent applications:

● U.S. patent application Ser. No. 09/993087 entitled "Multiple-Access Multiple-Input Multiple-output (MIMO) communication System", filed on 11/6/2001;

● U.S. patent application Ser. No. 09/854235 entitled "Method and Apparatus for processing Data in a Multiple-Input Multiple-output (MIMO) Communication System adapting Channel State Information", filed on 11/5/2001;

● U.S. patent application Ser. Nos. 09/826481 and 09/956449, each entitled "Method and apparatus for Utilizing Channel State Information in an aWireless Communication System", filed on 3/23 and 9/18, 2001, respectively;

● U.S. patent application Ser. No. 09/776075, entitled "Coding Scheme for aWireless Communication System", filed on 2/1/2001; and

● U.S. patent application Ser. No. 09/532492, entitled "High Efficiency, High Performance Communications System Employing Multi-Carrier modulation", filed on 3/30/2000.

These patent applications are assigned to the assignee of the present invention and are incorporated herein by reference.

MIMO OFDM systems may be designed to support multiple modes of operation for data transmission. These transmission modes include a diversity transmission mode, a spatial multiplexing transmission mode, and a beam steering transmission mode.

Spatial multiplexing and beam steering modes can be used to achieve higher bit rates under certain better channel conditions. These transmission Modes are described in the following U.S. patent application Ser. No. 10/085456 entitled "Multiple-Input, Multiple-output (MIMO) Systems with Multiple Transmission Modes", filed on 26.2.2002, assigned to the assignee of the present invention and incorporated herein by reference.

A diversity transmission mode may be used to obtain higher reliability for certain data transmissions. For example, diversity transmission mode may be used for overhead channels on the downlink, such as broadcast, paging, and other common channels. The diversity transmission mode may also be used for data transmission in the following cases: (1) whenever the transmitter does not have sufficient Channel State Information (CSI) for the communication channel, (2) when the channel conditions are sufficiently poor (e.g., under certain mobile conditions) and a more spectrally efficient transmission mode cannot be supported, and (3) for other situations. When a diversity transmission mode is used for downlink data transmission to the terminals, the rate and/or power of each terminal may be controlled to improve performance. Multiple diversity transmission modes may be supported and are described in detail below.

Diversity transmission mode attempts to achieve transmit diversity by establishing orthogonality among multiple signals transmitted from multiple transmit antennas. Orthogonality between the transmitted signals may be achieved in frequency, time, space, or any combination thereof. Transmit diversity may be established by one or a combination of the following processing techniques:

● frequency (i.e., sub-band) diversity. The inherent orthogonality between subbands provided by OFDM is used to provide diversity against frequency selective fading.

● use transmit diversity of orthogonal functions. Walsh functions or some other orthogonal function are applied to OFDM symbols transmitted from multiple transmit antennas to establish orthogonality among the transmitted signals. This scheme is also referred to herein as a "Walsh diversity" scheme.

● Space Time Transmit Diversity (STTD). Spatial orthogonality is established between pairs of transmit antennas while preserving the high spectral efficiency potential provided by MIMO techniques.

In general, frequency diversity schemes can be used that are resistant to frequency selective fading and operate within the frequency and spatial dimensions. The Walsh diversity scheme and the STTD scheme operate in both time and space dimensions.

For clarity, the above-described processing techniques and certain combinations thereof are described below for an example MIMO OFDM system. In this system, each access point is equipped with four antennas for transmitting and receiving data, and each terminal may be equipped with one or more antennas.

Frequency diversity

Fig. 4 is a block diagram of an embodiment of a TX diversity processor 320a, which may be used to implement a frequency diversity scheme. For OFDM, the subbands are inherently orthogonal to each other. Frequency diversity may be established by transmitting the same modulation symbols on multiple subbands.

As shown in fig. 4, modulation symbols s (n) from TX data processor 210 are provided to a symbol repetition unit 410. Unit 410 repeats each modulation symbol based on the (double or quadruple) diversity provided for the modulation symbol. Demultiplexer 412 then receives the repeated symbols and pilot symbols and demultiplexes these symbols into N_TA stream of transmit symbols. The modulation symbols for each data stream mayTo be transmitted on a corresponding group of one or more subbands assigned to the data stream. Some of the available subbands may be reserved for pilot transmission (e.g., using FDM). Or pilot symbols may be sent using TDM or CDM along with modulation symbols.

In general, it is desirable to transmit repeated symbols within subbands that are spaced apart from one another by at least a coherence bandwidth of a communication channel. Moreover, the modulation symbols may be repeated on any number of subbands. Higher repetition factors correspond to higher redundancy and improved likelihood of correct reception at the receiver, at the expense of reduced efficiency.

For clarity, a particular implementation of the frequency diversity scheme is described below for a particular MIMO OFDM system having some of the characteristics defined by IEEE standard 802.11 a. The specification for the IEEE standard is described in section entitled "11: wireless LAN Medium Access Control (MAC) and physical layer (PHY) specifications: high speed physical layer in the 5GHz band, 9 months 1999, which is publicly available and is included herein by reference. The system has an OFDM waveform structure of 64 subbands. Of these 64 subbands, 48 subbands (with indices ± { 1., 6, 8., 20, 22., 26} are used for data, four subbands (with indices ± {7, 21} are used for pilot, the DC subband (with index 0) is not used, and the remaining subbands are not used, but are used as guard subbands.

Table 2 shows a specific implementation of the dual and quad frequency diversity of the above system. For dual frequency diversity, each modulation symbol is transmitted on two subbands that are 26 or 27 subbands apart. For four frequency diversity, each modulation symbol is transmitted on four subbands separated by 13 or 14 subbands. Other frequency diversity schemes may also be used and are within the scope of the invention.

Table 2

The frequency diversity scheme may be used for transmitters (e.g., terminals) that are not equipped with multiple transmit antennas. In this case, one transmit symbol stream is provided by TX diversity processor 310 a. Each modulation symbol within s (n) may be repeated and transmitted on multiple subbands. For single antenna terminals, frequency diversity may be used to provide robust performance in the presence of frequency selective fading.

Frequency diversity schemes may also be used where there are multiple transmit antennas available. This may be achieved by transmitting the same modulation symbols on different subbands or groups of subbands from all transmit antennas. For example, in a four transmit antenna device, every fourth subband may be assigned to one of the transmit antennas. Each transmit antenna may be associated with N_FA different group of/4 subbands is associated. For four frequency diversity, each modulation symbol may be transmitted on a set of four subbands, one in each of four groups of subbands, each group associated with a particular transmit antenna. The four subbands in the set may also be selected such that they are as large apart as possible. For dual frequency diversity, each modulation is transmitted on a set of two subbands, one in each of the two subband groups. Other implementations of frequency diversity with multiple transmit antennas are also contemplated and are within the scope of the present invention. Frequency diversity may also be used with one or more other transmit diversity schemes, as described below.

Walsh transmit diversity

Fig. 5 is a block diagram of an embodiment of a TX diversity processor 320b that may be used to implement a Walsh diversity scheme. For this diversity scheme, an orthogonal function (or code) is used to establish time orthogonality, which can then be used to establish full transmit diversity across all transmit antennas. This may be achieved by repeating the same modulation symbols on the transmit antennas and time spreading the symbols using different orthogonal functions for each transmit antenna, as described below. In general, various orthogonal functions may be used, such as Walsh functions, Orthogonal Variable Spreading Factor (OVSF) codes, and the like. For clarity, the following description uses Walsh functions.

Shown in FIG. 5In an embodiment, modulation symbols s (N) from TX data processor 210 are provided to demultiplexer 510, which demultiplexes the symbols into N_BOne modulation symbol stream for each sub-band used for data transmission (i.e., each sub-band carrying data). Each modulation symbol substream s_k(n) are provided to respective TX subband processors 520.

Within each TX sub-band processor 520, a sub-stream s_kThe modulation symbols within (N) are provided to N_TN of transmitting antenna_TMultipliers 524a through 524d (here for this example system N)_T4). In the embodiment shown in fig. 5, one modulation symbol s is provided to all four multipliers 524 for every 4 symbol periods_kThis corresponds to (4T)_OFDM)^-1The symbol rate of (c). Each multiplier also receives a different Walsh function with four chips (i.e., each multiplier receives a different Walsh function with four chips)And is assigned to the transmit antenna j associated with the multiplier. Each multiplier then combines the symbols s_kMultiplied by the Walsh function W_j ⁴And provides four sequences of transmit symbols {(s)_k·w_1j)，(s_k·w_2j)，(s_k·w_3j)，and(s_k·w_4j) Which is sent in four consecutive OFDM symbol periods on subband k for transmit antenna j. The four transmitted symbols have the same s as the original modulation symbol_kThe same amplitude. However, each transmitted symbol within the sequence is determined by the Walsh chip symbol used to generate the transmitted symbol. The Walsh function is then used to time spread each modulation symbol over four symbol periods. The four multipliers 524a through 524d of each Tx subband processor 520 provide four transmit symbol streams to the buffers/multiplexers 530a through 530d, respectively.

Each buffer/multiplexer 530 is driven from N_BTX subband processors 520a through 520f receive pilot symbols and N_BA stream of transmit symbols. Each unit 530 then multiplexes the transmit symbols and pilot symbols for each symbol period and provides a stream of transmit symbols x to a corresponding IFFT unit 330_j(n) of (a). Each IFFT unit 330 receives and processes a respective transmit symbol stream x in the manner described above_j(n)。

In the embodiment shown in fig. 5, N is the number of transmission antennas from all four transmit antennas in every 4 symbol periods_BOne modulation symbol is transmitted on each of the data-carrying subbands. When four transmit antennas are used for data transmission, the spectral efficiency obtained with the Walsh diversity scheme is equal to the spectral efficiency obtained with the four-frequency diversity scheme, where one modulation symbol is transmitted on four data-carrying subbands for each symbol period. In a Walsh diversity scheme with four transmit antennas, the Walsh function is four OFDM symbols in duration or length (e.g., at W)_j ⁴Indicated by the superscript in). Since the information within each modulation symbol is distributed over four consecutive OFDM symbols, demodulation at the receiver is achieved based on the four consecutive received OFDM symbols.

In other embodiments, increased spectral efficiency may be obtained by transmitting different modulation symbols (rather than the same modulation symbols) on each transmit antenna. For example, demultiplexer 510 may be designed to provide four different modulation symbols s to multipliers 524a through 524d every 4 symbol periods₁、s₂、s₃And s₄. Each multiplier 524 then multiplies a different modulation symbol with its Walsh function to provide four different transmissionsA sequence of symbols. The spectral efficiency of this embodiment would then be four times that of the embodiment shown in fig. 5. As another example, demultiplexer 510 may be designed to provide two different modulation symbols for every 4 symbol periods (e.g., provide s to multipliers 524a and 524 b)₁Provides s to multipliers 524c and 524d₂)。

Space Time Transmit Diversity (STTD)

Space-time transmit diversity (STTD) supports simultaneous transmission of two substantially independent symbol streams on two transmit antennas while maintaining orthogonality at the receiver. The STTD scheme may provide higher spectral efficiency than the Walsh transmit diversity scheme shown in fig. 5.

The STTD scheme operates as follows. Assume two modulation symbols, labeled s₁And s₂To be transmitted on a given subband. The transmitter generates two vectorsAndeach vector comprising two elements to be transmitted sequentially from a respective transmit antenna over two symbol periods (i.e., the vector is transmitted from antenna 1)x ₁Transmitting the vector from the antenna 2x ₂)。

If the receiver includes a single receive antenna, the received signal may be represented in matrix form as follows:

wherein r is₁And r₂Is two symbols received in two consecutive symbol periods at the receiver;

h₁and h₂Is the path gain from the two transmit antennas to the receive antenna for the subband under consideration, where the path gain is assumed to be constant over the subband and static over a2 symbol period; and

n₁and n₂Is compared with two received symbols r₁And r₂The associated noise.

The receiver can then derive s for the two transmitted symbols₁And s₂The estimation of (c) is as follows:

and Eq (2)

In other implementations, the transmitter may generate two vectorsx ₁＝[s₁ s₂]^TAndthe elements of the two vectors are transmitted sequentially from the two transmit antennas over two symbol periods. The received signal may be expressed as:

the receiver may then derive two transmitted symbol estimates as follows:

and

when two antennas are used for data transmission, the STTD scheme has a spectral efficiency twice that of the dual frequency diversity scheme and the Walsh diversity scheme with two transmit antennas. The STTD scheme effectively transmits one independent modulation symbol per subband on two transmit antennas per symbol period, wherein the dual frequency diversity scheme transmits only a single modulation symbol per two subbands per symbol period, and the Walsh diversity scheme transmits only a single modulation symbol per subband in two symbol periods. Since the information within each modulation symbol is distributed over two consecutive OFDM symbols for the STTD scheme, demodulation is achieved at the receiver based on the two consecutive received OFDM symbols.

Fig. 6 is a block diagram of an embodiment of TX diversity processor 320c, which may be used to implement the STTD scheme. In this embodiment, modulation symbols s (N) from TX data processor 210 are provided to demultiplexer 610, which demultiplexes the symbols to 2N_BTwo sub-streams per sub-band carrying data. Each pair of modulation symbol substreams is provided to a respective TX subband processor 620. Each modulation symbol substream includes one modulation symbol for each 2-symbol period, which corresponds to (2T)_OFDM)^-1The symbol rate of (c).

Within each TX subband processor 620, the pairs of modulation symbol streams are provided to a space-time encoder 622. For each pair of modulation symbols in the two substreams, space-time encoder 622 provides two vectors,andeach vector includes two transmit symbols to be transmitted in two symbol periods. The two transmitted symbols in each vector have a symbol s which is identical to the original modulation symbol₁And s₂The same amplitude. However, each transmit symbol may be phase rotated with respect to the original modulation symbol. Each TX sub-band processor 620 thus provides two transmit symbol sub-streams to two buffer/multiplexers 630a and 630b, respectively.

Each buffer/multiplexer 630 is from N_BMultiple TX subband processors 620a through 620f receive pilot symbols and N_BA sub-stream of transmission symbols, multiplexing the transmission symbols and pilot symbols for each symbol period, and providing a stream of transmission symbols x to a corresponding IFFT unit 330_j(n) of (a). Each IFFT unit 330 then processes a respective transmit symbol stream in the manner described above.

The STTD scheme is further detailed in the S.M. Alamouti paper entitled "A Simple Transmission Technique for Wireless Communications", IEEE Journal on selected Areas in Communications, Vol.16, No.8, October1998, pgs.1451-1458, which is incorporated herein by reference. The STTD approach is further detailed in U.S. patent application Ser. No. 09/737602, entitled "Method and System for incorporated Bandwidth affinity in Multiple Input-Multiple Output Channels", filed on 5.1.2001, assigned to the assignee of the present invention and incorporated herein by reference.

Walsh-STTD

The Walsh-STTD scheme uses a combination of Walsh diversity and STTD as described above. The Walsh-STTD scheme may be used for systems with more than two transmit antennas. For Walsh-STTD with a repeated symbol scheme (which is also referred to as a repeated Walsh-STTD scheme), two transmit vectors are generated for each pair of modulation symbols to be transmitted from two transmit antennas on a given subbandx ₁Andx ₂as described above for fig. 6. The two transmit vectors are also repeated over multiple pairs of transmit antennas using Walsh functions to obtain orthogonality over the transmit antenna pairs and provide additional transmit diversity.

Fig. 7 is a block diagram of an embodiment of TX diversity processor 320d for implementing a duplicate Walsh-STTD scheme. The modulation symbols s (N) from TX data processor 210 are provided to demultiplexer 710, which demultiplexes the symbols into 2N_BTwo sub-streams per sub-band carrying data. Each modulation symbol substream includes one modulation symbol for every 4 symbol periods, which corresponds to a symbol rate of (4T)_OFDM)^-1. Each pair of modulation symbol substreams is provided to a respective TX subband processor 720.

A space-time encoder 722 within each TX subband processor 720 receives the pairs of modulation symbol substreams and forms a modulation symbol s for each 4 symbol period₁And s₂For, one symbol from each of the two substreams. Modulation symbol pair s₁And s₂Then used to form two vectors,andeach vector spans a 4 symbol period. Space-time coder 722 transforms the first vectorx ₁Is provided to multipliers 724a and 724c and provides a second vectorx ₂To multipliers 724b and 724 d. Multipliers 724a and 724b also each receive a Walsh function with two chips (i.e., W)₁ ²＝{w₁₁，w₂₁}) and are assigned to transmit antennas 1 and 2. Likewise, multipliers 724c and 724d each also receive a Walsh function W with two chips₂ ²And is assigned to transmit antennas 3 and 4. Each multiplier 724 then vectors itx _jEach symbol in (a) is multiplied by its Walsh function to provide two transmit symbols sent in two consecutive symbol periods on subband k of transmit antenna j.

In particular, the multiplier 724a will transfer the vectorx ₁Multiplying each symbol in the set by the Walsh function W₁ ²And provides four transmission codesMeta sequence {(s)₁·w₁₁)，(s₁·w₂₁)，(s₂ ^*·w₁₁)，and(s₂ ^*·w₂₁) Which is transmitted in four consecutive symbol periods. Multiplier 724b will vectorx ₂Multiplying each symbol in the set by the Walsh function W₁ ²And provides four transmit symbols {(s)₂·w₁₁)，(s₂·w₂₁)，(-s₁ ^*·w₁₁)，and(-s₁ ^*·w₂₁)}. Multiplier 724c will vectorx ₁Multiplying each symbol in the set by the Walsh function W₂ ²And provides four sequences of transmit symbols {(s)₁·w₁₂)，(s₁·w₂₂)，(s₂ ^*·w₁₂)，and(-s₂ ^*·w₂₂)}. And multiplier 724d will vectorx ₂Multiplying each symbol in the set by the Walsh function W₂ ²And provides four sequences of transmit symbols {(s)₂·w₁₂)，(s₂·w₂₂)，(-s₁ ^*·w₁₂)，and(-s₁ ^*·w₂₂)}. Walsh functions are used for each symbol or vector over two symbol periodsxThe elements within are time extended. The four multipliers 724a through 724d of each TX subband processor 720 provide four transmit symbol substreams to four buffer/multiplexers 730a through 730d, respectively.

Each buffer/multiplexer 730 is driven from N_BMultiple TX subband processors 720a through 720f receive pilot symbols and N_BA sub-stream of transmission symbols, multiplexes pilot and transmission symbols in each symbol period, and provides a stream of transmission symbols x to a corresponding IFFT unit 330_j(n) of (a). The sequential processing is described below.

The duplicate Walsh-STTD scheme (with four transmit antennas) shown in fig. 7 has the same spectral efficiency as the STTD scheme shown in fig. 6, and is twice the spectral efficiency of the Walsh diversity scheme shown in fig. 5. However, additional diversity is provided by the Walsh-STTD scheme by transmitting the repeated symbols over multiple transmit antenna pairs. The Walsh-STTD processing provides full transmit diversity (per subband) for signals transmitted from all transmit antennas.

Fig. 8 is a block diagram of an embodiment of TX diversity processor 320e, which implements Walsh-STTD without a repeated symbol scheme (which is also referred to as a non-repeated Walsh-STTD scheme). This scheme can be used to increase spectral efficiency at the cost of less diversity than the scheme shown in fig. 7. As shown in FIG. 8, modulation symbols s (N) are provided to demultiplexer 810, which demultiplexes the symbols into 4N_BFour sub-streams each carrying a data sub-band. Each set of four modulation symbol substreams is provided to a respective TX subband processor 820.

Within each Tx subband processor 820, a space-time encoder 822a receives a first pair of modulation symbol substreams and a space-time encoder 822b receives a second pair of modulation symbol substreams. For each modulation symbol pair in the two substreams in the first pair, space-time encoder 822a provides two vectors to multipliers 824a and 824b, respectivelyAndlikewise, for each modulation symbol pair in the two substreams in the second pair, space-time encoder 822b provides two vectors to multipliers 824c and 824d, respectivelyAnd

multipliers 824a and 824b also each receive a Walsh function W₁ ²Multipliers 824c and 824d are further coupledReceive Walsh function W₂ ². Each multiplier 824 then vectors itx _jEach symbol in (a) is multiplied by its Walsh function to provide two transmit symbols for transmission in two consecutive symbol periods on subband k of transmit antenna j. Four multipliers 824a through 824d for each TX subband processor 820 provide four transmit symbol substreams to four buffer/multiplexers 830a through 830d, respectively.

Each buffer/multiplexer 830 from N_BTX subband processors 820a through 820f receive pilot symbols and N_BA sub-stream of transmission symbols, multiplexing pilot symbols and transmission symbols for each symbol period, and providing a stream of transmission symbols x to a corresponding IFFT unit 330_j(n) of (a). The sequential processing is described below.

The spectral efficiency of the non-duplicate Walsh-STTD scheme (with four transmit antennas) shown in fig. 8 is twice that of the duplicate Walsh-STTD scheme shown in fig. 7. The same process can be extended to systems with any number of transmit antenna pairs. Instead of repeating two transmit vectors over a pair of transmit antennas, each pair of transmit antennas can be used to transmit a separate symbol stream. This results in greater spectral efficiency but may be at the expense of diversity performance. Some of this diversity can be recovered by using Forward Error Correction (FEC) coding.

The Walsh-STTD scheme is also detailed in the aforementioned U.S. patent application serial No. 09/737602.

frequency-STTD

The frequency-STTD scheme uses a combination of frequency diversity and STTD. The frequency-STTD scheme also uses antenna diversity for systems with more than one pair of transmit antennas. For the frequency-STTD scheme, each modulation symbol is transmitted on a plurality (e.g., two) of subbands and provided to a plurality of TX subband processors. The selection of subbands for each modulation symbol may be such that their spacing is as large as possible (e.g., as shown in table 1) or based on some other subband allocation scheme. If four transmit antennas are available, two pairs of modulation symbols are processed using STTD for each subband. A first pair of modulation symbols is transmitted from a first pair of antennas (e.g., transmit antennas 1 and 2) and a second pair of modulation symbols is transmitted from a second pair of antennas (e.g., transmit antennas 3 and 4).

Each modulation symbol is thus transmitted on multiple subbands and multiple transmit antennas. For simplicity, for a given modulation symbol s with four transmit antennas and using a dual frequency diversity system_aThe treatment of (2) may be performed as follows. Modulation code element s_aIs initially provided to two TX subband processors (e.g., for subbands k and k + N_F/2). Within subband k, a symbol s is modulated_aWith another modulation symbol s_bWith STTD processing to form two vectorsAndthey are respectively transmitted from the emitting dayLines 1 and 2 are sent. At subband k + N_FWithin/2, modulating the symbol s_aWith another modulation symbol s_cWith STTD processing to form two vectorsAndwhich are transmitted from the transmit antennas 3 and 4, respectively. Modulation code element s_cCan be associated with modulation symbol s_bThe same or different modulation symbols.

For the implementation of the frequency-STTD scheme, the modulation symbols within each subband have two levels of transmit diversity provided by STTD processing. There is four levels of transmit diversity per modulation symbol to be transmitted plus some frequency diversity provided by using two subbands and STTD. The frequency-STTD scheme has the same frequency efficiency as the repeated Walsh-STTD scheme. However, the total transmission time of each modulation symbol is two symbol periods with the frequency-STTD scheme, which is half of the total transmission time of each modulation symbol of the Walsh-STTD scheme because the frequency-STTD scheme does not implement Walsh processing.

In one embodiment of the frequency-STTD scheme, all subbands are used by each pair of transmit antennas for data transmission. For quad diversity, each modulation symbol is provided to two subbands for two transmit antenna pairs, as described above. In another embodiment of the frequency-STTD scheme, each pair of transmit antennas is assigned a different group of subbands for data transmission. For example, in a device with two pairs of transmit antennas, every other subband may be assigned to a transmit antenna pair. Each transmit antenna pair may then be associated with a different N_FThe/2 subband groups are associated. For quad diversity, each modulation symbol may be transmitted on two subbands, one in each of two subband groups, each group associated with a particular transmit antenna pair. The two subbands for each modulation symbol may be selected such that they are spaced as far apart as possible. Other implementations of frequency-STTD diversity with multiple transmit antenna pairs are also contemplated and are within the scope of the invention.

As described above, various diversity schemes may be implemented using the various processing techniques described above. For clarity, implementations of various diversity schemes are described for a particular system. Variations of these diversity schemes are also contemplated and are within the scope of the invention.

Moreover, other diversity schemes may also be implemented based on other combinations of processing techniques described herein and are within the scope of the invention. For example, another diversity scheme may utilize frequency diversity as well as Walsh transmit diversity, and another diversity scheme may utilize frequency diversity, Walsh diversity, and STTD.

Diversity transmission mode

Multiple diversity transmission modes may be implemented using the transmit processing schemes described above. These diversity transmission modes may include the following:

● frequency diversity transmission mode-frequency diversity is used only (e.g., double, quadruple, or some other integer multiple of frequency diversity).

● Walsh diversity transmission mode-Walsh transmit diversity is used only.

● STTD transmission mode-STTD only is used.

● Walsh-STTD transmission mode-uses Walsh transmit diversity and STTD with repeated or non-repeated symbols.

● frequency-STTD transmission mode-using frequency diversity and STTD.

● frequency-Walsh transmission mode-use frequency diversity and Walsh transmit diversity.

● frequency-Walsh-STTD Transmission mode-Using frequency diversity, Walsh Transmit diversity and STTD

A diversity transmission mode may be used for data transmission between the access point and the terminal. The particular transmission mode used for a given data stream may depend on various factors such as (1) the type of data being transmitted (e.g., whether the same for all terminals or user-specific for a particular terminal), (2) the number of antennas available at the transmitter and receiver, (3) the channel conditions, (4) the data transmission requirements (e.g., the required packet error rate), and so on.

Each access point within the system may be equipped with, for example, four antennas for data transmission and reception. Each terminal may be equipped with one, two, four, or some other number of antennas for data transmission and reception. A default diversity transmission mode may be defined and used for each terminal type. In a particular embodiment, the following diversity transmission modes are used as defaults:

● Single antenna terminal-frequency diversity transmission mode with double or quadruple diversity is used.

● dual antenna terminal-uses STTD transmission mode for dual diversity and frequency-STTD transmission mode for quad diversity.

● four antenna terminal-STTD transmission mode for dual diversity and Walsh-STTD transmission mode for quad diversity.

Other diversity transmission modes may also be selected as the default mode and this is within the scope of the invention.

Diversity transmission modes may also be used to increase the reliability of data transmissions received by all terminals in the system on an overhead channel. In one embodiment, a particular diversity transmission mode is used for the broadcast channel and this mode is known a priori by all terminals in the system (i.e., no signaling is required to identify the transmission mode for the broadcast channel). In this way, the terminal can process and recover the data transmitted on the broadcast channel. The transmission mode for the other overhead channels may be fixed or dynamically selected. In a dynamic selection scheme, the system determines which transmission mode is most reliable (and spectrally efficient) for each remaining overhead channel based on the mix of served terminals. The transmission mode and other configuration information used for these overhead channels may be signaled to the terminal, e.g., over a broadcast channel.

In OFDM, subbands may be processed as different transmission channels and the same or different diversity transmission modes may be used for the subbands. For example, one diversity transmission mode may be used for all data-carrying subbands, or a separate diversity transmission mode may be selected for each data-carrying subband. Also, for a given subband, different diversity transmission modes may be used for different sets of transmit antennas.

In general, each data stream (either of the overhead channels or of a particular receiver device) may be coded and modulated based on a coding and modulation scheme selected for that data stream to provide modulation symbols. The modulation symbols are further processed based on a diversity transmission mode selected for the data stream to provide transmit symbols. The transmit symbols are further processed and transmitted on one or more subband groups from one or more sets of transmit antennas designated for the data stream.

Receiver unit

Fig. 9 is a block diagram of a receiver unit 900, which is a receiver portion embodiment of multi-antenna terminal 106. The downlink modulated signals from access point 104 are received by antennas 252a through 252r and the received signal from each antenna is provided to a respective receiver 254. Each receiver 254 processes (e.g., conditions, digitizes, and data demodulates) the received signal to provide a stream of received transmission symbols, which is then provided to a corresponding OFDM demodulator within a receive processor 260 a.

Each OFDM demodulator includes a cyclic prefix removal unit 912 and a Fast Fourier Transform (FFT) unit 914. A unit 912 removes the cyclic prefix that has been appended within each transmission symbol to provide a corresponding received OFDM symbol. Cyclic prefix removal may be performed by determining N for each received transmission symbol_AA set of samples and select these N_AA subset of samples as N of the received OFDM symbol_FOne sample. FFT 914 then transforms each received OFDM symbol (or each N using a fast Fourier transform_FA set of samples) to pair N_FOne subband provides N_FA vector of received symbols. FFT units 914a through 914r provide N to RX diversity processor 920_ROne received symbol stream, i.e. r₁(n) to

RX diversity processor 920 pairs N_RDiversity processing of the received symbol streams to provide recovered symbolsThis is an estimate of the modulation symbols s (n) transmitted by the transmitter. The processing performed by RX diversity processor 920 depends on the transmission mode used for each data stream to be recovered, as indicated by the transmission mode control. The RX diversity processor 920 is described in detail below.

RX diversity processor 920 provides recovered symbols for all data streams to be recovered to RX data processor 262aWhich is an embodiment of RX data processor 262 in fig. 2. Within processor 262a, symbol demapping element 942 demodulates the recovered symbols for each data stream according to a demodulation scheme that is complementary to the modulation scheme used for the data stream. A channel deinterleaver 944 then deinterleaves the demodulated data in a manner complementary to the interleaving performed for the data stream at the transmitter, and the deinterleaved data is further decoded by a decoder 946 in a manner complementary to the encoding performed at the transmitter. A Turbo decoder or a Viterbi decoder may be used for decoder 946 if Turbo or convolutional coding is implemented at the transmitter, respectively, for example. The decoded data from decoder 946 represents an estimate of the recovered transmitted data. The decoder 946 may also provide the status of each received packet (e.g., indicating that it was received correctly or in error).

In the illustrated embodiment of fig. 9, channel estimator 950 estimates various channel characteristics such as channel response and noise variance (e.g., based on recovered pilot symbols) and provides these estimates to controller 270. The controller 270 may be designed to implement various functions related to the diversity processing at the receiver. For example, controller 270 may determine a transmission mode for each data stream to be recovered and further direct the operation of RX diversity processor 920.

Fig. 10 is a block diagram of an embodiment of an RX diversity processor 920x, which may be used in a multi-antenna receiver device. In this embodiment, N_RN of one receiving antenna_RA received symbol stream is provided to N_RAnd RX antenna processors 1020a through 1020 r. Each RX antenna processor 1020 processes a respective received symbol stream r_i(n) and provides corresponding recovered symbol streams for associated receive antennasIn another embodiment, one or more RX antenna processors 1020 are time-shared and used for processingAll N_RA stream of received symbols.

Combiner 1030 then goes from N_RThe RX antenna processors 1020a through 1020r receive and combine N_RA single recovered symbol stream to provide a single recovered symbol streamThe combining may be performed on a per symbol basis. In one embodiment, for a given subband k, from N for each symbol period_RN of one receiving antenna_RA recovered symbol (this is denoted asi＝(1，2，...，N_R) By initially being assigned to N_RN of one receiving antenna_RThe weights are scaled. For sub-bands k, N_RThe scaled symbols are then summed to provide a recovered symbolThe weights may be selected to obtain maximum ratio combining and may be determined based on channel quality (e.g., SNR) associated with the receive antennas. The weighted scaling may also be achieved by an Automatic Gain Control (AGC) loop maintained for each receive antenna, as is known in the art.

For a single antenna receiver device, there is only one received symbol stream. In this case, only one RX antenna processor 1020 is needed. The design of RX antenna processor 1020 is described below.

The recovered symbol stream provided by combiner 1030May include recovered symbols for all data streams transmitted by the transmitter. Or, flowMay include one or moreRecovered symbols of a data stream to be recovered by a receiver device.

Fig. 11 is a block diagram of an RX antenna processor 1020x that may be used to implement receive processing for the Walsh diversity scheme shown in fig. 5. RX antenna processor 1020x processes the received symbol stream r for one receive antenna_i(n) and may be used for each RX antenna processor 1020a through 1020r in fig. 10.

In the embodiment shown in fig. 11, the received symbol stream r_i(n) is provided to demultiplexer 1110, which will output r_i(N) demultiplexing received symbols into N_BA substream of received symbols (this is denoted as r)₁ToWhere the index i is discarded for simplicity), one sub-stream per sub-band carrying the data stream. Each received symbol substream r_kAnd then provided to respective RX subband processors 1120.

Each RX subband processor 1120 may include multiple receive processing paths, one for each transmit antenna used for data transmission (four receive processing paths are shown in fig. 11 for four transmit antennas). For each processing path, the received symbols in the substream are provided to a multiplier 1122, which may also receive the scaled Walsh functionWhereinIs the complex conjugate of the channel response estimate between the transmit antenna j (associated with the multiplier) and the receive antenna for subband k, and (W)_j ⁴)^*Is the complex conjugate Walsh function assigned to transmit antenna j. Each multiplier 1122 then multiplies the received symbol by the scaled Walsh function and provides the result to a correlation integrator 1124. Integrator 1124 is then aligned over the length of the Walsh function (i.e., four symbol periods)The multiplier result is integrated and the integrated output is provided to summer 1126. One received symbol is provided to multiplier 1122 for each symbol period (i.e., rate (T) — T)_OFDM)^-1) And integrator 1124 provides an integrated output for every 4 symbol periods (i.e., rate ═ 4T)_OFDM)^-1)。

Summer 1126 combines the four outputs from integrators 1124a through 1124d for every 4 symbol periods to provide a recovered symbol for subband kThis is for modulation symbol s transmitted within that subband_kIs estimated. For every 4 symbol periods, the RX subband processors 1120a to 1120f are N_BProviding N for data carrying sub-bands_BA recovered code elementTo

For receive antenna i, multiplier 1140 receives the recovered symbols from RX subband processors 1120a through 1120f and multiplexes the symbols into a stream of recovered symbols

Fig. 12 is a block diagram of an RX subband processor of RX subband processor 1120x that may be used to perform receive processing for the Walsh-STTD schemes shown in fig. 7 and 8. RX subband processor 1120x processes a received symbol substream r for a subband of a receive antenna_kAnd may be used for each of RX subband processors 1120a through 1120f in fig. 11.

In the embodiment shown in fig. 12, the substream r_kThe received symbols in (a) are provided to two receive processing paths, one for each transmit antenna used for data transmission (four for fig. 12)The transmit antenna shows two receive processing paths). For each processing path, the received symbols are provided to a multiplier 1222 that also receives the Walsh function complex conjugate (W) of the transmit antenna pair assigned to the processing of that path_j ²)^*. Each multiplier 1222 then multiplies the received symbol with a Walsh function and provides the result to an associated integrator 1224. Integrator 1224 then integrates the multiplier result over the Walsh function length (i.e., two symbol periods) and provides an integrated output to delay element 1226 and element 1228. One received symbol is provided to multiplier 1222 for each symbol period (i.e., rate (T) — T)_OFDM)^-1) And the integrator provides one integrated output for every 2 symbol periods (i.e., rate ═ 2T)_OFDM)^-1)。

Returning to FIG. 8, for the non-duplicate Walsh-STTD scheme, four modulation symbols s_k1，s_k2，s_k3And s_k4Is sent on four transmit antennas in four symbol periods for subband k (where the index k is used to represent subband k). Code element pair s_k1And s_k2Is transmitted on a first transmit antenna pair, and a symbol pair s_k3And s_k4And transmitting on a second transmitting antenna pair. Each modulation symbol is transmitted in two symbol periods using a2 chip Walsh function assigned to the transmit antenna pair.

Returning to fig. 12, complementary operations are implemented at the receiver to recover the modulation symbols. Integrator 1224 provides the received symbol pairs { r } for every 4 symbol periods corresponding to new symbol pairs transmitted from each transmit antenna pair for subband k_k1And r_k2}. For the first symbol in the pair (i.e., r)_k1) Delay element 1226 then provides a two symbol period delay (i.e., T)_W＝T_OFDMWhich is the length of the Walsh function), and unit 1228 provides the complex conjugate (r) of the second symbol within the pair_k2 ^*)。

The multipliers 1230a through 1230d and summers 1232a and 1232b together then implement the calculation shown in equation (2) for the first transmit antenna pair. In particular, multiplier 1230a multiplies symbol r_k1Multiplying by a channel response estimateMultiplier 1230b multiplies symbol r_k2 ^*Multiplying by a channel response estimateMultiplier 1230c multiplies the symbol r_k1Multiplying by a channel response estimateMultiplier 1230d multiplies symbol r_k2 ^*Multiplying by a channel response estimateWhereinIs the channel response of subband k from transmit antenna j to the receive antenna. Summer 1232a then subtracts the output of multiplier 1230b from the output of multiplier 1230a to provide the pair { s }_k1And s_k2Estimation of the first modulation symbolSummer 1232b adds the output of multiplier 1230c to the output of multiplier 1230d to provide an estimate of the inner second modulation symbol

The second path processing for the second transmit antenna pair is similar to that described for the first path above. However, channel response estimation for the second pair of transmit antennas for subband kAndfor the first timeAnd two processing paths. For every 4 symbol periods, the second processing path is a modulation symbol pair s_k3And s_k4Provide symbol estimatesAnd

for the non-duplicate Walsh-STTD scheme shown in figure 8,andrepresenting four modulation symbols s_k1，s_k2，s_k3And s_k4The four symbols are transmitted on four antennas in subband k in a 4 symbol period. These symbol estimates may be multiplexed into a subband k-recovered symbol substreamIt is then provided to the multiplexer in fig. 11.

For the duplicate Walsh-STTD scheme shown in FIG. 7, one symbol pair s is transmitted on two transmit antenna pairs in subband k in every 4 symbol periods_k1And s_k2}. Symbol estimationAndmay be combined by a summer (not shown in fig. 2) to provide an estimate of the first symbol within a pair, and the symbol estimatesAndmay likewise be combined by another summer to provide an estimate of the second symbol within the pair. The symbol estimates from the two summers may be multiplexed into a recovered symbol substream for subband kIt is then provided to multiplexer 1140 in fig. 11.

For clarity, various details are specifically described for downlink data transmission from the access point to the terminal. The techniques described herein may also be used for the uplink, and this is within the scope of the invention. For example, the processing schemes shown in fig. 4, 5, 6, 7, and 8 may be implemented in a multi-antenna terminal for uplink data transmission.

The MIMO OFDM systems described herein may also be designed to implement one or more multiple access schemes, such as Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), and the like. CDMA may provide advantages over other types of systems, such as increased system capacity. The MIMO OFDM system may also be designed to implement various processing techniques described in CDMA standards, such as IS-95, CDMA2000, IS-856, W-CDMA, and so on.

The techniques described herein for transmitting and receiving data using multiple diversity transmission modes may be implemented in various ways. For example, these techniques may be implemented in hardware, software, or a combination thereof. For a hardware implementation, the elements used to implement any one or a combination of the techniques (e.g., TX diversity processor, RX diversity processor, TX subband processor, RX antenna processor, RX subband processor, etc.) may be implemented in the following elements: one or more Application Specific Integrated Circuits (ASICs), Digital Signal Processors (DSPs), Digital Signal Processing Devices (DSPDs), Programmable Logic Devices (PLDs), Field Programmable Gate Arrays (FPGAs), processors, controllers, micro-controllers, microprocessors, other electronic units designed to perform the functions described herein, or a combination thereof.

For a software implementation, any one or combination of the techniques may be implemented with modules (e.g., procedures, functions, and so on) that perform the functions described herein. The software codes may reside in memory units (e.g., memory 232 and 272 in fig. 2) and executed by processors (e.g., controllers 230 and 270). The memory unit may be implemented within the processor or external to the processor, in which case it can be communicatively coupled to the processor via various means as is known in the art.

Headings are included herein for reference and to help locate the sections. These headings are not intended to limit the concepts described below and these concepts may apply to other subsections of the entire specification.

The previous description of the preferred embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without the use of the inventive faculty. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (75)

1. A method for processing data for transmission within a wireless communication device, comprising:

selecting a diversity transmission mode from a plurality of diversity transmission modes, wherein the plurality of diversity transmission modes includes a space-time transmission diversity mode, wherein space-time transmission diversity is used to transmit a first pair of transmission symbols using a first pair of antennas and to transmit a second pair of transmission symbols using a second pair of antennas, wherein the first pair of antennas is different from the second pair of antennas;

encoding and modulating at least one data stream to provide first and second pairs of modulation symbols; and

processing the first pair of modulation symbols based on a space-time diversity transmission mode to provide a first pair of transmission symbols transmitted on the first pair of antennas, and processing the second pair of modulation symbols based on a space-time diversity mode to provide a second pair of transmission symbols transmitted on the second pair of antennas.

2. The method of claim 1, wherein the first pair of modulation symbols and the second pair of modulation symbols are transmitted on different subbands.

3. The method of claim 1, wherein at least one symbol of the first pair of modulation symbols and the second pair of modulation symbols is the same modulation symbol.

4. The method of claim 1, wherein the plurality of diversity transmission modes further comprises a frequency diversity transmission mode.

5. The method of claim 1, wherein the plurality of diversity transmission modes further comprises a Walsh diversity transmission mode.

6. The method of claim 1, wherein the at least one data stream corresponds to an overhead channel.

7. The method of claim 1, wherein selecting a diversity transmission mode comprises selecting based on a type of the at least one data stream.

8. The method of claim 1, wherein selecting the diversity transmission mode comprises selecting based on a type of terminal received for one of the first pair of modulation symbols and the second pair of modulation symbols.

9. The method of claim 1, wherein selecting the diversity transmission mode comprises selecting based on a hybrid terminal type for communicating with the access point.

10. The method of claim 1, wherein selecting a diversity transmission mode comprises selecting one of a plurality of diversity transmission modes or a spatial multiplexing mode.

11. The method of claim 10, wherein selecting a diversity transmission mode comprises selecting based on channel information.

12. The method of claim 1, further comprising multiplexing pilot symbols with modulation symbols.

13. The method of claim 1, wherein the encoding comprises using turbo codes.

14. The method of claim 1, wherein encoding comprises using a convolutional code.

15. A transmitter unit within a wireless communication system, comprising:

a controller configured to select a diversity transmission mode from a plurality of diversity transmission modes, wherein the plurality of diversity transmission modes includes a space-time transmission diversity mode, wherein space-time transmission diversity is used to transmit a first pair of transmission symbols using a first pair of antennas and to transmit a second pair of transmission symbols using a second pair of antennas, wherein the first pair of antennas is different from the second pair of antennas;

a processor configured to encode and modulate at least one data stream to provide first and second pairs of modulation symbols; and

another processor configured to process the first pair of modulation symbols based on a space-time diversity transmission mode to provide a first pair of transmission symbols transmitted on the first pair of antennas, and process the second pair of modulation symbols based on a space-time diversity mode to provide a second pair of transmission symbols transmitted on the second pair of antennas.

16. The apparatus of claim 15, wherein the first pair of modulation symbols and the second pair of modulation symbols are transmitted on different subbands.

17. The apparatus of claim 15, wherein at least one symbol of the first pair of modulation symbols and the second pair of modulation symbols is a same modulation symbol.

18. The apparatus of claim 15, wherein the plurality of diversity transmission modes further comprises a frequency diversity transmission mode.

19. The apparatus of claim 15, wherein the plurality of diversity transmission modes further comprises a Walsh diversity transmission mode.

20. The apparatus of claim 15, wherein the at least one data stream corresponds to an overhead channel.

21. The apparatus of claim 15, wherein the controller is configured to select based on a type of the at least one data stream.

22. The apparatus of claim 15, wherein the controller is configured to select based on a type of terminal received for one of the first pair of modulation symbols and the second pair of modulation symbols.

23. The apparatus of claim 15, wherein the controller is configured to select based on a mix of terminal types communicating with an access point.

24. The apparatus of claim 15, wherein the controller is configured to select one of a plurality of diversity transmission modes or a spatial multiplexing mode.

25. The apparatus of claim 24, wherein the controller is configured to select based on channel information.

26. An apparatus, comprising:

means for selecting a diversity transmission mode from a plurality of diversity transmission modes, wherein the plurality of diversity transmission modes includes a space-time transmission diversity mode, wherein space-time transmission diversity is used to transmit a first pair of transmission symbols using a first pair of antennas and to transmit a second pair of transmission symbols using a second pair of antennas, wherein the first pair of antennas is different from the second pair of antennas;

a processor configured to encode and modulate at least one data stream to provide first and second pairs of modulation symbols; and

means for processing the first pair of modulation symbols based on a space-time diversity transmission mode to provide a first pair of transmission symbols transmitted on the first pair of antennas, and processing the second pair of modulation symbols based on a space-time diversity mode to provide a second pair of transmission symbols transmitted on the second pair of antennas.

27. The apparatus of claim 26, wherein the first pair of modulation symbols and the second pair of modulation symbols are transmitted on different subbands.

28. The apparatus of claim 26, wherein at least one symbol of the first pair of modulation symbols and the second pair of modulation symbols is the same modulation symbol.

29. The apparatus of claim 26, wherein the plurality of diversity transmission modes further comprises a frequency diversity transmission mode.

30. The apparatus of claim 26, wherein the at least one data stream corresponds to an overhead channel.

31. The apparatus of claim 26, wherein the means for selecting comprises means for selecting based on a type of the at least one data stream.

32. The apparatus of claim 26, wherein the means for selecting comprises means for selecting based on a type of terminal received for one of the first pair of modulation symbols and the second pair of modulation symbols.

33. The apparatus of claim 26, wherein the means for selecting comprises means for selecting based on a mixed terminal type for communicating with the access point.

34. The apparatus of claim 26, wherein the means for selecting comprises means for selecting one of a plurality of diversity transmission modes or a spatial multiplexing mode.

35. The apparatus of claim 34, wherein the means for selecting comprises means for selecting based on channel information.

36. A method for processing data for transmission from a wireless communication device, comprising:

providing two pairs of modulation symbols;

processing each pair of modulation symbols according to a space-time diversity transmission mode to provide a first pair of transmission symbols from the two pairs of modulation symbols and a second pair of transmission symbols from the two pairs of modulation symbols; and

providing the first pair of transmission symbols for transmission using a first pair of antennas, and providing the second pair of transmission symbols for transmission using a second pair of antennas, wherein the first pair of antennas is different from the second pair of antennas.

37. The method of claim 36, wherein the first pair of transmission symbols and the second pair of transmission symbols are transmitted on different subbands.

38. The method of claim 36, wherein the two pairs of modulation symbols correspond to overhead channels.

39. The method of claim 36, wherein providing two pairs of modulation symbols comprises encoding using a turbo code.

40. The method of claim 36, wherein providing two pairs of modulation symbols comprises using a convolutional code.

41. The method of claim 36, wherein processing comprises processing a first pair of the two pairs of modulation symbols to form a first pair of transmission symbols and processing a second pair of the two pairs of modulation symbols to form a second pair of transmission symbols.

42. The method of claim 41, wherein at least one symbol of the first pair of modulation symbols and the second pair of modulation symbols is the same modulation symbol.

43. A wireless communication device, comprising:

a first processor configured to provide two pairs of modulation symbols; and

a second processor configured to process each pair of modulation symbols according to a space-time diversity transmission mode to provide a first pair of transmission symbols from the two pairs of modulation symbols and a second pair of transmission symbols from the two pairs of modulation symbols and to provide the first pair of transmission symbols for transmission using a first pair of antennas and the second pair of transmission symbols for transmission using a second pair of antennas, wherein the first pair of antennas is different from the second pair of antennas.

44. The apparatus of claim 43, further comprising a controller configured to transmit the first pair of transmission symbols and the second pair of transmission symbols on different subbands.

45. The apparatus of claim 43, wherein the two pairs of modulation symbols correspond to overhead channels.

46. The apparatus of claim 43, wherein the first processor is configured to provide the two pairs of modulation symbols using a turbo code.

47. The apparatus of claim 43, wherein the first processor is configured to provide the two pairs of modulation symbols using a convolutional code.

48. The apparatus of claim 43, wherein the second processing is configured to process a first pair of the second pair of modulation symbols to form a first pair of transmission symbols, and to process a second pair of the two pairs of modulation symbols to form a second pair of transmission symbols.

49. The apparatus of claim 48, wherein at least one symbol of the first pair of modulation symbols and the second pair of modulation symbols is the same modulation symbol.

50. An apparatus for processing data for transmission from a wireless communication device, comprising:

means for providing two pairs of modulation symbols;

means for providing a first pair of transmission symbols from the two pairs of modulation symbols and a second pair of transmission symbols from the two pairs of modulation symbols using a space-time diversity transmission mode; and

means for providing the first pair of transmission symbols for transmission using a first pair of antennas, and providing the second pair of transmission symbols for transmission using a second pair of antennas, wherein the first pair of antennas is different from the second pair of antennas.

51. The apparatus of claim 36, wherein the first pair of transmission symbols and the second pair of transmission symbols are transmitted on different subbands.

52. The apparatus of claim 36, wherein the two pairs of modulation symbols correspond to overhead channels.

53. The apparatus of claim 36, wherein the means for using a space-time diversity transmission mode comprises processing a first pair of the two pairs of modulation symbols to form a first pair of transmission symbols, and processing a second pair of the two pairs of modulation symbols to form a second pair of transmission symbols.

54. The apparatus of claim 44, wherein at least one symbol of the first pair of modulation symbols and the second pair of modulation symbols is the same modulation symbol.

55. A method for processing data for transmission from a wireless communication device, comprising:

selecting a space-time transmission diversity mode for transmitting a first pair of transmission symbols using a first pair of antennas and for transmitting a second pair of transmission symbols using a second pair of antennas, wherein the first pair of antennas is different from the second pair of antennas;

encoding and modulating at least one data stream to provide first and second pairs of modulation symbols; and

processing the first pair of modulation symbols based on a space-time diversity transmission mode to provide a first pair of transmission symbols transmitted on the first pair of antennas, and processing the second pair of modulation symbols based on a space-time diversity mode to provide a second pair of transmission symbols transmitted on the second pair of antennas.

56. The method of claim 55, wherein the first pair of modulation symbols and the second pair of modulation symbols are transmitted on different subbands.

57. The method of claim 55, wherein at least one symbol of the first pair of modulation symbols and the second pair of modulation symbols is the same modulation symbol.

58. The method of claim 55, wherein the at least one data stream corresponds to an overhead channel.

59. The method of claim 55, further comprising multiplexing pilot symbols with modulation symbols.

60. The method of claim 55 wherein the encoding comprises using turbo codes.

61. The method of claim 55 wherein the encoding comprises using a convolutional code.

62. A transmitter unit in a wireless communication system, comprising:

a controller configured to select a space-time transmission diversity mode for transmitting a first pair of transmission symbols using a first pair of antennas and for transmitting a second pair of transmission symbols using a second pair of antennas, wherein the first pair of antennas is different from the second pair of antennas;

a processor configured to encode and modulate at least one data stream to provide first and second pairs of modulation symbols; and

another processor configured to process the first pair of modulation symbols based on a space-time diversity transmission mode to provide a first pair of transmission symbols transmitted on the first pair of antennas, and process the second pair of modulation symbols based on a space-time diversity mode to provide a second pair of transmission symbols transmitted on the second pair of antennas.

63. The transmitter unit of claim 62, wherein the first pair of modulation symbols and the second pair of modulation symbols are transmitted on different subbands.

64. The transmitter unit of claim 62, wherein at least one symbol of the first pair of modulation symbols and the second pair of modulation symbols is a same modulation symbol.

65. The transmitter unit of claim 62, wherein the at least one data stream corresponds to an overhead channel.

66. The transmitter unit of claim 62, further comprising a multiplexer configured to multiplex pilot symbols with modulation symbols.

67. The transmitter unit of claim 62, wherein the processor configured to encode is further configured to encode using a turbo code.

68. The transmitter unit of claim 62, wherein the processor configured to encode is further configured to encode using a convolutional code.

69. An apparatus, comprising:

means for selecting a space-time transmission diversity mode for transmitting a first pair of transmission symbols using a first pair of antennas and for transmitting a second pair of transmission symbols using a second pair of antennas, wherein the first pair of antennas is different from the second pair of antennas;

means for encoding and modulating at least one data stream to provide first and second pairs of modulation symbols; and

means for processing the first pair of modulation symbols based on a space-time diversity transmission mode to provide a first pair of transmission symbols transmitted on the first pair of antennas, and processing the second pair of modulation symbols based on a space-time diversity mode to provide a second pair of transmission symbols transmitted on the second pair of antennas.

70. The apparatus of claim 69, wherein the first pair of modulation symbols and the second pair of modulation symbols are transmitted on different subbands.

71. The apparatus of claim 69, wherein at least one symbol of the first pair of modulation symbols and the second pair of modulation symbols is the same modulation symbol.

72. The apparatus of claim 69, wherein the at least one data stream corresponds to an overhead channel.

73. The apparatus of claim 69, further comprising means for multiplexing pilot symbols with modulation symbols.

74. The apparatus of claim 69, wherein the means for encoding comprises means for encoding using a turbo code.

75. The apparatus of claim 69, wherein the means for encoding comprises means for encoding using a convolutional code.