Spatial spreading with space-time and space-frequency transmit diversity schemes for a wireless communication system

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Description

BACKGROUND

II. Field [0001] The present disclosure relates generally to communication, and more specificallyto techniques fortransmitting data in a multiple-antenna communication system.

Ili. Background [0002] A multi-antenna communication system employs multiple (N_T) transmit antennas and one or more (N_R) récéivé antennas fór data transmission. The N_T transmit antennas may be used to increase system throughput by transmitting different data from the antennas or to improve reliability by transmitting data redundantly.

[0003] In the multi-antenna communication system, a propagation path exists between each pair of transmit and récéivé antennas. N_TN_R different propagation paths are formed between the N_T transmit antennas and the N_R récéivé antennas. These propagation paths may experience different channel conditions (e.g., different fading, multipath, and interference effects) and may achieve different signal-to-noise-and-interference ratios (SNRs). The channel responses ofthe N_tN_r propagation paths may thus vary from path to path, and may further vary over time fór a time-variantwireless channel and across frequency fór a dispersive wireless channel. The variant natúré of the propagation paths makes it challenging to transmit data in an efficient and reliable manner.

[0004] Transmit diversity refers to redundant transmission of data across space, frequency, time, or a combination of these dimensions to improve reliability fór the data transmission. One goal of transmit diversity is to maximize diversity fór the data transmission across as many dimensions as possible to achieve robust performance. Another goal is to simplify the Processing fór transmit diversity at both a transmitter and a receiver.

[0005] There is therefore a need in the art fór techniques to transmit data with transmit diversity in a multi-antenna communication system.

[0006] US 2004/0136349 (A1) discloses a ΜΙΜΟ system which supports multiple spatial multiplexing modes fór improved performance and greater flexibility. These modes may include (1) a single-user steered mode that transmits multiple data streams on orthogonal spatial channels to a single receiver, (2) a single-user non-steered mode that transmits multiple data streams from multiple antennas to a single receiver without spatial Processing at a transmitter, (3) a multi-user steered mode that transmits multiple data streams simultaneously to multiple receivers with spatial Processing at a transmitter, and (4) a multi-user non-steered mode that transmits multiple data streams from multiple antennas (co-located or non co-located) without spatial Processing at the transmitter(s) to receiver(s) having multiple antennas. Fór each set of user terminal(s) selected fór data transmission on the downlink and/or uplink, a spatial multiplexing mode is selected fór the user terminál set from among the multiple spatial multiplexing modes supported by the system.

[0007] US 2004/0146018 (A1) discloses a user terminál which supports multiple spatial multiplexing (SM) modes such as a steered mode and a non-steered mode. Fór data transmission, multiple data streams are coded and modulated in accordance with their selected rates to obtain multiple data Symbol streams. These streams are then spatially processed in accordance with a selected SM mode (e.g, with a mátrix of steering vectors fór the steered mode and with the identity mátrix fór the non-steered mode) to obtain multiple transmit Symbol streams fór transmission from multiple antennas. Fór data reception, multiple received symbol streams are spatially processed in accordance with the selected SM mode (e.g, with a mátrix of eigenvectors fór the steered mode and with a spatial filter mátrix fór the non-steered mode) to obtain multiple recovered data symbol streams. These streams are demodulated and decoded in accordance with their selected rates to obtain multiple decoded data streams.

SUMMARY [0008] Techniques fór transmitting data using a combination of transmit diversity schemes are described herein. These transmit diversity schemes include spatial spreading, continuous beamforming, cyclic delay diversity, space-time transmit diversity (STTD), space-frequency transmit diversity (SFTD), and orthogonal transmit diversity (OTD), all of which are described below. The invention is defined in the independent claims.

[0009] In an embodiment, a transmitting entity processes (e.g, encodes, interleaves, and symbol maps) one or more (N_d) data streams to generate N_D data symbol streams. The transmitting entity further processes the N_D data symbol streams based on a transmit diversity scheme (e.g, STTD, SFTD, or OTD) to generate multiple (N_c) coded symbol streams. Each data symbol stream may be sent as a single coded symbol stream or as multiple (e.g, two) coded symbol streams using STTD, SFTD, or OTD. The transmitting entity may perform spatial spreading on the N_c coded symbol

ΕΡ 1 790 089 Β1 streams with different matrices to generate multiple (N_T) transmit Symbol streams fór transmission from N_T antennas. Additionally or alternatively, the transmitting entity may perform continuous beamforming on the N_T transmit symbol streams in either the time domain or the frequency domain. A receiving entity performs the complementary Processing to recover the N_D data streams.

[0010] Various aspects and embodiments ofthe invention are described in further detail below.

BRIEF DESCRIPTION OF THE DRAWINGS [0011]

FIG. 1 shows a block diagram of a multi-antenna transmitting entity.

FIG. 2 shows a block diagram of a transmit (TX) data processor, a TX STTD processor, and a spatial spreader at the transmitting entity.

FIG. 3 shows a block diagram of N_T modulators at the transmitting entity.

FIG. 4 shows a block diagram of a single-antenna receiving entity and a multi-antenna receiving entity.

DETAILED DESCRIPTION [0012] The word exemplary is used herein to mean serving asan example, instance, orillustration. Any embodiment described herein as exemplary is nőt necessarily to beconstrued as preferredoradvantageousover other embodiments. [0013] The transmission techniques described herein may be used fór multiple-inputsingle-output(M ISO) and multipleinput multiple-output (ΜΙΜΟ) transmissions. A MISO transmission utilizes multiple transmit antennas and a single récéivé antenna. A ΜΙΜΟ transmission utilizes multiple transmit antennas and multiple récéivé antennas.

[0014] The transmission techniques may be used fór single-carrier and multi-carrier communication systems. A multicarrier system may utilize orthogonal frequency division multiplexing (OFDM), somé other multi-carrier modulation scheme, orsome other construct. OFDM effectively partitions the overall system bandwidth intő multiple (N_F) orthogonal frequency subbands, which are alsó called tones, subcarriers, bins, frequency channels, and so on. With OFDM, each subband is associated with a respective subcarrier that may be modulated with data. A single-carrier system may utilize single-carrier frequency division multiple access (SC-FDMA), code division multiple access (CDMA), or somé other single-carrier modulation scheme. An SC-FDMA system may utilize (1) interleaved FDMA (IFDMA) to transmit data and pilot on subbands that are distributed across the overall system bandwidth (2) localized FDMA (LFDMA) to transmit data and pilot on a group of adjacent subbands, or (3) enhanced FDMA(EFDMA) to transmit data and pilot on multiple groups of adjacent subbands. In generál, modulation symbols are sent in the time domain with SC-FDMA (e.g., IFDMA, LFDMA, and EFDMA) and in the frequency domain with OFDM. Fór clarity, much ofthe description below is fór a system that utilizes OFDM, with all N_F subbands being available fór transmission.

[0015] Transmit diversity may be achieved using various schemes including STTD, SFTD, OTD, spatial spreading, continuous beamforming, and so on. STTD transmits a pair of data symbols from two antennas on one subband in two symbol periods to achieve space and time diversity. SFTD transmits a pair of data symbols from two antennas on two subbands in one symbol period to achieve space and frequency diversity. OTD transmits multiple (N_o) data symbols from N_o antennas on one subband in N_o symbol periods using No orthogonal codes to achieve space and time diversity, where N_o > 2. As used herein, a data symbol is a modulation symbol fór traffic/packet data, a pilot symbol is a modulation symbol fór pilot (which is data that is known a priori by both the transmitting and receiving entities), a modulation symbol is a complex value fór a point in a signal constellation fór a modulation scheme (e.g., M-PSK or M-QAM), a transmission symbol (e.g., an OFDM symbol) is a sequence of time-domain samples generated by a single-carrier or multi-carrier modulation scheme fór one symbol period, and a symbol is typically a complex value.

[0016] Spatial spreading refersto the transmission of a symbol from multipletransmitantennassimultaneously, possibly with different amplitudes and/or phases determined by a steering vector used fór that symbol. Spatial spreading may alsó be called steering diversity, transmit steering, pseudo-random transmit steering, space-time scrambling, r and so on. Spatial spreading may be used in combination with STTD, SFTD, OTD, and/or continuous beamforming to improve performance and/or to extend the normál operation of these transmit diversity schemes. Fór example, STTD normally transmits one data symbol stream from two antennas. Spatial spreading may be used with STTD to transmit more than one data symbol stream from more than two antennas simultaneously.

[0017] Continuous beamforming refers to the use of different beams across the N_F subbands. The beamforming is continuous in that the beams change in a gradual instead of abrupt manner across the subbands. Continuous beamforming may be performed in the frequency domain by multiplying the symbols fór each subband with a beamforming mátrix fór that subband. Continuous beamforming may alsó be performed in the time domain by applying different cyclic delays fór different transmit antennas. Time-domain continuous beamforming is alsó called cyclic delay diversity. [0018] Transmit diversity may be achieved using a combination of transmit diversity schemes. Fór example, transmit

ΕΡ 1 790 089 Β1 diversity may be achieved using a combination of STTD, SFTD or OTD with either spatial spreading or continuous beamforming. As another example, transmit diversity may be achieved using a combination of STTD, SFTD, or OTD with both spatial spreading and cyclic delay diversity. Fór clarity, much ofthe following description assumes the use of

STTD.

[0019] FIG. 1 shows a block diagram of an embodiment of a multi-antenna transmitting entity 110, which may be part of an access point or a user terminál. An access point may alsó be called a base station, a base transceiver system, or somé otherterminology. A user term inai may alsó be called a mobile station, a wirelessdevice.or somé other terminology. [0020] Forthe embodiment shown in FIG. 1, transmitting entity 110 may use a combination of STTD, spatial spreading, and continuous beamforming fór data transmission. A TX data processor 112 receives and processes N_D data streams and provides N_Ddata Symbol streams, where N_D> 1. TXdata processor 112 may process each data stream independently or may jointly process multiple data streams together. Fór example, TX data processor 112 may formát, scramble, encode, interleave, and Symbol map each data stream in accordance with a coding and modulation scheme selected fór that data stream. A TX STTD processor 120 receives the N_D data Symbol streams, performs STTD encoding on zero, one, or multiple data symbol streams, and provides N_c coded symbol streams, where N_c > N_D. In generál, TX STTD processor 120 may process any number of data symbol streams with STTD, SFTD, OTD, or somé other transmit diversity scheme. Each data symbol stream may be sent as one coded symbol stream or multiple coded symbol streams, as described below.

[0021] A spatial spreader 130 receives and multiplexes the coded symbols with pilotsymbols, performs spatial spreading by multiplying the coded symbols and pilotsymbols with different steering matrices, and provides N_T transmit symbol streams fór the N_T transmit antennas, where N_T > N_c. Each transmit symbol is a complex value to be sent from one transmit antenna on one subband in one symbol period. N_T modulators (MÓD) 132a through 132nt récéivé the N_Ttransmit symbol streams. Foran OFDM-based system, each modulátor 132 performs OFDM modulation on its transmit symbol stream and provides a stream of time-domain samples. Each modulátor 132 may alsó apply a different cyclic delay fór its antenna, as described below. N_T modulators 132a through 132nt provide N_T sample streams to N_Ttransmitter units (TMTR) 134a through 134nt, respectively. Each transmitter unit 134 conditions (e.g., converts to analóg, amplifies, filters, and frequency upconverts) its sample stream and generates a modulated signal. N_T modulated signals from N_Ttransmitter units 134a through 134nt are transmitted from N_T transmit antennas 136a through 136nt, respectively. [0022] Controller 140 Controls the operation at transmitting entity 110. Memory 142 Stores data and/or program codes fór transmitting entity 110.

[0023] Transmitting entity 110 may transmit any number of data symbol streams with STTD and any number of data symbol streams without STTD, dependingon the num bér of transmit and récéivé antennas available fór data transmission. The STTD encoding fór one data symbol stream may be performed as follows. Fór each pair of data symbols s_a and s_b to be sent in two symbol periods, TX STTD processor 120 generates two vectors s₁ = [s_a s_b] ^rand s₂ = [s_b - S¹*] ^T , where * denotes the complex conjugate and Τ' denotes the transpose. Alternatively, TX STTD processor 120 may generate two vectors Sj = [s_a - S_b] ^T and s2 = [.Sb ] ^T fór the pair of data symbols sa and s_b. Fór both STTD encoding schemes, each vector Sj, fór t = 1,2, includes two coded symbols to be sent from N_T transmit antennas in one symbol period, where N_T > 2. Vector s₁ is sent in the first symbol period, and vector s₂ is sent in the next symbol period. Each data symbol is included in both vectors and is thus sent in two symbol periods. The m-th coded symbol stream is formed by the m-th element of the two vectors s₁ and s₂. Fór clarity, the following description is fór the STTD encoding scheme with s₁ = [s_a s_b]^rand S₂ = [s_b -5_a]^T. Fór this STTD encoding scheme, the first coded symbol stream * * includes coded symbols s_a and s_b , and the second coded symbol stream includes coded symbols s_b and - $ . [0024] Table 1 listsfour configurations that may be used fór data transmission. An N_D X N_c configuration denotes the transmission of N_D data symbol streams as N_c coded symbol streams, where N_D > 1 and N_c > N_D. The first column identifies the four configurations. Fór each configuration, the second column indicates the number of data symbol streams being sent, and the third column indicates the number of coded symbol streams. The fourth column lists the N_D data symbol streams fór each configuration, the fifth column lists the coded symbol stream(s) fór each data symbol stream, the sixth column gives the coded symbol to be sent in the first symbol period (f = 1) fór each coded symbol stream, and the seventh column gives the coded symbol to be sent in the second symbol period (f = 2) fór each coded symbol stream. The number of data symbols sent in each 2-symbol interval is equal to twice the number of data symbol streams, or 2N_d. The eighth column indicates the number of transmit antennas required fór each configuration, and the ninth column indicates the number of récéivé antennas required fór each configuration.

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Table 1

<td> Config</td><td> Num Data Symbol Streams N_d</td><td> Num Coded Symbol Streams N_c</td><td> Data Symbol Stream</td><td> Coded Symbol Stream</td><td> Coded Symbol (f = 1) 21</td><td> Coded Symbol (f = 2) S2</td><td> Req NumTX Ants N_T</td><td> Req Num RX Ants ⁿr</td>

<td rowspan="2"> 1X2</td><td rowspan="2"> 1</td><td rowspan="2"> 2</td><td rowspan="2"> 1</td><td> 1</td><td>^sa</td><td> * Sb</td><td rowspan="2"> N_T &gt; 2</td><td rowspan="2"> N_r&gt;1</td>

<td> 2</td><td>^sb</td><td> * -S_a</td>

<td colspan="9"></td>

<td rowspan="3"> 2X3</td><td rowspan="3"> 2</td><td rowspan="3"> 3</td><td rowspan="2"> 1</td><td> 1</td><td>^sa</td><td> * Sb</td><td rowspan="3"> N_T&gt; 3</td><td rowspan="3"> Nr&gt;2</td>

<td> 2</td><td>^sb</td><td> *</td>

<td> 2</td><td> 3</td><td>^sc</td><td> * Sd</td>

<td colspan="9"></td>

<td rowspan="4"> 2X4</td><td rowspan="4"> 2</td><td rowspan="4"> 4</td><td rowspan="2"> 1</td><td> 1</td><td>^sa</td><td> * Sb</td><td rowspan="4"> N_T &gt; 4</td><td rowspan="4"> N_r&gt;2</td>

<td> 2</td><td>^sb</td><td> *</td>

<td rowspan="2"> 2</td><td> 3</td><td>^sc</td><td> * Sd</td>

<td> 4</td><td>^sd</td><td> * ’S_C</td>

<td colspan="9"></td>

<td rowspan="4"> 3X4</td><td rowspan="4"> 3</td><td rowspan="4"> 4</td><td rowspan="2"> 1</td><td> 1</td><td>^sa</td><td> * S_b</td><td rowspan="4"> N_T &gt; 4</td><td rowspan="4"> N_r&gt;3</td>

<td> 2</td><td>^sb</td><td> * ~ s_a</td>

<td> 2</td><td> 3</td><td>^sc</td><td> * S_d</td>

<td> 3</td><td> 4</td><td>^se</td><td> # Sf</td>

[0025] As shown in Table 1, a data Symbol stream may be sent as two coded Symbol streams with STTD orone coded Symbol stream without STTD. Fór the embodiment shown in Table 1, fór each data Symbol stream sent without STTD, the data Symbol sent in the second Symbol period (f = 2) is conjugated to match the conjugation performed on the data Symbol stream(s) sent with STTD.

[0026] Fór the 1X2 configuration, one data Symbol stream is STTD encoded to generate two coded Symbol streams.

τ Γ * * -» T

Fór each 2-symbol interval, vectors s₁ = [s_a s_b]' and S₂ = Lfo ^aJ ^are 9^enerat^ed with data symbols s_a and s_b. Vector s₁ is transmitted from at least two transmit antennas in the first Symbol period, and vector s₂ is transmitted from the same antennas in the second Symbol period. A receiving entity uses at least one récéivé antenna to recover the data Symbol stream.

[0027] Fór the 2X3 configuration, two data Symbol streams are sent as three coded Symbol streams. The first data symbol stream is STTD encoded to generate two coded symbol streams. The second data symbol stream is sent without STTD as the third coded Symbol stream. Fór each 2-symbol interval, vectors s₁ = [s_a s_b s_c]^rand S2 =[sb -5 íd]^Tare generated with data symbols sa, s_b, s_c and s_d, where s_a and s_b are from the first data symbol stream, and s_c and s_dare from the second data symbol stream. Vector s₁ is transmitted from at least three transmit antennas in the first symbol period, and vector s₂ is transmitted from the same antennas in the second symbol period. A receiving entity uses at least two récéivé antennas to recover the two data symbol streams.

[0028] Fór the 2X4 configuration, two data symbol streams are sent asfour coded symbol streams. Each data symbol

EP 1 790 089 Β1 stream is STTD encoded to generate two coded Symbol streams. Fór each 2-symbol interval, vectors s₁ = [s_a s_b s_c s_d] ¹ and s₂ — |_£_b -J_a 5_d -5_CJ are generated with data symbols s_a, s_b, s_c and s_d, where s_a and s_b are from the first data Symbol stream, and s_c and s_d are from the second data Symbol stream. Vector s₁ is transmitted from at least four transmit antennas in the first Symbol period, and vector s₂ is transmitted from the same antennas in the second Symbol period. A receiving entity uses at least two récéivé antennas to recover the two data Symbol streams.

[0029] Fór the 3X4 configuration, three data symbol streams are sent as four coded symbol streams. The first data Symbol stream is STTD encoded to generate two coded symbol streams. The second data symbol stream is sent without STTD as the third coded symbol stream, and the third data symbol stream is sent without STTD as the fourth coded symbol stream. Fór each 2-symbol interval, vectors s₁ = [s_a s_b s_c s_e]' and S₂ = -í 5_d S_{ J are generated with data symbols s_a, s_b, s_c, s_d, s_e and s_f, where s_a and s_b are from the first data symbol stream, s_c and s_d are from the second data symbol stream, and s_e and s_f are from the third data symbol stream. Vector s₁ is transmitted from at least four transmit antennas in the first symbol period, and vector s₂ is transmitted from the same antennas in the second symbol period. A receiving entity uses at least three récéivé antennas to recover the three data symbol streams. [0030] Table 1 shows four exemplary configurations that may be used fór data transmission, with each configuration having at least one data symbol stream sent with STTD. Other configurations may alsó be used fór data transmission. A configuration may alsó use a combination of STTD, SFTD, and OTD.

[0031] In generál, any number of data symbol streams may be sent as any number of coded symbol streams from any number of transmit antennas, where N_D &gt; 1, N_c &gt; N_D, N_T &gt; N_c, and N_R &gt; N_D. Each data symbol stream may or may nőt be encoded with STTD, SFTD, OTD, or somé other transmit diversity scheme. Each data symbol stream may be sent as one coded symbol stream or multiple (e.g., two) coded symbol streams.

[0032] The transmitting entity may process the coded symbols fór spatial spreading and continuous beamforming, as follows:

xXfc) = B(fc)-V(fc)-G(fc)-s,(fc) , fór í = l, 2, Eq(l) where s_t(k) is an N_c X 1 vector with N_c coded symbols to be sent on subband k in symbol period t;

G(/r) is an N_c X N_c diagonal mátrix with N_c gain values along the diagonal fór the N_c coded symbols in s_t(k'f and zeros elsewhere;

V(/c) is an Ν_τ X N_c steering mátrix fór spatial spreading fór subband k\

B(/r) is an Ν_τ X N_T diagonal mátrix fór continuous beamforming fór subband k\ and x_f(/r) is an N_T X1 vector with N_T transmit symbols to be sent from the N_T transmit antennas on subband k in symbol period t.

[0033] Vector s₁ contains N_c coded symbols to be sent in the first symbol period, and vector s₂ contains N_c coded symbols to be sent in the second symbol period. Vectors s₁ and s₂ may be formed as shown in Table 1 fór the four configurations in the table.

[0034] Gain mátrix G(/r) determines the amount of transmit power to use fór each of the N_c coded symbol streams. The gain mátrix may be a function of subband index k, as shown in equation (1), or may be a function that is independent of index k. The totál transmit power available fór transmission may be denoted as Ptotal- '^{n an} ernbodiment, equal transmit power is used fór the N_c coded symbol streams, and the diagonal elements of G(/c) have the same valueof-^P_total / N_c . In another embodiment, equal transmit power is used fór the N_D data symbol streams, and the N_c gain values along the diagonal of G(/c) are defined to achieve equal transmit power fór the N_D data symbol streams. The N_c gain values may or may nőt be equal depending on the configuration. As an example, fór the 2X3 configuration, the first data symbol stream is sent as two coded symbol streams and the second data symbol stream is sent as one coded symbol stream. To achieve equal transmit power fór the two data symbol streams, a 3X3 gain mátrix G(/c) may include gain values of V^total / 4 , -y/P_tota] / 4 ’ ^ar|d y/^total / along the diagonal fór the three coded symbol streams. Each coded symbol in the third coded symbol stream is then scaled by -^P_totel /2 and is transmitted with twice the power as the other two coded symbols sent in the same symbol period. Fór both embodiments, the N_c coded symbols fór each symbol period may be scaled to utilize the maximum transmit power available fór each transmit antenna. In generál, the diagonal elements of G(/c) may be selected to utilize any amounts of transmit power fór the N_c coded symbol streams and to

ΕΡ 1 790 089 Β1 achieve any desired SNRs fór the N_D data symbol streams. The power scaling fór the N_c coded symbol streams may alsó be achieved by scaling the columns of the steering mátrix V(A) with appropriate gains.

[0035] A given data symbol stream (which is denoted as {s}) may be sent as one coded symbol stream (which is denoted as {s}) in various manners. In one embodiment, the gain mátrix G(k) contains ones along the diagonal, and coded symbol stream {s} is transmitted at the same power level as other coded symbol streams. Fór this embodiment, data symbol stream {s} is transmitted at lower transmit power than an STTD encoded data symbol stream and hence achieves a lower received SNR at the receiving entity. The coding and modulation fór data symbol stream {s} may be selected to achieve the desired performance, e.g, the desired packet error rate. In another embodiment, each data symbol in data symbol stream {s} is repeated and transmitted in two symbol periods. As an example, fór the 2X3 configuration, data symbol s_c may be sent in two symbol periods, then data symbol s_d may be sent in two symbol periods, and so on. This embodiment may achieve similar received SNRs fór the N_D data symbol streams, which may simplify the coding and modulation at the transmitting entity and the demodulation and decoding at the receiving entity.

[0036] Steering mátrix V(Aj spatially spreads the N_c coded symbols fór each symbol period such that each coded symbol is transmitted from all N_T transmit antennas and achieves spatial diversity. Spatial spreading may be performed with various types of steering matrices, such as Walsh matrices, Fourier matrices, pseudo-random matrices, and soon, which may be generated as described below. The same steering mátrix V(A) is used fór the two vectors s^k) and s₂(A) fór each subband k. Different steering matrices may be used fór different subbands and/or different time intervals, where each time interval may span an integer multiple of two symbol periods fór STTD.

[0037] Mátrix B(Aj performs continuous beamforming in thefrequencydomain. Foran OFDM-based system, a different beamforming mátrix may be used fór each subband. The beamforming mátrix fór each subband k may be a diagonal mátrix having the following form:

bw=

<img file="HUE024175T2_D0001.tif" />

b₂(k) fór k = 1,...,N_f , Eq(2) o o ··· &amp;N_T(fc) where b,{k) is a weight fór subband k of transmit antenna /'. The weight b_t(k) may be defined as:

fór z = 1,N_T and £ = 1,...,N_F,

Eq(3) where ΔΤ,· is the time delay on transmit antenna /;

Δ/ is the frequency spacing between adjacent subbands; and f(A) Δ/ is the actually frequency corresponding to subband index k.

Fór example, if N_F = 64, then subband index k may go from 1 to 64, and f(A) may be equal to A - 33 and may rangé from -32 to +31. If the overall system bandwidth is 20 MHz and N_F = 64, then Δ/ = 20 MHz / 64 = 3.125 kHz. f(A) Δ/ provides the actual frequency (in Hertz) fór each value of k. The weights fe,(A) shown in equation (3) correspond to a Progressive phase shift across the N_F totál subbands fór each transmit antenna, with the phase shift changing at different rates fór the N_T transmit antennas. These weights effectively form a different beam fór each subband.

[0038] Continuous beamforming may alsó be performed in the time domain as follows. Fór each symbol period, an N_F-point inverse discrete Fourier transform (IDFT) or inverse fást Fourier transform (IFFT) may be performed on N_Ftransmit symbols to be sent on N_F subbands of each transmit antenna / to generate N_F time-domain samples fór that transmit antenna. The N_F time-domain samples fór each transmit antenna / may be cyclically or circularly delayed by

T, Fór example, T,· may be defined as: T,· = (/ -1) ΔΤ, fór / = 1.....N_T, where ΔΤ may be equal to one sample period, a fraction of a sample period, or more than one sample period. The time-domain samples fór each antenna are then cyclically delayed by a different amount.

[0039] In equation (1), the scaling by the gain mátrix G(A) may be omitted by setting G(A) = X the spatial spreading may be omitted by setting V(A) =X and the continuous beamforming may be omitted by setting B(A) =X whereXis the identity mátrix containing ones along the diagonal and zeros elsewhere. The transmitting entity may thus selectively perform scaling, spatial spreading, and continuous beamforming by using appropriate matrices. The matrices fór spatial spreading and continuous beamforming may alsó be combined as V_B(A) = B(A) V(A). The matrices fór scaling, spatial spreading, and continuous beamforming may alsó be combined as V_BG (A) = B(A)V(A)G(A). The transmitting entity may

EP 1 790 089 Β1 then perform spatial Processing on data vector s^k) with V_B(/c) or V_BG(/c).

[0040] The transmitting entity may alsó use a combination of SFTD, spatial spreading, and possibly continuous beamforming. Fór SFTD, the transmitting entity may generate two vectors s₁ and s₂ as described above fór STTD and may send these vectors on two subbands in one Symbol period. Fór the 1 X2 configuration, two vectors s₁ = [s_a s_b]⁷ and

S₂=K* ^T may be generated fór each pair of data symbols to be sent on two subbands in one Symbol period fór one data Symbol stream. Fór the 2X3 configuration, two data Symbol vectors s₁ = [s_a s_b s_c]⁷ and may be generated fór two pair of data symbols to be sent on two subbands in one Symbol period fór two data Symbol streams. Fór the 2X4 configuration, two vectors s₁ = [s_a s_b s_c s_d]⁷and 83=(¾ - 5* 5^ -$*] ^T may be generated fór two pairs of data symbols to be sent on two subbands in one Symbol period fór two data Symbol streams. Fór the 3x4 configuration, two vectors s₁ = [s_a s_b s_c s_e]⁷ and s₂ — [$&amp; - £* S_d Sf] ^T may be generated fór three pair of data symbols to be sent on two subbands in one Symbol period fór three data Symbol streams. Fór all configurations, the transmitting entity may spatially spread and transmit vector s₁ on one subband in one Symbol period and may spatially spread and transmit vector s₂ on another subband in the same Symbol period. The two subbands are typically adjacent to one another. [0041] The transmitting entity may alsó use a combination of OTD, spatial spreading, and possibly continuous beamforming. Fór OTD, the transmitting entity may generate multiple (No) vectors s₁ and s_No and may send these vectors on one subband in No symbol periods. Fór N_o = 2, the transmitting entity may generate two vectors and S2 fór two data symbols s_a and s_b by (1) multiplying data symbol s_a with a first orthogonal code of {+1 +1} to generate two coded symbols s_a and s_a fór one transmit antenna, (2) multiplying data symbol s_b with a second orthogonal code of {+1 -1} to generate two coded symbols s_b and -s_b fór another transmit antenna, and (3) forming s₁ = [s_a s_b] ^T and s2 = [sa - sj⁷. In generál, No data symbols may be multiplied with No different orthogonal codesto generate No coded symbol sequences fór No transmit antennas. Each coded symbol sequence contains No coded symbols and is generated by multiplying one data symbol with a specific orthogonal code of length No. The orthogonal codes may be Walsh codes, OVSF codes, and so on, [0042] In generál, transmit diversity may be achieved in various manners and in the time, frequency and/or spatial domains. In one embodiment, transmit diversity is achieved by multiplying vector s/k) with steering mátrix V(k) to generate transmit vector x_t(k), as shown in equation (1). In another embodiment, transmit diversity is achieved by cyclicallydelaying the time-domain samples fór each transmit antenna. In yet another embodiment, transmit diversity is achieved with a combination of spatial Processing with V(k) and cyclic delay ofthe time-domain samples. Fór all ofthe embodiments, vector s_t(k) may be formed with STTD, SFTD, OTD, or somé other transmit diversity scheme.

[0043] FIG. 2 shows a block diagram of an embodiment of TX data processor 112, TX STTD processor 120, and spatial spreader 130 at transmitting entity 110. Fór the embodiment shown in FIG. 2, TX data processor 112 includes N_d data stream processors 210a through 210nd that independently process the N_D data streams. Within each data stream processor 210, an encoder 212 encodes traffic data in accordance with a coding scheme and generates code bits. The encoding scheme may include a convolutional code, a Turbo code, a low density parity check (LDPC) code, a cyclic redundancy check (CRC) code, a block code, and soon, óra combination thereof. An interleaver214 interleaves (or reorders) the code bits based on an interleaving scheme. A symbol mapper216 maps the interleaved bits in accordance with a modulation scheme and provides data symbols. The coding and modulation fór each data stream may be determined by a rate selected fór that data stream. Data stream processors 210a through 210nd provide N_D data symbol streams.

[0044] In another embodiment, which is nőt shown in FIG. 2, TX data processor 112 jointly processes the data symbol stream(s) to be sent with STTD and the data symbol stream(s) to be sent without STTD. Fór example, TX data processor 112 may récéivé a single data stream, encode the data stream based on a coding scheme, demultiplex the code bits intő N_d coded bit streams, and perform interleaving and symbol mapping separately fór the N_D coded bit streams to generate N_D data symbol streams. In yet another embodiment, which is alsó nőt shown in FIG. 2, TX data processor 112 independently processes the data symbol stream(s) to be sent with STTD and the data symbol stream(s) to be sent without STTD. Fór example, TX data processor 112 may récéivé a first data stream to be sent with STTD and a second data stream to be sent without STTD. TX data processor 112 may encode, interleave, symbol map, and demultiplex the first data stream to generate (N_C-N_D) data symbol streams to be sent with STTD. TX data processor 112 may alsó encode, interleave, symbol map, and demultiplex the second data stream to generate (2N_D-N_C) data symbol streams to be sent without STTD. TX data processor 112 may alsó process the data stream(s) in other manners, and this is within the scope ofthe invention.

[0045] Fór the embodiment shown in FIG. 2, TX STTD processor 120 includes N_D STTD encoders 220a through 220nd fór the N_D data symbol streams. Each STTD encoder 220 performs STTD encoding on its data symbol stream and provides two coded symbol streams to a multiplexer(Mux) 222. Multiplexer 222 receives the N_Ddata symbol streams

ΕΡ 1 790 089 Β1 from TX data processor 112 and the N_D pairs of coded symbol streams from STTD encoders 220a through 220nd. Fór each data symbol stream, multiplexer 222 provides either that data symbol stream orthe associated pair of coded symbol streams. Multipliers 224a through 224nc récéivé and scale the N_c symbol streams from multiplexer 222 with gains g₁through g_Nc, respectively, and provides N_c coded symbol streams. The scaling may alsó be performed at other locations within the transmit path.

[0046] Fór the embodiment shown in FIG. 2, spatial spreader 130 includes N_F spatial processors 230a through 230nf fór the. N_f subbands. A demultiplexer (Demux) 228 receives the N_c coded symbol streams and pilot symbols, provides the coded symbols on subbands and symbol periods used fordata transmission, and provides pilot symbols on subbands and symbol periods used fór pilot transmission. Each spatial processor 230 receives N_c coded symbols and/or pilot symbols to be sent on the associated subband k in one symbol period, multiplies the coded symbol and/or pilot symbols with a steering mátrix V(/c), and provides N_T transmit symbols to be sent from the N_T transmit antenna on subband k. A multiplexer 232 receives the transmit symbols from all N_F spatial processors 230a through 230nf and maps the N_Ttransmit symbols from each spatial processor 230 to the N_T transmit symbol streams. Each transmit symbol stream includes N_F transmit symbols from the N_F spatial processors 230a through 230nf fór one transmit antenna.

[0047] FIG. 3 shows a block diagram of an embodiment of modulators 132a through 132nt at transmitting entity 110. Within each modulátor 132, an IDFT unit 312 performs an N_F-point IDFT or IFFT on N_F transmit symbols to be sent on the N_f subbands in one symbol period and provides N_F time-domain samples. A parallel-to-serial converter (P/S Conv) 314 serializes the N_F time-domain samples. A circular shift unit 316 performs a cyclic or circular shift of the N_F timedomain samples by Τ,·= (/-1)·ΔΤ, where ΔΤ is a fixed period (e.g., one sample period) and T₍ is the amount of cyclic shift fór transmit antenna i. A cyclic prefix generátor 318 receives the N_F circularly shifted samples from unit 316, appends a cyclic prefix of N_cp samples, and provides an OFDM symbol (or transmission symbol) containing N_F + N_cp samples. The time-domain continuous beamforming may be disabled by having cyclic shift units 316a through 316nt simply pass the time-domain samples from P/S converters 314a through 3164nt to cyclic prefix generators 318a through 3168nt, respectively. Circular shift units 316a through 316nt may alsó just delay (instead of circularly delay) the time-domain samples from P/S converters 314a through 3164nt by different amounts, so that the transmissions from antennas 136a through 136nt are delayed by different amounts.

[0048] FIG. 4 shows a block diagram of an embodiment of a single-antenna receiving entity 150x and a multi-antenna receiving entity 150y. Each receiving entity may be part of a base station or a user terminál.

[0049] At single-antenna receiving entity 150x, an antenna 152x receives the N_T modulated signals transmitted by transmitting entity 110 and provides a received signal to a receiver unit (RCVR) 154x. Receiver unit 154x conditions (e.g., amplifies, filters, frequency downconverts, and digitizes) the received signal and provides a stream of received samples to a demodulator (Demod) 156x. Fór an OFDM-based system, demodulator 156x performs OFDM demodulation on the received samples to obtain received symbols, provides received data symbols to a detector 158, and provides received pilot symbols to a channel estimator 162. Channel estimator 162 derives an effective channel response estimate forasingle-inputsingle-output(SISO) channel between transmitting entity 110 and receiving entity 150x fór each subband used fór data transmission. Detector 158 performs data detection (e.g., equalization) on the received data symbols fór each subband based on the effective SISO channel response estimate fór that subband and provides recovered data symbols fór the subband. An RX data processor 160 processes (e.g., symbol demaps, deinterleaves, and decodes) the recovered data symbols and provides decoded data.

[0050] At multi-antenna receiving entity 150y, N_R antennas 152a through 152nr récéivé the N_T modulated signals, and each antenna 152 provides a received signal to a respective receiver unit 154. Each receiver unit 154 conditions its received signal and provides a received sample stream to an associated demodulator(Demod) 156. Each demodulator 156 performs OFDM demodulation (if applicable) on its received sample stream, provides received data symbols to an RX spatial processor 170, and provides received pilot symbols to a channel estimator 166.

[0051] Channel estimator 166 obtains received pilot symbols fór all N_R récéivé antennas and derives a channel response estimate fór the actual or effective ΜΙΜΟ channel between transmitting entity 110 and receiving entity 150y fór each subband used fordata transmission. If transmitting entity 110 performs spatial Processing on the pilot symbols in the same manner as the data symbols, as shown in FIG. 1, then the steering matrices may be viewed as being part of the wireless channel. In this case, receiving entity 150y may dérivé an estimate ofthe effective ΜΙΜΟ channel, which includes the actual ΜΙΜΟ channel response as well as the effects of the steering matrices. If transmitting entity 110 does nőt perform spatial Processing on the pilot symbols, then receiving entity 150y may dérivé an estimate ofthe actual ΜΙΜΟ channel and may then dérivé an estimate of the effective ΜΙΜΟ channel based on the actual ΜΙΜΟ channel response estimate and the steering matrices.

[0052] A matched filter generátor 168 derives a spatial filter mátrix M(/c) fór each subband used fór transmission based on the channel response estimate fór that subband. RX spatial processor 170 obtains received data symbols fór all N_Rrécéivé antennas and performs pre-processing on the received data symbols to account fór the STTD scheme used by transmitting entity 110. RX spatial processor 170 further performs receiver spatial Processing (or spatial matched filtering) on the pre-processed data symbols fór each subband with the spatial filter mátrix fór that subband and provides detected

EP 1 790 089 Β1 symbols fór the subband. An RX STTD processor 172 performs post-processing on the detected symbols based on the STTD scheme used by transmitting entity 110 and provides recovered data symbols. An RX data processor 174 processes (e.g., Symbol demaps, deinterleaves, and decodes) the recovered data symbols and provides decoded data.

[0053] Controllers 180x and 180y control the operation at receiving entities 150x and 150y, respectively. Memories 182x and 182y store data and/or program codes fór receiving entities 150x and 150y, respectively.

[0054] Various types of steering matrices may be used fór spatial spreading. Fór example, steering mátrix V(/c) may be a Walsh mátrix, a Fourier mátrix, or somé other mátrix. A 2X2 Walsh mátrix W2X2 be expressed as

A larger size Walsh mátrix W_2Nx2n ^maY be formed from a smaller size Walsh mátrix W_NxN, ^as follows:

2NX2N

W_NXN W_NxN w - w

JLi-NXN -LLnxN

Eq(4)

An NXN Fourier mátrix D_NxN has element d_nm in the n-th row ofthe m-th column, which may be expressed as:

n,m

- j2n· fór n = 1,...,N and zn = l,...,N.

Eq (5)

Fourier matrices of any square dimension (e.g., 2, 3, 4, 5, and so on) may be formed.

[0055] A Walsh mátrix W_NxN, a Fourier mátrix P_NxN, or somé other mátrix may be used as a base mátrix B_NxN to form other steering matrices. Fór an NXN base mátrix, each ofrows 2 through N ofthe base mátrix may be independently multiplied with one of M different possible scalars. M^N_1 different steering matrices may be obtained from M^N_1 different permutations ofthe M scalars fór the N -1 rows. Fór example, each ofrows 2 through N may be independently multiplied with a scalar of +1,-1, +/, or -j, where j = yf—ΐ. Fór N = 4, 64 different steering matrices may be generated from a base mátrix B4_X4 with the four different scalars. Additional steering matrices may be generated with other scalars, e.g., _e±j3M_{t e}±jM, _e±pd8_{t anc}| _{so on} |_n generál, each row ofthe base mátrix may be multiplied with any scalar having the form ei^Q, where θ may be any phase value. A set of NXN steering matrices may be generated from the NXN base mátrix as X(0 ^— &lt;?n ’BnxN ’ where = 1/VN and B'_NxN is the /-th steering mátrix generated with the base mátrix

B_NxN. The scaling by = ensures that each column of V(/) has unit power. The steering matrices in the set may be used fór different subbands and/or time intervals.

[0056] The steering matrices may alsó be generated in a pseudo-random manner. The steering matrices are typically unitary matrices having columns that are orthogonal to one another. The steering matrices may alsó be orthonormal matrices having orthogonal columns and unit power fór each column, so that V^H V=X A steering mátrix of dimension that is nőt square may be obtained by deleting one or more columns of a square steering mátrix.

[0057] Different steering matrices may be used fór different time intervals. Fór example, different steering matrices may be used fór different Symbol periodsforSFTD and fór different 2-symbol intervals fór STTD and OTD. Fór an OFDMbased system, different steering matrices may be used fór different subbands fór STTD and OTD and fór different pairs of subbands fór SFTD. Different steering matrices may alsó be used fór different subbands and different Symbol periods. The randomization provided by steering diversity (across time and/or frequency) with the use of different steering matrices can mitigate deleterious effects of a wireless channel.

[0058] The transmission techniques described herein may be implemented by various means. Fór example, these techniques may be implemented in hardware, firmware, software, óra combination thereof. Fór a hardware implementation, the Processing unitsatthe transmitting entity may be implemented within one or more application specificintegrated circuits (ASICs), digital signal processors (DSPs), digital signal Processing devices (DSPDs), programmable logicdevices (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.

[0059] Fór a software implementation, the techniques may be implemented with modules (e.g., procedures, functions, and so on) that perform the functions described herein. The software codes may be stored in a memory and executed by a processor. The memory may be implemented within the processor or external to the processor, in which case it

ΕΡ 1 790 089 Β1 can be communicatively coupled to the processor via various means as is known in the art.

[0060] The previous description ofthe disclosed 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 departing from the scope ofthe invention. Thus, the present invention is nőt intended to be limited to the embodiments shown herein bút is to be accorded the widest scope consistent with the claims.