Rate adaptive transmission scheme for mimo systems

RATE ADAPTIVE TRANSMISSION SCHEME FOR

ΜΙΜΟ SYSTEMS

[0001] This application claims the benefit of provisional U.S. Application Serial No. 60/419,319, entitled “ΜΊΜΟ Signaling Schemes for Rate Adaptive Systems,” filed October 16, 2002, assigned to the assignee of the present application, and incorporated herein by reference in its entirety for all purposes.

BACKGROUND

I. Field of the Invention

[0002] The present invention relates generally to data communication, and more specifically to a rate adaptive transmission scheme for multiple-input multiple-output (ΜΙΜΟ) communication systems.

II. Background

[0003] A ΜΙΜΟ system employs multiple (Nr) transmit antennas and multiple (Nr) receive antennas for data transmission. A ΜΙΜΟ channel formed by the N_T transmit and TV/? receive antennas may be decomposed into 7V$ independent channels, where N_s < min{/V_r, N_K}. Each of the Ns independent channels corresponds to a dimension. The ΜΙΜΟ system can provide improved performance (e.g., higher throughput and/or greater reliability) if the additional dimensionalities created by the multiple transmit and receive antennas are utilized.

[0004] In a wireless communication system, data to be transmitted is typically processed (e.g., coded and modulated) to provide data symbols. For a ΜΙΜΟ system, one or multiple streams of data symbols may be sent from a transmitter to a receiver. Multiple data symbol streams may be transmitted in parallel from multiple transmit antennas using spatial multiplexing, which exploits the additional dimensionalities of the MEMO channel. To attain high throughput, it is desirable to transmit as many data symbol streams in parallel as possible. However, the number of data symbol streams that may be transmitted and the rates that may be used for these streams are typically dependent on the channel condition. Various transmission schemes for spatial multiplexing are cumently available, including (1) an “antenna multiplexing” scheme that transmits one data symbol stream from each antenna and (2) an “etgenmode multiplexing״ scheme that transmits one data symbol stream on each independent channel of the ΜΙΜΟ channel.

(0005] Alternatively, a single data symbol stream may be transmitted from multiple transmit antennas using transmit divemity to increase reliability of the data transmiss.on. Diversity is achieved by the use of mult.pl־ transmit antennas as well as multiple receive antennas 0־ provide a number of propagation paths for the data symbol stream. Transmit diversity may be used if greater reliability is desired or if the channel condition is so poor that it is better to use al! of the available transmit power for one data symbol stream. Various transmission schemes for transmit diversity are currently available, including (1) a -space-time diversity״ scheme described by S.M. Alamoutt m a paper entitled “A Simple Transmit Diversity Technique for Wireless Communications, IEEE JSAC, Oct. 1998, and (2) a “delay diversity״ scheme descnbed by B. Raghothaman « al. in a paper entitled “Performance of Closed Loop Transmit Diversity with Feedback Delay, Thirty-Fourth Asilomar Conference on Signals, Systems and Computers, 2000.

[0006] or more

To achieve high performance, a ΜΙΜΟ system may be designed to support one transmission schemes for spatial multiplexing and one or more transmission schemes for transmit diversity. For such a ΜΙΜΟ system, in any given transmission interval a specific transmission scheme may be selected for use depending on the channel condition and the destred result (e.g., higher throughput or greater reliability). However, conventional transmission schemes for spatial multiplexing different in design from conventional transmission schemes for transmit diversity. Thus, the complexity of the transmitter and receiver in the system may be greatly increased if they are requ.red to support multiple (and different) transmission schemes for spatial multiplexing and transnut diversity. Moreover, for high performance, ״ is desirable to fully utilise the total transmit power available for the system and the full power available for each of the Nt transmit antennas for data transnussion, regardless of the number of data symbol streams being transmitted.

[0007] There is therefore a need in the a״ for a transmission scheme that can support spatial multiplexing, prov.de transmit diversity, and fully utilize th־ '™nsmit nower in ΜΙΜΟ systems, k

[0008]

[0009]

[0010]

[0011]

SUMMARY

A rate adaptive transmission scheme that supports spatial multiplexing and provides transmit diversity for ΜΙΜΟ systems is provided herein. The rate adaptive transmission scheme has a number of desirable characteristics, including: (1) support transmission of a variable number of data symbol streams, thus making it suitable for use in rate adaptive systems, (2) provide transmit diversity for each data symbol stream, and (3) allow the full power available for each transmit antenna to be used for data transmission regardless of the number of data symbol streams being transmitted, thus making it power efficient. The rate adaptive transmission scheme is well suited for single-carrier ΜΙΜΟ systems and may also be used for multi-carrier ΜΙΜΟ systems.

In an embodiment, a method is provided for processing data for transmission in a ΜΙΜΟ system. In accordance with the method, at least one stream of data symbols is received for transmission from a plurality of transmit antennas. Each data symbol stream is scaled with a respective weight corresponding to the amount of transmit power allocated to that data symbol stream. The total amount of transmit power allocated to all of the at least one data symbol stream is less than or equal to the total transmit power available for the system. The scaled data symbol stream(s) are then multiplied with a transmit basis matrix to provide a plurality of streams of transmit symbols, one transmit symbol stream for each transmit antenna.

The transmit basis matrix is defined such that (1) each data symbol stream is transmitted from the plurality of transmit antennas and (2) each transmit symbol stream is transmitted at (or near) the full power available for the associated antenna. The transmit basis matrix may be a Walsh-Hadamard matrix, a discrete Fourier transform (DFT) matrix, or some other matrix.

| Various aspects and embodiments of the invention are described in further detail below.

[0012] 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:

HG. 1 shows a flow diagram of a process for transmitting Nd data symbol streams from N_T antennas using the rate adaptive transmission scheme,

FIG. 2 shows a block diagram of a transmitter system and a receiver system in a

MEMO system;

FIG. 3 shows the spatial processing at the transmitter and receiver systems for the rate adaptive transmission scheme; and

HG. 4 shows a block diagram of a transmit (TX) spatial processor withm the transmitter system.

[0013]

[0014]

[0015]

[0016]

[0017]

DETAILED DESCRIPTION

A rate adaptive transmission scheme for MMO systems is described herein. For a multi-carrier ΜΙΜΟ system, the transmission scheme may be used for each of the multiple carriers available for data transmission. For clarity, the rate adaptive transmission scheme is described below for a single-carrier ΜΙΜΟ system.

[0018] For a singfe-carrier ΜΙΜΟ system, the MMO channel formed by th־ N_rtransmit and N״ receive antennas may be decomposed into Ns independent channels, with N_s < min |N_T,N,). The number of independent channels is determined by the number of eigenmodes for the ΜΙΜΟ channel, which in turn is dependent on a channel response matrix H that describes the response between the N, transmit and Ν» receive antennas. For simplicity, the description below assumes that N_T < N, and that the channel response matrix H is full rank (i.e, N_s ־ N_T < Λ׳,)- With assumptions, for each symbol period, up to Nr symbols may be transmitted in parallel from the Nr transmit antennas.

[0019] The model for a single-earner ΜΙΜΟ system may be expressed as:

v =Hx+n Eq(l) where x is an {2V_r xl} “data” vector with Nt entries for the data symbols to be transmitted from the Nt transmit antennas, y is an (N״xll ״receive״ vector with N, entries for ths symbols received via the Nr receive antennas;

H is the \N_RxN_r} channel response matrix; and n is a vector of additive white Gaussian noise (AWGN).

The data vector x is assumed to be such that E[xx ] = I י ^{where E 1s the exp}operation, “ ״ ״ is th־ conjugate transpose, and I is th־ identity matrix with ones along the diagonal and zeros everywhere ־Is־ Th־ v־ctor ״ is assumed to have zero mean andacovariancematrixof Λ17= ״¼.where σ¹ is the vanance of the noise.

_[0020! In a typical system, there ar־ constraints on (1) th־ total —t power. , that may be used for 11־N_T trans״״, antennas and (2) the maxtmum or full power, P״, for each transimt antenna. Typically, the per—a power P״ is »״־״ as P ־ P IN . These constraints may be imposed by (1) limitation of the power amplifier used to drive each transmit antenna, (2) regulatory require־״־!״, and (3) possibly other factors. The model for a MMO system with these power constrants may then be expressed as:

—Hx+n ,

Eq (2) where ^{factor ltat aC}“^UnlS '°^Γ constraints.

[00211 I״ one conventional transmisston scheme, Nd data symbol streams ar־ transmitted concunently from the Nr transmit antennas using antenna multiplexing, where Nd may be any integer from 1 to Nr (i־. Nj * ^N° ^{2 1} >' ^{For lhls convent1ona}transmission scheme, in any g.v־n symbol period. Nd data symbo.s are transmitted simultaneously from Nd —־־. and he (N_T - N_o) remaining antennas ar־ not use . _lf the to.״ transmit power and the per— power are constramed as desenbed above, then this transmission scheme will exhibit a power loss if fewer than Nra״t״־nas are used for data transmission, which is the case if N״ <N_r. Because of P antenna power constraint, more of the total transmit power P״ cannot be allocated to the Nd a״ ־־״״־״s־d for data transmission when N_o < Ν_τ. Moreover, if the Nd data symbol streams ־״ redundant (i.e., the same) streams, then there is a ״sk of cancellation of these streams at the receiver.

[0022] The specific number of data symbol streams to transmit may be dependent on various factors such as, for example, the channel condition, the amount of data to transmit, and so on. As noted above, different independent channels may experience different channel conditions and achieve different signal-to-noise ratios (SNRs). For a rank deficient ΜΙΜΟ channel, the optimal strategy is to transmit fewer than N_T data symbol streams but allocate more of the total transmit power P_lol to the data symbol streams that achieve higher SNRs. However, for the antenna multiplexing transmission scheme described above whereby each data symbol stream is transmitted from one antenna, the optimal allocation of the total transmit power cannot be achieved because of the per־antenna power constraint. As a result, some loss in performance will occur.

[0023] The rate adaptive transmission scheme described herein supports spatial multiplexing, provides transmit diversity, and has the following beneficial features.

• Support the transmission of a variable number of data symbol streams (from one to Nt) using the same transmit and receive spatial processing while retaining key characteristics.

. Provide better performance than the space-time diversity scheme for a single data symbol stream via transmission from all N_T transmit antennas.

. Allow the full power P_nnr of each of the N_T transmit antennas to be used for data transmission, regardless of the number of data symbol streams being transmitted, thus making it power efficient with no power loss when fewer than N_T data symbol streams are being transmitted.

• Allow for flexible allocation of the total transmit power P_l0, among the data symbol streams being transmitted.

The rate adaptive transmission scheme and its beneficial features are described in further detail below.

[0024] The general model for a single-carrier ΜΙΜΟ system and applicable for the rate adaptive transmission scheme may be expressed as.

y = ΗΜΛχ + η = Η^Λχ + η = Ηχ + η ,

Eq (ג) where M is an (N_r X N-} transmit basis matrix, which is a unitary matrix, A is an {/V_T xNJ diagonal matrix;

X is an (N_r xl) ‘transmit״ vector with Nr entries for Nr transmit symbol־ sent from the N_T transmit antennas; and

H is an effective” channel response matrix, which is defined as H,_f = HM

A unitary matnx U is charactenzed by the property U״L=I, which indicates that each column of the unitary matrix is orthogonal to all other columns of (he matrix, and each row of the unitary matrix is also orthogona! to all other rows. The d.agonal matnx

Λ contains ״־״-negative real values along the diagonal and zeros everywhere else. These diagonal entries are indicative of the amount of transmit power allocated to the

N_d data symbol streams being transmitted.

[0025] As described in further detail below, the diagonal matrix A may be used to allocate different transmit powers to the No data symbol streams while conforming to the total transmit power constraint of P״ The transmit basis matrix M allows each data symbol stream to be sent from Nr transmit antennas and further allows the full power P״, of each transmit antenna to be utilized for data transmission.

100261 From equation (3), the transmit vector x may be expressed as:

x = MAx .

Eq (4)

The transmil symbol x, for the Mi transmit antenna (i.־., the Mi element of the transmit vector x) may be expressed as:

x_k=^M_k-_t_u^ ,forfceK,

Eq (5) where M is the element in the λ-th row and i-th column of the transmit basis matnx

M,

Λ is the i-th diagonal element of the matrix A,

x. is z-th element of the data vector x, x_k is the λ-th element of the transmit vector x; and

K is the set of all transmit antennas (i.e., K - {1, 2, .., N_T}).

_|0027) Equation (3) rapres־* »״־ g״ &lt;™״־»*' « both equate (1) ״־ ) _Th1s Is achieved by prepay defining th־ — M ״־d the diagonal matrix A For «ample, equation (3) can be made equal to ־q״־״on (2) by (1) defmmg the transmit basis matrix M as M־[m, m, .. a״J. ^wl'^ere ®י ,_nd־x״ vector for the i-th column of M and is defined with 1״. - h־ “0” elsewhere, and (2) defining the diagonal matrix A as A = JpJNA However, other beneficial characteristics may be obtained by defining the trans״״ basis M and the diagonal matrix Λ in some other manner, as described below.

_I0028! For th־ following anriysis, consider an arbitrary transnut basis matnx M and an arbitrary diagonai matrix A with ״on-r^ve diagona! ־־״־״־ The transtnri power for _the vector x is equal <־ - of the square of the diagonal ״ .* -־״־<־>“>

transmit power constraint may then be expressed as:

Eq (6) trace(/\²)^P,״_t .

׳״irh nf the Nt transmit antennas may

[0029] From equation (5), the transmit power for each of th be expressed as:

er«;1=S^m״i².^ ׳^for*^eK׳

1=1 .rmtp The ner-antenna power constraint may where “*״ denotes the complex conjugate. The per antenn μ be expressed as:

N P ν' ן ρ נ - &lt; p = -צ!- for k e K 2JM_U| A.-'״״׳ - _N -¹ i=) ^T

Eq (8) (0030, Since trace (A^־)&lt;f:., as shown in equation (6), the per-antenna power constraint .״־״,־ ״on (8) may be ״־״־״־־ by any Ml rank matnx M whose ־!־ments satisfy the following:

, for ie K and k&amp; K.

Eq (9)

Equation (9) indicates that the elements of a ״did matrix M have magnitude equal to yfc. Equation (9) represents a sufficient condition (but not a necessary condition) needed to satisfy the per-antenna power constraint.

_[0031) The matrix M may be defined in vanous manners while sattsfy.־״ the P־rantenna power constraint. In one embodiment, the matrix M is defined as:

ן Eq (10)

M = -T==W -

7^7 ־־ where W is a Walsh-Hadamard matrix. As illustration, for N_T=4, the Walsh Hadamard matrix W_4x4 may be expressed as:

T 1

-1

1

1־ 1

<img file="IL167299A_D0001.tif" />

Eq (11)

A larger size Walsh-Hadamard matrix W_2Nx2n may ^{be def1ned as}

W_NXN

W_NxNW_2NX2N= W_NxN -W_NxN

Eq (12)

10032] In another embodiment, the matrix M is defined as:

<img file="IL167299A_D0002.tif" />

Eq (13) where Q is a discrete Fourter transform (DFT) matrix. As illustration, for N_T 4 ־. the

DFT matrix Q_4x4 may be expressed as:

<td></td><td></td><td> 1</td><td> 1</td><td> 1</td>

<td></td><td> 1</td><td></td><td> - (4tr/4 e ־</td><td> -j6?r;4</td>

<td> 24X4 =</td><td> 1</td><td> - jiirr/4 e</td><td> -J8rt/4 e</td><td> -.;I2rM</td>

<td></td><td> 1</td><td> -jbn/4 e</td><td> -jllirll e</td><td>_g־jl8״״»</td>

Eq (14) may be defined such that the (M)־^{th entr}V’

In general, an NxN DFT matrix Q_NxN qf ., is given as:

_N _ for k = 11 .. Nl ^and¹¹־ ׳ - ^N} ’

9k,i~^e

Eq (15) ,׳!״ ״.trices and this is within the scope of the may also be defined with ״anons other ma .

_־.. ,ד. -- “—^a ״* ־״״. . ־“

[0033] By using a pp h the ner-antenna power constraint can matrix A, the total transmit power constraint an _sat1sfied _by both be satisfied. In particular, the total transmit ^w _ . oi elements of A such that equation (6) is satisneu defining the diagonal elements 01 _L_{n hp} ^_1sfied by defining the elements of M sue power constraint may e _{n Λ is} indicative of the amount of .ansndt power ־־0 0־^ an assoc.ated data symbo. stream,.

constraint on the vain־ of any individua! diagonal ־״־״־&lt;־ Δ. ״ ־ ״!־»־' P may be allocated to the No data symbol streams m vanou the total transmit power P,״ Y ־״,.antenna power manners while still satisfying the total ™⁵™‘ ζζ״ ” _{available lr}a״_smit power constraints. This then affords great fle—ty ״ a״o־a״״g th־ among the No data symbol streams. _rf

[0034! The rate adapt!־״ transtmss.״־ schem Y _{The ״ansmlKe}r performs data symbol streams (t.e 0 * _{data syrab}ol spatial processing sh־wnby _sl״ams being transnutte . .

data symbol streams and A_r N_D Each of the A_D

4. ״״.,I element in the matnx A. Eacn 01 me _υ associated with a respective non-zero lag _basjs data symbol streams is _{wh1ch 1s} defined by a matnx M for transnnss.o״ on a respect.

r״r ״f the effective channel response matrix . specific column or eigenvector ot the ettectiv _roo351 It can be shown that the tat־ adaptive transtntsston scheme can provide improved performance over conventional transmit diversity schemes. For example, the space-time diversity scheme described by S.M. Alamouti is ״ft״־ used to transmrt a sinole data symbol stream from a single pair of transmit antennas to achteve transrmt diversity However, it can be shown that the rate adaptive transmtsston scheme can provide improved performance for the transmission of the stngl־ data symbol stream. The received SNR, SNR,., for the data symbol stream transmitted ״smg th־» ־ adaptive transmission scheme with the best column of !1״ may be expressed as:

SNR_ra^{w maX}i {(II II ' Fiat I ’ where denotes proportionality; and

I h״, If is the 2-norm of h.״, which is the ί-th column or eigenvector of the effective channel response matrix H_i#.

Equation (16) indicates that the SNR of the sing,־ best data symbol stream using the rate adaptive transmission scheme is proportional &lt;0 the 2-״0״n of the best etgenvector _of H To obtain the SNR of equation (16), the receiver would need to send back information indicating the best column of H״ for use by the transmitter.

[0036] The received SNR, SNR״. for ־he single data symbol stream —ed using the space-time diversity scheme may be expressed as:

sNR״“t(ll!!4״־l7״(^־ .

Eq (17)

Equation (17) indicates that the SNR of the single data symbol stream using the spacetime diversity scheme is proportional to the average of the 2-noms of the Nr eigenvectors of H_ti. Equations (16) and (17) both assume transtmssion at full rate (i.e. without rate loss). However, since the space-time diversity scheme uses only two antennas for transmitting the single data symbol stream, if N_T > 2 (hen th־״־ wtll be a rate loss.

[0037] It is well known that the following expression is always true:

PCT7US2003/032773 max, I **^1,2׳.»־ and thus

Eq (18a)

Eq (18b)

SNR_rn>SNR״ .

_״ga) and (18b) indicate that the rat־ adaptive transmission scheme can _Equa״־״s (18a) an ) _scher״e.

provide the same or P ״renter transmit diversity er the rate adaptive transmission scheme can provi g _time diversity scheme transmit antennas. Transmission of th g v result in a rate -ו,! for the snace-time diversity scheme but may resuu in antennas may be possible for the space loss or some other performance penalty.

,״ .״״Should also be noted that the ns־ of the trans״״. bas.s mat״x _ >

,_cheme allows for full utilization of both the total transmit power adaptive transmission scheme _of ״״wer P for data transmission, regardless ui p and the per־antenna power P_anl dal symbol stream being transmitted. If the transmit basis matrix M is not ־. ־־״. _if M-0 ״־d ־ sing!־ data symbol stream is transmitted from the sing!־ best ך״־ _us1,_lg antenna multiplexing, then th־ received SNR for th.s data symbo! stream may ־ expressed as:

SNR״״ “max, ((||h_;l|²)־^ ״ can also be shown that the following expression max, U|h.1״n^^־^ra“t ^,״Μ2) ' i ך י.

is also always true:

Eq (19)

Eq (20)

l. I״ ״־ntnerforms the antenna multiplexing

Thus, the rate adapt־״ transmission scheme also outperforms transmission scheme. ״rocess 100 for

->״ shows a now diagram of an embodiment of a process

I⁰³״” ^F!C1 ־ _h . _{arems from} Nr antennas using the rate adapt־״ transmitting N_D uata symbol streams trom '13 transmission scheme.

As noted above, W ^{te an}>׳ ^{value frOm} ‘ ° *

[0040] I״iti״־y. “tai transmit power P_m is allocated to the No data symbol streams (denoted by x)(־t־_P H2). The specific number of data symbo) streams to transmit and _the amount of power to aUocate to each data symbol stream may both be d—d based on the chan־״! condition. For example, . ‘Wer-filW procedure may be used _t0 determine the number of data symbol streams to tntnsm״ and the amount 0 P״v־׳r 0 use for each data symbol stream such that the overall throughput ts maxtmtzed. Wa ־r_fllling is described in detatl tn commonly assigned U.S. Pa־״־־ Application S־nal No.

20030139196, ״־titled .’Reallocation of Excess Power for Full Channel-Slate Informafon (CSI) Multiple-Input. Multiple-Output (MW) Systems, published July 24,200 , a״ _by Robert G- Gallager in “Wo״״ation Theory and Reliable Common,oat,on, John Wiley and Sons, 1968, both of which are incorporated herein by reference.

_[004״ The amount of transmit power ailocated to each data symbol stream x, ts denoted by a respective weight 2,., Th־ «r ^dia8°^{al elementS} °^f “ composed of No weights for the No data symbol streams and (N_T -NJ zeros. The total amount of tiansmit power allocated to the No data symbol streams is less than or

Nt equal to the total transmit power of the system (i.e., £2_U - )

[₀₀₄₂₁ A transmit basis matrix M s next selected for use (step 4״) The transmit basis matrix M may be defined such that each data symbo! stream ts transmuted from _all Nr antennas and the full power ־ ־״״־- ^־ '1״ ^data '™”'“'⁰י״ transmit bas.s matnx M may be defined as (1) ־h־ Walsh-Hadamard malnx W described in equations (10) through (12), (2) the DPT matnx descnbed ,״ equations (13) through (15), or (3) some other matrix.

[₀₀₄₃₁ Each data symboi stream q ts then scaied with its assoctated we.ght 2,., m ־״ dmttonai matnx A (step 116). This scaling results in each data symbol stream being allocated power. The No scaled data symbol streams are then transmit basis matnx M to obtain Nr transmit symbol streams the Nr transm״ antennas (step 118). The scaling of the No data transmitted with its multiplied with the (denoted by x ) i°^r symbol streams with the diagonal matrix A and the multiplication with the transmit basis matrix M are shown in equation (4). Each transmit symbol stream x_t is furthei processed and then transmitted from an associated antenna (step 120).

[0044] FIG. 2 shows a block diagram of an embodiment of a transmitter system 210 and a receiver system 250 in a ΜΙΜΟ system 200. At transmitter system 210, data for Nd streams is provided by a data source 212 and coded and modulated by a transmit (TX) data processor 214 to provide modulation symbols, which are also referred to as data symbols. The data rate, coding, and modulation for each stream may be determined by controls provided by a controller 230. The data symbols are further scaled with the diagonal matrix A and spatially processed with the transmit basis matrix M by a TX spatial processor 220 to provide transmit symbols. Pilot symbols, which may be used for channel estimation, are multiplexed with the transmit symbols. One stream of multiplexed transmit and pilot symbols is provided to, and processed by, each transmitter (TMTR) 222 to provide a corresponding RF modulated signal. The N_Tmodulated signals from transmitters 222a through 222t are then transmitted from Nt antennas 224a through 224t.

[0045] At receiver system 250, the Nt transmitted signals are received by N_R antennas 252a through 252r. Each receiver (RCVR) 254 processes a received signal from an associated antenna 252 to provide a corresponding received symbol stream. A receive (RX) spatial processor 260 then processes the Nr received symbol streams from N_Rreceivers 254a through 254r to provide N_D “recovered” symbol streams, which are estimates of the Nd data symbol streams transmitted by the transmitter system. The N_Drecovered symbol streams are further processed by an RX data processor 270 to obtain decoded data, which is an estimate of the data transmitted by the transmitter system.

[0046] RX spatial processor 260 may also derive an estimate of the channel response between the N_T transmit and Nr receive antennas (e.g., based on the pilot symbols). Channel estimation is described in detail in provisional U.S. Patent Application Senal No. 60/438,601, entitled “Pilot Transmission Schemes for Wireless Multi-Camer Communication Systems,” filed January 7, '2003, assigned to the assignee of the present application and incorporated herein by reference. The channel response estimate H may be used io perform spatial processing or equalization at the receiver. RX spatial processor 260 may further estimate the SNRs of the recovered symbol streams and/or the received piiol symbol. Controller 280 receives the ־״״״!־! -ponse ך _and the received SNRs and provides feedback regards the — ehanoe ״־d/or e streams For example, the feedback may indicate the number of data symbol streams trans־״״, which ones of the spattal channels or etgenvectors to use for data trans« an ״rd SNR or rate for each stream. The feedback ts processed by a TX and the recci ._p processor 290, conditioned by transimlteis processor 288, farther processed by a ΓΧ ״ Ρ, P _{286 fu|1ct},o_lls ,״ the

254a through 254r,^{־nd 5}“jTxcept in some cases it may only provide one data stream.

same way as data sou , modulated _teceivCT_IOW7) At transmitter system 210, svstem 250 are received by antennas 224, conditioned py r £L־d by an RX spa־״! processor 240, and processed by an RX data process» 242 to recover the feedback sent by the receiver system. The feedback is then prov.ded to controller 230 and may be used to (!) deterge the number of data symbol s r to transmit (2) d־t״־r״״e the rate and coding and moduiabon scheme to use for ־־־h It“! stream, a״d (3) genera־־ -rots for TX data processor 214 and systems, respec^y. Memory umts 232 and 282 provide storage for program and data used by controllers 230 and 280, respectively.

_IOW9] FIG. 3 shows a biock diagram of the spa־״! processing at the —er an receiver systems for the rate adaptive transnussion scheme. WUhin spa 1a

..־“'-י־.-־.״..«־-.,״.-....־;״

....,,.-..-.---4--------.- Tbp vector x is then _matnx M by a unit 312 to obtain the transmit vector x. The ״ IM 11חר transmitted over the ΜΙΜΟ channel to receiver processed by a transmitter 314 and. transmi system 250. Unit 312 performs the spatial processing for the transmitter sy _Iwo, At reaver system 250, the .״״sotted - processed by a recover 354 to obtain the receive vector y. W״l״״ RX ־P®> P^״ ’ ״“.²⁶⁰״-״

״. , ׳'׳״ A_n effective channel response first multiplied wkh a mauix H,_־ by a umt 356. An י׳ ^w . h , ״ - irM and the matrix H״r '^s '¹'^1e estimme matnx H., may be obtained as a_־JM.

r ft The matrix S״, is al» refemd :0 as the matched niter conjugate transpose ot - ¹ , resultant vector from unit 356 is matrix for the rate adaptive transm.ss.״־ scheme. The resultant further s־a!ed by an inverse diagonal matrix Λ־' by a ־ ״. 358 ״״״«- vector x processing (i.e., matched filtering) for the receiver system.

_|0051| FIG. 4 shows a h.och diagram of a TX spatial processor 220x, ^ch is an embodiment of TX spatial processor 220 in FIG. 2. TX spatm! processor 220x includes amumber of data symbol stream spatial processors 410a through 4101, one processor for --ס of the No data symbol streams to be transmitted. Each processor 41 rec״־« a assigned data symbol stream x״ the ״eight Λ״ for the ass.gned corresponding vector m, from the transmit bas.s matnx M.

_[00521 Within each processor 410, the data symhois in the assigned stream x, are rs sea.ed.with the weight Λ״, by a muhipher 4,2. The sc־« data symbols are further _mult,p־״d by N_T multipliers 414a through 414t with Nr elements M ^M ־ respectively, from the vector m,. Each data symbo! stream x, 1־ . _3U Nr antennas ״־d represented by a vector x,, which may be expressed as:

Eq (21)

2L - 51. ’ A.! 1* ־ .

!00531 Th־ output symbols from multipliers 414־ through 414t arc then proved 10 Nr

[9053] , _transrnj_t antenna. Each summers 420a through 420t, respectively, one summ _N_summer 420 receives the ־utput symbois for its assigned antenna, ״h.ch are :Zhem 414 »it״״ No signed “ , ״ '־—.׳־. . - .־*״'~ be expressed as:

, ~ fnr .he ׳-ih daia symbol stream; and where is the fc-th element in the vec.or .־ tor . .

T, is the transmit symbol stream for the k-ih transmit antenna.

The transmit symbols from each summer 420 are provided to a respective multiplexer

430 and multiplexed with pilot symbols to provide a stream of multiplexed transmit and pilot symbols for the associated antenna.

[0054] The rate adaptive transmission scheme described herein may be used for singlecarrier MMO systems as well as multi-carrier ΜΙΜΟ systems. For a multi carrier M1M0 system, each of the multiple carriers available for data transmission may be viewed as a single-carrier ΜΙΜΟ system. The total transmit power P״ and the perantenna power may be divided equally (or poss.bly unequally) among Nr earners such that F,,־,״P״/N_f. ^{The rate adap}^{Ve tranSmSSi}°ⁿ scheme may then be applied to each of the N_F carriers with the pcr-canier total power constraint of and the per-antenna/carrier power constraint of P.״,.,.

[0055] The rate adaptive transmission scheme described herein may be implemented by various means at the transmitter and receiver systems. For example, the processing for the rate adaptive transmission scheme may be implemented in hardware, software, or a combination thereof. For a hardware rmplementation, the elements used to perform the processing 1־ the transmitter and receiver systems may be implemented within 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 (FPOAs), processors, controllers, micro-controllers, microprocessors, other electronic units designed to perform the functions described herein, or a combination thereof.

[00561 For a software implementation, the processing for the rate adaptive transmission scheme 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 unit (e.g., memory units 232 and 282 in FIG. 2) and executed by a processor (e.g., controllers 230 and 280). Each 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.

!00571 The previous desenpoon of the 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 .0 other embodiments without departing from not intended to be the widest scope the spirit or scop־ of th־ i״™.™ ^Thus^the “ limited to the embodiments shown herein but is to be accorded consistent wtth the principles and novel features disclosed her״,־.