CA2495356C - Transmitter diversity technique for wireless communications - Google Patents

Abstract

A simple block coding arrangement is created with symbols transmitted over a plurality of transmit channels, in connection with coding that comprises only simple arithmetic operations, such as negation and conjugation. The diversity created by the transmitter utilizes space diversity and either time or frequency diversity. Space diversity is effected by redundantly transmitting over a plurality of antennas, time diversity is effected by redundantly transmitting at different times, and frequency diversity is effected by redundantly transmitting at different frequencies. Illustratively, using two transmit antennas and a single receive antenna, one of the disclosed embodiments provides the same diversity gain as the maximal-ratio receiver combining (MRRC) scheme with one transmit antenna and two receive antennas. The principles of this invention are applica-ble to arrangements with more than two antennas, and an illustrative embodiment is disclosed using the same space block code with two transmit and two receive antennas.

Description

Transmitter Diversity Technique for Wireless Communications Background of the Invention This invention relates to wireless communication and, more particularly, to techniques for effective wireless communication in the presence of fading and other 1 o degradations.
The most effective technique for mitigating rnultipath fading in a wireless radio channel is to cancel the effect of fading a~ the transmitter by controlling the transmitter's power. That is, if the channel conditions are known at the transmitter (on one side of the link), then the transmitter c2n pre-distort the signal to overcome 15 the effect of the channel at the receiver (on the other side). However, there are two fundamental problems with this approach. The first problem is the transmitter's dynamic range. For the transmitter to overcome an x dB fade, it must increase its power by x dB which, in most cases, is not practical because of radiation power limitations, and the size and cost of amplifiers. The second problem is that the 2o transmitter does not have any knowledge of the channel as seen by. the receiver (except for time division duplex systems, when the transmitter receives power from a known other transmitter over the. same chann~:l). Therefore, if one wants to control a transmitter based on channel characteristics, channel information has to be sent from the receiver to the transmitter, which results in throughput degradation 25 and added complexity to both the transmitter aad the receiver.
Other effective techniques are time and frequency diversity. Using time interleaving together with coding can provide diversity improvement. The same holds for frequency hopping and spread spectnan. However, time interleaving results in unnecessarily large delays when the channel is slowly varying.

Equivalently, frequency diversity techniques are ineffective when the coherence bandwidth of the channel is large (small delay spread).
It is well known that in most scattering environments antenna diversity is the most practical and effective technique for reducing the effect of multipath fading.
The classical approach to antenna diversity is to use multiple antennas at the receiver and perform combining (or selection) to improve the quality of the received signal.
The major problem with using the receiver diversity approach in current wireless communication systems, such as IS~ 136 and GSM, is the cost, size and ~ o power consumption constraints of the receivers. For obvious reasons, small size, weight and cost are paramount. The addition of multiple antennas and RF chains (or selection and switching circuits) in receivers is presently not be feasible. As a result, diversity techniques have often bean E.pplied only to improve the up-link (receiver to base) transmission quality with multiple antennas (and receivers) at the 15 base station. Since a base station often serves thousands of receivers, it is more economical to add equipment to base station; rather than the receivers Recently, some interesting approaches for transmitter diversity have been suggested. A delay diversity scheme was proposed by A. Wittneben in "Base Station Modulation Diversity for Digital SIMULCAST," Proceeding of the 1991 2o IEEE Vehicular Technology Conference (V'l.'C 41 st), PP. 848-853, May 1991, and in "A New Bandwidth Efficient Transmit Antenna Modulation Di~rersity Scheme For Linear Digital Modulation," in Proceeding of the 1993 IEEE International Conference on Communications (IICC '93), PP.1630-1634, May 1993. The proposal is for a base station to transmit a sequence of symbols through one 25 antenna, and the same sequence of symbols --but delayed - through another antenna.
U.S. patent 5,479,448, issued to Nambirajan Seshadri on December 26, 1995, discloses a similar arrangement where a sequence of codes is transmitted through two antennas. The sequence of codes is routed through a cycling switch that directs each code to the various antenna;, in succession. Since copies of the same symbol are transmitted through multiple antennas at different times, both space and time diversity are achieved. A maxirlum likelihood sequence estimator (MLSE) or a minimum mean squared error (Mr~ISE) equalizer is then used to resolve multipath distortion and provide diversity gain. See also N. Seshadri, J.H.
Winters, "Two Signaling Schemes for Improving the Error Performance of FDD
Transmission Systems Using Transmitter Antetuia Diversity,' Proceeding of the 1993 IEEE Vehicular Technology Conference (VTC 43rd), pp. 508-511, May 1993;
and J. H. Winters, "The Diversity Gain of Transmit Diversity in Wireless Systems with Rayleigh Fading," Proceeding of the 1994 ICClSUPERCOMM, New Orleans, 1o Vol. 2, PP. 1121-1125, May 1994.
In still another interesting approach symbols are encoded according to the antennas through which they are simultaneously transmitted, and are decoded using a maximum likelihood decoder.
s More specifically, the process at the transmitter handles the information in blocks of Ml bits, where M1 is a multiple ofM2, i.e., M1=k*M2. It converts each successive group of M2 bits into information symbols (generating thereby k information symbols), encodes each sequence of k information symbols into n channel codes (developing thereby a group of n channel codes for each sequence of k information symbols), and applies each code of a group of codes to a different ~utenna.
Summary The problems of prior art systems are cwercome, and an advance in the art is realized with a simple block coding arrangement where symbols are transmitted over a plurality of transmit channels and the coding comprises only simple arithmetic operations, such as negation and conjugation. The diversity created by the transmitter utilizes space diversity and eitl~~er time diversity or frequency diversity. Space diversity is effected by redundantly transmitting over a plurality of antennas; time diversity is effected by redundantly transmitting at different times;
and frequency diversity is effected by redun~3antly transmitting at different frequencies. Illustratively, using two transn-.at antennas and a single receive antenna, one of the disclosed embodiments provides the same diversity gain as the maximal-ratio receiver combining (MRRC) scheme with one transmit antenna and two receive ~ntennas_ The novel approach d oes not require any bandwidth expansion or feedback from the receiver to the transmitter, and has the same decoding complexity as the MRRC. The diversity improvement is equal to applying maximal-ratio receiver combining (MRRC) at the receiver with the same number of ~0 antennas. The principles of this invention are applicable to arrangements with more than two antennas, and an illustrative embodiment is disclosed using the same space block code with two transmit and two receive antennas. This scheme provides the same diversity gain as four-branch MRRC.
15 Brief Description of the Drawings FIG. 1 is a block diagram of a first embodiment in accordance with the principles of this invention;
FIG. 2 presents a block diagram of a second embodiment, where channel estimates are not employed;
20 FIG. 3 shows a block diagram of a third embodiment, where channel estimates are derived from recovered signals; and FIG. 4 illustrates an embodiment wh~;re two transmitter antennas and two receiver antennas are employed 25 Detail Description In accordance with the principles of this invention, effective communication is achieved with encoding of symbols that comprises merely negations and conjugations of symbols (which really is merely negation of the imaginary part) in S
combination with a transmitter created diversity. Space diversity and either frequency diversity or time diversity are employed.
FIG. 1 presents a block diagram of an Furangement where the two controllable aspects of the transmitter that are 'used are space and time.
That is, the FIG. 1 arrangement includes multiple transmitter antennas (providing space diversity) and employs multiple time intervals. Specifically, transmitter 10 illustratively comprises antennas 11 and 12, and it handles incoming data in blocks n symbols, where n is the number of transmitter antennas, and in the illustrative embodiment of FIG. 1, it equals 2, and each block takes n symbol intervals to 1o transmit. Also illustratively, the FIG. 1 arranl;ement includes a receiver 20 that comprises a single antenna 21.
At any given time, a signal sent by a t~~ansmitter antenna experiences interference effects of the traversed channel, which consists of the transmit chain, the air-link, and the receive chain. The channel may be modeled by a complex is muItiplicative distortion factor composed of a. magnitude response and a phase response. In the exposition that follows therefore, the channel transfer function from transmit antenna 11 to receive antenna ::1 is denoted by ho and from transmit antenna 12 to receive antenna 21 is denoted t~y h, , where:
ho = aoe~a°
20 h, = a~e''~' .
(1) Noise from interference and other sources is added at the two received signals and, therefore, the resulting baseband signal received at any time and outputted by reception and amplification section 25 is 25 r(t)=aae~°sl +a~e'~'sl +n(t),

(2) where s, and s~ are the signals being sent b;y transmit antenna 11 and 12, respectively.

As indicated above, in the two-antenna embodiment of FIG. 1 each block comprises two symbols and it takes two symbol intervals to transmit those two symbols. More specifically, when symbols s; 2nd s~ need to be transmitted, at a first time interval the transmitter applies signal s; to antenna 11 and signal s~ to antenna 12, and at the next time interval the transmitter applies signal - s, * to antenna 11 and signal so *., to antenna 12. This is clearly a very simple encoding process where only negations and conjugations are employed. As demonstrated below, it is as effective as it is simple. Corresponding to the above-described transmissions, in the first time interval the received signal is to r(t) = hos, + h,s~ + n(t),

(3) and in the next time interval the received sign,il is r(t+T) _-laos~ *+h,s; *+n(t+T).

(4) Table 1 illustrates the transmission pattern over the two antennas of the FIG.

arrangement for a sequence of signals { so , s, , sz , s3 , s, , ss ,... } .
Table 1 Time: t t+T t+27' t+3T t+4T t+ST

Antenna * * * .....
11 SO sl s1 S3 S4 SS

Antenna s~ so s3 sz ss s4 .....
12 * * *

The received signal is applied to channel estimator 22, which provides signals representing the channel characteristi~a or, rather, the best estimates thereof.
2o Those signals are applied to combiner 23 and to maximum likelihood detector 24.
The estimates developed by channel estimator 22 can be obtained by sending a known training signal that channel estimator 22 recovers, and based on the recovered signal the channel estimates are computed. This is a well known approach.

Combiner 23 receives the signal in the first time interval, buffers it, receives the signal in the next time interval, and combines the two received signals to develop signals s; =ho*r(t)+h,r*(t+T) s~ =h, *r(t)-hor*(t+T)_

(5) Substituting equation (1) into (5) yields s; =(ao +a; )s;+ho*n(t)+h,n*(t+T) s~ =(ao +a; )s~ -hon*(t+T)+h, *n(t), io (6 ) where ao = hoho * and a; = h, h, * , demonstrating that the signals of equation (6) are, indeed, estimates of the transmitted sign,ils (within a multiplicative factor).
Accordingly, the signals of equation (6) are : ent to maximum likelihood detector 24.
~5 In attempting to recover s,, two kind of signals are considered: the signals actually received at time t and t+T, and the signals that should have been received if s; were the signal that was sent. As demonstrated below, no assumption is made regarding the value of s~ . That is, a decision is made that s, = s,~ for that value of x for which 2o dZ[r(t),(hosX+hts~)]+dz[r(t+T~,(-h,s~*+hasr*)]
is less than dz[r(t),(hosk +h~sj)]+d2[r(t+T),1;-h,st *+hosk*)], where d s (x, y) is the squared Euclidean distance between signals x and y, i.e., Zs dI(X,y)=~r-y~?.

Recognizing that ho = ho +nnise that i~~ independent of the transmitted symbol, and that h, = h, +noise that is independent of the transmitted symbol, equation (7) can be rewritten to yield 2 2 x ~ x x 2 ~
(a~ +a~ ~S~I -SjSs -S~ *Sx < (a~ -1-CC~ ~Skl -S~Sk -Sr * Sk (g) r where ao = haho * and a; = h,h, * ; or equiv alently, ~au+ai _l~s~~x+dx~snsX~<~ao+ai -I~SkIx+dx~s;~sk~.
(9) In Phase Shift Keying modulation, all symbols carry the same energy, which ~o means that Isxlx = Isk Ix and, therefore, the decision rule of equation (9) may be simplified to choose signal s, = sx iff d x ~s" sx ) <_ ~~x (s,,sk ) .
(10) Thus, maximum likelihood detector 24 develops the signals sk for all values of k, 15 with the aid of ho and h, from estimator 22, develops the distances d x (s;
, sk ) , identifies x for which equation (10) holds an3 concludes that s, = s,~. A
similar process is applied for recovering s j .
In the above-described embodiment each block of symbols~is recovered as a block with the aid of channel estimates ho arid h, . However, other approaches to 2o recovering the transmitted signals can also be employed. Indeed, an embodiment for recovering the transmitted symbols exist;> where the channel transfer functions need not be estimated at all, provided an initial pair of transmitted signals is known to the receiver (for example, when the initial -pair of transmitted signals is prearranged). Such an embodiment is shown in FIG. 2, where maximum likelihood 25 detector 27 is responsive solely to combiner 26. (Elements in FIG. 3 that are referenced by numbers that are the same as reference numbers in FIG. 1 are like elements.) Combiner 26 of receiver 30 develops the signals ro =r(t)=hoso +h,s, +rto r, =r(t+T~=h,so *-hos, *+n, ri =r(t+2T~=hosZ +h,s~ +ni r3 =r(t+3T7=hisZ *-~tpS3 *+ns, (1 1) then develops intermediate signals A and B
A = ror3 * -r2r, B = riro * +r,r3 * , (12) and finally develops signals s2 = As, * +Bso s3 = -Aso * +Bs, , (13) where N3 and Nt are noise terms. It may be noted that signal ri is actually rz = host + h,s3 = host + h,s3 + nz, and similf~rly for signal r3 . Since the makeup of signals A and B makes them also equal to -2o A=(ao +a~ Xs~s, -s,so)+N, B=(ao +a; )(s~so *+s;s,*)+N~, (14) where N 1 and N2 are noise terms, it follows that signals s2 and s3 are equal to sZ = (ao + a; )(~so ~2 + ~s, ~2 )sz + N3 s, _ (ao + a~ )~so h + Is, IZ )s~ + N4 .
(15) When the power of all signals is constant (and normalized to 1) equation (15) reduces to s~ _ (ao + a; )sz + N3 s; _ (ao + a; )s3 + N, .
5 (16) Hence, signals s2 and s3 are, indeed, estimatfa of the signals s2 and s3 (within a multiplicative factor). Equation (15) dern~nstrates the recursive aspect of equation (13), where signal estimates s~ and s3 are ev,iluated with the aid of recovered signals sa and s, that are fed back from the output of the maximum likelihood 1 o detector.
Signals s2 and s3 are.applied to maximum likelihood detector 24 where recovery is effected with the metric expressed by equation (10) above. As shown in FIG. 2, once signals sz and sz are recovered, they are used together with received signals r~ , r3 , r4 , and rs to recover signals s4 and s s , and the process repeats.
is FIG. 3 depicts an embodiment that does not require the constellation of the transmitted signals to comprise symbols of edual power. (Elements in FIG. 3 that are referenced by numbers that are the same ;is reference numbers in FIG. 1 are like elements.) In FIG. 3, channel estimator 43 of receiver 40 is responsive to the output signals of maximum likelihood detector 42. Having access to the recovered signals 2o so and s, , channel estimator 43 forms the estimates _ roso *-r,si _ so *no +s~n, ISOIZ +IslI2 ~ ~0I2 +~S~I2 ros, *-r,so s, *no +son, he = Isolz +'n'Iz =~ + IsoIZ +Isch (1'~
and applies those estimates to combiner 23 and to detectoi 42. Detector 24 recovers 25 signals s~ and s3 by employing the approach used by detector 24 of FIG. 1, except that it does not employ the simplification of equation (9). The recovered signals of detector 42 are fed back to channel estimator ~.3, which updates the channel estimates in preparation for the next cycle.
The FIGS. 1-3 embodiments illustrate the principles of this invention for arrangements having two transmit antennas anal one receive antenna. However, those principles are broad enough to encompass a plurality of transmit antennas and a plurality of receive antennas. To illustrate,1~IG. 4 presents an embodiment where two transmit antennas and two receive antennas are used; to wit, transmit antennas 31 and 32, and receive antennas S1 and S2. The signal received by antenna S1 is t0 applied to channel estimator S3 and to combir~er SS, and the signal received by antenna 52 is applied to channel estimator 54 and to combiner 55. Estimates of the channel transfer functions ho and h, are applied by channel estimator 53 to combiner SS and to maximum likelihood detector 56. Similarly, estimates of the channel transfer functions hz and h3 are appl ied by channel estimator 54 to combiner 55 and to maximum likelihood detector S6. Table 2 defines the channels between the transmit antennas and the receivE: antennas, and table 3 defines the notion for the received signals at the two receive antennas.
Table :?
Antenna Antenna '~ 1 52 Antenna ho hi Antenna h, hj Table 3 Antenna Antenna 'i 1 52 Time t ro r2 Time t+T
r, r3 Based on the above, it can be shown that the received signals are ro = hoso + h,s~ + no r, =-hos, *+h,sp *+n, rZ = h2so + has, + n2 r3 = -h2s, * +h3so * +n3 (18) where no,n~,n" and n3 are complex random variables representing receiver thermal noise, interferences, etc.
In the FIG. 4 arrangement, combiner S'_. develops the following two signals that are sent to the maximum likelihood detector:
so=ho*ro+h, r,*+h2*rz+h~r3*
si = h, * ro - hors * +h3 * rz - h2r3 * .
to (19) Substituting the appropriate equations results i:n so = (ao +a; +a2 +a3 )so +ho * np + h,n, *+h2 * n2 +h3n3 s~ _ (ao + a; + aZ + a; )s, + h, * no - Jan, * +h3 * n~ - h~ ns * , (~0) which demonstrates that the signalsso and s~ are indeed estimates of the signals sa and si. Accordingly, signals so and s~ are sent to maximum likelihood decoder 56, which uses the decision rule of equation (10) to recover the signals so and s,.
As disclosed above, the principles of tlus invention rely on the transmitter to force a diversity in the signals received by a receiver, and that diversity can be 2o effected in a number of ways. The illustrated embodiments rely on space diversity -effected through a multiplicity of transmitter antennas, and time diversity -effected through use of two time intervals for transmitting the encoded symbols. It should be realized that two different transmission frequencies could be used instead of two time intervals. Such an embodiment would double the transmission speed, but it would also increase the hardware in the receiver, because two different frequencies need to be received and processed simultaneo,.~sly.

The above illustrated embodiments are., obviously, merely illustrative implementations of the principles of the invent ion, and various modifications and enhancements can be introduced by artisans without departing from the spirit and scope of this invention, which is embodied in the following claims. For example, all of the disclosed embodiments are illustrated for a space-time diversity choice, but as explained above, one could choose the space-frequency pair. Such a choice would have a direct effect on the construction of the receivers.

Claims (28)

WHAT IS CLAIMED IS:

1. A transmitter apparatus for wireless signal transmission, the transmitter receiving incoming signals, wherein the incoming signals are in blocks of symbols, wherein the transmitter comprises:
a coder that encodes the incoming signals, wherein encoding includes negation and complex conjugation of selected symbols; and multiple antennas, for transmitting the encoded signals, wherein the multiple antennas create space diversity in the transmitted signals, and wherein the transmitter creates a further type of diversity in the transmitted signal chosen from a group comprising time diversity and frequency diversity.

2. The transmitter of claim 1, wherein the incoming signals are in blocks of n symbols, and the multiple antennas comprise n antennas.

3. The transmitter of claim 1, wherein the transmitted symbols have equal energy.

4. A receiver for wireless communication, comprising:
a combiner that combines signals representing estimates of transmit channel characteristics derived from received non-noise signals, wherein the received non-noise signals are space diverse and either time diverse or frequency diverse, and wherein the received non-noise signals comprise sequences of encoded symbols, and wherein encoding includes negating selected symbols and complex conjugating selected symbols and a maximum likelihood detector that receives the combined signals and recovers a transmitted signal using a channel transfer function to determine a distance for which a relationship between the transmitted signal and the estimated channel characteristics holds.

5. The receiver of claim 4, further comprising:
at least one receiving antenna, wherein the at least one receiving antenna receives signals from each one of multiple transmitting antennas; and at least one channel estimator that generates the estimates of transmit channel characteristics and forwards the estimates to the combiner and to the maximum likelihood detector.

6. The receiver of claim 5, wherein the sequences of encoded signals comprise block of symbols S 0 and S1 that have been encoded into a sequence of symbols S 0 and -S 1*, and into a sequence of symbols S1 and S o*, where S i*
is the complex conjugate of S i.

7. The receiver of claim 6, wherein, the sequences of encoded signals are received from more than one transmitting antenna, including a first transmitting antenna and a second transmitting antenna, and wherein an encoded sequence {S o,-S1*,S2,-S3*,S4,-S5*. . .} is applied to the first transmitting antenna, and an encoded sequence {S1,S0*,S3,S2* S5 S4*. . .} is applied to the second transmitting antenna, where S i* is the complex conjugate of S i.

8. The receiver of claim 4, wherein the sequences of encoded signals are received from more than one transmitting antenna, and wherein the more than one transmitting antenna includes K transmitting antennas to effect K
distinct channels, wherein n.m symbols are distributed to the K antennas over L time intervals, where K=m and L=n, or K=n and L=m.

9. The receiver of claim 4, wherein the sequences of encoded signals are received from more than one transmitting antenna, and wherein the more than one transmitting antenna includes K transmitting antennas to effect K
distinct channels, wherein n.m symbols are distributed to the K antennas over L frequencies, where K=m and L=n, or K=n and L=m.

10. The receiver of claim 4, wherein the symbols have equal energy.

11. A receiver comprising:
a combiner responsive to non-noise signals received by an antenna from space-diverse paths and to detected information symbols, for developing sets of information symbol estimates, where the combiner develops the sets of information symbol estimates by combining the non-noise signals received by the antenna with the detected information symbols with operations that involve multiplications, negations, and conjugations; and a detector responsive to the sets of information symbol estimates that employs maximum likelihood decisions regarding information symbols encoded into channel symbols and embedded in the non-noise signals received by the antenna, to develop thereby the detected information symbols.

12. The receiver of claim 11 where the combiner develops a set of n information symbols from n.m received channel symbols, where m is the number of concurrent paths for which the channel estimator develops channel estimates.

13. A receiver comprising:
a first channel estimator responsive to a first antenna, for developing two space-diverse channel estimates;
a second channel estimator responsive to a second antenna, for developing two space-diverse channel estimates;
a combiner responsive to non-noise signals received by the first antenna and the second antenna and to channel estimates developed by the first and the second channel estimators, for developing sets of information symbol estimates, where the combiner develops the sets of information symbol estimates by combining the non-noise signals received by the antenna with the channel estimates obtained from the first and the second channel estimators, with operations that involve multiplications, negations, and conjugations; and a detector responsive to the sets of information symbol estimates that develops maximum likelihood decisions regarding information symbols encoded into channel symbols and embedded in the non-noise signals received by the first and second antennas.

14. A system for wireless communication, comprising:
transmitter means that receives incoming data, wherein the incoming data is handled in blocks of symbols; the transmitter means comprises;
coder means that encodes the incoming data, wherein encoding includes negation and complex conjugation of selected symbols; and multiple transmitting antenna means for transmitting the encoded data, wherein the multiple transmitting antenna means create space diversity in the transmitted data, and wherein the transmitter means creates a further type of diversity in the transmitted data chosen from a group comprising time diversity and frequency diversity.

15. The system of claim 14, wherein the incoming data is handled in blocks of n symbols, and the multiple transmitting antenna means comprise n transmitting antenna means.

16. The system of claim 14 or 15, further comprising receiver means that receives the transmitted data, wherein the receiver means comprises means for developing estimates of transmit channel characteristics based on the received data.

17. The system of claim 16, further comprising:
combiner means that combines the estimates of transmit channel characteristics developed from the transmitted data.

18. The system of claim 17, further comprising:
maximum likelihood detector means that receives the combined data and recovers the transmitted data.

19. The system according to one of claims 15, 16, 17 or 18, wherein the symbols have equal energy.

20. The system of claim 16, wherein the receiver means further comprises at least one channel estimator means that derives estimates of transmit channel characteristics on the basis of the received data.

21. The system of claim 20, wherein the receiver means further comprises:
multiple receiving antenna means for receiving the transmitted data, wherein each of the multiple receiving antenna means receives transmitted data from the multiple transmitting antenna means.

22. The system according to one of claims 14, 15, 16, 17, 18, 19, 20 or 21, wherein the incoming data are in blocks of n symbols, and the multiple transmitting antenna means comprise n transmitting antenna means, and wherein encoding further includes encoding an incoming block of symbols so and S1 into a sequence of symbols S0 and -S1*, and into a sequence of symbols S1 and S0*, where S i* is the complex conjugate of S i.

23. The system of claim 22, wherein the multiple transmitting antenna means comprise n transmitting antenna means, and wherein in response to a sequence {S0,-S1,S2,S3,S4. . .} of incoming symbols the coder develops a sequence {S1,-S1*,S2,-S3*,S4,-S5*. . .} that is applied to a first transmitting antenna means, and a sequence {S1,S0*,S3,S2* S5 S4*. . .} that is applied to a second transmitting antenna means, where S i* is the complex conjugate of S i.

24. A transmitter for wireless communication, comprising:
a coder that receives incoming data in blocks of n symbols, wherein the coder generates coded sequences of symbols, and wherein generating includes selectively negating symbols and selectively complex conjugating symbols; and at least two transmitting antennas for transmitting the coded sequences of symbols with space diversity, wherein each of the at least two transmitting antennas transmits a differently coded sequence, and wherein the transmitter creates further diversity in the transmitted coded sequences, based on time diversity or frequency diversity.

25. The transmitter of claim 24, wherein:
n = 2, and wherein the coder encodes an incoming block of symbols S0 and S1 into a sequence of symbols S0 and S1*, and into a sequence of symbols S1 and S0*, where S i* is the complex conjugate of S i; and wherein the at least two transmitting antennas comprise a first transmitting antenna and a second transmitting antenna, and in response to a sequence {S0,S1,S2,S3,S4. . .}of incoming symbols, the coder develops a sequence {S0,-S1*,S2,-S3*,S4, -S5*. . .} that is applied to the first transmitting antenna, and a sequence {S1,S0*,S3,S2*,S5,S4*. . .} that is applied to the second transmitting antenna, where S i* is the complex conjugate of S i.

26. The transmitter of claim 24 or 25, wherein the symbols are symbols of equal energy.

27. The transmitter of claim 24, wherein the transmitting antennas include K
transmitting antennas to effect K distinct channels, wherein n.m symbols are distributed to the K antennas over L time intervals, where K=m and L=n, or K=n and L=m.

28. The transmitter of claim 24, wherein the at least two transmitting antennas include K transmitting antennas to effect K distinct channels, wherein n-m symbols are distributed to the K antennas over L frequencies, where K=m and L=n, or K=n and L=m.