Transmitter diversity technique for wireless communications

• US 6,185,258 B1
• Filed: 05/07/1998
• Issued: 02/06/2001
• Est. Priority Date: 09/16/1997
• Status: Expired due to Term

• Current Assignee: AT&T Mobility II LLC (AT&T, Inc.)
• Original Assignee: AT&T Wireless Services Incorporated (AT&T, Inc.)
• Inventors: Alamouti, Siavash, Tarokh, Vahid
• Primary Examiner(s): Pham, Chi H.
• Assistant Examiner(s): Webster, Bryan
• Application Number:
  US09/074,224
• Time in Patent Office: 1,006 Days
• Field of Search: 375/267, 375/295, 375/299, 375/262, 375/340, 375/341, 375/346, 375/347, 375/260, 455/132, 371/43.6, 371/43.7, 371/43.8, 371/37.11
• US Class Current: 375/260
• CPC Class Codes: H04B 1/02 Transmitters
• CPC Class Codes: H04B 7/0613 using simultaneous transmission H04B7/0686 takes precedence
• CPC Class Codes: H04B 7/0615 of weighted versions of same signal
• CPC Class Codes: H04B 7/0667 of delayed versions of same signal using space-time coding H04L1/0618
• CPC Class Codes: H04B 7/0669 using different channel coding between antennas space-time coding H04L1/0618
• CPC Class Codes: H04B 7/0671 using different delays between antennas
• CPC Class Codes: H04B 7/0689 using different transmission schemes, at least one of them being a diversity transmission scheme
• CPC Class Codes: H04B 7/0837 using pre-detection combining H04B7/0868 takes precedence
• CPC Class Codes: H04B 7/0845 per branch equalization, e.g. by an FIR-filter or RAKE receiver per antenna branch rake receivers as such H04B1/7115
• CPC Class Codes: H04B 7/0854 using error minimizing algorithms, e.g. minimum mean squared error [MMSE], "cross-correlation" or matrix inversion
• CPC Class Codes: H04B 7/0857 using maximum ratio combining techniques, e.g. signal-to- interference ratio [SIR], received signal strenght indication [RSS]
• CPC Class Codes: H04B 7/0891 Space-time diversity rake receivers H04B1/7115; space-time decoding H04L1/0631
• CPC Class Codes: H04B 7/12 Frequency diversity
• CPC Class Codes: H04L 1/0054 Maximum-likelihood or sequential decoding, e.g. Viterbi, Fano, ZJ algorithms
• CPC Class Codes: H04L 1/04 using frequency diversity
• CPC Class Codes: H04L 1/0606 Space-frequency coding
• CPC Class Codes: H04L 1/0618 Space-time coding
• CPC Class Codes: H04L 1/0625 Transmitter arrangements
• CPC Class Codes: H04L 1/0631 Receiver arrangements
• CPC Class Codes: H04L 1/0643 block codes
• CPC Class Codes: H04L 1/0668 : Orthogonal systems, e.g. using Alamouti codes
• CPC Class Codes: H04L 1/08 : by repeating transmission, e.g. Verdan system H04L1/1858 and H04L1/189 take precedence
• CPC Class Codes: H04L 25/0202 : Channel estimation

Abstract

A simple block coding arrangement is created with symbols transmitted over a plurality of transmit channels, in connection with coding that comprises only of 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 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.

Claims

1. An arrangement comprising:

a coder responsive to incoming symbols, forming a set of channel symbols that incorporate redundancy, where the coder employs replications and, at least for some of the channel symbols, forms a negative of an incoming symbol, forms a complex conjugate of an incoming symbol, or forms a negative complex conjugate of an incoming symbol; and

an output stage that applies said channel symbols to at least one transmitter antenna to form at least two distinct channels over a transmission medium.

2. The arrangement of claim 1 where said at least two distinct channels direct information to a single receiver antenna.

3. The arrangement of claim 1 where each of said at least two distinct channels transmits a channel symbol for each incoming symbol encoded by said coder.

4. The arrangement of claim 1 where said coder encodes incoming symbols in blocks of n symbols.

5. The arrangement of claim 4 where, when n=2, 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.

6. The arrangement of claim 1 where said output stage comprises a first antenna and a second antenna, and where in response to a sequence {s₀,s₁,s₂,s₃,s₄,s₅ . . . } of incoming symbols said coder develops a sequence {s₀,−

S₁*,s₂,−

s₃*,s₄,−

s₅* . . . } that is applied said first antenna by said output stage, and a sequence {s₁,s₀*,s₃,s₂*,s₅,s₄* . . . } that is applied to said second antenna by said output stage, where s_i* is the complex conjugate of s_i.

7. The arrangement of claim 4 where said coder develops n•

m channel symbols for each block of n incoming symbols, where m is the number of said distinct channels.

8. The arrangement of claim 7 where said n•

m channel symbols are distributed to said m distinct channels.

9. The arrangement of claim 8 where said transmitter employs K transmitter antennas to effect K distinct channels, and where said n•

m channel symbols are distributed to said K antennas over L time intervals, where K=m and L=n, or K=n and L=m.

10. The arrangement of claim 8 where said transmitter employs K transmitter antennas to effect K distinct channels, and where said n•

m channel symbols are distributed to said K antennas over L frequencies, where K=m and L=n, or K=n and L=m.

11. The arrangement of claim 1 further comprising a receiver having a single antenna that is adapted to receive and decode signals transmitted by said output stage.

12. The arrangement of claim 1 further comprising a receiver having two receive antennas that is adapted to receive and decode signals transmitted by said output stage.

13. A transmitter comprising:

first means, responsive to incoming symbols, for forming a set of channel symbols with redundancy in said set of channel symbols, where at least in forming some of the channel symbols the coder replicates other channel symbols, replicates and negates said other channel symbols, or replicates and negates a part of said other channel symbols, and

second means, for transmitting to a transmission medium channel symbols formed by said first means over at least two antennas.

14. A transmitter comprising:

first means for transmitting channel symbols over two different and distinct transmitter channel types, thereby providing transmitter-created diversity, where one of the channel types is space diversity, and the other of the transmitter channel types is taken from a set including frequency diversity and time diversity;

a coder for encoding incoming symbols in blocks of n symbols to form n•

m channel symbols; and

third means for distributing m groups of n channel symbols each to said first means.

15. The transmitter of claim 14 where each one of said groups is applied to a first of said distinct transmitter channels.

16. The transmitter of claim 14 where one of said distinct transmitter channels is effected with a plurality of transmitter antennas, providing space diversity, and another of said distinct transmitter channels is effected with a plurality of time intervals.

17. The transmitter of claim 16 where the number of said transmitter antennas is m and said m groups of channel symbols are distributed to said m transmitter antennas.

18. The transmitter of claim 17 where n=2.

19. A method for transmitting over a transmission medium information corresponding to incoming symbols, comprising the steps of:

encoding incoming symbols in block of n symbols, to form n•

m channel symbols, where m is a number of distinct space diverse channels over which said method transmits symbols over said transmission medium, where said encoding involves replication of incoming symbols and, for at least some of said channel symbols, involve replication and negation; and

distributing said n•

m channel symbols over said m channels so that each incoming symbol has a corresponding channel symbol in each of said m channels.

20. The method of claim 19 where said encoding involves forming a complex conjugate of incoming symbols.

21. The method of claim 19 where said encoding consists of replicating an incoming symbol, forming a complex conjugate of an incoming symbol, forming a negative of an incoming symbols, or forming a negative complex conjugate of an incoming symbol.

22. A method for transmitting information corresponding to incoming symbols, comprising the steps of:

encoding incoming symbols in block of n symbols, to form n•

m channel symbols, where m is a number of distinct space diverse channels over which said method transmits symbols over said transmission medium; and

distributing said n•

m channel symbols over said m channels so that each incoming symbol had a corresponding channel symbol in each of said m channels;

where said encoding involves replication of incoming symbols and, for at least some of said channel symbols, involves replication and negation operation.

23. A receiver comprising:

a combiner responsive to signals received by an antenna and to channel estimates developed for at least two concurrent space diverse paths over which said signals arrive at said antenna, for developing sets of information symbol estimates, where said combiner develops said sets of information symbol estimates by combining said signals received by said antenna with said channel estimates via operations that involve multiplications, negations, and conjugations;

a detector responsive to said sets of information symbol estimates that develops maximum likelihood decisions regarding information symbols encoded into channel symbols and embedded in said signals received by said antenna; and

a channel estimator responsive to said signals received by said antenna for developing said channel estimates;

where said signal received by said antenna at a given time interval corresponds to

24. The receiver of claim 23 where said detector settles on symbol {tilde over (s)}_i=s_x iff d²({tilde over (s)}₁,s_x)≦

d²({tilde over (s)}₁,s_k), where d²({tilde over (s)}₁,s_x) corresponds to (s_i−

s_x)(s_i*−

s_x*).

25. The receiver of claim 23 further comprising a channel estimator, responsive to said sets of information symbols developed by said combiner, for developing said channel estimates.

26. The receiver of claim 23 further comprising a channel estimator, responsive to output signals of said detector, for developing said channel estimates.

27. The receiver of claim 26 where said channel estimator develops channel estimates {tilde over (h)}₀ and {tilde over (h)}₁ by evaluating the expressions ${\tilde{h}}_0=\frac{r_0}{}$

s0*-r1

s1

s0

2+

s1

2${\tilde{h}}_1=\frac{r_0<br><br>s_1^{*}-r_1<br><br>s_0}{{<br><br>s_0<br><br>}^2+{<br><br>s_1<br><br>}^2}$

where symbols s₀ and s_i are output symbols of said detector, r₀ is a signal received at said antenna at a given time interval, r₁ is a signal received at said antenna at a next time interval, s_i* is the complex conjugate of s_i, and |s_i|² is the magnitude, squared, of symbol s_i.

29. The receiver of claim 23 where said combiner develops a set of n information symbols from n•

m received channel symbols, where m is the number of concurrent paths for which said channel estimator develops channel estimates.

28. A receiver comprising:

a combiner responsive to signals received by an antenna from space-diverse paths and to detected information symbols, for developing sets of information symbol estimates, where said combiner develops said sets of information symbol estimates by combining said signals received by said antenna with said detected information symbols with operations that involve multiplications, negations, and conjugations; and

a detector responsive to said sets of information symbol estimates that employs maximum likelihood decisions regarding information symbols encoded into channel symbols and embedded in said signals received by said antenna, to develop thereby said detected information symbols;

where said signal received by said antenna at a given time interval corresponds to

30. An arrangement comprising:

a coder responsive to incoming symbols, forming a set of channel symbols that incorporate redundancy, where the coder creates some channel symbols by replicating other channel symbols or by replicating and negating other channel symbols or parts thereof; and

an output stage that applies said channel symbols to at least one transmitter antenna to form at least two distinct channels over a transmission medium.