System and method for antenna diversity using joint maximal ratio combining

• US 6,687,492 B1
• Filed: 06/19/2002
• Issued: 02/03/2004
• Est. Priority Date: 03/01/2002
• Status: Expired due to Fees

• Current Assignee: IPR Licensing Incorporated (InterDigital, Inc.)
• Original Assignee: Cognio, Inc. (Cisco Systems, Inc.)
• Inventors: Sugar, Gary L., Vaidyanathan, Chandra, Tesfai, Yohannes
• Primary Examiner(s): Chin, Vivian
• Assistant Examiner(s): Persino, Raymond B
• Application Number:
  US10/174,728
• Time in Patent Office: 594 Days
• Field of Search: 455/506, 455/562.1, 455/423, 455/25, 455/69, 455/67.11, 455/82, 455/129, 455/575.7, 455/63.1, 455/63.4, 455/107, 455/114.2, 455/289, 455/279.1, 455/273, 455/276--27, 455/125, 375/347, 375/295, 375/148, 375/267, 370/294, 342/378, 342/383, 342/174, 342/380
• US Class Current: 455/276.1
• CPC Class Codes: H01Q 3/28 varying the amplitude
• CPC Class Codes: H03G 3/3042 in modulators, frequency-changers, transmitters or power amplifiers transmission power control in bidirectional transmission systems H04W52/04
• CPC Class Codes: H03G 3/3089 Control of digital or coded signals
• CPC Class Codes: H04B 1/0483 Transmitters with multiple parallel paths
• CPC Class Codes: H04B 7/0417 Feedback systems
• CPC Class Codes: H04B 7/0615 of weighted versions of same signal
• CPC Class Codes: H04B 7/0617 for beam forming
• 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 7/0845 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 7/0848 Joint weighting
• 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: H04L 1/06 using space diversity
• CPC Class Codes: H04L 2025/03426 transmission using multiple-input and multiple-output channels
• CPC Class Codes: H04L 2025/03611 Iterative algorithms
• CPC Class Codes: H04L 25/0204 of multiple channels
• CPC Class Codes: H04L 25/0228 with direct estimation from sounding signals
• CPC Class Codes: H04L 25/0242 using matrix methods
• CPC Class Codes: H04L 25/03343 Arrangements at the transmitter end
• CPC Class Codes: H04L 27/2602 : Signal structure
• CPC Class Codes: H04L 27/2626 : Arrangements specific to the transmitter only
• CPC Class Codes: H04L 5/0007 : the frequencies being orthogonal, e.g. OFDM(A), DMT
• CPC Class Codes: H04W 52/42 : in systems with time, space, frequency or polarisation diversity

Abstract

A composite beamforming technique is provided wherein a first communication device has a plurality of antennas and the second communication has a plurality of antennas. When the first communication device transmits to the second communication device, the transmit signal is multiplied by a transmit weight vector for transmission by each the plurality of antennas and the transmit signals are received by the plurality of antennas at the second communication device. The second communication device determines the best receive weight vector for the its antennas, and from that vector, derives a suitable transmit weight vector for transmission on the plurality of antennas back to the first communication device. Several techniques are provided to determine the optimum transmit weight vector and receive weight vector for communication between the first and second communication devices so that there is effectively joint or composite beamforming between the communication devices.

Claims

1. A method for communicating signals between a first communication device and a second communication device using radio frequency (RF) communication techniques, comprising:

a. applying a transmit antenna vector to a baseband signal to be transmitted from the first communication device to the second communication device, the transmit antenna weight vector comprising a complex transmit antenna weight for each of the N plurality of antennas, wherein each complex transmit antenna weight has a magnitude and a phase whose values may vary with frequency across a bandwidth of the baseband signal, thereby generating N transmit signals each of which is weighted across the bandwidth of the baseband signal such that at substantially all frequencies of the baseband signal, the sum of the power of the transmit signals across the N plurality of antennas of the first communication device is equal to a constant;

b. receiving the N transmit signals at M plurality of antennas of the second communication device;

c. determining a receive weight vector comprising a complex receive antenna weight for each of the M plurality of antennas of the second communication device from the N transmit signals received by the M plurality of antennas, wherein each receive antenna weight has a magnitude and a phase whose values may vary with frequency across a bandwidth of a baseband signal derived from the N transmit signals received by the second communication device;

d. computing a transmit weight vector comprising a plurality of complex transmit antenna weights for the M plurality of antennas of the second communication device by computing a conjugate of the receive weight vector divided by the norm of the receive weight vector; and

e. applying the transmit weight vector to a baseband signal to be transmitted from the second communication device to the first communication device, thereby generating M plurality of transmit signals such that at substantially all frequencies of the baseband signal, the sum of the power of the transmit signals across the M plurality of antennas of the second communication device is equal to a constant.

2. The method of claim 1, and further comprising steps of:

f. receiving at the N plurality of antennas of the first communication device the M plurality of transmit signals transmitted by the second communication device;

g. determining a receive weight vector from the signals received from the second communication device by the N plurality of antennas; and

h. updating the transmit weight vector for the N plurality of antennas of the first communication device for transmitting signals to the second communication device by computing a conjugate of the receive weight vector of the first communication device divided by a norm of the conjugate of the receive weight vector and repeating step (a) when transmitting back to the second communication device.

3. The method of claim 2, and further comprising repeating steps (a) through (h) and converging to transmit weight vectors used by the first and second communication devices that optimize a signal-to-noise ratio for communication between the first and second communication devices.

4. The method of claim 2, and further comprising storing in the first communication device optimum transmit antenna weights indexed against an identifier for the second communication device.

5. The method of claim 2, and further comprising storing in the first communication device optimum transmit antenna weights indexed against corresponding identifiers for each of a plurality of communication devices that the first communication device communicates with.

6. The method of claim 1, wherein the step of determining the receive weight vector at the second communication device comprises matching the receive antenna weights to the received signal.

7. The method of claim 1, wherein steps (a) through (e) are performed for each of K frequency sub-bands of the baseband signal that correspond to sub-carriers of a multi-carrier baseband signal or to synthesized frequency sub-bands of a single carrier baseband signal.

8. The method of claim 7, and further comprising storing in the first communication device, for each of the N antennas, complex transmit antenna weights for a subset of the K frequency sub-bands or sub-carriers.

9. The method of claim 8, and further comprising retrieving the stored subset of complex transmit antenna weights and generating therefrom the complete set of antenna weights for all of the K frequency sub-bands or sub-carriers using interpolation techniques.

10. A method for communicating signals between a first communication device and a second communication device using radio frequency (RF) communication techniques, comprising:

a. applying a transmit antenna vector to a baseband signal to be transmitted from the first communication device to the second communication device, the transmit antenna weight vector comprising a complex transmit antenna weight for each of the N plurality of antennas, wherein each complex transmit antenna weight has a magnitude and a phase whose values may vary with frequency across a bandwidth of the baseband signal, thereby generating N transmit signals each of which is weighted across the bandwidth of the baseband signal such that at substantially all frequencies of the baseband signal, the sum of the power of the transmit signals across the N plurality of antennas of the first communication device is equal to a constant;

b. receiving at the N plurality of antennas of the first communication device at least one signal that was transmitted by the second communication device;

c. determining a receive weight vector comprising a plurality of complex receive antenna weights for the N plurality of antennas of the first communication device from one or more signals received at the N plurality of antennas from the second communication device, wherein each receive antenna weight has a magnitude and a phase whose values may vary with frequency; and

d. updating the transmit weight vector for the plurality of antennas of the first communication device for transmitting signals to the second communication device by computing a conjugate of the receive weight vector of the first communication device divided by a norm of the conjugate of the receive weight vector and repeating step (a) when transmitting back to the second communication device.

11. The method of claim 10, wherein steps (a) through (d) are performed for each of K frequency sub-bands of the baseband signal that correspond to sub-carriers of a multi-carrier baseband signal or to synthesized frequency sub-bands of a single carrier baseband signal.

12. The method of claim 11, and further comprising storing in the first communication device, for each of the N antennas, complex transmit antenna weights for a subset of the K frequency sub-bands or sub-carriers.

13. The method of claim 12, and further comprising retrieving the stored subset of complex transmit antenna weights and generating therefrom the complete set of antenna weights for all of the K frequency sub-bands or sub-carriers using interpolation techniques.

14. The method of claim 10, and further comprising storing in the first communication device optimum transmit antenna weights indexed against an identifier for the second communication device.

15. The method of claim 14, and further comprising storing in the first communication device optimum transmit antenna weights indexed against corresponding identifiers for each of a plurality of communication devices that the first communication device communicates with.

16. The method of claim 10, and further comprising repeating steps (a) through (d) for each exchange of signals between the first communication device and the second communication device and converging to transmit weight vectors used by the first communication device that optimize a signal-to-noise ratio for communication from the first communication device to the second communication device.

17. A medium encoded with instructions that, when executed, perform a method comprising steps of:

a. applying a transmit antenna vector to a baseband signal to be transmitted from a first communication device to a second communication device, the transmit antenna weight vector comprising a complex transmit antenna weight for each of the N plurality of antennas, wherein each complex transmit antenna weight has a magnitude and a phase whose values may vary with frequency across a bandwidth of the baseband signal, thereby generating N transmit signals each of which is weighted across the bandwidth of the baseband signal such that at substantially all frequencies of the baseband signal, the sum of the power of the transmit signals across the N plurality of antennas of the first communication device is equal to a constant;

b. determining a receive weight vector comprising a plurality of complex receive antenna weights for the N plurality of antennas of the first communication device from one or more signals received by the N plurality of antennas from the second communication device, wherein each receive antenna weight has a magnitude and a phase whose values may vary with frequency; and

c. updating the transmit weight vector for the plurality of antennas of the first communication device for transmitting signals to the second communication device by computing a conjugate of the receive weight vector of the first communication device divided by a norm of the conjugate of the receive weight vector and repeating step (a) when transmitting back to the second communication device.

18. The medium of claim 17, and further comprising instructions for performing steps (a) through (c) at each of K frequency sub-bands of the baseband signal that correspond to sub-carriers of a multi-carrier baseband signal or to synthesized frequency sub-bands of a single carrier baseband signal.

19. The medium of claim 18, and further comprising instructions for storing in the first communication device, for each of the N antennas, complex transmit antenna weights for a subset of the K frequency sub-bands or sub-carriers.

20. The medium of claim 19, and further comprising instructions for retrieving the stored subset of complex transmit antenna weights and generating therefrom the complete set of antenna weights for all of the K frequency sub-bands or sub-carriers using interpolation techniques.

21. The medium of claim 17, wherein the instructions are implemented by a plurality of gates.

22. A baseband signal processor comprising the medium of claim 21.

23. A communication device comprising the baseband signal processor of claim 22, and further comprising a radio transceiver coupled to the baseband signal processor that upconverts the transmit signals for transmission by the plurality of antennas and that downconverts signals received by each of the plurality of antennas.

24. The medium of claim 17, wherein the instructions are processor readable instructions, that when executed by a processor, cause the processor to perform steps (a) through (c).

25. An integrated circuit comprising the medium of claim 17.

26. The integrated circuit of claim 25, and further comprising a processor that executes the instructions encoded on the medium.

27. A communication device comprising the medium of claim 17, and further comprising:

a. a transmitter that upconverts transmit signals for transmission;

b. a receiver that downconverts received signals; and

c. a processor coupled to the transmitter and to the receiver that processes instructions encoded on the medium.

28. The medium of claim 17, and further comprising instructions encoded on the medium that, when executed, repeat steps (a) through (c) for each exchange of signals between the first communication device and the second communication device and converging to transmit weight vectors used by the first communication device that optimize a signal-to-noise ratio for communication from the first communication device to the second communication device.

29. A method for communicating signals from a first communication device to a second communication device using radio frequency (RF) communication techniques, comprising:

a. transmitting a first signal by one of N plurality of antennas of the first communication device;

b. receiving the first signal transmitted by the first communication device at two antennas of the second communication device;

c. transmitting a first response signal from the second communication device to the first communication device using a first of two antennas at the second communication device;

d. at the first communication device, receiving at the plurality of antennas the first response signal transmitted by the first antenna of the second communication device and deriving therefrom a first row of a channel response matrix that describes the channel response between the first communication device and the second communication device;

e. transmitting a second signal by the plurality of antennas of the first communication device using a transmit weight vector that is orthogonal to the first row of the channel response matrix;

f. receiving the second signal transmitted at the second communication device at the two antennas;

g. transmitting a second response signal from the second communication device using a second of the two antennas;

h. at the first communication device, receiving the second response signal transmitted by the second antenna of the second communication device and deriving therefrom a second row of the channel response matrix; and

i. at the first communication device, selecting one of the first and second rows of the channel response matrix that provides better signal-to-noise at the second communication device as the transmit weight vector for further transmission of signals to the second communication device.

30. The method of claim 29, and further comprising the step of computing a norm of each row of the channel response matrix, and wherein the step of selecting comprises selecting the row that has the greater norm.

31. The method of claim 29, wherein the steps (a) through (i) are performed at each of a plurality of frequencies corresponding to sub-carrier frequencies of a multi-carrier baseband signal or synthesized frequency sub-bands of a single carrier baseband signal.

32. The method of claim 31, and further comprising storing in the first communication device, for each of the N antennas, complex transmit antenna weights for a subset of the frequency sub-bands or sub-carriers.

33. The method of claim 32, and further comprising retrieving the stored subset of complex transmit antenna weights and generating therefrom the complete set of antenna weights for all of the frequency sub-bands or sub-carriers using interpolation techniques.

34. The method of claim 29, wherein the second communication device selects one of the two antennas for transmitting signals to the first communication device based on which of the two antennas more strongly received a signal from the first communication device.

35. The method of claim 29, wherein the step of transmitting the second signal from the first communication device to the second communication device using a transmit weight vector that is orthogonal to the row of the channel response matrix forces the second communication device to select the second antenna based on received signal strength at each of two antennas of second communication device.

36. The method of claim 29, wherein at substantially all frequencies of the baseband signal, the magnitude of the complex transmit antenna weights are such that the sum of the power across the plurality of antennas of the first communication device is constant.

37. A method for communicating signals from a first communication device to a second communication device using radio frequency (RF) communication techniques, comprising:

a. transmitting a first signal by one of N plurality of antennas of the first communication device;

b. receiving a first response signal at the plurality of antennas of the first communication device transmitted from a first of two antennas of the second communication device;

c. deriving a first row of a channel response matrix that describes the channel response between the first communication device and the second communication device;

d. transmitting a second signal by the plurality of antennas of the first communication device using a transmit weight vector that is orthogonal to the first row of the channel response matrix;

e. receiving a second response signal transmitted by a second of the two antennas of the second communication device and deriving therefrom a second row of the channel response matrix; and

f. selecting one of the first and second rows of the channel response matrix that provides better signal-to-noise at the second communication device as the transmit weight vector for further transmission of signals to the second communication device.

38. The method of claim 37, and further comprising the step of determining when a signal received at the first communication device from the second communication device indicates at least a minimum difference in a row of the channel response matrix, and repeating steps (a)-(f) in response thereto.

39. The method of claim 37, and further comprising the step of computing a norm of each row of the channel response matrix, and wherein the step of selecting comprises selecting the row that has the greater norm.

40. The method of claim 37, wherein the steps (a) through (f) are performed at each of a plurality of frequencies corresponding to sub-carrier frequencies of a multi-carrier baseband signal or synthesized frequency sub-bands of a single carrier baseband signal.

41. The method of claim 40, and further comprising storing in the first communication device, for each of the N antennas, complex transmit antenna weights for a subset of the frequency sub-bands or sub-carriers.

42. The method of claim 41, and further comprising retrieving the stored subset of complex transmit antenna weights and generating therefrom the complete set of antenna weights for all of the frequency sub-bands or sub-carriers using interpolation techniques.

43. The method of claim 37, wherein at substantially all frequencies of the baseband signal, the magnitude of the complex transmit antenna weights are such that the sum of the power across the plurality of antennas of the first communication device is constant.

44. A medium encoded with instructions that, when executed, perform steps of:

a. generate a first signal for transmission by one of a plurality of antennas of a first communication device to a second communication device;

b. process a first response signal received at the plurality of antennas that was transmitted from a first of two antennas of the second communication device and generating a first row of a channel response matrix that describes the channel response with the other communication device;

c. applying to a second signal a transmit weight vector that is orthogonal to the first row of the channel response matrix for transmission via the plurality of antennas of the first communication device to the second communication device;

d. processing a second response signal received at the plurality of antennas that was transmitted from a second of two antennas of the second communication device and generating therefrom a second row of the channel response matrix; and

e. selecting one of the first and second rows of the channel response matrix that provides better signal-to-noise at the second communication device as the transmit weight vector for further transmission of signals to the other communication device.

45. The medium of claim 44, and further comprising instructions to compute a norm of each row of the channel response matrix, and select the row that has the greater norm as the transmit weight vector.

46. The medium of claim 44, wherein the instructions perform steps (a) through (e) are performed at each of a plurality of frequencies corresponding to sub-carrier frequencies of a multi-carrier baseband signal or synthesized frequency sub-bands of a single carrier baseband signal.

47. The medium of claim 44, wherein the instructions are implemented by a plurality of gates.

48. The medium of claim 44, wherein the instructions are processor readable instructions, that when executed by a processor, cause the processor to perform steps (a) through (e).

49. A communication device comprising the medium of claim 44, and further comprising:

a. a transmitter that upconverts signals to be transmitted;

b. a receiver that downconverts received signals;

c. a processor coupled to the transmitter and to the receiver that processes the instructions encoded on the medium.

50. An integrated circuit comprising the medium of claim 44.

51. The integrated circuit of claim 44, and further comprising a processor that executes the instructions encoded on the medium.

52. A method for communicating signals between a first communication device and a second communication device using radio frequency (RF) communication techniques, comprising:

a. transmitting a message from the first communication device to the second communication device to determine whether the second communication device is capable of transmitting signals back to the first communication device using an adjustable transmit weight vector;

b. generating a training sequence comprising a sequence of N consecutive symbols, where N is a number of antennas of the first communication device, and the N symbols are multiplied by respective ones of N linearly independent vectors that span columns of a channel response matrix between the plurality of antennas of the first communication device and a plurality of antennas of the second communication device, thereby producing N transmit signals;

c. transmitting the N transmit signals from the plurality of antennas of the first communication device;

d. receiving the N transmit signals at each of a plurality of antennas at the second communication device;

e. at the second communication device, deriving from signals received by the plurality of antennas the channel response matrix between the first communication device and the second communication device; and

f. at the second communication device, generating a transmit weight vector from the channel response matrix for transmitting a signal from the second communication device to the first communication device using the plurality of antennas of the second communication device.

53. The method of claim 52, and further comprising:

a. appending the training sequence to a data unit for transmission from the first communication device to the second communication device;

b. transmitting the data unit with the appended training sequence by the antennas of the first communication device; and

c. at the second communication device, receiving the data unit and the appended training sequence and decoding the data unit.

54. The method of claim 52, wherein the step of appending the training sequence comprises appending the training sequence to a directed media access control (MAC) protocol data unit in accordance with the IEEE 802.11 communication standard.

55. The method of claim 52, wherein the step of generating the training sequence comprises generating N consecutive 2-symbol long preamble sequences in accordance with the IEEE 802.11 communication standard.

56. The method of claim 52, wherein the step of generating the transmit weight vector comprises updating the transmit weight vector for transmitting a signal to the first communication device.

57. The method of claim 52, and further comprising the step of storing at the second communication device information describing the transmit weight vector to be used for transmitting signals to the first communication device.

58. The method of claim 57, wherein the step of storing comprises storing at the second communication device information describing transmit weight vectors to be used for transmitting signals to each of a plurality of corresponding communication devices.

59. The method of claim 52, wherein steps (b) through (f) are performed at each of a plurality of frequencies corresponding to sub-carrier frequencies of a multi-carrier baseband signal or synthesized frequency sub-bands of a single carrier baseband signal so as to generate frequency dependent transmit antenna weights for the transmit weight vector.

60. The method of claim 52, wherein the step of generating the training sequence comprises applying to the N symbols respective ones of the transmit weight vectors [1 0 . . . 0]₀^T, [0 1 0 . . . 0]₁^T, . . . , [0 0 . . . 1]_N−

1^T.

61. The method of claim 52, wherein steps (b) through (f) are performed when the second communication device responds to indicate that it is capable of transmitting signals using an adjustable transmit weight vector.

62. A method for communicating signals between a first communication device and a second communication device using radio frequency (RF) communication techniques, comprising:

a. generating a training sequence comprising a sequence of N consecutive symbols, where N is a number of antennas of the first communication device, and the N symbols are multiplied by respective ones of N linearly independent vectors [1 0 . . . 0]₀^T, [0 1 0 . . . 0]₁^T, . . . , [0 0 . . . 1]<sub>N−

1</sub>^T, thereby producing N transmit signals;

b. transmitting the N transmit signals from the plurality of antennas of the first communication device;

c. receiving the N transmit signals at each of a plurality of antennas at the second communication device;

d. at the second communication device, deriving from signals received by the plurality of antennas the channel response matrix between the first communication device and the second communication device; and

e. at the second communication device, generating a transmit weight vector from the channel response matrix for transmitting a signal from the second communication device to the first communication device using the plurality of antennas of the second communication device.

63. The method of claim 62, and further comprising:

a. appending the training sequence to a data unit for transmission from the first communication device to the second communication device;

b. transmitting the data unit with the appended training sequence by the antennas of the first communication device; and

c. at the second communication device, receiving the data unit and the appended training sequence and decoding the data unit.

64. The method of claim 62, wherein the step of appending the training sequence comprises appending the training sequence to a directed media access control (MAC) protocol data unit in accordance with the IEEE 802.11 communication standard.

65. The method of claim 62, wherein the step of generating the training sequence comprises generating N consecutive 2-symbol long preamble sequences in accordance with the IEEE 802.11 communication standard.

66. The method of claim 62, wherein the step of generating the transmit weight vector comprises updating the transmit weight vector for transmitting a signal to the first communication device.

67. The method of claim 62, and further comprising the step of storing at the second communication device information describing the transmit weight vector to be used for transmitting signals to the first communication device.

68. The method of claim 67, wherein the step of storing comprises storing at the second communication device information describing transmit weight vectors to be used for transmitting signals to each of a plurality of corresponding communication devices.

69. The method of claim 62, wherein steps (a) through (e) are performed at each of a plurality of frequencies corresponding to sub-carrier frequencies of a multi-carrier baseband signal or synthesized frequency sub-bands of a single carrier baseband signal so as to generate frequency dependent transmit antenna weights for the transmit weight vector.

70. The method of claim 62, and further comprising the step of transmitting a message from the first communication device to the second communication device to determine whether the second communication device is capable of transmitting signals back to the first communication device using an adjustable transmit weight vector.

71. The method of claim 70, wherein steps (a) through (e) are performed when the second communication device responds to indicate that it is capable of transmitting signals using an adjustable transmit weight vector.

72. A method for communicating signals between a first communication device and a second communication device using radio frequency (RF) communication techniques, comprising:

a. applying a transmit antenna vector to a baseband signal to be transmitted from the first communication device to the second communication device, the transmit antenna weight vector comprising a complex transmit antenna weight for each of the N plurality of antennas, wherein each complex transmit antenna weight has a magnitude and a phase whose values may vary with frequency across a bandwidth of the baseband signal, thereby generating N transmit signals each of which is weighted across the bandwidth of the baseband signal;

b. receiving the N transmit signals at M plurality of antennas of the second communication device;

c. determining a receive weight vector comprising a complex receive antenna weight for each of the M plurality of antennas of the second communication device from the N transmit signals received by the M plurality of antennas, wherein each receive antenna weight has a magnitude and a phase whose values may vary with frequency across a bandwidth of the baseband signal;

d. computing a transmit weight vector comprising a plurality of complex transmit antenna weights for the M plurality of antennas of the second communication device by computing a conjugate of the receive weight vector divided by the norm of the receive weight vector; and

e. applying the transmit weight vector to a baseband signal to be transmitted from the second communication device to the first communication device, thereby generating a plurality of transmit signals each of which is weighted across the bandwidth of the baseband signal to be transmitted;

wherein steps (a) through (e) are performed for each of K frequency sub-bands of the baseband signal that correspond to sub-carriers of a multi-carrier baseband signal or to synthesized frequency sub-bands of a single carrier baseband signal, and at the first and second communication devices, further comprising a step of storing, for each of the antennas, complex transmit antenna weights for a subset of the K frequency sub-bands or sub-carriers.

73. The method of claim 72, and further comprising a step of retrieving the stored subset of complex transmit antenna weights and generating therefrom the complete set of antenna weights for all of the K frequency sub-bands or sub-carriers using interpolation techniques.

74. A method for communicating signals between a first communication device and a second communication device using radio frequency (RF) communication techniques, comprising:

a. applying a transmit antenna vector to a baseband signal to be transmitted from the first communication device to the second communication device, the transmit antenna weight vector comprising a complex transmit antenna weight for each of the N plurality of antennas, wherein each complex transmit antenna weight has a magnitude and a phase whose values may vary with frequency across a bandwidth of the baseband signal, thereby generating N transmit signals each of which is weighted across the bandwidth of the baseband signal;

b. receiving at the N plurality of antennas of the first communication device at least one signal that was transmitted by the second communication device;

c. determining a receive weight vector comprising a plurality of complex receive antenna weights for the N plurality of antennas of the first communication device from one or more signals received at the N plurality of antennas from the second communication device, wherein each receive antenna weight has a magnitude and a phase whose values may vary with frequency; and

d. updating the transmit weight vector for the plurality of antennas of the first communication device for transmitting signals to the second communication device by computing a conjugate of the receive weight vector of the first communication device divided by a norm of the conjugate of the receive weight vector;

wherein steps (a) through (d) are performed for each of K frequency sub-bands of the baseband signal that correspond to sub-carriers of a multi-carrier baseband signal or to synthesized frequency sub-bands of a single carrier baseband signal, and further comprising the step of storing in the first communication device, for each of the N antennas, complex transmit antenna weights for a subset of the K frequency sub-bands or sub-carriers.

75. The method of claim 74, and further comprising a step of retrieving the stored subset of complex transmit antenna weights and generating therefrom the complete set of antenna weights for all of the K frequency sub-bands or sub-carriers using interpolation techniques.

76. A medium encoded with instructions that, when executed, perform a method comprising steps of:

a. applying a transmit antenna vector to a baseband signal to be transmitted from a first communication device to a second communication device, the transmit antenna weight vector comprising a complex transmit antenna weight for each of the N plurality of antennas, wherein each complex transmit antenna weight has a magnitude and a phase whose values may vary with frequency across a bandwidth of the baseband signal, thereby generating N transmit signals each of which is weighted across the bandwidth of the baseband signal;

b. determining a receive weight vector comprising a plurality of complex receive antenna weights for the N plurality of antennas of the first communication device from one or more signals received by the N plurality of antennas from the second communication device, wherein each receive antenna weight has a magnitude and a phase whose values may vary with frequency; and

c. updating the transmit weight vector for the plurality of antennas of the first communication device for transmitting signals to the second communication device by computing a conjugate of the receive weight vector of the first communication device divided by a norm of the conjugate of the receive weight vector;

and further comprising instructions for performing steps (a) through (c) at each of K frequency sub-bands of the baseband signal that correspond to sub-carriers of a multi-carrier baseband signal or to synthesized frequency sub-bands of a single carrier baseband signal, and storing in the first communication device, for each of the N antennas, complex transmit antenna weights for a subset of the K frequency sub-bands or sub-carriers.

77. The medium of claim 76, and further comprising instructions for retrieving the stored subset of complex transmit antenna weights and generating therefrom the complete set of antenna weights for all of the K frequency sub-bands or sub-carriers using interpolation techniques.

78. A radio communication system comprising:

a. a first communication device having N plurality of antennas, a baseband signal processor that generates transmit signals and that recovers data from receive signals and a radio transceiver coupled to the baseband signal processor that upconverts the transmit signals for transmission via N plurality of antennas and downconverts signals received by the N plurality of antennas to produce receive signals, wherein the baseband signal processor of the first communication device applies a transmit antenna vector to a baseband signal to be transmitted from the first communication device to the second communication device, the transmit antenna weight vector comprising a complex transmit antenna weight for each of the N plurality of antennas, wherein each complex transmit antenna weight has a magnitude and a phase whose values may vary with frequency across a bandwidth of the baseband signal, thereby generating N transmit signals each of which is weighted across the bandwidth of the baseband signal such that at substantially all frequencies of the baseband signal, the sum of the power of the transmit signals across the N plurality of antennas of the first communication device is equal to a constant; and

b. a second communication devices having M plurality of antennas, a baseband signal processor that generates transmit signals and that recovers data from receive signals and a radio transceiver coupled to the baseband signal processor that upconverts the transmit signals for transmission via M plurality of antennas and downconverts signals received by the M plurality of antennas to produce receive signals, wherein the baseband signal processor of the second communication device;

determines a receive weight vector comprising complex receive weights for each of the M plurality of antennas from the N transmit signals received by the M plurality of antennas, wherein each receive antenna weight has a magnitude and phase whose values may vary with frequency across a bandwidth of a baseband signal derived from the N transmit signals received by the second communication device;

computes a transmit weight vector comprising a plurality of complex transmit antenna weights for the M plurality of antennas of the second communication device by computing a conjugate of the receive weight vector divided by the norm of the receive weight vector; and

applies the transmit weight vector to a baseband signal to be transmitted from the second communication device to the first communication device, thereby generating M plurality of transmit signals such that at substantially all frequencies of the baseband signal, the sum of the power of the transmit signals across the M plurality of antennas of the second communication device is equal to a constant.

79. The system of claim 78, wherein the baseband signal processor of the first communication device further determines a receive weight vector from the signals received from the second communication device by the N plurality of antennas, and updates the transmit weight vector for the N plurality of antennas of the first communication device for transmitting signals to the second communication device by computing a conjugate of the receive weight vector of the first communication device divided by a norm of the conjugate of the receive weight vector, and wherein the baseband signal processor of the first communication device and baseband signal processor of the second communication device update their respective transmit weight vectors each time signals are received from the other communication device so as to converge to transmit weight vectors that optimize a signal-to-noise ratio for communication between the first communication device and second communication device.