System and method for antenna diversity using equal power joint maximal ratio combining

• US 6,785,520 B2
• Filed: 06/19/2002
• Issued: 08/31/2004
• Est. Priority Date: 03/01/2002
• Status: Expired due to Term

• Current Assignee: IPR Licensing Incorporated (InterDigital, Inc.)
• Original Assignee: Cognio, Inc. (Cisco Systems, Inc.)
• Inventors: Sugar, Gary L., Vaidyanathan, Chandra
• Primary Examiner(s): Urban, Edward F.
• Assistant Examiner(s): Jackson, Blane J.
• Application Number:
  US10/174,689
• Publication Number:
  US 20040072546A1
• Time in Patent Office: 804 Days
• Field of Search: 455/101, 455/127.1, 455/137, 455/269, 455/272, 455/334, 455/276.1, 455/562.1, 455/522, 375/299, 375/347, 375/144, 375/260
• US Class Current: 455/101
• 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 7/0465 taking power constraints at power amplifier or emission constraints, e.g. constant modulus, into account
• 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 7/0837 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: H04L 1/06 using space diversity
• CPC Class Codes: H04L 2025/03445 Time domain
• CPC Class Codes: H04L 25/0204 of multiple channels
• CPC Class Codes: H04L 27/2601 Multicarrier modulation systems
• CPC Class Codes: H04L 5/0023 Time-frequency-space
• CPC Class Codes: H04W 52/42 in systems with time, space, frequency or polarisation diversity

Abstract

An equal gain composite beamforming technique which constrains that the power of the signal output by each antenna is the same, and is equal to the total power of the transmit signal divided by the number N of transmit antennas from which the signal is to be transmitted. By reducing output power requirements for each power amplifier, the silicon area of the power amplifiers are reduced by as much as N times (where N is equal to the number of transmit antennas) relative to a non-equal gain CBF.

Claims

1. A method for communicating between a first communication device having N plurality of antennas and a second communication device using radio frequency (RF) communication techniques, comprising:

a. applying a transmit weight vector to a baseband signal to be transmitted from the first communication device to the second communication device, the transmit 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, wherein the magnitude of the complex transmit antenna weights associated with each antenna is such that the power to be output at each antenna is the same and is equal to the total power to be output by all of the N antennas divided by N and such that the sum of the power at each corresponding frequency across the N transmit signals is equal to a constant; and

b. transmitting the N transmit signals from corresponding ones of the plurality of antennas to the second communication device.

2. The method of claim 1, wherein the bandwidth of the baseband signal comprises K plurality of frequency sub-bands, and the magnitude of the complex transmit antenna weights associated with each antenna is such that the power to be output by each antenna is the same and is equal to 1/(KN) of the total power to be output for all of the K frequency sub-bands.

3. The method of claim 1, wherein step (a) is performed for each of K frequency sub-bands of the baseband signal that correspond to sub-carriers of a multi-carrier baseband signal or synthesized frequency sub-bands of a single carrier baseband signal.

4. The method of claim 3, 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.

5. The method of claim 4, 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.

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

a. applying a transmit weight vector to a baseband signal to be transmitted from the first communication device to the second communication device, the transmit weight vector comprising a complex transmit antenna weight for each of N plurality of antennas as of the first communication device, 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 to be transmitted from corresponding ones of the N plurality of antennas to the second communication device, wherein the magnitude of the complex transmit antenna weight associated with each antenna is such that the power to be output at each antenna is the same and is equal to the total power to be output by all of the N antennas divided by N and such that the sum of the power at each corresponding frequency across the N transmit signals is equal to a constant; and

;

b. receiving the N transmit signals at one or more antennas of the second communication device;

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

d. computing a transmit weight vector comprising one or more complex transmit antenna weights for the one or more antennas of the second communication device by gain normalizing the receive weight vector and computing a conjugate thereof; and

c. applying to a baseband signal to be transmitted from the second communication device to the first communication device the transmit weight vector associated with the one or more antennas of the second communication device, wherein the transmit weight vector comprises one or more complex transmit antenna weight having a magnitude and a phase whose values may vary with frequency across the bandwidth of the baseband signal to be transmitted, thereby generating one or more transmit signals each of which is weighted across the bandwidth of the baseband signal to be transmitted from a corresponding one or ones of the one or more antennas of the second communication device to the first communication device.

7. The method of claim 6, wherein the second communication device comprises M plurality of antennas, and wherein the step (d) of computing a transmit weight vector comprises gain normalizing the receive weight vector, and computing a conjugate thereof, to generate a plurality of complex transmit antenna weights having a magnitude and phase whose values may vary with frequency, and wherein step (c) of applying comprises applying the transmit weight vector to the baseband signal to generate M plurality of transmit signals for transmission by corresponding ones of the M plurality of antennas, and wherein the magnitude of the complex transmit antenna weight associated with each antenna is such that the power to be output at each antenna is the same and is equal to the total power to be output by all of the M antennas divided by M and such that the sum of the power at each corresponding frequency across the M transmit signals is equal to a constant.

8. The method of claim 6, and further comprising the steps of:

f. receiving one or more transmit signals from the second communication device at the N plurality of antennas of the first communication device;

g. 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 the one or more signals received at the N plurality of antennas, wherein each receive antenna weight has a magnitude and a phase whose values may vary with frequency across the bandwidth of the baseband signal; and

h. updating the transmit weight vector for the N plurality of antennas of the first communication device by gain normalizing the receive weight vector and computing a conjugate thereof.

9. The method of claim 8, and further comprising repeating steps (a) through (h) for signals transmitted between the first and second communication devices.

10. The method of claim 6, wherein the bandwidth of the baseband signal to be transmitted from the first communication device to the second communication device comprises K plurality of frequency sub-bands, and further comprising the step of computing the plurality of complex transmit antenna weights at the first communication device such that the power to be output by each antenna is the same and is equal to 1/(KN) of the total power to be output for all of the K frequency sub-bands.

11. The method of claim 6, 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 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.

52. The method of claim 7, and further comprising the steps of:

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

g. 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 the signals received at the N plurality of antennas, wherein each receive antenna weight has a magnitude and a phase whose values may vary with frequency across the bandwidth of the baseband signal; and

h. updating the transmit weight vector for the N plurality of antennas of the first communication device by gain normalizing the receive weight vector and computing a conjugate thereof.

53. The method of claim 52, and further comprising repeating steps (a) through (h) for signals transmitted between the first and second communication devices.

54. The method of claim 52, wherein the bandwidth of the baseband signal to be transmitted from the second communication device to the first communication device comprises K plurality of frequency sub-bands, and further comprising the step of computing the plurality of complex transmit antenna weights at the second communication device such that the power to be output by each of the M plurality of antennas is the same and is equal to 1/(KM) of the total power to be output for all of the K frequency sub-bands.

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

a. applying a transmit weight vector to a baseband signal to be transmitted from the first communication device to the second communication device, the transmit weight vector comprising a complex transmit antenna weight for each of N plurality of antennas of the first communication device, 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, wherein the magnitude of the complex transmit antenna weight associated with each antenna is such that the power to be output at each antenna is the same and is equal to the total power to be output by all of the N antennas divided by N and such that the sum of the power at each corresponding frequency across the N transmit signals is equal to a constant;

b. receiving at the N plurality of antennas of the first communication device one or more signals 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 the one or more signals received by the N plurality of antennas, 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 N plurality of antennas of the first communication device for transmitting signals to the second communication device by gain normalizing the receive weight vector and computing a conjugate thereof.

15. The method of claim 14, wherein the step of determining a receive weight vector comprises matching the receive antenna weights to the receive signal at the N plurality of antennas.

16. The method of claim 14, and further comprising repeating steps (a) through (d) for signals transmitted between the first and second communication devices.

17. The method of claim 14, wherein the bandwidth of the baseband signal comprises K plurality of frequency sub-bands, and the magnitude of the complex transmit antenna weights associated with each of the N plurality of antennas is such that the power to be output by each antenna is the same and is equal to 1/(KN) of the total power to be output for all of the K frequency sub-bands.

18. The method of claim 14, 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 synthesized frequency sub-bands of a single carrier baseband signal.

19. The method of claim 18, 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.

20. The method of claim 19, 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.

21. A medium encoded with instructions that, when executed, perform a method comprising the step of applying a transmit weight vector to a baseband signal to be transmitted from a first communication device to a second communication device, the transmit 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, wherein the magnitude of the complex transmit antenna weights associated with each antenna is such that the power to be output at each antenna is the same and is equal to the total power to be output by all of the N antennas divided by N and such that the sum of the power at each corresponding frequency across the N transmit signals is equal to a constant.

22. The medium of claim 21, and further comprising instructions that apply the transmit antenna weights for each of K frequency sub-bands of the baseband signal that correspond to sub-carriers of a multi-carrier baseband signal or synthesized frequency sub-bands of a single carrier baseband signal.

23. The medium of claim 22, 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.

24. The medium of claim 23, 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.

25. The medium of claim 22, and further comprising instructions encoded on the medium for applying the transmit weight vector such that the power to be output by each antenna is the same and is equal to 1/(KN) of the total power to be output for all of the K frequency sub-bands.

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

27. The medium of claim 21, wherein the instructions are processor readable instructions, that when executed by a processor, cause the processor to perform the applying step.

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

a. applying a transmit weight vector to a baseband signal to be transmitted from a first communication device to a second communication device, the transmit weight vector comprising a complex transmit antenna weight for each of N plurality of antennas of the first communication device, 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, wherein the magnitude of the complex transmit antenna weight associated with each antenna is such that the power to be output at each antenna is the same and is equal to the total power to be output by all of the N antennas divided by N and such that the sum of the power at each corresponding frequency across the N transmit signals is equal to a constant;

b. from a signal transmitted by a second communication device and received at the plurality of antennas of the first communication device, 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 the signals received by the N plurality of antennas, 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 N plurality of antennas of the first communication device for transmitting signals to the second communication device by gain normalizing the receive weight vector and computing a conjugate thereof.

29. The medium of claim 28, and further comprising instructions that apply the transmit antenna weights for each of K frequency sub-bands of the baseband signal that correspond to sub-carriers of a multi-carrier baseband signal or synthesized frequency sub-bands of a single carrier baseband signal.

30. The medium of claim 29, 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.

31. The medium of claim 30, 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.

32. The medium of claim 29, and further comprising instructions for applying the transmit weight vector such that the power to be output by each antenna is the same and is equal to 1/(KN) of the total power to be output for all of the K frequency sub-bands.

33. The medium of claim 28, wherein the instructions are implemented by a plurality of gates.

34. The medium of claim 28, wherein the instructions are processor readable instructions, that when executed by a processor, cause the processor to perform steps (a) through (c).

35. An integrated circuit comprising the medium of claim 33.

36. A system comprising the medium of claim 34, and further comprising a processor that executes the instructions encoded on the medium.

37. A communication device comprising the integrated circuit of claim 35, and further comprising:

a. a transmitter to be coupled to N plurality of antennas to upconvert transmit signals for transmission via respective ones of the plurality of antennas; and

b. a receiver to be coupled to the N plurality of antennas to downconvert signals received by the plurality of antennas.

61. The medium of claim 28, and further comprising instructions encoded on the medium for repeating steps (a) through (c) for signals transmitted between the first and second communication devices.

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

a. applying to a first signal to be transmitted from the first communication device to the second communication device a transmit weight vector, the transmit 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, wherein the magnitude of the complex transmit antenna weights associated with each antenna is such that the power to be output at each antenna is the same and is equal to the total power to be output by all of the N antennas divided by N;

b. transmitting the first signal to the second communication device;

c. 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;

d. deriving 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, and wherein the transmit weight vector comprises a plurality of complex transmit antenna weights, wherein each complex transmit antenna weight has a magnitude and a phase whose values may vary with frequency across a bandwidth of the second signal, thereby generating N transmit signals each of which is weighted across the bandwidth of the baseband signal, wherein the magnitude of the complex transmit antenna weights associated with each antenna is such that the power to be output at each antenna is the same and is equal to the total power to be output by all of the N antennas divided by N;

f. 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

g. 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.

39. The method of claim 38, 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 38, wherein at substantially all frequencies of the baseband signal, the sum of the magnitude of the complex transmit antenna weights across the plurality of antennas of the first communication device is constant.

41. The method of claim 40, wherein the bandwidth of the baseband signal comprises K plurality of frequency sub-bands, and the magnitude of the complex transmit antenna weights associated with each antenna is such that the power to be output by each antenna is the same and is equal to 1/(KN) of the total power to be output for all of the K frequency sub-bands.

42. The method of claim 41, wherein steps (a), (d) and (g) 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 synthesized frequency sub-bands of a single carrier baseband signal.

43. The method of claim 42, 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.

44. The method of claim 43, 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.

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

i. applying to a first signal to be transmitted from the first communication device to the second communication device a transmit weight vector, the transmit 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, wherein the magnitude of the complex transmit antenna weights associated with each antenna is such that the power to be output at each antenna is the same and is equal to the total power to be output by all of the N antennas divided by N;

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

iii. applying to a second signal for transmission by the plurality of antennas of the first communication device a transmit weight vector that is orthogonal to the first row of the channel response matrix, and wherein the transmit weight vector comprises a plurality of complex transmit antenna weights, wherein each complex transmit antenna weight has a magnitude and a phase whose values may vary with frequency across a bandwidth of the second signal, thereby generating N transmit signals each of which is weighted across the bandwidth of the baseband signal, wherein the magnitude of the complex transmit antenna weights associated with each antenna is such that the power to be output at each antenna is the same and is equal to the total power to be output by all of the N antennas divided by N;

iv. deriving a second row of the channel response matrix from a second response signal received from a second of the two antennas of the second communication device; and

v. 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.

46. The medium of claim 45, and further comprising instructions that compute a norm of each row of the channel response matrix, and selects the row that has the grater norm as the transmit weight vector.

47. The medium of claim 45, and further comprising instructions that apply the transmit antenna weights for each of K frequency sub-bands of the baseband signal that correspond to sub-carriers of a multi-carrier baseband signal or synthesized frequency sub-bands of a single carrier baseband signal.

48. The medium of claim 45, and further comprising instructions that store, for each of the N antennas, complex transmit antenna weights for a subset of the K frequency sub-bands or sub-carriers.

49. The medium of claim 48, and further comprising instructions that retrieve the stored subset of complex transmit antenna weights and generate therefrom the complete set of antenna weights for all of the K frequency sub-bands or sub-carriers using interpolation techniques.

50. The medium of claim 45, and further comprising instructions that set the magnitude of the complex transmit antenna weights such that at substantially all frequencies of the baseband signal, the sum of the power across the plurality of antennas is constant.

51. A communication device comprising the medium of claim 45, and further comprising:

a. a transmitter that upconverts signals to be transmitted via N plurality of antennas;

b. a receiver that downconverts signals received by the N plurality of antennas; and

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

55. A radio communication system comprising:

a. a first communication device having N plurality of antennas, a baseband signal processor that generates N transmit signals and that recovers data from N receive signals and a radio transceiver coupled to the baseband signal processor that upconverts the N transmit signals for transmission via corresponding ones of the N plurality of antennas and downconverts signals received by corresponding ones of the N plurality of antennas to produce the N receive signals, wherein the baseband signal processor of the first communication device applies a transmit weight vector to a baseband signal to be transmitted from the first communication device to the second communication device, the transmit weight vector comprising a complex transmit antenna weight for each of N plurality of antennas of the first communication device, 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, wherein the magnitude of the complex transmit antenna weight associated with each antenna is such that the power to be output at each antenna is the same and is equal to the total power to be output by all of the N antennas divided by N and such that the sum of the power at each corresponding frequency across the N transmit signals is equal to a constant; and

b. a second communication device having M plurality of antennas, a baseband signal processor that generates M transmit signals and that recovers data from M receive signals and a radio transceiver coupled to the baseband signal processor that upconverts the M transmit signals for transmission via corresponding ones of the M plurality of antennas and downconverts signals received by corresponding ones of the M plurality of antennas to produce the M 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 the power to be output at each antenna is the same and is equal to the total power to be output by all of the M antennas divided by M and such that the sum of the power at each corresponding frequency across the M transmit signals is equal to a constant.

56. The system of claim 55, wherein the baseband signal processor of the first communication device further determines a receive weight vector from the M transmit 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 for signals received from the other communication device.

57. A radio communication device comprising:

a. N plurality of antennas;

b. a baseband signal processor that generates transmit signals and that recovers data from receive signals; and

c. a radio transceiver coupled to the baseband signal processor that upconverts the transmit signals for transmission via corresponding ones of the N plurality of antennas and downconverts signals received by corresponding ones of the N plurality of antennas to produce receive signals;

d. wherein the baseband signal processor applies a transmit weight vector to a baseband signal to be transmitted to another communication device, the transmit 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, wherein the magnitude of the complex transmit antenna weights associated with each antenna is such that the power to be output at each antenna is the same and is equal to the total power to be output by all of the N antennas divided by N and such that the sum of the power at each corresponding frequency across the N transmit signals is equal to a constant.

58. The radio communication device of claim 57, wherein the bandwidth of the baseband signal comprises K plurality of frequency sub-bands, and the baseband signal processor sets the magnitude of the complex transmit antenna weights associated with each antenna such that the power to be output by each antenna is the same and is equal to 1/(KN) of the total power to be output for all of the K frequency sub-bands.

59. The radio communication device of claim 57, wherein the baseband signal processor determines a receive weight vector based on one or more signals received at the N plurality of antennas from the other communication device, the receive weight vector comprising a plurality of complex receive antenna weights for the N plurality of antennas, and updates the transmit weight vector for the N plurality of antennas for transmitting signals to the second communication device by gain normalizing the receive weight vector and computing a conjugate thereof.

60. The radio communication device of claim 57, wherein the baseband signal processor updates the transmit weight vector each time a transmission is received from the other communication device.