Multiple antenna processing on transmit for wireless local area networks

• US 20060072524A1
• Filed: 10/01/2004
• Published: 04/06/2006
• Est. Priority Date: 10/01/2004
• Status: Active Grant

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Inventors: Hart, Brian, Douglas, Bretton Lee, Perahia, Eldad, Lyons, Daniel Joseph
• Granted Patent: US 9,002,299 B2
• Time in Patent Office: Days
• US Class Current: 370/338
• CPC Class Codes: H04B 7/0602 using antenna switching H04B7/0686 takes precedence; antenna beam directivity switching H01Q3/24
• CPC Class Codes: H04B 7/0608 Antenna selection according to transmission parameters
• CPC Class Codes: H04B 7/0615 of weighted versions of same signal
• CPC Class Codes: H04L 2027/0095 in a preamble or similar structure
• CPC Class Codes: H04L 25/022 of frequency response
• CPC Class Codes: H04L 25/0224 using sounding signals
• CPC Class Codes: H04L 25/03343 Arrangements at the transmitter end
• CPC Class Codes: H04L 27/2601 Multicarrier modulation systems
• CPC Class Codes: H04W 84/12 WLAN [Wireless Local Area Networks]

Abstract

A method and an apparatus in a first wireless station of a network transmitting to a second wireless station. The network uses multi-tone OFDM signals. The first station includes multiple antennas and a receive and a transmit signal path per antenna. Each receive signal path includes a discrete Fourier transformer determining the tones in a received signal, and each transmit signal path includes an inverse discrete Fourier transformer converting tones to a signal. The method includes determining channel estimates for each tone and each receive path while receiving from the second station, determining transmit weights to transmit to the second station, tone-by-tone weighting a signal for transmission to the second station to produce weighted tone sets for each transmit signal path, and transmitting the weighted tone sets. The first station is configured so that the weighting produces additive beamforming without the second station needing multiple antennas.

Claims

1. A method at a first wireless station of transmitting to a second wireless station, the first and second wireless stations for communicating packets of information using OFDM signals that include a plurality of frequency tones, the first station including a plurality of antennas for receiving and transmitting coupled to a corresponding plurality of receive signal paths for receiving and to a corresponding plurality of transmit signal paths for transmitting, the method comprising:

determining the channel response for each receive signal path, the channel response determining using signals received at the first station corresponding to a part of a packet transmitted from the second station, the part of the packet having known values for a set of tones, the channel determining including performing a discrete Fourier transform to determine received tones corresponding to the part of the packet and generating channel estimates for the receive signal paths for each tone whose value is known in the part of the packet;

determining a set of transmit weights for each tone for each transmit signal path, the transmit weight set determining using the channel estimates;

tone-by-tone weighting a signal for transmission by the set of determined transmit weights to produce weighted tone sets for transmission via each transmit signal path;

inverse discrete Fourier transforming the weighted tone sets to produce antenna signals for transmission via the transmit signal paths; and

transmitting the set of antenna signals for transmission via each transmit signal path via the antennas,

wherein the first station is configured such that the channel response at the receiving second station includes an additive contribution for transmissions via each transmitting antenna of the first station,

such that the second station can receive the signal for transmission without the second station requiring a plurality of receive antennas and without any first-station-specific calibration required at the second station.

2. A method as recited in claim 1, wherein the number of antennas is two, such that there are two transmit and two receive signal paths.

3. A method as recited in claim 1, wherein the packets substantially conform to one of the OFDM variants of the IEEE 802.11 standard or derivatives thereof, wherein each packet includes a preamble having at least one long symbol having known tones, and wherein the packet part having the known tones includes at least one of the long symbols.

4. A method as recited in claim 3, wherein the first station is an access point.

5. A method as recited in claim 3, wherein the first station is a client station.

6. A method as recited in claim 3, wherein the determining of the channel responses of the receive signal path includes:

for each received tone corresponding to a long symbol, determining a rough estimated channel response; and

smoothing the rough estimated channel response for a tone with the rough estimated channel responses of neighboring tones.

7. A method as recited in claim 3, wherein the packet includes two long symbols and wherein determining of the channel responses of the receive signal path includes:

averaging the channel responses calculated from received tones corresponding to each long symbol.

8. A method as recited in claim 3, wherein the transmit weights determining and the tone-by-tone weighting together comprise:

for each tone, selecting one of the transmit signal paths for transmitting the signal for transmitting, the selecting according to the determined channel response that has the largest magnitude, such that for each tone, the selecting is equivalent to weighting the signal for transmitting via the selected transmit signal path by one, and weighting the signal for transmitting via each other transmit signal path by zero.

9. A method as recited in claim 1, wherein the transmit weight for each transmit signal path corresponding to each antenna has a phase angle which is the negative of the phase angle of the determined channel response for a corresponding receive signal path connected to the same antenna.

10. A method as recited in claim 9, wherein each transmit signal path of the first station includes a transmit digital signal path whose output is coupled to a digital-to-analog converter whose output is coupled to a transmit RF signal path coupled to the antenna corresponding to the transmit signal path, such that the magnitude and phase response of the transmit digital signal path is substantially the same for each transmit signal path, wherein the first station is configured such that the magnitude and phase response of each RF transmit signal path is substantially equal.

11. A method as recited in claim 10, wherein each receive signal path of the first station includes a receive RF signal path coupled to the antenna corresponding to the receive signal path, the output of each receive RF signal path coupled to an analog-to-digital converter whose output is coupled to a receive digital signal path, such that the magnitude and phase response of the receive digital signal path is substantially the same for each receive signal path, and wherein the first station is configured such that the phase response of each RF transmit signal path is substantially equal.

12. A method at a first wireless station of transmitting to a second wireless station, the first and second wireless stations for communicating packets of information using OFDM signals that include a plurality of frequency tones, the first station including a plurality of antennas for receiving and transmitting coupled to a transmit selector coupled to a transmit signal path for transmitting, the method comprising:

determining a measure of the EVM for signals received from the second station via each of the antennas of the first station;

selecting one of the transmit antennas for transmitting to the second station based on the measure of the EVM signals received from the second station; and

transmitting a signal for transmission to the second station via the selected antenna,

such that the second station can receive the signal for transmission without the second station requiring a plurality of receive antennas and without any first-station-specific calibration required at the second station.

13. A method as recited in claim 12, wherein the number of antennas is two.

14. A method as recited in claim 12, wherein the packets substantially conform to one of the OFDM variants of the IEEE 802.11 standard or derivatives thereof, wherein each packet includes a preamble, and wherein the determining of the measures of the EVM via each antenna occurs during receiving at the first station of signals corresponding to the preamble of a packet transmitted from the second station.

15. A method as recited in claim 14, wherein the first station is an access point.

16. A method as recited in claim 14, wherein the first station is a client station.

17. A method as recited in claim 14, wherein the first station includes a receive antenna selector coupled to each of the antennas, and wherein the determining of the measure of the EVM includes sequentially switching between each of the antennas during receiving of the preamble part to determine the measure of the EVM for the signals received from the second station via each of the antennas.

18. A method as recited in claim 17, wherein the sequentially switching between each of the antennas during receiving is prior to conducting automatic gain control at the first station.

19. A method as recited in claim 14, wherein the first station includes a receive signal path coupled to each antenna, and wherein the determining of the measure of the EVM includes determining the measure of the EVM for the signals received from the second station via each of the receive signal paths corresponding to each of the antennas.

20. A method at a first wireless station of transmitting to a second wireless station, the first and second wireless stations for communicating packets of information using OFDM signals that include a plurality of frequency tones, the first station including a plurality of antennas for receiving and transmitting coupled to a corresponding plurality of receive signal paths for receiving and to a corresponding plurality of transmit signal paths for transmitting, the method comprising:

determining the channel response for each receive signal path, the channel response determining using signals received at the first station corresponding to a part of a packet transmitted from the second station, the part of the packet having known values for a set of tones, the channel determining including performing a discrete Fourier transform to determine received tones corresponding to the part of the packet and generating channel estimates for the receive signal paths for each tone whose value is known in the part of the packet;

for each tone, selecting one of the transmit signal paths for transmitting the signal for transmitting, the selecting according to the determined channel response that has the largest magnitude, such that the selecting is equivalent to weighting the signal for transmitting via the selected transmit signal path by one, and weighting the signal for transmitting via each other transmit signal path by zero forming a weighted tone set for each transmit signal path;

inverse discrete Fourier transforming the weighted tone sets to produce antenna signals for transmission via the transmit signal paths; and

transmitting the set of antenna signals for transmission via each transmit signal path via the antennas,

such that the second station can receive the signal for transmission without the second station requiring a plurality of receive antennas and without any first-station-specific calibration required at the second station.

21. A method as recited in claim 20, wherein the number of antennas is two, such that there are two transmit and two receive signal paths.

22. A method as recited in claim 20, wherein the packets substantially conform to one of the OFDM variants of the IEEE 802.11 standard or derivatives thereof, wherein each packet includes a preamble having at least one long symbol having known tones, and wherein the packet part having the known tones includes at least one of the long symbols.

23. A method as recited in claim 22, wherein the first station is an access point.

24. A method as recited in claim 22, wherein the first station is a client station.

25. A method as recited in claim 22, wherein determining of the channel responses of the receive signal path includes:

for each received tone corresponding to a long symbol, determining a rough estimated channel response; and

smoothing the rough estimated channel response for a tone with the rough estimated channel responses of neighboring tones.

26. A method as recited in claim 22, wherein the packet includes two long symbols and wherein determining of the channel responses of the receive signal path includes:

averaging the channel responses calculated from received tones corresponding to each long symbol.

27. An apparatus in a first wireless station for transmitting to a second wireless station, the first and second wireless stations for communicating packets of information using OFDM signals that include a plurality of frequency tones, the first station including a plurality of antennas for receiving and transmitting coupled to a corresponding plurality of receive signal paths for receiving and to a corresponding plurality of transmit signal paths for transmitting, the apparatus comprising:

means for determining the channel response for each receive signal path, the means for channel response determining accepting signals received at the first station corresponding to a part of a packet transmitted from the second station, the part of the packet having known values for a set of tones, the channel determining means including means for performing a discrete Fourier transform to determine received tones corresponding to the part of the packet and means for generating channel estimates for the receive signal paths for each tone whose value is known in the part of the packet;

means for determining a set of transmit weights for each tone for each transmit signal path, the transmit weight set determining using the channel estimates;

means for tone-by-tone weighting a signal for transmission by the set of determined transmit weights to produce weighted tone sets for transmission via each transmit signal path;

means for inverse discrete Fourier transforming the weighted tone sets to produce antenna signals for transmission via the transmit signal paths; and

means for transmitting the set of antenna signals for transmission via each transmit signal path via the antennas,

wherein the first station is configured such that the channel response at the receiving second station includes an additive contribution for transmissions via each transmitting antenna of the first station,

such that the second station can receive the signal for transmission without the second station requiring a plurality of receive antennas and without any first-station-specific calibration required at the second station.

28. An apparatus as recited in claim 27, wherein the number of antennas is two, such that there are two transmit and two receive signal paths.

29. An apparatus as recited in claim 27, wherein the packets substantially conform to one of the OFDM variants of the IEEE 802.11 standard or derivatives thereof, wherein each packet includes a preamble having at least one long symbol having known tones, and wherein the packet part having the known tones includes at least one of the long symbols.

30. An apparatus as recited in claim 29, wherein the first station is an access point.

31. An apparatus as recited in claim 29, wherein the first station is a client station.

32. An apparatus as recited in claim 29, wherein the means for determining the channel responses of the receive signal path includes:

means for determining a rough estimated channel response for each received tone corresponding to a long symbol; and

means for smoothing the rough estimated channel response for a tone with the rough estimated channel responses of neighboring tones.

33. An apparatus as recited in claim 29, wherein the packet includes two long symbols and wherein the means for determining the channel responses of the receive signal path includes:

means for averaging the channel responses calculated from received tones corresponding to each long symbol.

34. An apparatus as recited in claim 29, wherein the means for determining transmit weights and the means for tone-by-tone weighting together comprise:

means for selecting one of the transmit signal paths for transmitting the signal for transmitting, the means for selecting according to the determined channel response that has the largest magnitude, such that for each tone, the means for selecting weights the signal for transmitting via the selected transmit signal path by one, and weights the signal for transmitting via each other transmit signal path by zero.

35. An apparatus as recited in claim 27, wherein the transmit weight for each transmit signal path corresponding to each antenna has a phase angle which is the negative of the phase angle of the determined channel response for a corresponding receive signal path connected to the same antenna.

36. An apparatus as recited in claim 35, wherein each transmit signal path of the first station includes a transmit digital signal path whose output is coupled to means for digital-to-analog converting whose output is coupled to a transmit RF signal path coupled to the antenna corresponding to the transmit signal path, such that the magnitude and phase response of the transmit digital signal path is substantially the same for each transmit signal path, wherein the first station is configured such that the magnitude and phase response of each RF transmit signal path is substantially equal.

37. An apparatus as recited in claim 36, wherein each receive signal path of the first station includes a receive RF signal path coupled to the antenna corresponding to the receive signal path, the output of each receive RF signal path coupled to means for analog-to-digital converting whose output is coupled to a receive digital signal path, such that the magnitude and phase response of the receive digital signal path is substantially the same for each receive signal path, and wherein the first station is configured such that the phase response of each RF transmit signal path is substantially equal.

38. An apparatus in a first wireless station for transmitting to a second wireless station, the first and second wireless stations for communicating packets of information using OFDM signals that include a plurality of frequency tones, the first station including a plurality of antennas for receiving and transmitting coupled to a transmit selector coupled to a transmit signal path for transmitting, the apparatus comprising:

means for determining a measure of the EVM for signals received from the second station via each of the antennas of the first station;

means for selecting one of the transmit antennas for transmitting to the second station, the selecting means accepting the measures of the EVM signals received from the second station for selecting the one transmit antenna; and

means for transmitting a signal for transmission to the second station via the antenna selected by the means for selecting,

such that the second station can receive the signal for transmission without the second station requiring a plurality of receive antennas and without any first-station-specific calibration required at the second station.

39. An apparatus as recited in claim 38, wherein the number of antennas is two.

40. An apparatus as recited in claim 38, wherein the packets substantially conform to one of the OFDM variants of the IEEE 802.11 standard or derivatives thereof, wherein each packet includes a preamble, and wherein the determining of the measures of the EVM via each antenna occurs during receiving at the first station of signals corresponding to the preamble of a packet transmitted from the second station.

41. An apparatus as recited in claim 40, wherein the first station is an access point.

42. An apparatus as recited in claim 40, wherein the first station is a client station.

43. An apparatus as recited in claim 40, wherein the first station includes means for selecting a receive antenna, the receive antenna selecting means coupled to each of the antennas, and wherein the means for determining the measure of the EVM sequentially switches between each of the antennas during receiving of the preamble part to determine the measure of the EVM for the signals received from the second station via each of the antennas.

44. An apparatus as recited in claim 43, wherein the sequential switching between each of the antennas during receiving is prior to conducting automatic gain control at the first station.

45. An apparatus as recited in claim 40, wherein the first station includes a receive signal path coupled to each antenna, and wherein the means for determining the measure of the EVM includes means for determining the measure of the EVM for the signals received from the second station via each of the receive signal paths corresponding to each of the antennas.

46. An apparatus in a first wireless station for transmitting to a second wireless station, the first and second wireless stations for communicating packets of information using OFDM signals that include a plurality of frequency tones, the first station including a plurality of antennas for receiving and transmitting coupled to a corresponding plurality of receive signal paths for receiving and to a corresponding plurality of transmit signal paths for transmitting, the apparatus comprising:

means for determining the channel response for each receive signal path, the channel response determining means using signals received at the first station corresponding to a part of a packet transmitted from the second station, the part of the packet having known values for a set of tones, the channel determining means including means for performing a discrete Fourier transform to determine received tones corresponding to the part of the packet and means for generating channel estimates for the receive signal paths for each tone whose value is known in the part of the packet;

means for selecting one of the transmit signal paths for each tone for transmitting the signal for transmitting, the means for selecting according to the determined channel response that has the largest magnitude, such that the means for selecting is equivalent to means for weighting the signal for transmitting via the selected transmit signal path by one, and weighting the signal for transmitting via each other transmit signal path by zero forming a weighted tone set for each transmit signal path;

means for inverse discrete Fourier transforming the weighted tone sets to produce antenna signals for transmission via the transmit signal paths; and

means for transmitting the set of antenna signals for transmission via each transmit signal path via the antennas,

such that the second station can receive the signal for transmission without the second station requiring a plurality of receive antennas and without any first-station-specific calibration required at the second station.

47. An apparatus as recited in claim 46, wherein the number of antennas is two, such that there are two transmit and two receive signal paths.

48. An apparatus as recited in claim 46, wherein the packets substantially conform to one of the OFDM variants of the IEEE 802.11 standard or derivatives thereof, wherein each packet includes a preamble having at least one long symbol having known tones, and wherein the packet part having the known tones includes at least one of the long symbols.

49. An apparatus as recited in claim 48, wherein the first station is an access point.

50. An apparatus as recited in claim 48, wherein the first station is a client station.

51. An apparatus as recited in claim 48, wherein the means for determining of channel responses of the receive signal path includes:

means for determining a rough estimated channel response for each received tone corresponding to a long symbol; and

means for smoothing the rough estimated channel response for a tone with the rough estimated channel responses of neighboring tones.

52. An apparatus as recited in claim 48, wherein the packet includes two long symbols and wherein the means for determining the channel responses of the receive signal path includes:

means for averaging the channel responses calculated from received tones corresponding to each long symbol.

53. An apparatus in a first wireless station for transmitting to a second wireless station, the first and second wireless stations for communicating packets of information using OFDM signals that include a plurality of frequency tones, the first station including a plurality of antennas for receiving and transmitting coupled to a corresponding plurality of receive signal paths for receiving and to a corresponding plurality of transmit signal paths for transmitting, the apparatus comprising:

in each receive signal path;

a radio receiver coupled to the antenna of the receive signal path;

an analog-to-digital converter coupled to the radio receiver to produce a received signal for the antenna of the receive signal path;

a discrete Fourier transformer coupled to the analog-to-digital converter to output tones corresponding to the signal received at the antenna of the receive signal path; and

a channel estimator coupled to the discrete Fourier transformer, the channel estimator accepting received tones corresponding to a part of a packet transmitted from the second station and received by the radio receiver, the part of the packet having known values for a set of tones, the channel estimator configured to determine channel estimates for the receive signal path for each tone whose value is known in the part of the packet;

the apparatus further comprising;

a weight calculator coupled to each receive signal path'"'"'s channel estimator and configured to determine a set of transmit weights for each tone for each transmit signal path, the transmit weight set determining using the channel estimates;

a transmit beamformer coupled to the weight calculator configured to tone-by-tone weight a signal for transmission by the set of determined transmit weights to produce weighted tone sets for transmission via each transmit signal path; and

for each transmit signal path;

an inverse discrete Fourier transformer coupled to the transmit beamformer and configured to produce from the transmit signal path'"'"'s weighted tone set an antenna signal for transmission via the transmit signal path;

a digital-to-analog converter coupled to the inverse discrete Fourier transformer to convert the antenna signal for transmission to an analog signal for transmission; and

a radio transmitter coupled to the digital-to-analog converter configured to accept the analog signal for transmission and transmit the analog signal via the transmit signal paths antenna,

wherein the first station is configured such that the channel response at the receiving second station includes an additive contribution for transmissions via each transmitting antenna of the first station,

such that the second station can receive the signal for transmission without the second station requiring a plurality of receive antennas and without any first-station-specific calibration required at the second station.

54. An apparatus as recited in claim 53, wherein the number of antennas is two, such that there are two transmit and two receive signal paths.

55. An apparatus as recited in claim 53, wherein the packets substantially conform to one of the OFDM variants of the IEEE 802.11 standard or derivatives thereof, wherein each packet includes a preamble having at least one long symbol having known tones, and wherein the packet part having the known tones includes at least one of the long symbols.

56. An apparatus as recited in claim 55, wherein the first station is an access point.

57. An apparatus as recited in claim 55, wherein the first station is a client station.

58. An apparatus as recited in claim 55, wherein each channel estimator is configured to determine the channel response of the receive signal path including:

determining a rough estimated channel response for each received tone corresponding to a long symbol; and

smoothing the rough estimated channel response for a tone with the rough estimated channel responses of neighboring tones.

59. An apparatus as recited in claim 55, wherein the packet includes two long symbols and wherein each channel estimator is configured to determine the channel response of the receive signal path including:

averaging the channel responses calculated from received tones corresponding to each long symbol.

60. An apparatus as recited in claim 55, wherein the weight calculator and transmit beamformer are configured to, for each tone, select one of the transmit signal paths for transmitting the signal for transmitting according to the determined channel response that has the largest magnitude, such that for each tone, the selecting weights the signal for transmitting via the selected transmit signal path by one, and weights the signal for transmitting via each other transmit signal path by zero.

61. An apparatus as recited in claim 53, wherein the weight calculator is configured to determine a transmit weight for each transmit signal path that has a phase angle which is the negative of the phase angle of the determined channel response for the corresponding receive signal path connected to the same antenna.

62. An apparatus as recited in claim 61, wherein the radio transmitters are configured to have substantially the same magnitude and phase response.

63. An apparatus as recited in claim 62, wherein the radio receivers are configured to have substantially the same phase response.

64. An apparatus in a first wireless station for transmitting to a second wireless station, the first and second wireless stations for communicating packets of information using OFDM signals that include a plurality of frequency tones, the first station including a plurality of antennas for receiving and transmitting coupled to an antenna selector, the antenna selector coupled to a transmit signal path for transmitting and to a receive signal path for receiving, the apparatus comprising:

a radio receiver coupled to the selector to receive a signal;

an analog-to-digital converter coupled to the radio receiver output to produce a digital received signal;

an EVM calculator coupled to the analog-to-digital converter and coupled to the antenna selector, the EVM calculator configured to determine a measure of the EVM of signals received from the second station via each of the antennas of the first station; and

a radio transmitter accepting a signal for transmitting and coupled to the selector, the radio transmitter configured to transmit via the antenna selected by the selector,

wherein the EVM calculator is configured to generate a transmit selector signal for selecting one transmit antenna for transmitting to the second station,

such that the second station can receive the signal for transmission without the second station requiring a plurality of receive antennas and without any first-station-specific calibration required at the second station.

65. An apparatus as recited in claim 64, wherein the number of antennas is two.

66. An apparatus as recited in claim 64, wherein the packets substantially conform to one of the OFDM variants of the IEEE 802.11 standard or derivatives thereof, wherein each packet includes a preamble, and wherein the determining the measures of the EVM via each antenna occurs during receiving at the first station of signals corresponding to the preamble of a packet transmitted from the second station.

67. An apparatus as recited in claim 66, wherein the first station is an access point.

68. An apparatus as recited in claim 66, wherein the first station is a client station.

69. An apparatus as recited in claim 66, wherein the EVM calculator and selector further are configured to sequentially switch between each of the antennas during receiving of the preamble part to determine the measure of the EVM for the signals received from the second station via each of the antennas.

70. An apparatus as recited in claim 69, wherein the sequential switching between each of the antennas during receiving is prior to conducting automatic gain control at the first station.

71. An apparatus in a first wireless station for transmitting to a second wireless station, the first and second wireless stations for communicating packets of information using OFDM signals that include a plurality of frequency tones, the first station including a plurality of antennas for receiving and transmitting coupled to a corresponding plurality of receive signal paths for receiving and to a corresponding plurality of transmit signal paths for transmitting, the apparatus comprising:

in each receive signal path;

a radio receiver coupled to the antenna of the receive signal path;

an analog-to-digital converter coupled to the radio receiver to produce a received signal for the antenna of the receive signal path;

a discrete Fourier transformer coupled to the analog-to-digital converter to output tones corresponding to the signal received at the antenna of the receive signal path; and

a channel estimator coupled to the discrete Fourier transformer, the channel estimator accepting received tones corresponding to a part of a packet transmitted from the second station and received by the radio receiver, the part of the packet having known values for a set of tones, the channel estimator configured to determine channel estimates for the receive signal path for each tone whose value is known in the part of the packet;

the apparatus further comprising;

a transmit weight calculator/beamformer coupled to each receive signal path'"'"'s channel estimator and configured to select one of the transmit signal paths for each tone for transmitting, the selecting according to the determined channel response that has the largest magnitude, such that the weight calculator/beamformer weights the signal for transmitting via the selected transmit signal path by one, and weighting the signal for transmitting via each other transmit signal path by zero forming a weighted tone set for each transmit signal path; and

for each transmit signal path;

an inverse discrete Fourier transformer coupled to the transmit weight calculator/beamformer and configured to produce from the transmit signal path'"'"'s weighted tone set an antenna signal for transmission via the transmit signal path; and

a digital-to-analog converter coupled to the inverse discrete Fourier transformer to convert the antenna signal for transmission to an analog signal for transmission; and

a radio transmitter coupled to the digital-to-analog converter configured to accept the analog signal for transmission and transmit the analog signal via the transmit signal paths antenna,

such that the second station can receive the signal for transmission without the second station requiring a plurality of receive antennas and without any first-station-specific calibration required at the second station.

72. An apparatus as recited in claim 71, wherein the number of antennas is two, such that there are two transmit and two receive signal paths.

73. An apparatus as recited in claim 71, wherein the packets substantially conform to one of the OFDM variants of the IEEE 802.11 standard or derivatives thereof, wherein each packet includes a preamble having at least one long symbol having known tones, and wherein the packet part having the known tones includes at least one of the long symbols.

74. An apparatus as recited in claim 73, wherein the first station is an access point.

75. An apparatus as recited in claim 73, wherein the first station is a client station.

76. An apparatus as recited in claim 73, wherein each channel estimator is configured to determine the channel response of the receive signal path including:

determining a rough estimated channel response for each received tone corresponding to a long symbol; and

smoothing the rough estimated channel response for a tone with the rough estimated channel responses of neighboring tones.

77. An apparatus as recited in claim 73, wherein the packet includes two long symbols and wherein each channel estimator is configured to determine the channel response of the receive signal path including:

averaging the channel responses calculated from received tones corresponding to each long symbol.

78. A carrier medium carrying computer readable code segments to instruct one or more processors of a processing system to execute a method at a first wireless station of transmitting to a second wireless station, the first and second wireless stations for communicating packets of information using OFDM signals that include a plurality of frequency tones, the first station including a plurality of antennas for receiving and transmitting coupled to a corresponding plurality of receive signal paths for receiving and to a corresponding plurality of transmit signal paths for transmitting, the method comprising:

determining the channel response for each receive signal path, the channel response determining using signals received at the first station corresponding to a part of a packet transmitted from the second station, the part of the packet having known values for a set of tones, the channel determining including performing a discrete Fourier transform to determine received tones corresponding to the part of the packet and generating channel estimates for the receive signal paths for each tone whose value is known in the part of the packet;

determining a set of transmit weights for each tone for each transmit signal path, the transmit weight set determining using the channel estimates;

tone-by-tone weighting a signal for transmission by the set of determined transmit weights to produce weighted tone sets for transmission via each transmit signal path;

inverse discrete Fourier transforming the weighted tone sets to produce antenna signals for transmission via the transmit signal paths; and

transmitting the set of antenna signals for transmission via each transmit signal path via the antennas,

wherein the first station is configured such that the channel response at the receiving second station includes an additive contribution for transmissions via each transmitting antenna of the first station,

such that the second station can receive the signal for transmission without the second station requiring a plurality of receive antennas and without any first-station-specific calibration required at the second station.

79. A carrier medium as recited in claim 78, wherein the number of antennas is two, such that there are two transmit and two receive signal paths.

80. A carrier medium as recited in claim 78, wherein the packets substantially conform to one of the OFDM variants of the IEEE 802.11 standard or derivatives thereof, wherein each packet includes a preamble having at least one long symbol having known tones, and wherein the packet part having the known tones includes at least one of the long symbols.

81. A carrier medium as recited in claim 80, wherein the transmit weights determining and the tone-by-tone weighting together comprise:

for each tone, selecting one of the transmit signal paths for transmitting the signal for transmitting, the selecting according to the determined channel response that has the largest magnitude, such that for each tone, the selecting is equivalent to weighting the signal for transmitting via the selected transmit signal path by one, and weighting the signal for transmitting via each other transmit signal path by zero.

82. A carrier medium as recited in claim 78, wherein the transmit weight for each transmit signal path corresponding to each antenna has a phase angle which is the negative of the phase angle of the determined channel response for a corresponding receive signal path connected to the same antenna.