Multiple antenna processing on transmit for 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.

What is claimed is: 
     
         1 . A method comprising:
 determining, for each of a plurality of antennas included in a first wireless access point, a corresponding error vector magnitude (EVM) value for a corresponding signal received from each of a respective one or more of a plurality of wireless access points;   determining a corresponding selection of one or more of the plurality of antennas for communicating with a respective one of a plurality of wireless access points based on the determined EVM values; and   selecting an antenna of the plurality of antenna for transmitting to a second wireless access point, based at least on one of the EVM values and the antenna selections, so that the second wireless access point is able receive packets transmitted from the first wireless access point without calibration between the first and second wireless access points.   
     
     
         2 . The method of  claim 1 , wherein each of the plurality of antennas of the first wireless access point is coupled to a receive signal path for receiving and to a transmit signal path for transmitting, wherein the first wireless access point is operative to communicate with a plurality of wireless access points. 
     
     
         3 . The method of  claim 2 , wherein the first wireless access point is configured to transmit and receive packets of information using OFDM. 
     
     
         4 . The method of  claim 3 , wherein the packets conform to at least one of the 01-DM variants of the IEEE 802.11 standard or derivatives thereof, wherein each packet includes a pre-defined part. 
     
     
         5 . The method of  claim 1 , wherein determining the selection includes a combination of maximum ratio combining on a tone-by-tone weighted basis and selecting a subset of antennas by setting corresponding antenna weights to respective ones or zeros. 
     
     
         6 . The method of  claim 1 , further comprising:
 storing at least one of the EVM values and the antenna selections in a non-transitory memory associated with each of the plurality of wireless access points; and   retrieving from the non-transitory memory at least one of the stored EVM values and the antenna selections in order to select an antenna for transmitting the second wireless access point.   
     
     
         7 . The method of  claim 6 , wherein the non-transitory memory includes at least one of the EVM values and the antenna selections associated with one or more of the plurality of wireless access points with which the first wireless access point recently communicated. 
     
     
         8 . The method of  claim 1 , wherein the first wireless access point includes a receive antenna selector coupled to each of the plurality of antennas, and wherein determining the corresponding EVM values includes sequentially switching between each of the plurality of antennas during reception of a pre-defined part of one or more packets. 
     
     
         9 . The method of  claim 8 , wherein sequentially switching between each of the plurality of antennas during reception of pre-defined parts of packets occurs prior to conducting automatic gain control at the first wireless access point. 
     
     
         10 . The method of  claim 1 , wherein the first wireless access point includes a receive signal path coupled to each antenna, and wherein the determining of the EVM values includes determining EVM values for the signals received from the second wireless access point on each of the receive signal paths corresponding to each of the plurality of antennas. 
     
     
         11 . An apparatus comprising:
 a plurality of antennas provided to communicate with a plurality of wireless access points including a second wireless access point using OFDM signals;   a transceiver coupled to the plurality of antennas, the transceiver including at least one receive signal path and at least one transmit signal path;   an error vector magnitude (EVM) calculator, the EVM calculator configured to determine, for each of a plurality of antennas, a corresponding EVM value for a corresponding signal received from each of a respective one or more of the plurality of wireless access points;   a controller configured to determine a selection of a respective one or more of the plurality of antennas for communicating with a corresponding one of a plurality of wireless access points based on the determined EVM values; and   an antenna selector coupled to effect selection of one of the plurality of antennas for transmitting to the second wireless access point, based at least on one of the EVM values and the antenna selections, so that the second wireless access point is able receive packets transmitted from the first wireless access point without calibration between the first and second wireless access points.   
     
     
         12 . The apparatus of  claim 11 , wherein each of the at least one receive signal paths comprises:
 a radio receiver coupled to a corresponding one of the plurality of antennas;   an analog-to-digital converter coupled to the radio receiver to produce a received signal for the corresponding one of the plurality of antennas; and   
     
     
         13 . The apparatus of  claim 11 , further comprising a non-transitory memory coupled to the EVM calculator and provided to store at least one of the EVM values and the antenna selections. 
     
     
         14 . The apparatus of  claim 13 , wherein the non-transitory memory stores at least one of the EVM values and the antenna selections for one or more of the plurality of wireless access points with which the first wireless access point communicated during a set time frame. 
     
     
         15 . The apparatus of  claim 11 , wherein the controller is coupled to a non-transitory memory and to the transmit signal path, and wherein the controller is configured to retrieve the at least on one of the EVM values and the antenna selections in order to communicate with any one of the plurality of wireless access points by selecting at least one of the plurality of antennas. 
     
     
         16 . The apparatus of  claim 15 , wherein the at least one transmit signal path further comprises a radio transmitter coupled to the antenna selector. 
     
     
         17 . The apparatus of  claim 11 , wherein the transceiver is configured to conform to at least one of the OFDM variants of the IEEE 802.11 standard or derivatives thereof, and wherein packets transmitted or received by the transceiver each include a pre-defined part. 
     
     
         18 . The apparatus of  claim 17 , wherein the controller is configured to determine antenna selections by determining a combination of maximum ratio combining on a tone-by-tone weighted basis and selecting a subset of antennas by setting corresponding antenna weights to respective ones or zeros. 
     
     
         19 . The apparatus of  claim 17 , wherein the EVM calculator is configured to determine EVM values by sequentially switching between each of the plurality of antennas during reception of a pre-defined part of one or more packets. 
     
     
         20 . The apparatus of  claim 19 , wherein sequentially switching between each of the plurality of antennas during reception of pre-defined parts of packets occurs prior to conducting automatic gain control.