Uplink sounding for wlan system

Abstract

An access point operates in a wireless local area network. The access point includes one or more memories and a processor, coupled to the one or more memories. The one or more memories include instructions, which when executed by the processor cause the access point to transmit a first frame to a plurality of stations in the wireless network and receive null data packet frames from the plurality of stations. After an interframe space period following the first frame, the instructions cause the access point to generate beamforming information based on the null data packet frames and transmit the beamforming information to the plurality of stations. The first frame indicates to the plurality of stations to each transmit a null data packet frame to the access point.

What is claimed is: 
     
         1 . An access point operating in a wireless network, the access point comprising:
 one or more memories; and   a processor coupled to the one or more memories, wherein the one or more memories include instructions, which when executed by the processor cause the access point to:
 transmit a first frame to a plurality of stations in the wireless network, wherein the first frame indicates to the plurality of stations to each transmit a null data packet frame to the access point; 
 receive the null data packet frames from the plurality of stations; 
 after an interframe space period following the first frame, generate beamforming information based on the null data packet frames; and 
 transmit the beamforming information to the plurality of stations. 
   
     
     
         2 . The access point of  claim 1 , wherein the first frame includes resource allocation information for the plurality of stations that participate in an UL OFDMA transmission. 
     
     
         3 . The access point of  claim 1 , wherein the first frame is a trigger frame. 
     
     
         4 . The access point of  claim 1 , wherein the beamforming information describes a wireless channel between the access point and the plurality of stations. 
     
     
         5 . The access point of  claim 1 , wherein subsequent multi-user downlink transmissions use the beamforming information. 
     
     
         6 . The access point of  claim 1 , wherein the first frame indicates a number of long-training symbols to be included in the plurality of the null data packet frames. 
     
     
         7 . The access point of  claim 6 , wherein the number of long-training symbols is equal for all null data packet frames and is set to a maximum rank value. 
     
     
         8 . A first station operating in a wireless network, the first station comprising:
 one or more memories; and   a processor coupled to the one or more memories, wherein the one or more memories include instructions, which when executed by the processor, cause the first station to:
 receive a trigger frame from an access point that triggers a sounding sequence from a set of stations in the wireless network; 
 transmit a first null data packet frame to the access point as part of a first multi-user uplink transmission, wherein the first multi-user uplink transmission involves the first station and the other stations within the set or stations; and 
 receive a multi-user downlink transmission from the access point based on the first multi-user uplink transmission. 
   
     
     
         9 . The first station of  claim 8 , wherein the multi-user downlink transmission includes first beamforming information describing a channel between the first station and the access point and second beamforming information describing the channels between the remaining stations of the set of stations and the access point. 
     
     
         10 . The first station of  claim 9 , wherein the one or more memories include further instructions, which when executed by the processor, cause the first station to:
 transmit data to the access point as part of a second multi-user uplink transmission,
 wherein the second multi-user uplink transmission is a beamformed transmission that is configured according to the first beamforming information. 
   
     
     
         11 . The first station of  claim 8 , wherein the trigger frame indicates a number of long training symbols to include in null data packet frames included in the first multi-user uplink transmission. 
     
     
         12 . The first station of  claim 11 , wherein a long-training sequence is used for the long training symbols and is spread across tones of the long training symbols, including pilot tones; and
 wherein the first beamforming information and second beamforming information is generated based on the long training symbols and indicates which tones of the long training symbols were used for generating the first beamforming information and the second beamforming information.   
     
     
         13 . The first station of  claim 8 , wherein the multi-user downlink transmission is a beamformed transmission that is configured according to beamforming information generated by the access point using the first null data packet frame and each of null data packet frames transmitted by other stations within the set of wireless stations. 
     
     
         14 . The first station of  claim 8 , wherein the trigger frame includes an indication that wireless stations within the set of stations are to transmit a null data packet frame to the access point. 
     
     
         15 . The first station of  claim 14 , wherein the trigger frame indicates a length of the first multi-user uplink transmission and the length of the first multi-user uplink transmission is set to indicate that the first station is to transmit a null data packet frame to the access point. 
     
     
         16 . The first station of  claim 8 , wherein the trigger frame includes first station specific information that indicates information for the first station to perform sounding; and
 wherein the trigger frame includes second station specific information and common information that further includes information that indicates information for both the first station and other stations within the set of stations to perform sounding.   
     
     
         17 . The first station of  claim 16 , wherein the first station specific information includes an identifier of the first station and indicates a number of spatial streams for the first station in the first multi-user uplink transmission;
 wherein the second station specific information includes identifiers of the other stations within the set of wireless stations and indicates a number of spatial streams for the other stations within the set of wireless stations in the first multi-user uplink transmission; and   wherein the common information includes frequency allocation information for the first station and the other stations within the set of wireless stations in the first multi-user uplink transmission.   
     
     
         18 . The first station of  claim 8 , wherein the multi-user downlink transmission includes beamforming information used by the first station for performing beamforming operations with the access point.