Null data packet-based implicit sounding and calibration in a wireless local area network
This disclosure provides systems, devices, apparatus and methods, including computer programs encoded on storage media, for null data packet (NDP) based implicit sounding and calibration for a wireless local area network (WLAN). An AP may perform a calibration procedure with one or more stations (STAs) that involves NDP transmissions. The AP may calibrate an effective downlink channel response to an effective uplink channel to compensate for transmit and receive chain differences. The AP may initiate implicit sounding by transmitting a downlink message that includes an uplink NDP announcement frame to the one or more STAs, prompting uplink multi-user (MU) NDP transmission. The AP may estimate the uplink channel based on measuring the received NDPs and mirror the estimated uplink channel for reciprocal downlink channel estimation and precoding generation. The AP may perform MU multiple input multiple output (MIMO) downlink transmission that is precoded based on the channel estimation.
1. A method for wireless communication at a station (STA), comprising:
receiving, as part of an implicit sounding calibration procedure between an access point (AP) and the STA, a downlink message comprising an uplink null data packet announcement frame from the AP, the uplink null data packet announcement frame comprising scheduling information for transmission of an uplink null data packet by the STA;
transmitting the uplink null data packet based at least in part on the uplink null data packet announcement frame as part of the implicit sounding calibration procedure between the AP and the STA; and
receiving, after the implicit sounding calibration procedure between the AP and the STA, a downlink transmission from the AP as part of an implicit sounding procedure between the AP and the STA, the downlink transmission based at least in part on a downlink precoding matrix associated with the implicit sounding calibration procedure and comprising a single user beamformed transmission or a multi-user multiple-input multiple-output (MU-MIMO) transmission.
2. The method of claim 1 , wherein the implicit sounding calibration procedure comprises:
performing a downlink channel measurement of a downlink null data packet from the AP; and
transmitting the downlink channel measurement to the AP based at least in part on the performing.
3. The method of claim 2 , wherein the implicit sounding calibration procedure further comprises:
receiving a downlink null data packet announcement frame from the AP, the downlink null data packet announcement frame prompting the performing;
receiving the downlink null data packet following receiving the downlink null data packet announcement frame; and
wherein the downlink channel measurement is based at least in part on the received downlink null data packet.
4. The method of claim 3 , further comprising:
receiving a trigger frame requesting the downlink channel measurement; and
wherein the transmitting is based at least in part on the trigger frame.
5. The method of claim 4 , wherein the trigger frame comprises the uplink null data packet announcement frame and the downlink null data packet announcement frame.
6. The method of claim 3 , wherein the uplink null data packet announcement frame and the downlink null data packet announcement frame are received as a single null data packet announcement frame.
7. The method of claim 3 , wherein:
receiving the uplink null data packet announcement frame and transmitting the uplink null data packet occurs prior to receiving the downlink null data packet announcement frame.
8. The method of claim 3 , wherein:
receiving the uplink null data packet announcement frame and transmitting the uplink null data packet occurs after transmitting the downlink channel measurement.
9. The method of claim 3 , wherein the uplink null data packet announcement frame or the downlink null data packet announcement frame include an indication of a single user implicit sounding procedure or a multi user implicit sounding procedure.
10. The method of claim 3 , wherein the uplink null data packet announcement frame or the downlink null data packet announcement frame is configured to include a common info field, and the common info field is included as part of an extended STA info field of the uplink null data packet announcement frame or an extended STA info field of the downlink null data packet announcement frame.
11. The method of claim 3 , wherein the uplink null data packet announcement frame or the downlink null data packet announcement frame include an indication for the STA to use a single radio chain for transmit and receive operations during the implicit sounding calibration procedure.
12. The method of claim 1 , wherein:
the uplink null data packet announcement frame comprises an indication for the STA to use a fixed number of radio chains for transmit and receive operations during the implicit sounding procedure or during the implicit sounding calibration procedure; and
transmitting the uplink null data packet comprises transmitting to the AP a number of spatial streams and long training fields (LTFs) based at least in part on the fixed number of radio chains.
13. The method of claim 12 , further comprising:
transmitting to the AP a radio parameter comprising one or more of: a maximum number of supported spatial streams, a number of radio chains common to the transmission and reception, or a bitmap indicating a number of transmit antennas or a number of receive antennas; wherein the fixed number of radio chains is based at least in part on the radio parameter.
14. The method of claim 1 , wherein the implicit sounding procedure or the implicit sounding calibration procedure further comprises:
receiving power control information from the AP based at least in part on a power imbalance at the STA, the power control information configured to increase a transmit power of one or more radio chains.
15. The method of claim 14 , wherein the power control information is configured to match a total transmit power of the STA to a total transmit power of the AP.
16. The method of claim 1 , wherein performing the implicit sounding procedure or the implicit sounding calibration procedure further comprises:
transmitting error vector magnitude (EVM) control information to one or more STAs of a plurality of STAs, the EVM control information comprising one or more of: a modulation and coding scheme (MCS) in conformance with an EVM requirement, an EVM parameter, a power backoff parameter, or a target received signal strength indicator (RSSI).
17. The method of claim 1 , wherein the implicit sounding procedure or the implicit sounding calibration procedure further comprises:
receiving from the AP power mismatch control information based at least in part on a power imbalance at the STA, the power mismatch control information indicating a number of additional long training field (LTF) symbols to be included in a header of the uplink null data packet.
18. The method of claim 17 , wherein the power mismatch control information comprises one or more of: an LTF symbol repetition factor, a total number of spatial streams to transmit the uplink null data packet, or a number of LTF symbols in excess of a number of spatial streams to include in the header of the uplink null data packet.
19. An apparatus for wireless communication at a station (STA), comprising:
a processor, memory coupled with the processor; and
instructions stored in the memory and executable by the processor to cause the apparatus to:
receive, as part of an implicit sounding calibration procedure between an access point (AP) and the STA, a downlink message comprising an uplink null data packet announcement frame from the AP, the uplink null data packet announcement frame comprising scheduling information for transmission of an uplink null data packet by the STA;
transmit the uplink null data packet based at least in part on the uplink null data packet announcement frame as part of the implicit sounding calibration procedure between the AP and the STA; and
receive, after the implicit sounding calibration procedure between the AP and the STA, a downlink transmission from the AP as part of an implicit sounding procedure between the AP and the STA, the downlink transmission based at least in part on a downlink precoding matrix associated with the implicit sounding calibration procedure and comprising a single user beamformed transmission or a multi-user multiple-input multiple-output (MU-MIMO) transmission.