Calibration and implicit sounding using multi user multiple input multiple output transmissions

A wireless device, comprising:

• a first interface;
• a second interface;
• and
• a wireless modem configured to:
• perform a calibration process with one or more wireless devices of a plurality of wireless devices, the calibration process comprising transmitting, to the one or more wireless devices, a null data packet announcement including an indication of a number of antennas to use to measure a following null data packet (NDP) and to send measurement information for the NDP;
• output a trigger message over the first interface for transmission to the plurality of wireless devices, the trigger message prompting at least a first multi-user multiple input multiple output (MU-MIMO) transmission from the plurality of wireless devices;
• obtain over the second interface the first MU-MIMO transmission received from the plurality of wireless devices in response to the trigger message;
• perform a second MU-MIMO transmission to the plurality of wireless devices, wherein the second MU-MIMO transmission is beamformed according to the calibration process and an estimate of a channel that is in an opposite direction of the second MU-MIMO transmission and that is based at least in part on measuring a packet included in the first MU-MIMO transmission;
• update the estimate of the channel in the opposite direction of the second MU-MIMO transmission based at least in part on measuring at least a third MU-MIMO transmission comprising a block acknowledgement received for the second MU-MIMO transmission;
• and
• perform a fourth MU-MIMO transmission to the plurality of wireless devices based at least in part on the updated estimate of the channel.

A first wireless device for wireless communication, comprising:

• a first interface;
• a second interface;
• and
• a wireless modem configured to:
• output a null data packet announcement (NDPA) over the first interface for transmission to a set of wireless devices, the NDPA comprising an indication of a number of transmit and receive chains the set of wireless devices is to use for a calibration process with the first wireless device;
• output a null data packet (NDP) over the first interface for transmission to the set of wireless devices based at least in part on the NDPA;
• obtain over the second interface at least one report received from the set of wireless devices in response to the NDP, the at least one report comprising measurement information for a first channel between the first wireless device and a second wireless device in the set of wireless devices;
• determine measurement information for a second channel between the first wireless device and the second wireless device based at least in part on a preamble of the at least one report;
• and
• compute a channel response mismatch between a transmit chain and a receive chain of the first wireless device based at least in part on the measurement information for the first channel and the measurement information for the second channel.

A first wireless device, comprising:

• a first interface;
• a second interface;
• and
• a wireless modem configured to:
• obtain over the first interface a null data packet announcement (NDPA) received from a second wireless device, the NDPA comprising an indication of a number of chains the first wireless device is to use for receiving a subsequent downlink null data packet (NDP) as part of a calibration process with the second wireless device;
• obtain over the first interface the downlink NDP received using a set of chains that is based at least in part on the number of chains indicated in the NDPA;
• and
• output, for transmission over the second interface using the same set of chains, a report comprising measurement information for a channel between the first wireless device and the second wireless device.