Channel calibration for a time division duplexed communication system

A method for establishing peer-to-peer communications by a first user terminal (UT) in a wireless time division duplexed (TDD) multiple-input multiple-output (MIMO) communication system, comprising:

• calibrating with an access point, by:
• transmitting a pilot on an uplink channel;
• obtaining an estimate of an uplink channel response derived based on the pilot transmitted on the uplink channel;
• receiving a pilot on a downlink channel;
• obtaining an estimate of a downlink channel response derived based on the pilot received on the downlink channel;
• and
• determining first and second sets of correction factors based on the estimates of the downlink and uplink channel responses, wherein a calibrated downlink channel is formed by using the first set of correction factors for the downlink channel, and a calibrated uplink channel is formed by using the second set of correction factors for the uplink channel;
• and
• scaling symbols with the first set of correction factors prior to transmission on the downlink;
• scaling symbols with the second set of correction factors prior to transmission on the uplink channel;
• and
• establishing direct peer-to-peer communication with a second UT that has also calibrated with the access point, wherein the establishing is performed without further calibration between the first and second UTs.

A first user terminal (UT) in a wireless time division duplexed (TDD) multiple-input multiple-output (MIMO) communication system, comprising:

• means for calibrating with an access point, by:
• obtaining an estimate of a downlink channel response;
• obtaining an estimate of an uplink channel response;
• and
• determining first and second sets of correction factors based on the estimates of the downlink and uplink channel responses, wherein a calibrated downlink channel is formed by using the first set of correction factors for the downlink channel and a calibrated uplink channel is formed by using the second set of correction factors for the uplink channel;
• and
• determining a scaling value indicative of an average difference between the estimate of the downlink channel response and the estimate of the uplink channel response, wherein the estimates for the downlink and uplink channel responses are normalized to account for receiver noise floor;
• and
• means for establishing direct peer-to-peer communication with a second UT that has also calibrated with an access point, wherein the means for establishing is performed without further calibration between the first and second UTs.

In a system for calibrating downlink and uplink channels in a wireless time division duplexed (TDD) multiple-input multiple-output (MIMO) communication system including an access point, a first user terminal (UT) and a second UT, an access point comprising:

• a transmit (TX) spatial processor configured to transmit a pilot on the uplink channel for each of the first UT and the second UT;
• a receive (RX) spatial processor configured to, for each of the first UT and the second UT, obtain an estimate of an uplink channel response derived based on the pilot transmitted on the uplink channel, receive a pilot on the downlink channel, and obtain an estimate of a downlink channel response derived based on the pilot received on the downlink channel;
• and
• a controller configured to determine, for each of the first UT and the second UT, first and second sets of correction factors based on the estimates of the downlink and uplink channel responses, wherein a calibrated downlink channel for peer-to-peer communication between the first and second UTs is formed by using the first set of correction factors for the downlink channel, and a calibrated uplink channel for peer-to-peer communication between the first and second UTs is formed by using the second set of correction factors for the uplink channel, and the controller further configured to establish direct peer-to-peer communication between the first UT and the second UT without further calibration between them.

A method for communication in a wireless system, comprising:

• calibrating one or more communication links between a plurality of user stations and one or more access points, based on one or more sets of correction factors derived from estimates of channel responses associated with the one or more communication links, the plurality of user stations including a first user station and a second user station;
• and
• establishing direct peer-to-peer communication between the first and second user stations using steering without performing calibration between the first and second user stations, wherein the one or more access points includes a first access point associated with a first basic service set (BSS) and a second access point associated with a second BSS, wherein the first user station is calibrated with respect to the first access point and the second user station is calibrated with respect to the second access point, and wherein establishing the direct peer-to-peer communication between the first and second user stations comprises:
• sending, from the first user station, a pilot and a request to establish a communication link with the second user station;
• sending, from the second user station, a steered pilot and an acknowledgment in response to receiving the pilot and the request from first user station;
• and
• transmitting information between the first and second user stations using steering that is adjusted to compensate for a phase rotation caused by calibration of the first and second user stations with respect to different access points.

An apparatus for communication in a wireless system, comprising:

• means for calibrating one or more communication links between a plurality of user stations and one or more access points, based on one or more sets of correction factors derived from estimates of channel responses associated with the one or more communication links, the plurality of user stations including a first user station and a second user station;
• and
• means for establishing direct peer-to-peer communication between the first and second user stations using steering without performing calibration between the first and second user stations, wherein the one or more access points includes a first access point associated with a first basic service set (BSS) and a second access point associated with a second BSS, wherein the first user station is calibrated with respect to the first access point and the second user station is calibrated with respect to the second access point, and wherein the means for establishing the direct peer-to-peer communication between the first and second user stations comprises:
• sending, from the first user station, a pilot and a request to establish a communication link with the second user station;
• sending, from the second user station, a steered pilot and an acknowledgment in response to receiving the pilot and the request from first user station;
• and
• transmitting information between the first and second user stations using steering that is adjusted to compensate for a phase rotation caused by calibration of the first and second user stations with respect to different access points.