Double sided round trip time calibration

A method of providing calibrated timestamp values in a fine timing measurement (FTM) exchange, comprising:

• receiving a fine timing measurement (FTM) request message from an initiating station;
• transmitting a plurality of uncalibrated FTM messages to the initiating station,
• wherein the plurality of uncalibrated FTM messages include uncalibrated timestamp values;
• receiving a responding station calibration value from a client station,
• the responding station calibration value being based on a median of a plurality of differential round trip time (RTT) measurements received on the client station,
• each of the plurality of the differential RTT measurements being determined as:
• Diff_dist_IR=c*[tc1−tc2−TOF−(t1−t4)],
• wherein
• Diff_dist_IR is the differential distance between the initiating station and a responding station;
• c is the speed of light;
• tc1 is a time of arrival (ToA) of a FTM message (M) at the client station;
• tc2 is a ToA of an acknowledgement message (Ack) associated with the FTM message at the client station;
• TOF is a Time of Flight value based on the distance between the initiating station and the responding station;
• t1 is a time the responding station transmits the FTM message (M);
• t4 is a time the Ack message is received by the responding station;
• and
• transmitting a plurality of calibrated FTM messages to the initiating station,
• wherein the plurality of calibrated FTM messages include the calibrated timestamp values based on the responding station calibration value.

An apparatus for determining a round trip time calibration value, comprising:

• a memory unit;
• a wireless transceiver;
• a processing unit operably coupled to the memory unit and the wireless transceiver, and configured to:
• receive a fine timing measurement (FTM) exchange between an initiating station and a responding station;
• calculate a plurality of differential round trip time (RTT) measurements based on the FTM exchange,
• each of the plurality of the differential RTT measurements being determined as:
• Diff_dist_IR=c*[tc1−tc2−TOF−(t1−t4)],
• wherein
• Diff_dist_IR is the differential distance between the initiating and responding stations;
• c is the speed of light;
• tc1 is a time of arrival (ToA) of a FTM message (M) at the wireless transceiver;
• tc2 is a ToA of an acknowledgement message (Ack) associated with the FTM message at the wireless transceiver;
• TOF is a Time of Flight value based on the distance between the initiating station and the responding station;
• t1 is a time the responding station transmits the FTM message (M);
• t4 is a time the Ack message is received by the responding station;
• calculate a median of the plurality of differential RTT measurements;
• calculate a responding station calibration value based on the plurality of differential RTT measurements;
• and
• transmit the responding station calibration value to the responding station.

An apparatus for providing calibrated timestamp values in a fine timing measurement (FTM) exchange, comprising:

• a memory;
• a transceiver;
• at least one processor operably coupled to the memory and the transceiver and configured to:
• receive a fine timing measurement (FTM) request message from an initiating station;
• transmit a plurality of uncalibrated FTM messages to the initiating station, wherein the plurality of uncalibrated FTM messages include uncalibrated timestamp values;
• receive a responding station calibration value from a client station,
• the responding station calibration value being based on a median of a plurality of differential round trip time (RTT) measurements received on the client station,
• each of the plurality of the differential RTT measurements being determined as:
• Diff_dist_IR=c*[tc1−tc2−TOF−(t1−t4)],
• wherein
• Diff_dist_IR is the differential distance between the initiating station and the transceiver;
• c is the speed of light;
• tc1 is a time of arrival (ToA) of a FTM message (M) at the client station;
• tc2 is a ToA of an acknowledgement message (Ack) associated with the FTM message at the client station;
• TOF is a Time of Flight value based on the distance between the initiating station and the transceiver;
• t1 is a time the responding station transmits the FTM message (M);
• t4 is a time the Ack message is received by the transceiver;
• and
• transmit a plurality of calibrated FTM messages to the initiating station, wherein the plurality of calibrated FTM messages include the calibrated timestamp values based on the responding station calibration value.