Method of receiver window widening and autodrift calculation using packet timestamping

A wireless receiver comprising:

• a sleep clock having a sleep clock accuracy (SCA);
• a radio configured to periodically operate in a receive mode during a receive interval and to have sleep intervals (Tsleep) between receive intervals;
• a calculation engine configured to:
• determine, based on a start moment of a first received packet and an expected interval between packets (Tinterval), a nominal start moment to start the radio for a packet window (Window) until a nominal end moment for receiving a second packet;
• determine a widened window by extending the packet window duration in dependence on an estimated drift (drift_set) based on the SCA;
• and
• a clock circuit configured to measure a start moment of the second received packet within the widened window and a start moment of a third received packet within a third packet widened window;
• wherein the calculation engine is further configured to:
• determine a first offset (Delta_time1) from the start moment of the first received packet and the expected interval between packets (Tinterval);
• calculate, from the start moment of the second packet, an actual drift (drift_real);
• determine, based on the actual drift, an actual start moment to start the radio and an actual window duration for receiving the third packet;
• determine a nominal start moment to start the radio for a packet window (Window) until a nominal end moment for receiving the third packet;
• extend the actual window duration for receiving the third packet in dependence on the estimated drift (drift_set) based on the SCA to provide the third packet widened window;
• measure a start moment of the received third packet within the third packet widened window to determine a second offset (Delta_time2);
• calculate, from the start moment of the third packet, an updated actual drift (drift_real) by dividing a difference between the second offset (Delta_time2) and the first offset (Delta_time 1) by the expected interval between packets (Tinterval);
• and
• determine an actual start moment to start the radio and an actual window duration for receiving a fourth packet based on the updated actual drift.

A non-transitory computer-readable medium storing machine instructions which, when executed by at least one processor, cause the at least one processor to:

• receive a first packet having one of a start moment and a synchronization time reference;
• determine, from an expected interval between packets (Tinterval) and the one of the start moment and the synchronization time reference, a nominal start moment to start a radio for a packet window (Window) until a nominal end moment for receiving a second packet;
• extend a packet window duration in dependence on an estimated drift (drift_set) based on a sleep clock accuracy (SCA) of a sleep clock in the radio to provide a widened window;
• receive the second packet;
• measure a start moment of the second received packet within the widened window to determine a first offset (Delta_time1) from the expected interval between packets (Tinterval) and the one of the start moment and the synchronization time reference;
• calculate, from the start moment of the second packet, an actual drift (drift_real);
• determine, based on the actual drift, an actual start moment to start the radio and an actual window duration for receiving a third packet;
• determine a nominal start moment to start the radio for a packet window (Window) until a nominal end moment for receiving the third packet;
• extend the actual window duration for receiving the third packet in dependence on the estimated drift (drift_set) based on the SCA to provide a third packet widened window;
• receive the third packet;
• measure a start moment of the received third packet within the third packet widened window to determine a second offset (Delta_time2);
• calculate, from the start moment of the third packet, an updated actual drift (drift_real) by dividing a difference between the second offset (Delta_time2) and the first offset (Delta_time 1) by the expected interval between packets (Tinterval);
• and
• determine an actual start moment to start the radio and an actual window duration for receiving a fourth packet based on the updated actual drift.