Method to estimate and compensate for nlos bias in time difference of arrival estimate

A method to compensate for non-line-of-sight (“NLOS”) bias in a time difference of arrival estimate, using an uplink time difference of arrival (“UL-TDOA”) scheme, the method comprising:

• transmitting a first packet by a mobile device;
• receiving the first packet by at least one first anchor and then transmitting a second packet by the at least one first anchor;
• receiving the first packet and the second packet by at least one second anchor in range of the mobile device and at least one first anchor;
• estimating the time differences of arrival at the at least one second anchor;
• and
• correcting the time differences of arrival at the at least one second anchor by subtracting the NLOS bias between the at least one first anchor and at least one second anchor.

A method to compensate for the non-line-of-sight (“NLOS”) bias in a beacon synchronized time difference of arrival (“BS-TDOA”) estimate, the method comprising:

• transmitting a first packet by a first anchor;
• receiving the first packet by a mobile node and then transmitting a second packet by the mobile node;
• receiving the first packet and the second packet by at least one second anchor that is within range of the first anchor and the mobile node;
• and
• measuring the time differences of arrival between a direct packet transmission path and an indirect packet transmission path by the at least one second node;
• correcting the time differences of arrival with an estimated bias of fly-time between the first anchor and at least one second anchor.