Patent ID: 7463194

Claim:
A method for reducing errors in two-way ranging between two transceivers due to a clock frequency offset, comprising: measuring, in a first transceiver, a time C A1 between transmitting a request frame and receiving a reply frame, and a time C A2 between receiving a first information bit of the reply frame and receiving a last information bit of the reply frame; measuring, in a second transceiver, a time C B2 between receiving the request frame and transmitting the last information bit of the reply frame, and a time C B1 between receiving a first information bit of the request frame and a last information bit of the request frame; applying a correction factor α c = C B ⁢ ⁢ 1 C A ⁢ ⁢ 2 to the time C B2 to obtain an estimated time C ^ B ⁢ ⁢ 2 = C B ⁢ ⁢ 2 / α c ; and determining a one-way time of flight according to T ^ t = C A ⁢ ⁢ 1 - C ^ B ⁢ ⁢ 2 2 ⁢ T i , in which T i is an ideal period of the clocks of the first and second transceiver and the one-way time of flight corresponds to a range between the two transceivers.