| 摘要 |
A Passive Keyless Entry (PKE) system (1) is mounted in a vehicle (2) and determines distance to a radio transponder (4), e.g. housed in a key fob or such like. A response signal from the transponder (4) is received via two or more antennas (5, 6) and the outputs of the antennas are combined at a combining circuit (7). A signal processor (8) performs a correlation on the output of the combining circuit to derive the time of flight of the response signal. The derived time of flight is used to determine the distance between the transponder (4) and the vehicle (2), which can help the system (1) decide when to unlock the doors of the vehicle (2) or authorise starting of the vehicle's engine, e.g. at the press of a button. Using the combined output of two or more antennas (5, 6) for the time of flight measurement reduces problems of signal attenuation and multipath interference. |
