US Patent 9566945 Passive entry passive start (PEPS) system with relay attack prevention

A system includes a remote control unit, such as a fob, and a base station at a target, such as a vehicle. The control unit and the base station are configured to communicate authorization signals and time-of-flight (ToF) ranging signals concurrently between one another. The base station is further configured to confirm from the authorization signals whether the control unit is authorized for controlling a target function and to confirm from the ToF ranging signals whether the control unit is within range of the target. The base station is further configured to prevent the target function from being controlled by the control unit when the control unit is not within range of the target.