US Patent 10235823 Passive entry system of a vehicle having relay attack prevention

A passive entry system of a vehicle includes relay attack prevention. The passive entry system includes a control module in the vehicle, at least one antenna at the vehicle and a key fob. A predetermined number of signals are transmitted via the at least one antenna with each signal having a different power strength. The key fob is determines a power strength of each signal that the key fob receives and generates a measurement report to transmit to the control module. The control module is configured to determine whether the measurement report contains received signal strength indicators for at least half of the predetermined number of signals and whether the received signal strength indicator for each signal contained in the measurement report correlates to the power strength of that signal as transmitted by the at least one antenna.