US Patent 10431027 Vehicle communication system, vehicle-mounted device, and portable device

A vehicle communication system includes a vehicle-mounted device and a portable device. In the vehicle communication system, a transmission unit transmits a first to third radio signals having intensities weaker in this order, a measurement unit measures an intensity of each of the radio signals, and a determination unit that determines whether an intensity difference between any two of the radio signals among the radio signals measured by the measurement unit is larger than a threshold value. Control of a target mounted on the vehicle is permitted if the intensity difference is larger than the threshold value.