Patent ID: 7027771

Claim:
A mobile communications system providing, selectively, one-way and two-way communications between a preceding road vehicle and a succeeding road vehicle, comprising: in the succeeding road vehicle: a receiver receiving a carrier signal from the preceding road vehicle, a detector detecting whether a signal level of the carrier signal received from the preceding road vehicle is above a predetermined signal level and producing a corresponding detection output, and a communications controller, in response to the detection output of the detector, transmitting information on a modulated carrier signal to the preceding road vehicle; and in the preceding road vehicle: a detector detecting a carrier signal transmitted from the succeeding road vehicle and received by the preceding road vehicle and determining if communication is possible for the received and detected carrier signal and, if so, producing a corresponding carrier signal detection output, and a communications controller, in the absence of a carrier signal detection output from the detector indicating a detector determination that communication on the carrier is not possible, transmitting data to the succeeding terrestrial vehicle by one-way communication and, in response to the carrier signal detection output of the detector indicating a detector determination that communication on the carrier is possible, performing two-way communications between the succeeding and preceding terrestrial vehicles.