Abstract: An interface device for interfacing a set of wayside systems with a radio transmitter includes a plurality of input ports each having at least one input for receiving a signal representing a state of a corresponding wayside system and first and second parallel data paths coupled to the plurality of input ports. Each data path includes input protection circuitry coupled to the inputs of the input ports for preventing short-circuit and open-circuit conditions from triggering a false input state, a multiplexer for selecting between the input port; and a processor for scanning the input ports with the multiplexer to determine the state of current signals appearing at the inputs. In response to determining the state of the current signals appearing at the inputs, the processor generates a message communicating a current state of the wayside systems for delivery to the radio transmitter.

Abstract: A method for exchanging information within a radio communications system includes establishing communications between radio systems utilizing a carrier sense multiple access mode during a period of lower traffic load on the radio communications system and establishing communications between the radio systems utilizing a time division multiple access mode during a period of higher traffic load on the radio communications system.

Abstract: A technique for optimizing throughput on a communications channel shared by multiple users. A communications channel that must be shared by a large number of devices has the potential of being very inefficient because of collisions or overlapping of transmissions by the various devices. The system combines a carrier sense, multiple access (CSMA) mode with a time division multiple access (TDMA) mode to achieve a channel utilization greater than 90 percent. The remote units send a poll request to a base station using the CSMA mode and receive a poll signal from the base station with a poll sequence. The remote units send their data in their assigned time slot. The remote units do not have to all be in radio contact with each other to maintain synchronization. Each remote unit selects the base station that it wishes to communicate with based on signal strength of various base stations.