Abstract A vehicle location system having a plurality of stationary wayside stations positioned at predetermined geographical locations. The passage of a vehicle near a station references the location of the vehicle at that point in time and automatically supplies the remote headquarters with updated information as to the whereabouts of all vehicles operating in the system. The system enables low power radio frequency signals to automatically communicate error free location information between the wayside station and the vehicle by maintaining the integrity of the signal. Automatic transmission to a remote headquarters of a precoded message such as an emergency communication can be initiated from either the vehicle or a portable transmitter. A common radio frequency channel may be used for transmittal of both audio and digitally encoded messages to and from a plurality of vehicles and a discriminator in each vehicle automatically selects and displays only those digital communications directed to it. Simultaneous automatic transmissions on the same radio frequency channel are avoided by delaying energizing the vehicle transmitter until the preselected channel is open. Unpleasant and distracting noise in the vehicle is minimized by turning off the audio speaker during reception of digitally encoded data.
In a vehicle location system wherein stationary wayside stations at field locations are used to reference the field location of said vehicle at a given point in time and wireless paths are used for transmitting digitally encoded messages between said stationary wayside stations and said vehicle, the improvement comprising: a radio transmitter located at said field location for re-transmitting said digitally encoded message over a radio channel from said field location to a remote site, transmitter control means located at said field location for automatically turning on said radio transmitter upon receipt of said digitally encoded message over said wireless path, a radio receiver located at said field location and tuned to the channel over which said messages are transmitted from said field location to said remote site, and means located at said field location and responsively coupled to said receiver and operatively coupled to said transmitter control means for automatically delaying transmission of said encoded message to said remote site until said channel is clear so that simultaneous automatic transmissions on the same radio frequency channel are avoided.
Claim 2
Dependent Claim
179 words
In a vehicle location system wherein stationary wayside stations at field locations are used to reference the field location of said vehicle at a given point in time and wireless paths are used for transmitting digitally encoded messages between said stationary wayside stations and said vehicle, the improvement comprising: a radio transmitter located at said field location for re-transmitting said digitally encoded message over a radio channel from said field location to a remote site, transmitter control means located at said field location for automatically turning on said radio transmitter upon receipt of said digitally encoded message over said wireless path, a radio receiver located at said field location and tuned to the channel over which said messages are transmitted from said field location to said remote site, and means located at said field location and responsively coupled to said receiver and operatively coupled to said transmitter control means for automatically delaying transmission of said encoded message to said remote site until said channel is clear so that simultaneous automatic transmissions on the same radio frequency channel are avoided.
Claim 3
Dependent Claim
51 words
In the vehicle location system of claim 1 wherein: said radio receiver includes a squelch system for providing an output signal indicative that said channel is clear, and means responsive to said output signal for inhibiting transmission of said encoded message to said remote site until said output signal is received.