Abstract :
This paper describes an integrated system for automatic vehicle location and status reporting (AVM), and two-way mobile digital communications (MDC) operating in the 900 MHz band. In the AVM system developed by Hazeltine Corporation, vehicle location is derived from multilateration measurements in fixed site receivers (FSR´s) deployed throughout the coverage area. These measurements are made on pulse transmissions from simple equipments in the vehicle and are relayed from FSR´s to a central computer, where vehicle location is computed and presented on a CRT display. The basic AVM system also includes a two-way digital communications capability wherein vehicle status is appended to the location signal and transmitted to the dispatcher without use of the voice radio. The basic AVM system can be modularly expanded, using its digital communication capability to provide two-way transmission of extended length text messages between the dispatcher and vehicle operator. This is accomplished by (1) installing a mobile data terminal (MDT) in the vehicle, which communicates through the AVM transponder, and (2) by augmenting the central data processing sub-system to perform communications functions. The already-deployed FSR network needs no modification or expansion and land mobile radio channels are not required. In addition to dispatcher/vehicle data communications, the vehicle operator can directly access remote computer data bases via the MDT. Besides describing the basic AVM system, this paper summarizes the results of AVM test programs in Dallas and Philadelphia, and describes the Mobile Data Communication (MDC) capability of the integrated AVM/MDC system.
