Design of Transponder Signals and Recievers for Automatic Vehicle Location and Identification Systems

Systems which locate and identify moving vehicles without the active cooperation of either the vehicle operator or its passengers are being considered for various applications, including identification and subsequent billing for vehicles passing toll booths, and location and identification of railroad locomotives. This paper considers the design of identification signals transmitted from (to) a moving vehicle to (from) roadside receivers (transmitters) at various known locations. The paper includes: 1) discussion of some of the important design factors; 2) consideration of modulation/demodulation schemes suitable for vehicle identification and location (VLI) systems; 3) analysis of inexpensive and easily implemented schemes for improving vehicle-detection accuracy by averaging repeated sequences of vehicle-identification symbols; 4) evaluation of binary codes for vehicle identification; 5) analysis and evaluation of schemes for synchronizing binary-coded VLI sequences; and 6) a design example illustrating concepts developed in the paper. It is shown that use of simple binary codes, including constant ratio or single parity check codes, in conjunction with signal averaging, often yields better performance at less cost than systems which employ complex coding/decoding schemes.