Vehicle location in angular sectors based on signal strength

The results of field measurements carried out in center city Philadelphia and in the Whippany/Morristown, NJ suburban area to assess the accuracy of a vehicle location technique at 820 MHz based on signal strength comparison are described. Six co-sited directional antennas, each covering a 60° angular sector in azimuth, were used to detect the signal transmitted by the mobile. The angular location of the vehicle was determined by comparing the signal strengths received "simultaneously" through the directional antennas. The measured vehicle location was then compared against the true location of the vehicle at the time of the measurement to generate statistics on location accuracy. An estimate is made on the expected improvements in the locating accuracy when three co-sited directional antennas are used, each of which provides coverage for a 120° sector in the horizontal plane. Also described are the effects of signal sample "integration time" and antenna beam shaping on the accuracy of the position estimate. The measurement results presented put a bound on the expected range of accuracies in the signal-strength-based "angle-of-arrival" vehicle location technique.