Experimental Results About Traffic Flow Detection by Using GPS Reflected Signals

Traffic flow detection using global positioning system (GPS) reflected signals is presented in this paper for the first time, which is a new application in this field. The phase difference information of the reflected signal, which is the output of the phase-locked loop in the tracking process, has been extracted to determine the traffic flow density. In order to verify the reliability of the technology, the inversion model of traffic flow density based on the phase difference information has been established; an experiment has been conducted in a suburban area of Beijing, which is designed to provide auxiliary validation. A metal box is placed in the coverage area of a left-handed circular polarization antenna at two time-periods, i.e., 20-30 and 40-55 s; and a traffic flow experiment in an urban area of Beijing has been carried out. Besides that, a camera is employed to record the traffic flow during the data acquisition time-period. According to the experimental results, the conclusions that can be obtained are that after the time synchronization, the two time-periods of placing the metal box can be clearly observed from the phase difference information of the GPS reflected signal and that by comparing with the real-time traffic flow, the calculation result retrieved from GPS reflected signals is closer to the real situation, which proves the feasibility of traffic flow detection using the global navigation satellite system reflectometry technique.