Results of the high capacity FM subcarrier-based IVHS traffic data broadcast experiment

The technical challenges encountered when attempting to use FM broadcast subcarriers for high-rate digital transmission to moving vehicles in multipath environments like cities are discussed. The project has to deal not only with interference from the entertainment stereo spectrum to the digital channel, but also the reverse, since broadcasters will not accept any subcarrier that degrades the quality of their program material. A spectrally contained modulation method is selected, and is combined with an efficient approach to coding and error correction to obtain a robust, stable communication link in the presence of multipaths and fading. The results of the field tests in North Carolina and Washington, DC are presented, showing the data rates achieved and tradeoffs among channel rate, interference, and range.