The Intelligent Transportation System (ITS) relies heavily on data communications systems to link field equipment such as traflic: sensors, changeable message signs and incident response vehicles with traffic operations centers. The Federal Highway A~iministration (FHWA) has received an allocation of five channels in the 220 MHz band to provide a communication resource for ITS applications. This report investigates a high efficiency mobile \vireless modem with a spectral efficiency of 3 bps&. The modem incorporates the following techniques to compensate for the fading channel: transmitter antenna diversity, modulation using intentional frequency offset, interleaved block codles, symbol timing and frame synchr~mizationo ptimized for fading channels, soft decision decoding optimized for fading, and pilot symbol assisted modulation (PSAM) channel estimation. A prototype of this wireless modem has been constructed and subjected to full bench testing. Preliminary field testing has been performed and more is in progress.

Date of this Version

February 1996