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.
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