A Microprocessor-Based PSK Modem for Packet Transmission Over Satellite Channels

This paper describes a microprocessor-based modem developed for use in a packet switching network over satellite channels. This digital modem can process both BPSK and QPSK packets with near optimum error rate performance over channels with marginal signal energy-to-noise density ratio. Of principal concern is the development of the discrete time algorithms which form the basis of the microinstruction program. The processing of a packet can be decomposed into two basic stages: (1) the detection of the packet preamble and the rapid estimation of signal parameters (symbol timing and carrier frequency offset) for the specific packet, and (2) the demodulation of the data portion of the packet including the tracking of both symbol timing and carrier offset phase, phase ambiguity resolution and data symbol estimation. The paper concludes with details on the performance of the modem under operational conditions and a brief discussion of implementation of the processor.