Coherent Signal Processing for Packet Radio

Abstract

An advanced demodulation technique has been devised for the Low Cost Packet Radio (LCPR) under contract to CECOM/DARPA No. DAAK 80-81-C-0213. First, a brief introduction on packet radio signal format is given, then the design of the acquisition processor is presented. The impact of noise and multipath on demodulator options - standard DPSK with noncoherent integration, and PSK with a quasi-coherent reference are compared. Decision feedback combined with coherent surface acoustic wave signal processing are used to implement an adaptive matched filter to the fading, multipath distorted pulses received. This technique is made practical by the advent of high stability surface acoustic wave technology.[1],[2] Analytical results are presented which demonstrate that, over a certain broad range of parameters, the coherent technique described provides the performance of an adaptive matched filter. The technique is also shown to be easily extended to provide optimum, maximal ratio, explicit path diversity combining, which is an essential feature for packet radio operations.