A Study of Real Time Signal Processing Methods for Decoding Spread Spectrum Systems

摘要

Spread spectrum signals require several kinds of processing. First, the effects of tracking error, Doppler shifts, etc. must be compensated out or ignored in some clever way to give the 'raw' signal. Second, the raw signal at high bandwidth must be decoded to give the low bandwidth information stream. Often this requires comparison of the raw signal with a properly-synchronized pseudo random reference signal. Third, the low bandwidth signal may or may not be burst error correction coded and hence require appropriate decoding. In this study we found that all three steps in spread spectrum decoding could be approached optically. Specific, stand-alone developments from this program were two in number. First we developed a 'generalized matched filter' which can be used just as a matched filter but which out performs the matched filter in several important ways. Second, we developed a way of obtaining a high spectral resolution tunable acoustooptic filter using existing components. Both developments should find wide application outside spread spectrum decoding.