The potential application of analogue matched and adaptive filters in spread-spectrum communications

Spread-spectrum communication techniques use a common wideband channel to obtain subscriber accessing in secure, jam resistant links. Phase shift keying (p.s.k.) and frequency hopping (f.h.) under the control of a pseudo-noise (p.n.) code are favoured signal waveforms. The paper reviews the performance of surface acoustic wave and charge-coupled device fixed coded and electronically programmable analogue matched filters for the detection of short (13 to 1023 chip) 1 kHz to 20 MHz chip (clock) rate p.n.-p.s.k. coded signals. The extension of these matched filters to accommodate the longer codes 10000 chips) and integration times (several milliseconds) used in current spread-spectrum systems is reviewed, and their importance in reducing synchronization acquisition is highlighted. Surface acoustic wave device approaches to synthesize and detect the alternative f.h. spread-spectrum waveforms are also discussed. The realizations of digitally-controlled coherent frequency synthesizers using s.a.w. chirp filters and bandpass filterbanks are highlighted. Finally the paper identifies the problem in many spread-spectrum systems, where the input-signal-to-interference ratio is so low that code matched filtering alone is not sufficient to detect the transmitted data, and it investigates the use of adaptive signal processing techniques for further suppression of wide and narrowband interference.