CW interference excision in a DS/SS communication system using spectrally defined spreading/despreading functions

Direct sequence spread-spectrum (DS/SS) modulation may be used in situations where the transmitted signal must be robust against deliberate interference and difficult to detect by electronic support measures (ESM). The process gain advantage of a direct sequence system may be compromised by a determined enemy through the use of single tone, multiple tone or swept (chirp) jamming, particularly if the interference frequency is close to the DS carrier frequency. This paper presents a non-binary analogue noise-like spreading function with a flat amplitude and random phase spectra which is particularly robust to the above types of jamming. The spectrum of the despreading function may be modified in response to narrow band interference whether single tone, multiple tone or frequency agile, significantly reducing the effect of the interference. The wide-band signal has improved low probability of intercept (LPI) performance against delay and multiply receivers, and in common with all DS signals can be made robust to frequency selective fading, typical of mobile radio channels. An experimental base band system has been built which uses this type of spread spectrum signal and its bit error rate performance against a single tone interferer is presented The measured results for this new type of spreading sequence are compared against those obtained when using a conventional binary code sequence.