Techniques to improve anti-jam performance of spread spectrum systems

Improvement of the anti-jam performance of spread spectrum systems can be effected at many different levels of the signal and receiver structure. Spread spectrum processing gain, interleaved forward error correction coding, spectral excision of jammers, and nonlinear rejection of non-Gaussian jammers are some of the common methods. The present paper explores the use of nonlinear processing to reject a constant carrier envelope (and possibly wideband) jammer of a DS-SS spread spectrum link, with the additional objective of ensuring constant false alarm rate (CFAR) in the reception of the associated DS-SS synchronization preamble. That is, the false alarm performance of the preamble processor must remain fixed whether the jammer is present or not, and independently of any level of received thermal noise. This latter objective may also be named perfect automatic gain control (AGC). It is shown that the constant carrier envelope jammer can be rejected very effectively whether it is transmitted continuously or pulsed at some maximally damaging duty cycle. The effect of incidental additive Gaussian noise is also evaluated.