A novel LPI concept using filtered spreading codes

This paper presents a novel method to improve the low probability of intercept (LPI) properties of a direct sequence spread spectrum (DS-SS) system. The principle of the method is to generate the spreading code at a very high rate and to send it through a lowpass filter with a low cutoff frequency. This gives the spreading code multilevel amplitudes. The LPI performance of the proposed system is evaluated after a squaring and a delay-and-multiply detector. We show that the suggested spreading code has removed the spectral lines that reveal a normal DS-SS/BPSK signal. Another advantage with the proposed method is that it is easy to generate many different codes of considerable length with good auto- and cross-correlation properties