LPI technique based on random complex spreading code

A squaring circuit (SC) yields the line spectrum of a direct-sequence spread spectrum (DS-SS) signal at the chip rate and its harmonics around DC and ±2f_c. The spectrum around DC depends only on the variance of the spreading code amplitude distribution. The line spectrum around ±2f_c, however, can be eliminated by a uniform phase code. It is noted that a complex code based on Gaussian amplitude and uniform phase, if used with rectangular chips, is an ideal LPI technique against a SC chip rate detector. Analytical results are confirmed by computer simulation. The focus in the present work is on the SC chip rate detector