Interference Effects of Hard Limiting in PN Spread-Spectrum Systems

It is shown that the use of a hard limiter in PN spread-spectrum systems leads to the generation of intermodulation products which become narrow-band signals after the despreading process in the PN receiver. The analysis treats the situation where a bandpass limiter is inserted into the transmission path of the PN signal prior to the PN receiver. The input to the bandpass limiter is the superposition of the PN signal with white Gaussian noise and one interferer. This interferer may be either a narrow-band signal or another wide-band PN signal. It is found that the amplitudes of the resulting narrow-band intermodulation products are independent of the spread-spectrum processing gain and of the type of interference. A complete loss of the antijamming capability may thus result even with extremely large `processing gain'.