Interference effects of hard limiting in PN spread-spectrum systems

An explicit analysis is provided of the intermodulation terms which are generated when the input signal of a nonlinear device consists of a superposition of several deterministic and stochastic signals. The nonlinear device investigated is a bandpass limiter which can be considered to model a satellite repeater using a traveling wave tube as a power amplifier. The bandpass limiter is analyzed by calculating the received signal, and the spread-spectrum receiver is analyzed by analyzing the information signal, the interferer, the intermodulation products, and the noise signal. It is shown that a hard limiter in the transmission path may lead to the generation of strong narrow-band intermodulation products at the output of a spread-spectrum receiver. The transmission of a PN signal can be impeded even if a sufficient suppression of interference due to the processing gain is expected.