Coherent interference effects in a hard-limited satellite transponder for PN/SS systems

A theoretical analysis (confirmed and integrated by computer simulations) of the effect of coherent interference on a pseudo-noise/spread-spectrum (PN/SS) signal in satellite communications systems when a hard-limited transponder is used is presented. A general formula is derived which allows one to determine the signal-to-interference-power ratio degradation in the transponder, in the case of either continuous-wave or modulated interference, and in the presence of additive white Gaussian noise at the transponder input. Special attention is devoted to the phenomenon of complete annihilation of the spread-spectrum signal occurring for particular coherence relationships between signal and interferer. Interference characteristics of most commonly employed modulation schemes such as QPSK and MSK are explicitly reported