Cochannel uplink interference in PN spread QPSK satellite systems

The effect of a bandpass limiter in code division multiple access quadriphase shift keying (QPSK) satellite spread spectrum communication systems is investigated. The case of a cochannel interferer on the uplink is analyzed in detail. The nonlinear characteristics of the bandpass limiter result in the generation of intermodulation products which become narrowband signals after the despreading process in the spread spectrum receiver. These intermodulation products and the cochannel interference affect system performance. The assumptions made in deriving the theoretical performance of the system were checked by simulating the entire system using the Block Oriented Systems Simulator (BOSS) software package. The results of the simulation show good agreement with the theoretical calculations, within 1 to 2 dB in signal-to-noise ratio. In addition, by means of simulation, it was possible to explore some features of the system that could not be addressed analytically, such as the effect of processing gain and unbalanced codes on system performance.<
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