Performance evaluation of PN spread QPSK satellite systems with cochannel interference

The effect of a bandpass limiter in code-division multiple-access (CDMA) quadrature-phase-shift-keying (QPSK) satellite spread-spectrum communication systems is investigated. The case of a cochannel interferer on the uplink and downlink is analyzed in detail. The nonlinear characteristics of the bandpass limited result in the generation of intermodulation products which become narrowband signals after the despreading process in the receiver. These intermodulation products and the cochannel interference affect system performance. The symbol error rate of the system is calculated as a function of the signal-to-noise and signal-to-interference ratios. The assumptions made in deriving the theoretical performance of the system have been 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 SNR