Performance analysis of linear binary block coded optical PPM CDMA systems with soft-decision decoding

We obtain upper bounds on the bit-error rate (BER) for performance of linear binary block coded optical pulse position modulation (PPM) code-division multiple-access (CDMA) systems with soft-decision decoding. We use a union bounding technique to obtain these bounds, so our results correspond to the upper bounds. We consider systems using binary PPM (BPPM) and an avalanche photodiode (APD), and treat APD noise, thermal noise, and multi-user interference using a Gaussian approximation. We compare the performance of BCH-coded BPPM CDMA systems with soft-decision decoding with that of BCH-coded BPPM CDMA systems with hard-decision decoding. We show that BCH-coded optical PPM CDMA systems using soft-decision decoding can achieve much lower BER than BCH-coded optical PPM CDMA systems using hard-decision decoding.