Turbo-coding of Coherence Multiplexed Optical PPM CDMA System With Balanced Detection

Abstract

The effects of turbo-coding on the coherence multiplexed optical PPM CDMA systems are shown by evaluating bit error rate (BER) with respect to system parameters such as interleaver length (K), number of simultaneous users (N), code length (f), initial pulsewidth (t0) and normalized threshold (θ) by including the effects of thermal noise and shot noise. Turbo-codes increase the number of simultaneous users besides reducing the BER for a decreasing normalized threshold. As the initial pulsewidth reduces from 7ps to 5ps the BER reduces from 1.6392x10^-17 to 7.0167x10^-18. For a fixed number of simultaneous users (N=20), an initial pulsewidth, (t0 = 5ps) and a normalized threshold (θ = 0.84), it is seen that the turbo-codes of interleaver length 10 reduces BER in the order 10^-10, 10^-18 and 10^-32 for the code length varying as 63, 127 and 255 respectively. On comparison with the direct detection it is found that the balanced detection could accommodate an additional number of 8 users at a reduced BER of 10^-16.