M-Ary Convolutional Coding∗

MA) has been emerging as an attractive scheme in fiber optic communication systems as well as in space communication sys-tems in past few years [1]–[6]. In OCDMA systems, M-ary Pulse Position Modulation (PPM), has been regarded as an efficient signalling format which has the capability to reduce the chan-nel interference caused by the other users and also to increase the number of simultaneous users [3]–[5]. We apply error con-trol coding to improve the system performance of pulse position modulated OCDMA (PPM/OCDMA) systems and this paper investigates the performance of M-ary PPM/OCDMA systems with M-ary convolutional coding. Dual-k code [7] is used as the M-ary convolutional code and Optical Orthogonal Codes with the maximum cross correlation value of 1 and 2 are employed as the signature sequences. We derive an expression for the bit error probability of the new system and show that combining M-ary convolutional coding and M-ary PPM results in an im-proved error performance. Also it is shown that the number of simultaneous users can be significantly increased with the pro-posed system compared to the uncoded PPM/OCDMA system with the same bit error probability and with the same information bit rate. We also analyze the system with binary convolutional coding and a comparison with the proposed system is given. key words: optical CDMA, pulse-position modulation, M-ary, convolutional coding, dual-k cod