Performance analysis of fiber-optic BPPM CDMA systems with single parity-check product codes

The application of a family of single parity-check (SPC) product codes in the fiber-optic code-division multiple-access (CDMA) systems with binary pulse position modulation (BPPM) is considered in this paper. We evaluate the bit-error probabilities of the coded systems, taking into account the photodetector noise, thermal noise, and the multiple-access interference. In this paper, the performance of the employed coding schemes over a binary-input output-symmetric channel is analyzed, based on the density evolution approach. The validity of the analytically obtained bit-error rates (BERs) over binary symmetric channels (BSCs) for each of the decoding iterations is verified by the system simulation. It is then shown that the application of these coding schemes in the optical BPPM-CDMA communication system, which can be modeled as a BSC, significantly improves the system performance. Particularly, for a certain BER (less than 10^-7) and bandwidth, the coded systems not only permit a higher number (more than twice) of active users, compared with the uncoded systems, but also can operate at higher channel bit rate (up to four times) with more than 10% energy saving. Furthermore, by increasing the number of code dimensions, less power (less than 40%) is required to achieve the desired performance