Improving error performance of dicode pulse position modulation system using forward error correction codes

Dicode pulse position modulation (DiPPM) has been considered as a solution for the bandwidth consumption issue that other existing pulse position modulation (PPM) formats suffer from. This is because it has a line rate that is twice that of the original data rate. This paper considers for the first time forward error correction (FEC) Reed Solomon (RS) codes to improve the error performance of a DiPPM. The results show that the error performance in the system can be improved by using FEC code when the RS is working at its optimum parameters. The error performance of the uncoded DiPPM system has been compared with a RS coded DiPPM system and one using maximum likelihood sequence detector (MLSD) in terms of the number of photons per pulse, transmission efficiency, and bandwidth expansion. The DiPPM with RS code offers superior performance compared to the uncoded DiPPM and DiPPM using MLSD, requiring only 4.5 × 103 photons per pulse, when operating at a bandwidth equal or above to 0.9 times the original data rate. This is with an optimum code rate of approximately ¾, and a codeword length of 25.