The Low Density Parity Check (LDPC) forward error correction code provides significant results that have been very close to Shannon limit. This paper compares the Bit Error Rate (BER) performance of soft decision decoding algorithms of LDPC codes on AWGN channel. Devising soft decision decoding algorithms which are good in BER performance requires a comparison of probabilistic, log domain and Min-Sum methods. Simulations are conducted with different parameters using MATLAB workspace to evaluate the LDPC system performance. Results have shown that Min-Sum has outperformed the algorithms of Log Domain and Prob. Domain with a considerable amount of the Signal to Noise Ratio (SNR). Finally, the optimal LDPC parameter values have been selected based on the achieved results which provide superior results.

Several types of Pulse Position Modulation (PPM) formats were proposed as coding schemes for optical communication such as Differential Pulse Position Modulation (DPPM) and Multiple Pulse Position Modulation (MPPM). However, these coding schemes result in a large bandwidth expansion factor that deduces an excessively high final data rate. On the other hand, Dicode Pulse Position Modulation (DiPPM) is an unconventional coding scheme that has superior characteristics beyond the PPMs proposed. More specifically, DiPPM has been developed to resolve the bandwidth consumption issue of PPM formats. For the first time, this study intends to overcome the DiPPM errors issue via the implication of forwarding Error Correction (FEC). In this regard, low-density parity-check (LDPC) is used in conjunction with multi-level coding, multi-stage encoding, and trellis-based signal shaping to create a bandwidth-efficient modulation format. The optimum code rates for different fibre normalised bandwidths of maximum transmission efficacy will be investigated.

Dicode Pulse Position Modulation (DiPPM) has been presented as a new coding technique with several improvements over earlier PPM formats. Few analyses and experimental results have been published because it is a new coding scheme. To overcome the problem of bandwidth utilization in current PPM formats, DiPPM can be employed. The line rate is twice as fast as the original data rate. In order to increase DiPPM's error performance, two types of Forward Error Correction (FEC) codes, Reed-Solomon (RS) code and low-density parity-check (LDPC) code, are investigated in this article. When RS and LDPC function at their optimal parameters, the results show an improvement in DiPPM system error performance. The error performance of an uncoded DiPPM system was compared to that of a DiPPM-encoded LDPC system and a system utilizing the Reed-Solomon algorithm. Transmission efficiency is measured by the number of photons per pulse and bandwidth widening. When the bandwidth is 1x103 times or more than the initial data rate, DiPPM with LDPC code exceeds uncoded DiPPM and DiPPM with RS, using 1.821 x 103 photons per pulse, with a codeword length of 27 and code rate of 0.75.

Offset pulse position modulation (OPPM) and Dicode pulse position modulation (DiPPM) have been introduced as new attractive modulation techniques, however, they are suffering from erasure, wrong slot, and false alarm errors. in this paper, two types of error correction (EC) codes, Low‐Density Parity Check (LDPC) code and Reed Solomon (RS) code, where paired the OPPM and DiPPM systems to reduce bugs, analyze the best EC parameters, and choose the superlative EC system. In other words, the performance of OPPM engaging LDPC codes and DiPPM employing LDPC codes will be compared against the OPPM engaging RS codes and DiPPM employing RS codes. To systematically carry out this comparison, numbers of photons, transmission efficiency, and the code rate are computed. The evaluation has stated that the data transmission rate at the start has indicated that OPPM with LDPC requires only 1.2 × 103 photons/pulse compared to the necessity of 1.821 × 103 photons/pulse when the DiPPM used LDPC. Accordingly, the transmission efficiency has been increased due to a reduction of number of photons. Also, the coded OPPM with LDPC codes is better than the coded DiPPM with LDPC codes when operating at a code rate that is approximately 0.7.