Optimal code set selection in m-sequence spectral phase-encoded time spreading (SPECTS) OCDMA systems

In this paper, we perform a comprehensive analysis of a SPECTS-OCDMA system based on m-sequence codes aiming at finding optimal code-sets that produce minimum BER among all codes for a specific number of simultaneous users. We prove that each code interferes differently with other codes of the same family making each user to achieve a different performance in terms of bit error rate (BER) value. This procedure is crucial to improve overall system performance since only a small fraction of the available code-sets actually performs error-free (BER <;10^-12). We have found only 7 code-sets out of 31465 possible combinations (0.022%) for m-sequence 31 with 4 simultaneous users. Such analysis is crucial for SPECTS-OCDMA systems because it was always assumed that all codes of the same family have the same performance.