OCDMA system performance with Prime Codes under beat noise constraints

Abstract

The Optical Code Division Multiple Access (OCDMA) technique appears as an interesting solution for optical access networks to perform user and data differentiation. The simplest OCDMA scheme is based on the optical power and involves the use of unipolar temporal spreading code sequences. In this context, Multiple Access Interference (MAI) is the first inherent limitation. In addition, due to photodetection process, beatings between the different user contributions appear and degrade the performance. This limitation, known as beat noise, has a severe impact on the performance, depending on the optical to electrical bandwidth ratio. The study presented in this paper takes into account both limitations to evaluate the OCDMA system robustness using two main types of spreading codes having different cross correlation values: the OOC (Optical Orthogonal Codes) and the PC (Prime Codes). Beatings due to photodetection process are traduced by using a statistical chi-squared based signal distribution, which parameters depends on the OCDMA spreading code. Thanks to this statistical analysis, a theoretical error probability expression is determined. The code design under beat noise assumption is realized for several configurations and using different code families. The analysis highlights the interest of using PC instead of OOC for beat noise corrupted cases.