Secured relay-assisted atmospheric optical code-division multiple-access systems over turbulence channels

The authors propose a relay-assisted atmospheric optical code-division multiple-access (AO/CDMA) system for secured, multiuser optical communications. Chip detect-and-forward (CDF) scheme is used at relay nodes so that the complex multiuser decoding process can be avoided. The proposed system performance, in terms of bit-error rate (BER) and transmission confidentiality, is analysed over atmospheric turbulence channel taking into account channel loss due to atmospheric attenuation and beam divergence. Multiple-access interference and background noise are also included in the analysis. In addition, a quantitative analysis of data confidentiality is further examined in the study. The numerical results show that the relay transmission is an efficient solution to improve the system performance. Thanks to this solution, AO/CDMA systems can achieve low BER, long distance, and a large number of users. Moreover, high confidentiality can be attained by properly configuring system parameters, such as limiting the transmitted power and/or reducing the signal beam width.