Performance of relay-assisted free-space optical CDMA systems over log-normal atmospheric turbulence channels

In this paper, we propose to use relay transmission as a powerful technique for performance improvement of free-space optical code-division multiple-access (FSO/CDMA) systems. Relay nodes are based on chip detect-and-forward to avoid decoding process that makes the relay nodes more complex. We formulate a closed-form expression for bit-error rate (BER) of proposed FSO/CDMA systems over log-normal atmospheric turbulence channels taking into account channel loss due to attenuation and beam divergence. Multiple-access interference and background noise are also considered in our analysis. The numerical results show that the relay transmission is an efficient solution to improve the system performance. Thanks to this solution, FSO systems can achieve low BER, long distance, and high data rate. In addition, the advantages of using two-dimensional (2-D) prime code over 1-D one are also investigated in this paper.