Bit Error Rate Performance Analysis of Optical CDMA Time-Diversity Links over Gamma-Gamma Atmospheric Turbulence Channels

When we use the free space optical(FSO) communication in the near-ground, it will be great influenced by the atmospheric turbulence. There are many studies on the effects of atmospheric turbulence in FSO. Recently gamma-gamma is a widely accepted model for the optical propagating through the atmosphere in normal and strong turbulence. In order to enhance bit error rate(BER) performance influenced by turbulence-induced fading, we promote a new time-diversity scheme which use optical code division multiple access(OCDMA) as channel division code. As we know, time-diversity is an effective method to enhance the throughput performance of wireless communication system. In order to provide a higher performing and cost-efficient solution OCDMA time-diversity scheme is proposed. In this paper, we analyze the performance of the new scheme with gamma-gamma model. We first present the structure of the OCDMA time-diversity scheme. Then we present the temporal covariance of gamma-gamma model to get the independent time-interval of atmospheric turbulence. We use experiment data to confirm theoretical result. At last we give the theoretical analysis on the BER of new scheme, and use numerical results to prove the theoretical analysis. We find that the new OCDMA time-diversity scheme can enhance the BER for several orders in strong turbulence. Furthermore, the performance of the new scheme in strong turbulence is even better than the traditional scheme in normal turbulence.