Performance analysis of time-diversity atmospheric ocdm systems and their efficiency enhancement of a digital TV signal

In this paper, we propose a new scheme of time-diversity system using optical code division multiplexing (OCDM) in free space optical (FSO) communication. Our design is a full-optical communication system without optical and electrical conversion that facilitates synthesizing the time-diversity signals. We found that employment of the proposed scheme can effectively minimize the influence of scintillation caused by atmospheric turbulence. We analyze the bit error rate (BER) performance of the time-diversity scheme through atmospheric turbulence channels and its efficiency enhancement with a digital TV signal. It not only considers the intensity scintillation of atmospheric turbulence, but also considers scintillation temporal-frequency. We present the theoretical analysis which is based on lognormal models, and validate the performance of the proposed scheme through simulations. Simulation results are further demonstrated to confirm the analytical results. They show that under some circumstances the bit error rate can be improved by a few orders of magnitude using the time-diversity scheme to compensate for the scintillation.