Effect of weak atmospheric turbulence on the BER performance of an optical CDMA FSO link with Sequence Inverse Keying (SIK) balanced photodetector receiver

Analytical approach is presented to evaluate the effect of weak atmospheric turbulence on the bit error rate (BER) performance of an optical code division multiple access (OCDMA) free space optical (FSO) link using optical domain encoder and Sequence Inverse Keying (SIK) balanced photodetector receiver. The analysis is carried out to find the expression of the signal current and multi access interference (MAI) current at the output of the SIK receiver considering the effect of atmospheric turbulence of the channel. The conditional BER conditioned on a given atmospheric turbulence is evaluated and the average BER is obtained by averaging the conditional BER over the probability density function (pdf) of atmospheric turbulence. The results are evaluated for different code length, number of simultaneous users, turbulence variances and other system parameters. The performance of an OCDMA link is found to be highly degraded due to atmospheric scintillation and the power penalty due to turbulence effect is of the order of 2 to 10 dB depending on the turbulence variance. For example, power penalty is 3 dB to 10 dB at a BER of 10-9 for 12 numbers of users at 1 Gbps corresponding to turbulence variance 0.01 to 0.3 respectively. However, the penalty can be reduced significantly by increasing the processing gain.