Effect of atmospheric turbulence on the BER performance of an optical CDMA FSO link with SIK receiver

Abstract

An analytical approach is presented to evaluate the effect of 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 presented to find the expression of the signal current and multi access interference (MAI) current at the output of the SIK receiver taking into account the effect of atmospheric turbulenceand the channel effect due to pointing error. The conditional BER conditioned on a given atmospheric turbulence is evaluated. The average BER is obtained by averaging the conditional BER over the probability density function (pdf) of the atmospheric turbulence. The results are evaluated for different code length, number of simultaneous user, link distances and other system parameters. It is found that, the performance of an OCDMA system with a SIK receiver is highly degraded due to turbulence effect and suffers significant power penalty at a given BERwhich can be substantially reduced by increasing the code length using SIK receiver. The penalty is found to be 9 dB and 11.5 dB for link distance 3000m with user number 2 and 16 respectively at BER=10−9. The allowable number of simultaneous user at a given BER is also determined for a given code length.