Power limitations due to four wave mixing in a direct sequence optical CDMA transmission system

A theoretical analysis is presented to evaluate the bit error rate (BER) performance of a direct sequence optical code division multiple access (DS-OCDMA) system with dispersion shifted fiber (DSF) considering the effect of four wave mixing (FWM). To verify the analytical expression of BER, the BER performance is evaluated using Matlab simulation with 63 chips per bit m-sequence as well as Cold sequence and compared with analytical results. It is investigated that simulation and analytical results are similar in all cases. Further, BER performance is evaluated for 1023 chips per bit encoding using analytical expression. The BER performance is found to be degraded due to FWM effect if the transmitted power per channel and number of simultaneous users arc increased. It is investigated that maximum allowable transmitted power per channel is limited due to FWM effect. It is found that the maximum allowable transmitted power per channel is limited to -14 dBm for 10 users and -21 dBm for 20 users for a 10 Mb/s, 1000 km system with 1023 chips per bit encoding at a BER of 10(-9).