Research into Channel Capacity of Asynchronous OCDMA Systems

This paper has analyzed the capacity of an asynchronous OCDMA system by simulating information transmission of discrete memoryless channel and considering the multiple access interference at single-user detection and under the conditions of ideal noise-free channel and AWGN channel. It calculates the information capacity of the system at data signal transmission with different input probabilities of q, obtaining aggregate throughput capacity constraint of the system at different numbers of users and q under the condition of ideal noise-free channel. It also calculates the relationship between system capacity constraint and noise variance under different numbers of users and at the equivalent probability data input, and the relationship among throughput capacity of OCDMA system, different noise variances and different input probability distributions at certain number of users. The calculation shows that capacity constraint of asynchronous OCDMA system under single-user detection decreases with the increase of number of users. However, when there are rather many users, AWGN channel capacity drops very little compared with ideal noise-free channel. Ideal channel capacity and AWGN channel capacity basically maintain at 0.71–0.75bit/chip. The conclusions have laid foundations for further research into the application of OCDMA technology to all-optical network of large capacity.