异步OCDMA系统信道容量研究
doi: 10.3724/SP.J.1146.2006.01171
Capacity Research of Asynchronous OCDMA System
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摘要: 为研究异步光码分多址(OCDMA)系统的信道容量，模拟系统为离散无记忆信道信息传输模型，计算了系统的信息容量。在理论信息容量限为1 bit/chip 条件下，计算得到理想无噪信道单用户检测OCDMA系统的总容量随着用户数的增加有所下降, 但在用户数较多时基本保持在0.75 bit/chip的水平；高斯白噪声(AWGN)信道条件下，用户数较多时，系统总的吞吐容量限下降不大，基本保持在0.71bit/chip-0.75 bit/chip的水平。在用户数较少时，理想信道的信号输入概率偏离0.50越大，系统容量限越低；AWGN信道在低噪声方差下，用户数小的系统能达到较高的容量限。由此推证了异步OCDMA 系统在单用户检测下的理论信息容量限。Abstract: To research the information capacity of the Asynchronous Optical Code Division Multiple Access (OCDMA) system, the system model and its implementation under ideal channel and AWGN channel optical communications are presented. We modeled a discrete memoryless channel OCDMA system and evaluated the aggregate capacity from the probability of the output signal at the chip level. On the condition that the information capacity limited by 1 bit per chip, the results show that the interference caused by asynchronism reduces the capacity limit as the number of users increases, but for a sufficiently large number of users, both the ideal and the AWGN channel throughput limit varies slowly and the limit is around 0.71-0.75 bit/chip. With less number of users of the ideal channel, the more the input probability is lower than 0.50, the lower the largest capacity limit will be. With low noise variance of the AWGN channel, the system with smaller users can attain higher capacity limit. So the information capacity of the asynchronous OCDMA is gotten.
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