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从码字的非周期互相关函数出发,分析异步相干扩时光码分多址(OCDMA)系统的多址干扰(MAI)和差拍噪声(BN)。干扰用户不同的传输时延,非周期互相关强度均值随之变化,差拍噪声和多址干扰也随之变化。给出了差拍噪声和多址干扰与非周期互相关强度均值的关系,讨论了异步相干扩时OCDMA系统的误码率(BER)与非周期互相关强度均值的关系。最后,以码长511的Gold码为例,针对干扰用户之间不同的传输时延,得到了异步相干扩时OCDMA系统的误码率上界与平均误码率性能。在平均误码率情况下,OCDMA系统能支持12个干扰用户,而在最差情况下(误码率上界),系统容纳的干扰用户数不超过4个。
Based on the non-periodic cross-correlation function of codeword, the multiple access interference (MAI) and the beat noise (BN) of asynchronous coherent time-varying optical code division multiple access (OCDMA) system are analyzed. Interfere with the user’s different transmission delay, the average value of non-periodic cross-correlation strength changes, beat noise and multiple access interference also changes. The relationship between beat noise, multi-access interference and averaging of aperiodic cross-correlation is given. The relationship between the bit error rate (BER) and the aperiodic cross-correlation strength of asynchronous coherent-extended OCDMA system is discussed. Finally, taking the Gold code with a code length of 511 as an example, the upper bound and the average BER of the OCDMA system are obtained for different transmission delays among interfering users. At average bit error rates, OCDMA systems can support up to 12 interfering users, while in the worst case (upper bit error rate), the number of interfering users accommodated by the system does not exceed 4.