相干光码分多址系统中拍频噪声的影响

Impact Analysis of Beat Noise on Coherent OCDMA System

随着相位编解码器关键技术的突破,精确分析相位编码光码分多址(OCDMA)系统误码率性能显得十分必要。本文研究了相干光码分多址系统中拍频噪声、多址干扰、散粒噪声和热噪声对系统性能的影响。在充分考虑了干扰信号输入光偏振影响的情况下.根据系统噪声和干扰的矩母函数,采用高斯近似的方法得到误码率的计算公式,并比较了多址干扰和拍频噪声对系统性能的影响。当所有干扰用户与目标用户平行时得到误码率上界;当所有干扰用户与目标用户垂直时得到误码率下界;干扰用户随机偏振时的误码率介于两者之间。结果表明:拍频噪声是影响相干OCDMA系统性能的主要因素;随着接收光功率的增加,干扰信号偏振对系统误码率的影响趋于明显。当系统误码率小于10^(-10)时,误码率随用户数目的增加迅速增加;当误码率大于10^(-10)时,误码率随用户数目的变化缓慢。

With the key technologies breakthrough of phase encoding, it is necessary to analyze the bit error rate （BER） performance of coherent optical code division multi-access （OCDMA）. The impacts of beat noise, multi-access interference （MAI）, shot noise and thermal noise in coherent OCDMA are studied in this paper. A Gaussian approximation method, based on the moment generation function （MGF） of the noises, is introduced to evaluate the bit error rate by taking the polarization into account. Numerical result between beat noise and MAI is compared. When all the interference signals are parallel or upright with the targeted user, we derive the upper and lower bound of BER respectively, the BER of random polarization between them. It is shown that, the beat noise is the dominant factor which influence BER performance of the coherent OCDMA system. The impact of polarization is increasing with the receiving power increasing; when the BER is below 10^-10 , it increases quickly with the increasing of user number; when the BER is larger than 10^-10 , it changes slowly with the increasing user number.