光码分多址系统中双极性码的应用研究

基带双极性光码分多址(OCDMA)系统，采用码的极性转换思想，实现在考虑信道非理想下的单极性信道中传输双极性码。研究了Gold序列，m序列在系统中的应用和传输信道对光码分多址系统性能的影响。仿真得到了双极性码在光码分多址系统的自相关和互相关特性。基于不同码字的光码分多址系统用户数与误码率的关系和基于非理想传输信道的系统性能影响曲线。结果表明，Gold序列和m序列适合双极性光码分多址系统，但Gold序列较m序列更适合应用到双极性光码分多址系统，当系统激活用户数为20，系统误码率分别达到了10^-9，10^-7，非理想传输信道对系统性能有较大的影响(恶化近20dB)，在系统研究中不可忽略。

Investigation on Application of Optical Code Division Multiple Access System with Bipolar Codes

The base-band bipolar optical code division multiple access (OCDMA) system is introduced, with transform of unipolar-bipolar and bipolar-unipolar, transmission of signal with bipolar codes is realized through unipolar medium. Gold sequence and m sequence in OCDMA system, and channel effect on the performance of OCDMA system are studied here. The simulation results demonstrate that Gold sequence and m sequence are adapted to bipolar OCDMA system according to the performance of the auto/cross-correlation, but Gold sequence in bipolar OCDMA system is better than m sequence. When the number of users is 20, the bit error rate (BER) is 10-9 for Gold sequence, and about 10-7 for m sequence. Channel model significantly influences the performance of the OCDMA system (～20 dB).