Research on technology of mitigating channel collision in optical code division multiple access

1.提出了基于脉冲位置调制(PPM)的频谱相位编码光大气(OA)码分多址(CDMA)系统，并对系统的误码率进行了理论分析。在相同的码率和码片速率下，我们将该系统的误码率与时间编码的OA-PPM-CDMA系统的误码率进行了比较。结果表明，即使所提出的频谱相位编码的OA-PPM-CDMA系统不配备多址干扰(MAI)和闪烁抑制技术，由于其具有更高的码扩频增益和对噪声的更高的容忍度，无论是否具有MAI/闪烁抑制技术，所提出的系统都可以获得比两种时间编码的OA-PPM-CDMA系统更低的误码率。提出了一种基于OVSF码序列的多速率SPECTS-O-CDMA系统。与传统的单速率系统相比，提出的多速率系统在码率/误码率要求上实现了明显的区分，提高了高速率用户的误码率性能。在MWML(多权重多长度)-OOC(光正交码)光码分多址(CDMA)中，通过根据用户需求改变码长和权值个数，可以实现传输速率和服务质量(Qos)的区分。然而，在传统的MWML-OOC光码分多址中没有进行多址干扰(MAI)的抑制。本文针对MWML-OOC光码分多址，采用SOC(超正交码)技术，在不增加冗余比特和增加权数的情况下进行纠错，以减轻多址干扰。由于我们的方案可以减少光脉冲的数量，所以与传统方案相比，所提出的方案可以减轻多址干扰的影响。结果表明，与传统方案相比，该方案可以提高系统的误码率性能。

1. We propose spectral phase-encoded optical atmospheric (OA) code-division multiple-access (CDMA) systems with pulse-position modulation (PPM) and theoretically analyze the bit error rates (BERs). We compare the BERs of the proposed system to those of time-encoded OA-PPM-CDMA systems at the same bit rate and chip rate. We show that, even if the proposed spectral phase-encoded OA-PPM-CDMA system is equipped with no mitigation techniques of multiple access interference (MAI) and scintillation, the proposed system achieves lower BERs than both time-encoded OA-PPM-CDMA systems, both with and without a mitigation technique of MAI/scintillation, due to its higher code spreading gain and higher tolerance to noise.2. We propose a multi-rate SPECTS-O-CDMA system using OVSF code sequences. The proposed multi-rate system achieves a distinct differentiation on bit-rate/BER requirements and improves the BER performances of higher-rate users compared to the conventional single-rate system.3. In the MWML (Multiweight-Multilength)-OOC (Optical Orthogonal Code) Optical code division multiple access (CDMA), the differentiation of the transmission rate and QoS (Quality of Service) can be realized by changing the code-length and number of weights according to user requirement. However, mitigation of MAI (Multi Access Interference) is not done in the conventional MWML-OOC Optical CDMA. In this paper, we apply SOC (Super-Orthogonal Code) which can correct the error without addition of redundancy bit and an increase in number of weight for MWML-OOC Optical CDMA to mitigate MAI. Since our scheme can reduce the number of optical pulses, the proposed scheme can mitigate the effect of MAI compared with the conventional scheme. We show that the proposed scheme can improve the BER performance in comparison with the conventional scheme.