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

1. 本文提出了具有脉冲位置调制（PPM）的光谱相位编码光学大气（OA）码分多址（CDMA）系统，并从理论上分析了误码率（ber）。在相同的码率和片率下，我们将所提出的系统与时间编码的OA-PPM-CDMA系统的误码率进行了比较。研究结果表明，即使不采用多址干扰（MAI）和闪烁抑制技术，由于具有更高的码扩增益和更强的噪声容忍能力，所提出的频谱相位编码OA-PPM-CDMA系统的误码率也比两种时间编码的OA-PPM-CDMA系统低。提出了一种基于OVSF码序列的多速率cts - o - cdma系统。与传统的单速率系统相比，所提出的多速率系统在比特率/误码率要求上实现了明显的差异，并提高了高速率用户的误码率性能。在MWML (multi - weight- multilength)-OOC （Optical Orthogonal Code）光码分多址（CDMA）中，可以根据用户的需求，通过改变码长和权数来实现传输速率和QoS （Quality of Service）的区分。然而，在传统的MWML-OOC光CDMA中，并没有实现对多址干扰的抑制。在MWML-OOC光CDMA中，我们采用无需增加冗余位和增加权值就能纠错的SOC （Super-Orthogonal Code）来减轻MAI。由于该方案可以减少光脉冲的数量，因此与传统方案相比，该方案可以减轻MAI的影响。实验结果表明，与传统方案相比，该方案可以提高误码率。

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.