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

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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.