| Summary: | 博士 === 國立中正大學 === 電機工程研究所 === 92 === This dissertation proposes and investigates a general-and-easy method to construct multilength codes with constant-weight for simultaneously supporting multimedia services with different symbol rates in optical CDMA systems. Our research begins with the code construction algorithm and demonstration of the correlation properties. We prove that the proposed construction can expand an existing unipolar codeword to generate many different length codewords. The length of a multilength codeword can be any integer multiplier of that of the unipolar codeword. Meanwhile, the auto- and cross-correlation properties can be preserved.
To evaluate the performance of the proposed construction, we adapt this multilength construction to OOCs (one-dimensional unipolar codes) and prime-hop codes (two-dimensional unipolar codes). We analyze the performance of these multilength codes in the MAI-only and MAI-plus-noise environments. In addition to the proposed construction, we also study the performance of other methods proposed for multirate transmissions: the repeat code method, which implements the multirate function by transmitting each symbol many times, the repeat code with ARQ, which uses the repeat symbols to make a decision for issuing a positive or negative acknowledgement and the parallel approach, where several address codes are given to a terminal according to the user symbol rate.
Based on our performance analysis, we conclude that the performance (in terms of bit error probability and the maximum users accommodated in the system) of the proposed construction with prime-hop codes is superior to other approaches. In addition to easy hardware implementation, which can be achieved by modifying the existing hardware, the proposed construction with prime-hop codes finds possible application in multimedia transmission.
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