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椭圆中韦达定理失效的处理策略
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作者 杨静 《数理天地(高中版)》 2023年第11期5-6,共2页
处理直线与圆锥曲线问题的常用策略是将直线与曲线方程联立,利用韦达定理整体代换,设而不求.但某些问题中所得的关系式和韦达定理并不对应,因此不能直接代换,本文针对此类问题给出几种处理技巧.
关键词 韦达定理 圆锥曲线 构造代换
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Performance analysis of coded OFDM systems using a novel class of LDPC codes
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作者 何善宝 张立 赵春明 《Journal of Southeast University(English Edition)》 EI CAS 2004年第4期401-404,共4页
A new method of constructing regular low-density parity-check (LDPC) codes was proposed. And the novel class of LDPC codes was applied in a coded orthogonal frequency division multiplexing (OFDM) system. This method e... A new method of constructing regular low-density parity-check (LDPC) codes was proposed. And the novel class of LDPC codes was applied in a coded orthogonal frequency division multiplexing (OFDM) system. This method extended the class of LDPC codes which could be constructed from shifted identity matrices. The method could avoid short cycles in Tanner graphs with simple inequation in the construction of shifting identity matrices, which made the girth of Tanner graphs 8. Because of the quasicyclic structure and the inherent block configuration of parity-check matrices, the encoders and the decoders were practically feasible. They were linear-time encodable and decodable. The LDPC codes proposed had various code rates, ranging from low to high. They performed excellently with iterative decoding and demonstrate better performance than other regular LDPC codes in OFDM systems. 展开更多
关键词 Computer simulation Iterative methods Mobile telecommunication systems QUASICRYSTALS Turbo codes
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