快变信道OFDM系统自适应编码调制理论与技术

In rapidly varying wireless channels，the received signals manifest the feature of rapid variations of signal to noise ratio (SNR) within a wide dynamic range, which brings a challenge to reliable wireless communications. The project will investigate adaptive modulation and coding (AMC) technologies for OFDM systems over time-varying channels, which will help to significantly improve the performance of communication systems. (1) By modeling the rapidly varying channels as a parallel one combined with abrupt and random errors, new methods for RS-LDPC concatenation, construction of SC-LDPC codes, and their performance analysis and low-complexity decoding will be investigated. And new RS-LDPC concatenation structure and rate compatible SC-LDPC codes will be proposed for reliable communications in rapidly varying channels. (2) A new mapping scheme with variable weighting sets for rateless coding modulation (RCM) will be explored by exploiting different mapping matrices under various SNR regimes, making it have the advantages of continuously adjustable and high transmission rate and robustness to SNR estimation errors. And efficient algorithms will be proposed for RCM demodulation to significantly reduce the computational complexity while maintaining the same BER performance. (3) Joint LDPC and RCM optimization will be studied by taking into account the structural features of LDPC coding and RCM mapping matrices, aiming to propose low-complexity turbo techniques for joint LDPC decoding and RCM demodulation, and effective measures to lower the error-floors in the iterative processing. (4) A test platform will be developed for the verification of the proposed schemes. The research of this project will help to enhance the performance of wireless communications over rapidly varying channels.

在快变无线信道下,接收信号的信噪比呈现大动态变化，给通信系统设计带来挑战。本项目研究快变信道下的自适应编码调制理论与技术：（1）将OFDM快变信道等效为并行的突发与随机差错并存的复合信道，研究适用于快变信道的RS-LDPC级联方法、准循环SC-LDPC码构造与性能分析及低复杂度译码方法，提出新的RS-LDPC级联码结构和可变码率SC-LDPC码；（2）可变权重系数的码率兼容调制（RCM）技术：在不同信噪比区间，使用不同稀疏度和元素大小的映射矩阵，具有速率连续可调、高传输速率和对信噪比估计误差不敏感的优点，提出低复杂度RCM解调方法；（3）利用LDPC编码与RCM调制映射的结构特征，研究LDPC与RCM的联合优化设计方法，提出低复杂度双涡轮解码与解调技术、低差错平台的迭代处理技术；（4）开发系统验证试验平台，将所提技术在实验平台进行验证。本项目研究为改善快变信道下的无线通信性能提供支撑。

项目针对快变信道下,接收信号信噪比大动态变化给通信系统设计带来的挑战，开展自适应编码调制研究，取得的主要成果：（1）发现在低信噪比条件下，不同权重集RCM具有相同的信息传输速率。根据这一结论，提出了一种2比特信道信息反馈的可变权重集和无反馈的混合权重集RCM传输方案，在不降低传输性能的同时，能够显著降低RCM的解调复杂度和反馈开销；（2）提出了一种LDPC两级译码方法，通过对信任节点和可疑节点的有效选取与处理，加快译码速度，降低BP译码差错平台；（3）提出了LDPC与Polar Codes级联的优化设计方案，能显著提升有限长度Polar codes性能，特别是在Turbo迭代解码下，能获得更大的性能增益；（4）提出了一种Irregular LDPC-RCM 优化设计方案，利用Irregular LDPC的差异性保护特性，对不同权重集生成的符号进行分级保护，在BP Turbo联合迭代解码下，系统误码性能得到有效提升；（5）提出了一种优化保留子载波位置的正交投影谱编码OFDM旁瓣抑制 (SSOP-OM)方案，接收信号误码性能得到改善的同时，可获得超过100dB的旁瓣抑制性能；（6）开发了试验验证平台，部分方法在试验平台上得到验证。发表论文11篇，获发明专利3项，获湖北省自然科学二等奖1项。