为了能够同时优化局部可修复码的平均信息修复度、平均修复度以及更新复杂度,并降低构造局部可修复码的算法复杂度,通过分析Tanner图的特点,提出了一种新的构造方法。首先,对局部校验节点进行设计,在满足局部可修复码的平均信息修复度为最优的基础上,通过区分局部组的特点,对重叠组进行分类构造,优化码的平均修复度;其次,对全局校验节点进行设计,优化码的更新复杂度;最后对构造码的算法复杂度进行分析和对比。结果表明,所提出的方法优化了以上所述的性能,且降低了局部可修复码在构造过程中的复杂度。

变速率低密度校验码是一类可支持不同码率的码,在实际通信中具有非常重要的应用。常见的变速率低密度校验码主要有两种:码长固定的多速率低密度校验码以及信息位长度固定的速率兼容低密度校验码。结合代数和叠加构造方法,通过渐进改变

Multiuser detection based on the message passing algorithm (MPA) has been considered for sparse code multiple access (SCMA) systems. Recently, some complexity-reduced MPA detectors have been proposed, among which the MPA detector based on dynamic factor graph (DFG-MPA) has been shown to outperform other MPA detectors with comparable complexities. However, all these MPA detectors are somehow not very flexible in terms of performance-complexity tradeoff, i.e., the granularities of computational complexity reduction are relatively large. In this paper, a generalized scheme of DFG-MPA, termed as GDFG-MPA, is proposed to make a better and more flexible performance-complexity tradeoff. The proposed scheme features two aspects: (1) instead of banning a message update forever, a banned message update at some iteration is allowed to be updated at later iterations; (2) different numbers of message updates are banned from updating at different iterations. Optimization of GDFG-MPA can be made by allocating banned message updates among iterations. Numerical results have demonstrated that compared to DFG-MPA the proposed GDFG-MPA can achieve much better performance at the same computational complexity or achieve the same performance with much lower complexity. Moreover, the proposed GDFG-MPA is more flexible in tuning the performance and complexity tradeoff.

空口传输技术是天地融合通信网络的重要组成部分。作为非正交传输技术的代表之一,超奈奎斯特传输技术凭借其较高的频谱效率在空口传输技术中表现出极大的潜力,已经成为了卫星通信中的研究热点。针对超奈奎斯特(Faster⁃than⁃Nyquist,FTN

针对未来6G对更高的频谱与功率效率,以及更高的可靠性与更低时延的技术指标需求,研究了基于LDPC码的混合多层编码（MLC）和比特交织编码调制（BICM）方案,与传统的BICM方案相比,所提方案能达到更好的误码率性能与更低的复杂度。在此基础上,面向未来6G移动通信中的高频段、高速移动场景,对新型波形技术——正交时频空（OTFS）调制技术的基本原理与性能进行了详细的讨论和分析。结果表明,与正交频分复用（OFDM）相比,OTFS具有更好的鲁棒性、更低的峰均比,并且具有得到全分集增益的潜力。

To provide reliable transmissions with flexible rates for satellite communications, this paper presents a novel method of constructing multi-rate quasi-cyclic low-density parity-check (LDPC) codes. The basic idea is to generate low-rate codes from a high-rate mother code by combining shortening and extending, which ensures that the generated code family owns the same code length, in order to maintain the same frame structure. The code construction involves the design of base matrices and exponent matrices for the designed codes. A progressive row elimination and addition algorithm is proposed for designing the code base matrices from a high rate to low rates. This algorithm leads to the nested and systematic structure of the parity-check matrices, which are desirable for practical implementations of their encoders and decoders, while ensuring the optimal decoding thresholds. In addition, we construct a circulation coefficient matrix based on finite fields and select the optimal rows in this matrix to construct exponent matrices while considering of cycle structures. We demonstrate that the designed codes achieve better performance for all the code rates than the LDPC codes in DVB-S2X standards. In addition, the proposed codes do not exhibit error floors for their block error rates down to 10(-5).

In this paper, we concentrate on one algebraic-based quasi-cyclic low-density parity-check (QC-LDPC) code constructed from two subsets of a finite field and generalize it to propose a class of variable-rate QC-LDPC (VR-QC-LDPC) codes, whose parity-check matrices are nested horizontally and have constant number of rows. Thus the proposed codes are significant at least in terms of storage complexity and can be simply implemented. The constructed codes also inherit the original algebraic-based QC-LDPC codes and their exponent matrices can be obtained from two subsets of the given finite field. We hereby analyze the structural properties from the isomorphism perspective, and present some rules to significantly prune the size of search space and determine the non-isomorphic exponent matrices. By distinguishing the smaller quantities of non-isomorphic matrices with cycle property metric, we can easily construct a series of nested exponent matrices with better cycle distributions and obtain the VR-QC-LDPC codes. Numerical results demonstrate that the constructed codes have better iterative decoding performance within a range of code rates and decoding iterations.