基于稀疏编码的非正交多址接入基础理论与关键技术研究

Sparse code based non-orthogonal multiple access (SC-NOMA) scheme has received great attention recently due to its overloading capability from academia as well as industry. However, the related basic theory is not mature. Furthermore, the complexity of the receivers in high overloading scenarios is still too high to be implemented in practical applications. Regarding these challenges on the theory and practice, we plan to carry out the following research topics in this project: 1) Theoretical design of complexity-constrained SC-NOMA, analytical study on the capacity upper-bound of the complexity-constrained SC-NOMA; study on the highest achievable overload of the complexity-constrained SC-NOMA via density evolution (DE) and extrinsic information transfer (EXIT) chart approaches; 2) Design codebook that supports high overload and exhibits shaping gain and diversity gain via the factor graph and Gallager mapping approaches; 3) Research on low-complexity high performance receiver via Gaussian approximation (GA) of interference, Gaussian tree approximation (GTA) and iterative detection and decoding (IDD) approaches; 4) Study on the active-user detection based on sparse optimization paradigm to realize efficient grant-free uplink access; 5) Study on the combination of SC-NOMA with MIMO to enhance the overall system performance. The results derived from this project are expected to lay solid theoretical foundation for the design of the low complexity capacity-approaching SC-NOMA schemes and provide strong support for its practical application.

基于稀疏编码(Sparse Code)的NOMA(SC-NOMA)技术具有较好的过载性能，因此受到业界的广泛关注，但目前相关理论研究尚不充分，其应用仍面临接收机实现复杂度过高等诸多问题。为此，本项目拟开展以下相关研究：1)提出复杂度受限情况下SC-NOMA的理论设计模型，完善SC-NOMA可达速率理论，利用密度进化和外信息转移图等数学方法获取系统的可达速率和用户最大过载率；2)基于因子图和Gallager映射，设计兼具成形增益和分集增益且支持高过载的稀疏码本；3)建立联合检测和译码复合因子图模型，通过迭代结构优化及高斯近似等方法来降低接收机复杂度；4)提出稀疏优化方法，用于检测活跃用户以实现高效免调度SC-NOMA上行传输；5)研究SC-NOMA与MIMO的联合优化方法，进一步提升系统整体性能。本项目研究成果可为低复杂度逼近容量界SC-NOMA的设计提供理论和关键技术支撑。

在国家自然科学基金委的资助下，自然基金面上项目《基于稀疏编码的非正交多址接入基础理论与关键技术研究（批准号61871029）》开展了一系列面向非正交多址接入(Non-Orthogonal Multiple Access，NOMA)通信系统的优化设计，在基础理论、关键算法设计与平台搭建等方面取得了一系列创新性研究成果。典型成果归结为以下3部分：（1）基础理论方面，针对大规模机器通信(Massive Machine Type Communication，mMTC)场景下传统随机接入(Random Access，RA)方案接入成功概率低的问题，提出一种接入成功概率更高的模式分割随机接入(Pattern Division Random Access，PDRA)方案。（2）关键算法设计方面，针对大规模多输入多输出(Massive Multiple-input Multiple-output，M-MIMO)系统中基于期望传播(Expectation Propagation，EP)算法的接收机复杂度随基站天线数和服务用户数增加而增长过快的问题，提出基于星座点位置感知和可靠性感知算法低复杂度接收机设计方案；（3）平台建设方面，搭建NOMA链路仿真平台，对所提基于稀疏优化实现高效上行免调度的传输方案，进行仿真验证和性能分析；构建SC-NOMA与MIMO系统链路，对所提低复杂度信号检测算法进行仿真验证和性能分析。研究成果共计发表学术论文33篇（其中第一标注 30篇），其中包括IEEE Internet of Things J. 、 IEEE Trans. Wireless commun.、IEEE Commun. Lett.、IEEE Trans. Veh. Technol.等23篇（其中中科院一区2篇，2区12篇）以及国际会议WOCC4篇，最高影响因子10.238。此外，所提PDRA技术作为单独一章被纳入未来移动通信论坛（FuTURE论坛）在全球6G技术大会期间发布的《演进的多址接入技术》白皮书；向先进调制编码任务组介绍所提性能无损低复杂度多元LDPC译码器，该项技术被IMT-2030(6G)推进组发布的《先进调制编码技术研究报告》作为单独一节纳入，并作为27 篇基础参考文献之一被引用。本项目申请专利10项（已授权9项），培养博士生4名、硕士生17名，达到项目预期目标。