异步非正交多用户接入的基础理论与算法研究

As a promising candidate technique for the future 5G communication standards, Non-Orthogonal Multiple Access (NOMA) becomes a hot research topic interested by both academic and industry. Currently, most of the research about NOMA assumes symbol-level time synchronization among different users, i.e., synchronous NOMA. This assumption needs quite a few overloads to achieve the synchronization. Moreover, the performance of synchronous NOMA can be further improved. If we allow the symbols of different users added with time offset (symbol asynchronous NOMA), we can not only remove the synchronization cost but also increase the system capacity. Therefore, this project proposes symbol asynchronous NOMA (ANOMA) transmission and performs a systematic study. We will show that ANOMA has better performance and lower complexity than synchronous NOMA. In particular, this project first presents the system models of ANOMA, and tries to understand its mechanisms. After that, we will propose the precoded ANOMA scheme for downlink transmission and the block ANOMA for uplink transmission, based on different conditions of the downlink case and uplink case respectively. The excellent performance of the proposed ANOMA schemes will be theoretically analyzed. Then, we will extend the time domain ANOMA to a two dimensional ANOMA, where different users’ symbols are asynchronously added in both time domain and frequency domain. This scheme can achieve better performance and be compatible with the multi-carriers modulation in 5G. Finally, this project will implement a prototype of ANOMA with software defined radio to demonstrate the good performance of ANOMA. We believe that carrying out this project will provide new ideas, theories and algorithms for the multi-user access for 5G.

非正交接入（NOMA）是未来5G通信系统主要候选技术之一，是目前学术界与工业界的研究热点。关于NOMA的已有研究主要集中在同步情况（即不同用户的信号在时间上对齐叠加），同步开销大、性能受限。如果允许不同用户的信号在时间上偏移叠加（即符号异步NOMA），不仅减少了系统的同步开销，还能显著提高系统容量域。因此，本项目提出符号异步NOMA（ANOMA）方案并展开深入研究。具体而言，本项目首先建立ANOMA系统模型，理解ANOMA的理论机理；然后，针对上行链路和下行链路的不同情况分别提出下行预编码ANOMA方案和上行分块随机ANOMA方案，从理论上证明ANOMA可以获得显著的性能增益；之后，基于多载波传输方式，将时域ANOMA推广到时频域异步NOMA，获得更好的性能并兼容5G系统；最后，本项目利用软件无线电实现ANOMA演示验证平台。本项目的研究将为未来5G接入技术提供新思路、理论依据和技术支撑。

本项目针对异步非正交接入复用技术进行了系统的研究，主要研究内容包括三个部分（a）异步叠加信号的无线接入性能分析与低复杂度解码算法设计。（b）复杂场景NOMA系统接入算法与调制方式设计。（c）基于叠加信号的无线通信物理层安全应用研究。首先提出了基于叠加信号与BKIC算法的物理层认证算法，并将该算法用于点对点通信和多点NOMA通信方式，提高了物理层认证系统的安全性和效率；提出叠加接收端信号来保护信息安全，减少信息泄露的ROST物理层安全通信方案，实现比传统方案更高效果保密能力和更大的安全容量。为了降低传统BKIC算法的复杂度，提高该算法的精度，提出了基于高斯混合信息的盲已知干扰消除（BKIC）算法，该算法可以用于异步NOMA系统上行和下行的信号检测。针对非相干通信，提出在发送端使用差分PSK信号调制和LDS（低密度扩展）等信号格式，在基站接收端利用差分解调和置信传递BP算法实现非相干多天线NOMA信号的检测方案；针对无人机中继场景，提出无人机节点和地面节点使用NOMA下行广播传输，从而提高地面节点的传输速度。在项目执行期间，共发表相关论文25篇，其中中科院2区以上期刊论文20篇。项目申请专利10余项，获批2项。获得教育部自然科学二等奖和中国通信学会自然科学二等奖各一次。