干扰多址接入信道中干扰对齐与删除技术研究

Interference alignment is one of the inter-node coordination strategies for the 5G system, since it has recently produced many theoretical breakthroughs with respect to increasing the degrees of freedom (DoF). As a new branch of interference alignment, interference alignment and cancellation (IAC) can achieve more DoF than conventional interference alignment. However, the DoF bound of IAC has not been revealed so far, and the practical implementation of IAC is fundamentally limited by backhaul overhead. In this project, we study the DoF inner bound achieved through closed-form IAC solutions, as well as practical IAC schemes with low backhaul overhead for a interfering multiple access channel, both of which have important theoretical and practical value. More details of our research are given as follows. After analyzing the relationship between antenna configuration and spatial DoF, we create the longest connected alignment chain exploring the minimum antenna resources, so as to obtain the maximum interference compression ratio. Then, the DoF inner bound can be derived through finding the optimal closed-form IAC solution. Besides, we establish the optimization principle for the data-exchanging path in the backhaul links inspired by the inherent orientation of data-exchanging path, and then adjust alignment directions of the interference channels which are outside the connected alignment chain following our established principle. Finally, to achieve a given DoF requirement by IAC schemes, the minimum backhaul overhead and number of time slots for data-exchanging are found.

干扰对齐技术在自由度提升方面取得的重大理论突破促使其成为5G多点协作通信的重要策略之一，作为干扰对齐技术的新型分支，干扰对齐与删除技术（IAC）能够进一步提高传统干扰对齐的自由度性能。然而，IAC技术的自由度界限尚未得到论证，且实用化推广受到backhaul开销的制约。本项目针对广义干扰多址接入信道系统，探索IAC技术闭式解可达的自由度下界，并研究降低backhaul开销的实用化方案，具有重要的理论意义和实用价值，具体研究内容包括：分析天线配置与自由度的内在关联，利用最少天线配置生成最长对齐连通链，获得最大干扰重叠比，构造自由度性能最优的IAC闭式解，由此得到自由度下界；由backhaul链路中数据传递路径的指向性确立数据传递路径的优化原则，基于最长对齐连通链，在优化原则的指导下改进对齐连通链外干扰信道的合并方向，确定IAC方案获得特定自由度时backhaul开销与数据交互跳数的最低界限。

在协同接收的场景下将干扰对齐和干扰删除相结合，干扰对齐与删除技术能够获得优越的自由度性能。本项目主要研究干扰对齐与删除技术理论方面的自由度下界和实用化方面的backhaul开销降低，具体研究内容包括：1）利用现有文献中干扰多址接入信道下干扰对齐与删除闭式解的存在条件，证明了M天线的广义干扰多址接入信道中干扰对齐与删除闭式解的最大可达自由度为2M。2）将系统中经由全部有效backhaul链路传送的已解码数据包的总数目定义为backhaul开销，针对干扰多址接入信道，提出了能够获得最大可达自由度且有效降低backhaul开销的干扰对齐与删除方案，证明了干扰对齐与删除获得最大可达自由度2M时所需的最小backhaul开销为M。3）在其他干扰对齐的实用化研究方面，针对干扰信道设计了一种新型的反馈拓扑结构，能够降低发送节点获取干扰对齐预编码的信道状态信息开销。上述研究成果对干扰对齐与删除技术的实用化有积极的推进作用。