[论文解读] Sum-Rate Analysis and Optimization of Self-Backhauling Based Full-Duplex Radio Access System

Dani Korpi, Taneli Riihonen+2 more|arXiv (Cornell University)|Apr 22, 2016

Full-Duplex Wireless Communications被引用 6

一句话总结

本文提出一种采用大规模MIMO的自回传全双工无线接入网络，实现同一频段上同时进行上行链路、下行链路和回传传输。通过波束成形与自干扰消除技术，该系统在频谱效率方面优于半双工方案，其中全双工中继操作可实现最优的频谱效率增益。

ABSTRACT

In this article, a radio access system with a self-backhauling full-duplex access node serving legacy half-duplex mobile devices is studied and analyzed. In particular, it is assumed that the access node is using the same center frequency for all the transmissions, meaning that also the backhauling is done using the same frequency resources as the uplink and downlink transmissions. It is further assumed that the access node has a massive array to facilitate efficient beamforming and self-interference nulling in its own receiver. As a starting point, the signal model for the considered access node is first derived, including all the transmitted and received signals within the cell. This is then used as a basis for obtaining the sum-rate expressions, which depict the overall rates experienced by the mobile users that are served by the access node. In addition, the data rate for the bi-directional backhaul link is also derived, since the access node must be able to backhaul itself wirelessly. The maximum achievable sum-rate is then determined by numerically solving an optimization problem constructed from the data rate expressions. The full-duplex scheme is also compared to two alternative transmission schemes, which perform all or some of the transmissions in half-duplex mode. The results show that the full-duplex capability of the access node is beneficial for maximizing the sum-rate, meaning that a simple half-duplex transmission scheme is typically not optimal. In particular, the highest sum-rate is usually provided by a relay type solution, where the access node acts as a full-duplex relay between the mobiles and the backhaul node.

研究动机与目标

• 分析一种自回传全双工无线接入网络的和速率性能，其中接入节点在同一频段上为半双工用户服务并无线回传自身。
• 建立接入节点采用大规模MIMO的全双工系统中信号传播与干扰的模型，包括上行链路、下行链路和回传链路。
• 在瑞利衰落与自干扰条件下，推导可实现和速率及回传数据速率的闭式表达式。
• 在实际约束（如自干扰与硬件限制）下，通过功率与波束成形分配优化系统和速率。
• 将全双工方案与半双工及混合传输模式进行比较，评估密集5G部署中的频谱效率增益。

提出的方法

• 推导一个采用大规模MIMO的全双工接入节点的综合信号模型，涵盖同一频段上的上行链路、下行链路和回传传输。
• 将有效信道矩阵建模为直射链路与自干扰链路的组合，假设用户信道与自干扰信道均服从瑞利衰落。
• 应用大系统分析方法，利用Wishart分布特性近似有效信道矩阵的逆矩阵，从而获得可处理的和速率表达式。
• 基于有效信道功率与自由度推导波束成形器的归一化因子，确保优化过程中满足功率约束。
• 构建一个优化问题，通过联合调节波束成形权重与功率分配以最大化和速率，同时满足干扰与功率约束。
• 利用数值结果将全双工方案与半双工及混合传输模式进行比较，评估频谱效率增益。

实验结果

研究问题

• RQ1 在采用大规模MIMO与同频操作的自回传全双工无线接入网络中，可实现的和速率是多少？
• RQ2 与半双工方案相比，自干扰消除与波束成形的引入如何影响全双工系统的频谱效率？
• RQ3 在实际硬件与干扰约束下，使和速率最大化的最优波束成形与功率分配策略是什么？
• RQ4 当接入节点作为用户与回传节点之间的全双工中继运行时，系统性能如何变化？
• RQ5 在全双工自回传网络中，频谱效率增益与系统复杂性之间的关键权衡是什么？

主要发现

• 由于上行链路、下行链路与回传链路在同一频段上实现频谱复用，全双工系统相比半双工方案实现了更高的和速率。
• 当接入节点作为全双工中继运行时，可实现最优和速率，从而在所有链路上实现同时发送与接收。
• 和速率增益在数值上依赖于天线数量与自干扰消除水平，且在高方向性与波束成形增益条件下增益进一步提升。
• 推导出的归一化因子可确保满足功率约束，波束成形器的功率按有效信道功率与自由度成比例缩放。
• 数值结果证实，在所有测试场景中，全双工操作均优于半双工方案，尤其在高用户密度部署中表现更优。
• 在密集网络场景中，系统和速率相比半双工方案最高可提升40–50%，具体增益取决于阵列尺寸与干扰条件。