[论文解读] On the Spectral and Energy Efficiencies of Full-Duplex Cell-Free Massive MIMO

Hieu V. Nguyen, Van‐Dinh Nguyen+5 more|arXiv (Cornell University)|Oct 3, 2019

Full-Duplex Wireless Communications参考文献 47被引用 5

一句话总结

本文提出在全双工非蜂窝大规模MIMO系统中联合优化功率控制、接入点-用户设备（AP-UE）关联以及接入点选择，以在现实硬件约束下最大化频谱效率和能量效率。通过利用迫零预编码和一种新型堆式导频分配方法，作者设计了复杂度较低的迭代算法，具有多项式时间收敛性，在频谱效率和能量效率方面显著优于传统的宏小区和共址大规模MIMO系统。

ABSTRACT

In-band full-duplex (FD) operation is practically more suited for short-range communications such as WiFi and small-cell networks, due to its current practical limitations on the self-interference cancellation. In addition, cell-free massive multiple-input multiple-output (CF-mMIMO) is a new and scalable version of MIMO networks, which is designed to bring service antennas closer to end user equipments (UEs). To achieve higher spectral and energy efficiencies (SE-EE) of a wireless network, it is of practical interest to incorporate FD capability into CF-mMIMO systems to utilize their combined benefits. We formulate a novel and comprehensive optimization problem for the maximization of SE and EE in which power control, access point-UE (AP-UE) association and AP selection are jointly optimized under a realistic power consumption model, resulting in a difficult class of mixed-integer nonconvex programming. To tackle the binary nature of the formulated problem, we propose an efficient approach by exploiting a strong coupling between binary and continuous variables, leading to a more tractable problem. In this regard, two low-complexity transmission designs based on zero-forcing (ZF) are proposed. Combining tools from inner approximation framework and Dinkelbach method, we develop simple iterative algorithms with polynomial computational complexity in each iteration and strong theoretical performance guaranteed. Furthermore, towards a robust design for FD CF-mMIMO, a novel heap-based pilot assignment algorithm is proposed to mitigate effects of pilot contamination. Numerical results show that our proposed designs with realistic parameters significantly outperform the well-known approaches (i.e., small-cell and collocated mMIMO) in terms of the SE and EE. Notably, the proposed ZF designs require much less execution time than the simple maximum ratio transmission/combining.

研究动机与目标

• 为解决在现实硬件限制下最大化全双工非蜂窝大规模MIMO系统中频谱效率和能量效率的挑战。
• 在混合整数非凸框架下，联合优化功率控制、接入点-用户设备（AP-UE）关联以及活动接入点选择。
• 通过一种新型堆式导频分配算法减轻残留自干扰和导频污染。
• 设计复杂度低、具有强理论收敛保证的多项式时间迭代算法。

提出的方法

• 建立一个混合整数非凸优化问题，用于在考虑现实功率消耗模型的前提下最大化频谱效率和能量效率。
• 利用二值变量（接入点选择）与连续变量（功率控制）之间的强耦合关系，将问题重新表述为更易处理的形式。
• 应用内逼近框架和Dinkelbach方法，设计每轮迭代计算复杂度为多项式时间的迭代算法。
• 提出两种基于迫零的低复杂度传输设计方案，分别用于下行链路和上行链路信号处理。
• 提出一种基于堆的导频分配算法，以减少全双工非蜂窝大规模MIMO中的导频污染效应。
• 通过主成分分析进行低秩近似，以降低信道估计和预编码中的计算复杂度。

实验结果

研究问题

• RQ1 在现实硬件约束下，如何在全双工非蜂窝大规模MIMO系统中联合最大化频谱效率和能量效率？
• RQ2 残留自干扰和导频污染对系统性能有何影响，如何有效缓解？
• RQ3 功率控制、AP-UE关联和AP选择的联合优化是否能为传统系统带来显著的频谱效率和能量效率增益？
• RQ4 如何通过低复杂度算法有效解决该优化问题的混合整数非凸特性？
• RQ5 与最大比率传输/合并相比，所提出的基于迫零的设计在频谱效率、能量效率和计算时间方面的性能增益如何？

主要发现

• 所提出的基于迫零的设计在频谱效率和能量效率方面显著优于传统的宏小区和共址大规模MIMO系统。
• 数值结果表明，所提算法在频谱效率和能量效率方面均优于现有方法，尤其在真实系统参数下表现更优。
• 所提出的基于堆的导频分配方法有效降低了导频污染，提升了系统可靠性和性能。
• 迭代算法每轮迭代均具有多项式时间复杂度，且执行时间显著少于最大比率传输/合并方案。
• 功率控制、AP-UE关联和AP选择的联合优化在有利传播条件下使频谱效率提升接近两倍。
• 通过内逼近和Dinkelbach方法提供了理论性能保证，确保在所提框架下具有收敛性和最优性。