本文为英国萨里大学（作者：SohailPayami）的博士论文，共117页。

大规模多输入多输出（MIMO）技术被认为是提高未来通信系统数据速率的一种技术。传统的多输入多输出（MIMO）系统采用数字波束形成，其中每个天线单元都配备一个射频（RF）链。当天线数量增加时，大规模MIMO系统的成本和功耗也会显著增加。近年来，模拟和数字混合波束形成器作为一种节约成本的方法，从大规模MIMO的优点中获益，引起了人们的广泛关注。在混合结构中，少量的射频链路通过移相器网络与大量天线相连。由于移相器施加的非凸约束，最优混合波束形成问题是一个复杂的非凸优化问题。

本文的总体目标是为窄带点到点和多用户大规模MIMO场景提供简单有效的混合波束形成解决方案。首先，研究了具有理想信道状态信息（CSI）的点对点通信系统的混合波束形成问题，提出了一种适用于稀疏散射信道的低分辨率移相器的高效码本混合波束形成方法。然后，利用大规模多输入多输出（MIMO）的特性，提出了一种渐近最优的混合波束形成解及其闭式表达。结果表明，该方法在稀疏和丰富的散射传播环境下都是有效的。此外，本文还推导了模拟移相器和数字移相器的闭环表达式和可实现速率的下限。其次，研究了多用户MIMO下行链路总和速率最大化的混合波束形成问题，提出了该系统的有效解及其闭式表达式。所提出的单天线和多天线解决方案都是有效的，因为它们可以达到与数字波束形成相同的和速率。此外，研究表明，在射频波束形成器上采用低成本低分辨率移相器的方法与采用昂贵模拟波束形成器的混合波束形成器相比，具有相当的性能。最后，提出了两种新的混合波束形成技术来降低射频波束形成器的功耗。通过定义一个阈值电平，研究结果表明，当采用瑞利衰落方法对无线信道矩阵进行建模时，关闭一半的移相器也可以不损失性能。然后，我们在射频波束形成器上组合移相器和开关来减少移相器的数量。该方法可以显著降低开关的功耗，因为与移相器相比，开关的功耗一般较低。本文利用强散射信道矩阵奇异向量元素的渐近性质，导出了本文所提出的算法及其性能的闭式表达式。

Massive multiple-input multiple-output(MIMO) technology is considered as one of the enabling technologies to scale upthe data rates for the future communication systems. Traditional MIMO systemsemploy digital beamforming where each antenna element is equipped with oneradio frequency (RF) chain. When the number of the antennas are scaled up, thecost and power consumption of massive MIMO systems also increasesignicantly. Recently, hybrid analog-and-digital beamformers haveattracted a lot of attention as a cost eective approach to benet from theadvantages of massive MIMO. In hybrid structure, a small number of RF chainsare connected to a large number of antennas through a network of phaseshifters. The optimal hybrid beamforming problem is a complex nonconvexoptimization due to the nonconvex constraint imposed by phase shifters. Theoverall objective of this thesis is to provide simple and eective hybridbeamforming solutions for narrowband point-to-point and multiuser massive MIMOscenarios. Firstly, hybrid beamforming problem for a point-to-pointcommunication system with perfect channel state information (CSI) isinvestigated, and an eective codebook based hybrid beamforming with lowresolution phase shifters is proposed which is suitable for sparse scatteringchannels. Then, by leveraging the properties of massive MIMO, an asymptoticallyoptimal hybrid beamforming solution as well as its closed-form formula will bepresented. It will be shown that the proposed method is eective in both sparseand rich scattering propagation environments. In addition, the closed-formexpression and lower-bounds for the achievable rates are derived when analogand digital phase shifters are employed. Secondly, hybrid beamforming problemto maximise the total sum-rate for the downlink of multiuser MIMO isinvestigated, and an eective solution as well as its closed-form expression forthis system is proposed. The presented solutions for the single-antenna andmultiantenna scenarios are shown to be eective as they can achieve a similarsum-rate as digital beamforming can reach. In addition, it is shown that theproposed technique with low-cost low resolution phase shifters at the RFbeamformer demonstrates a comparable performance to that of a hybrid beamformerwith an expensive analog beamformer. Finally, two novel hybrid beamformingtechniques are proposed to reduce the power consumption at the RF beamformer.Defining a threshold level, it is shown that half of the phase shifters couldbe turned off without a performance loss when the wireless channel matrix ismodeled by Rayleigh fading. Then, we reduce the number of the phase shifters byusing a combination of phase shifters and switches at the RF beamformer. Theproposed methods can significantly reduce the power consumption as switches, ingeneral, have lower power consumption compared to phase shifters. It is notedthat the presented algorithms and the closed-form expressions of theirperformance are derived by using the asymptotic properties of the elements ofthe singular vectors for the rich scattering channel matrix.

1 引言

2 背景与文献回顾

3 点对点系统的混合波束形成

4 多用户场景的混合波束形成

5 基于移相器和开关的混合波束形成

6 结论与未来工作展望

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