本文為瑞典隆德大學（作者：XiangGao）的電子資訊博士論文，共271頁。

行動通訊正向著第五代（5G）演進。在不久的將來，預計生活中實現網路互連的裝置（如電話、平板電腦、感測器、車輛等）數量會爆炸性地增加。因此需要比現在4G系統更高的資料速率。在5G的願景中，還包括在偏遠地區進行更好的網路覆蓋，旨在將目前40億“未連線”的人口帶入網路世界。人們還對“綠色通訊”非常感興趣，因為ICT（資訊通訊技術）行業也要求消耗更少的能源。

大規模MIMO是滿足需求和願景的潛在技術。通過為基站配備大量(例如幾十到數百根)天線，許多終端可以在沒有嚴重使用者間干擾的情況下享受同一時頻資源的服務。通過積極有效的“空間複用”，可以在不增加所需頻譜的情況下實現更高的資料速率。可以通過增加基站的處理能力，從而允許終端採用簡單廉價的硬體。通過利用陣列的空間自由度，線性預編碼/檢測方案可用於實現接近最優的效能。大量的天線也帶來了陣列增益大的優點，使得接收訊號的強度增加，從而達到更好的覆蓋範圍。另一方面，降低基站和終端的發射功率可以提高能效。

在過去的五年中，已經進行了大量的理論研究，顯示了MIMO的巨大優勢。然而，這些研究主要基於具有獨立同分布(i.i.d.)高斯係數的理論通道，並且有時假設無限數量的天線。當這種新技術從理論應用到實際中時，使用實際的天線陣列來理解真實傳播通道中的大規模MIMO行為是很重要的。關於真實的大規模MIMO通道，以及關於大規模MIMO的論斷是否仍然成立，直到本論文的研究完成，人們還知之甚少。

本論文研究將理想的“理論世界”與非理想的工程實踐聯絡起來。在不同的傳播環境使用不同型別的天線陣列，對2.6GHz波段的大規模MIMO進行了通道測量。基於測量獲得的真實通道資料，研究主要包括：

1. 辨識大規模MIMO通道的重要特性；
    
   

2. 真實通道中傳播條件的評估及相應的大規模MIMO效能；
   

3. 捕獲大規模MIMO可辨識通道特徵的通道建模；
   

4. 通過天線選擇減少大規模MIMO的硬體複雜度。
   

本文的研究結果表明，大規模MIMO在實際傳輸環境中是有效的。在i.i.d. Rayleigh通道中觀察到的理論優勢也可以在實際通道中測試得到。對於大規模MIMO場景，包括大型陣列上的通道變化、多徑分量(MPC)壽命和3D傳播等重要的傳播效應都得到了確認。這些傳播特性被建模幷包含在COST 2100 MIMO通道模型中，作為大規模MIMO的擴充套件。對天線選擇的研究表明，真實通道的特性使得大規模MIMO複雜度顯著降低，但並沒有顯著的效能損失。作為世界上第一個研究真實傳播通道中大規模MIMO行為的工作，本論文的研究將大規模MIMO作為未來通訊系統的一種實用技術。

Mobile communications are now evolvingtowards the fifth generation (5G).In the near future, we expect an explosive increase in the number of connected devices,such as phones, tablets, sensors, connected vehicles and so on. Much higherdata rates than in today’s 4Gsystems are required. In the 5Gvisions, better coverage in remote regions is also included, aiming forbringing the current \4 billion unconnected" population into the onlineworld. There is also a great interest in \green communications", for lessenergy consumption in the ICT (information and communication technology)industry. Massive MIMO is a potential technology to fulfill the requirementsand visions. By equipping a base station with a large number, say tens tohundreds, of antennas, many terminals can be served in the same time-frequency resourcewithout severe inter-user interference. Through \aggressive" spatial multiplexing,higher data rates can be achieved without increasing the required spectrum.Processing efforts can be made at the base station side, allowing terminals tohave simple and cheap hardware. By exploiting the many spatial degrees offreedom, linear precoding/detection schemes can be used to achieve near-optimalperformance. The large number of antennas also brings the advantage of largearray gain, resulting in an increase in received signal strength. Bettercoverage is thus achieved. On the other hand, transmit power from base stationsand terminals can be scaled down to pursue energy efficiency. In the last fiveyears, a lot of theoretical studies have been done, showing the extraordinaryadvantages of massive MIMO. However, the investigations are mainly based ontheoretical channels with independent and identically distributed (i.i.d.)Gaussian coefficients, and sometimes assuming unlimited number of antennas.When bringing this new technology from theory to practice, it is important tounderstand massive MIMO behavior in real propagation channels using practicalantenna arrays. Not much has been known about real massive MIMO channels, andwhether the claims about massive MIMO still hold there, until the studies inthis thesis were done. The thesis study connects the \ideal" world oftheory to the \non-ideal"reality. Channel measurements for massive MIMO inthe 2.6 GHz band were performed, in different propagation environments andusing different types of antenna arrays. Based on obtained real-life channeldata, the studies include • channel characterization to identify importantmassive MIMO properties, • evaluation of propagation conditions in realchannels and corresponding massive MIMO performance, • channel modeling formassive MIMO to capture the identified channel properties, and • reduction ofmassive MIMO hardware complexity through antenna selection. The investigationsin the thesis conclude that massive MIMO works efficiently in real propagationenvironments. The theoretical advantages, as observed in i.i.d. Rayleighchannels, can also be harvested in real channels. Important propagation effectsare identified for massive MIMO scenarios, including channel variations overlarge arrays, multipath-component (MPC) lifetime, and 3D propagation. Thesepropagation properties are modeled and included into the COST 2100 MIMO channelmodel as an extension for massive MIMO. The study on antenna selection showsthat characteristics in real channels allow for significant reductions ofmassive MIMO complexity without significant performance loss. As one of theworld’s first research work on massive MIMO behavior in real propagationchannels, the studies in this thesis promote massive MIMO as a practicaltechnology for future communication systems.

1 引言

2 大規模MIMO的概念

3 通道測量

4 測量資料處理回顧

5 通道特性

6 測量通道的效能評估

7 通道建模

8 通過天線選擇簡化硬體

9 總結與本文貢獻

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