Interference management and resolution for large-scale wireless networks

Ph.D.This thesis studies the multiuser interference problem in large-scale wireless systems, where multiple users interfere with each other due to simultaneous transmission. This thesis consists of three parts that explore interference management and resolution methods for three different network setups. The first two parts focus on the degree of freedom (DoF) optimization for two types of large-scale multiway relay networks. The third part presents a new multiuser detection (MUD) scheme for the grant-free massive-device multiple access (MaDMA) system.The first part of the thesis studies the DoF of the symmetric multi-relay multiple-input multiple-output (MIMO) Y channel, where three user nodes communicate via multiple geographically separated relay nodes. Each user or relay node is equipped with multiple antennas. For this model, we establish a general DoF achievability framework based on linear precoding and post-processing methods. Under this framework, we convert the DoF achievability problem into a series of non-linear matrix equations with respect to user precoders, user post-processors, and relay precoders. To solve this problem, we adopt an asymmetric uplink-downlink design, where the user precoders are designed for signal alignment and the user post-processors are used for interference neutralization. For the design of relay precoders, we put forth a general method for solving matrix equations. Together with the techniques of antenna disablement and symbol extension, we derive an achievable DoF for an arbitrary antenna setup. We show that our asymmetric uplink-downlink design outperforms the conventional symmetric uplink-downlink design considerably. We also show that for certain antenna setups, our approach achieves the optimal DoF.The second part of this thesis studies the beamforming design for the MIMO multiway relay channel with clustered full data exchange. Specifically, we formulate the DoF optimization problem under a rank-constrained rank-minimization (RCRM) framework. We then decompose the RCRM problem into independent rank minimization subproblems and put forth an iterative algorithm for the beamforming design. The advantage of our algorithmic beamforming design is twofold. First, for symmetric antenna setups, our approach advances the state of the art by expanding the achievable DoF region. Second, for asymmetric antenna setups, our approach can be directly applied while prior approaches are not readily applicable.In the third part of this thesis, we study the MUD problem for a grant-free MaDMA system, where a large number of single-antenna user devices transmit sporadic data to a multi-antenna base station (BS). Specifically, we put forth two MUD schemes, termed random sparsity learning multiuser detection (RSL-MUD) and structured sparsity learning multiuser detection (SSL-MUD) for the time-slotted and non-time-slotted grant-free MaDMA systems, respectively. We show that by exploiting the sparsity embedded in the user signals, we can recover the user activity state, the channel, and the user data in a single phase, without using pilot signals for channel estimation and/or active user identification. To this end, we develop a message-passing statistical inference framework for the BS to blindly detect the user data without any prior knowledge of the identities and the channel state information (CSI) of active users. Simulation results show that our RSL-MUD and SSL-MUD schemes significantly outperform the conventional schemes in both reducing the transmission overhead and improving the error behavior of the system.本文研究了大規模無線系統中多用戶同時傳輸產生的干擾問題。本論文分為三個部分，分別探討了三種不同網絡配置下的干擾管理和解決方案。前兩部分主要關注兩種大規模多路中繼網絡的自由度（DoF）優化問題。第三部分介紹了一種用於無授權大規模多址接入（MaDMA）系統的多用戶檢測（MUD）新方案。論文的第一部分研究了對稱多中繼多輸入多輸出（MIMO）Y 信道的自由度。該信道中，三個用戶節點通過多個地理上分隔的中繼節點進行通信。每個用戶或中繼節點配備有多個天線。我們基於線性預編碼和線性後處理的思路，為該信道模型建立了一個普適的自由度可實現性框架。在此框架下，我們將自由度可實現性的問題轉換為一系列關於用戶預編碼器，用戶後處理器和中繼預編碼器的非線性矩陣方程。對這個問題，我們採用了一種非對稱的上下行鏈路設計，其中用戶預編碼器用於信號對齊，用戶後處理器用於乾擾中和。對於中繼預編碼器，我們提出了一種求解矩陣方程的通用方法來設計。結合天線部分禁用和符號擴展技術，我們為任意天線設置推導出了一種可實現的自由度。我們的結果表明，我們提出的非對稱上下行鏈路設計顯著優於傳統的對稱上下行鏈路設計。我們還證明，對於某些天線設置，我們的方法可以實現最佳自由度。論文的第二部分研究了分組全交換的多輸入多輸出多路中繼信道的波束成型設計。具體地，我們在秩約束秩最小化（RCRM）的框架下將自由度優化問題公式化。然後，我們將該RCRM 問題分解為若干獨立的秩最小化子問題，並為此提出了一種用於波束成型設計的迭代算法。我們的波束形成設計算法的優點有兩重。首先，對於對稱的天線配置，我們的方法擴展了現有的可實現自由度區域。其次，我們的方法可以直接應用於非對稱的天線配置，而現有的方法並不適用。在論文的第三部分，我們研究了大規模多址接入系統（MaDMA）中的多用戶檢測問題。該系統中，大量單天線用戶設備將偶發數據發送到一個多天線基站(BS)。具體地，我們分別為時隙和非時隙無授權MaDMA 系統提出了兩種多用戶檢測方案，稱為隨機稀疏性學習多用戶檢測（RSL-MUD）和結構化稀疏性學習多用戶檢測（SSL -MUD）。利用在用戶信號中嵌入的稀疏性，我們可以在單個階段中同時檢測用戶活躍狀態、信道、以及用戶數據，而無需使用導頻信號作信道估計和/或活躍用戶識別。為此，我們開發了一套基於統計推斷的檢測框架，使基站可以在事先不知道活躍用戶身份及其信道狀態信息（CSI）的情況下盲檢測用戶數據。仿真結果表明，我們的RSL-MUD和SSL-MUD 方案在降低傳輸開銷和改善系統傳輸錯誤率方面顯著優於傳統方案。Ding, Tian.Thesis Ph.D. Chinese University of Hong Kong 2019.Includes bibliographical references (leaves 105-114).Abstracts also in Chinese.Title from PDF title page (viewed on 7, April 2021)