Issues on next-generation wireless communication systems: spectrum-energy effciency, physical layer security and high mobility

To offer total smart life solutions in the immediate future, millions of sensors will be embedded into cities, vehicles, homes, industries, foods, toys, and other environments. Hence, it is imperative to develop advanced communication techniques that can support these applications. In order to realize the desired goals, spectrum-energy efficiency, wireless network security and high mobility communications are critical issues to facilitate ubiquitous wireless deployments. In this thesis, we address these challenges under various practical scenarios to ensure superior performance of next-generation wireless communication systems.In the first part, we focus on the energy-constrained networks and develop efficient strategies to enhance spectrum-energy efficiency and physical layer security. Specifically, we first develop a spectrum sharing and energy cooperation scheme in wireless powered cognitive radio (CR) networks, where the secondary users (SUs) help transfer energy to the primary user (PU) in the first phase, and in return, the PU allows the SUs to access the spectrum in the second phase. This is particularly beneficial when the PU is energy-limited wireless sensor node or IoT devices and the transmitters of SUs are base stations or access points with sufficient energy supply. We then investigate a robust secrecy design for multiple-input multiple-output (MIMO) simultaneous wireless information and power transfer (SWIPT) system, which consists of a transmitter, a full-duplex (FD) desired receiver (DR) and multiple energy receivers (ERs), i.e., potential eavesdroppers. The transmitter and DR can send artificial noise (AN) and jamming signals to improve both the transmission security and power transfer efficiency. We propose efficient iterative successive convex approximation (SCA) algorithms to tackle the formulated non-convexity problems for both scenarios. Our results demonstrate superior performance of the proposed solutions over other benchmarking approaches.In the second part, we consider a cooperative CR networks to facilitate distant proactive eavesdropping for effective legitimate wireless information surveillance. Specifically, an amplify-and-forward (AF) FD secondary transmitter helps to relay the received signal from suspicious users to legitimate monitor for wireless surveillance. In return, the secondary transmitter is granted to share the spectrum belonging to the suspicious users for its own information transmission. We consider two cases, referring to non-negligible processing delay (NNPD) and negligible processing delay (NPD) at the secondary transmitter. Our target is to maximize network energy efficiency (NEE) while guaranteeing the successful eavesdropping and quality of service (QoS) for SU. Due to the non-convexity of the formulated NEE maximization problem, we develop an efficient pathfollowing algorithm and a robust alternating optimization (AO) method as solutions under perfect and imperfect channel state information (CSI) conditions, respectively. The convergence and computational complexity of the proposed algorithms are analyzed and numerical results are provided to validate the effectiveness of our proposed schemes.In the final part, we study several receiver algorithms for orthogonal time frequency space (OTFS) modulation in high mobility communication systems. We propose to use fractionally spaced sampling (FSS) receiver architecture to achieving high diversity gain in high mobility point-to-point communications, and develop two efficient equalization algorithms, namely iterative combining message passing (ICMP) and turbo message passing (TMP) for symbol detection. We then extend the investigation to multiple users scenarios. Specifically, we propose an OTFS-based non-orthogonal multiple access (NOMA) (OBNOMA) configuration that groups stationary and mobile users by only utilizing OTFS modulation. We design an efficient iterative turbo receiver based on the principle of successive interference cancellation (SIC) to overcome the co-channel interference (CCI). In particular, we propose different symbol detection algorithms for stationary and mobile users. We also analyze the convergence performance of the new receivers and simplify the corresponding detector algorithms to further reduce receiver complexity. Experimental results demonstrate that the proposed receivers outperform the existing methods and have robustness to CSI uncertainty.為不久將來的全面智能生活提供解決方案，數以百萬計的傳感器將嵌入到城市、車輛、家庭、工業、食品、玩具和其他環境中。因此，研發能夠支持這些應用的先進通信技術勢在必行。為了實現預期目標，頻譜能量效率、無線網絡安全和高速移動通信是促進無處不在的無線部署的關鍵問題。在本論文中，我們在不同實際場景下解決這些挑戰，以確保下一代無線通信系統的卓越性能。在第一部分，我們專注於能量受限的網絡，並製定有效的策略來提高頻譜能量效率和物理層安全。具體而言，我們首先在無線供電的認知無線電網絡中提出一種頻譜共享和能量合作方案：在第一時隙，二級用戶傳輸能量給一級用戶；作為回報，一級用戶允許二級用戶在第二時隙訪問頻譜。這對於能量受限的一級用戶，比如無線傳感器節點或萬物互聯設備和具有足夠能量供應的基站或接入點的二級發射機是極其有益的。我們緊接著研究了由發射機，全雙工接收機和多個能量接收機（潛在竊聽者）組成的無線信息功率同時傳輸多輸入多輸出系統的安全魯棒性設計。發射機和接收機可以發送人工噪聲和乾擾信號，以提高傳輸安全性和功率傳輸效率。我們提出了有效地連續迭代凸近似算法來解決兩種通信場景下制定的非凸問題。我們的結果表明所提方案的性能優於其他基準測試方法。在第二部分，我們考慮了一個協作認知無線電網絡。該網絡可以促進遠程主動竊聽，以實現有效的合法無線信息監聽。具體而言，一個放大轉發全雙工的二級發射機將接收到的可疑用戶信號中繼給合法監聽器以進行無線監聽。作為回報，二級發射機被准許共享屬於可疑用戶的頻譜以用於其自身的信息傳輸。我們考慮兩種情況：二級發射機處不可忽略的處理延遲和可忽略的處理延遲。我們的目標是最大限度地提高網絡能量效率，同時保證竊聽成功和二級用戶的服務質量。由於製定的網絡能量效率最大化問題的非凸性，我們分別在完美和不完美的信道狀態信息條件下研發了一種有效的路徑跟踪算法和一種具有魯棒性交替優化的方法來解決此非凸問題。所提算法的收斂性和計算複雜度得以分析，數值結果也被提供以驗證我們提出的方案的有效性。在最後一部分，我們考慮高速移動通信系統並為正交時頻空間調製研究了幾種接收機算法。我們建議在高速移動點對點通信中使用分數間隔採樣接收機架構以實現高分集增益，並為符號檢測研發了迭代組合消息傳遞和Turbo消息傳遞兩種有效的均衡算法。我們緊接著將研究擴展到多個用戶場景。具體而言，我們提出了一種基於正交時頻空間調製的非正交多址接入方案。該方案僅通過使用正交時頻空間調製將靜態和動態用戶分組。我們設計了一種基於連續干擾消除原理的高效迭代Turbo 接收機，以克服共信道干擾。特別地，我們為靜態和動態用戶提出了不同的符號檢測算法。我們還分析了新接收機的收斂性能並簡化了相應的檢測器算法，以進一步降低接收機複雜度。實驗結果表明所提接收機優於現有方法，並且對信道狀態信息的不確定性具有魯棒性。Ge, Yao.Ph.D. Chinese University of Hong Kong 2021.Includes bibliographical references (leaves ).Abstracts also in Chinese.Title from PDF title page (viewed on …)