Interference-Assisted Techniques for Transmission and Multiple Access in Optical Communications

光通信技術的連接方式分為有線和無線方式。光纖通信技術使用有線的光纖連接發射機和接收機。受益於其高帶寬、低單位成本和穩定性，光纖通信技術在長距傳輸、接入網和數據中心市場上佔據了極大的份額。另一方面，光無線通信技術也正在成為通信市場的重要成員；其中的自由空間光通信和可見光通信正获得大量的研究和廣泛的商用化。干擾是來自於其它用戶的影響。長期以來，在光通信系統內，干擾被認為是有害的。然而，干擾也可以被利用。這一點引發了各式各樣的創新。本文關注其中的兩點：物理層網絡編碼和非正交多址接入。本文的第一部分內容有關光物理層網絡編碼。物理層網絡編碼最初用于無線通信中提升雙向中繼網絡的容量。作為網絡編碼的一種變體，物理層網絡編碼將共信道干涉轉化為一種天然的網絡編碼操作。本文將物理層網絡編碼用於三種光通信系統中。首先，我們將物理層網絡編碼應用到相干光正交頻分複用中，來提升多播網絡的容量；而僅帶來有限的光噪比損失。其次，我們研究了物理層網絡編碼在多樣服務的正交頻分複用無源光接入網中的應用。研究發現，物理層網絡編碼可在僅有少量功率代價的條件下同時實現有線和無線服務的虛擬專用網絡。再次，我們在基於中繼的可見光通信中加入了物理層網絡編碼，並提出了一種新的共相方案。物理層網絡編碼可以提升中繼處的容量瓶頸，而新提出的共相方法可以提升系統的誤碼率性能。本文的第二部分討論了另一種干擾利用技術：非正交多址接入。非正交多址接入在功率域上複用信號，而在時域、頻域、和碼域上混疊信號。在此我們提出了三種方案。第一種和第二種方案都將非正交多址接入應用於可見光通信中，惟使用了不同的多用戶檢測方案與不同的相位預失真方法。第三種方案是非正交多址接入與一種基於正交循環變換矩陣的多載波預編碼方案的聯合。這一聯合可以免去正交頻分複用系統中複雜的動態加載或者電域均衡，使得非正交多址接入技術在實際系統中更具可行性。Optical communications can be in wired or wireless form. Fiber optics communication (FOC) connects transmitters and receivers with optical fiber. Benefitting from its high bandwidth, low cost per volume and stability, it gains a significant market share in long-haul networks, access networks and data centers. Meanwhile, optical wireless communication (OWC) is also emerging as a crucial player in the communication market. In OWC, free-space optical communication (FSO) and visible light communication (VLC) are being studied and commercially deployed extensively.Interference is a common phenomenon in multi-user communication systems. In both FOC and OWC, interference has long been treated as a detrimental effect. However, it could also be beneficial to system applications. The effort of harnessing interference has spurred numerous innovations. Interesting examples are physical-layer network coding (PNC) and non-orthogonal multiple access (NOMA).The first part of this thesis in on the topic of PNC. PNC was firstly proposed in wireless communication to improve the throughput of a two-way relay network (TWRN). As a variation of network coding (NC), PNC turns the common channel interference (CCI) as a natural network coding operation. In this thesis, PNC is introduced into optical communication. Three schemes are proposed in different scenarios. Firstly, PNC is applied to a coherent optical orthogonal frequency division multiplexing (CO-OFDM) system so as to improve the throughput of the multicast network. The optical signal to noise ratio (OSNR) penalty is quite low. Secondly, we investigate the application of PNC in an OFDM passive optical network (OFDM-PON) supporting heterogeneous services. It is found that only minor receiver power penalties are observed to realize PNC-based virtual private networks (VPN), both in the wired service part and the wireless service part in an OFDM-PON with heterogeneous services. Thirdly, we innovate relay-based visible light communication (VLC) by adopting PNC, with a newly proposed phase-aligning method. PNC could improve the throughput at the bottlenecking relay node in a VLC system, and the proposed phase aligning method can improve the BER performance.The second part of this thesis discusses another interference-assisted technology in communication, that is, non-orthogonal multiple access (NOMA). NOMA multiplexes signals from multiple users in another dimension: power domain, with a non-orthogonal multiplexing in other dimensions such as time, frequency and code. Three schemes are proposed in this part. The first and the second schemes both realize NOMA in VLC, with different multiuser detection (MUD) techniques and a proposed phase pre-distortion method. Although both can decrease the system BER compared to conventional NOMA, the scheme using joint detection (JD) outperforms the one using successive interference cancellation (SIC). The third scheme investigated in this part is a combination of NOMA and a multicarrier precoding (MP) technology based on an orthogonal circulant transform matrix (OCT). This combination can avoid the complicated adaptive bit loading or electronic equalization, making NOMA more attractive in a practical system.Guan, Xun.Thesis Ph.D. Chinese University of Hong Kong 2017.Includes bibliographical references (leaves ).Abstracts also in Chinese.Title from PDF title page (viewed on …).Detailed summary in vernacular field only.Detailed summary in vernacular field only.Detailed summary in vernacular field only.Detailed summary in vernacular field only