Spectrum scarcity is one of the most important challenges in wireless communications networks due to the sky-rocketing growth of multimedia applications. As the latest member of the multiple access family, non-orthogonal multiple access (NOMA) has been recently proposed for 3GPP Long Term Evolution (LTE) and envisioned to be a key component of the 5th generation (5G) mobile networks for its potential ability on spectrum enhancement. The feature of NOMA is to serve multiple users at the same time/frequency/code, but with di erent power levels, which yields a signi cant spectral e ciency gain over conventional orthogonal multiple access (OMA). This thesis provides a systematic treatment of this newly emerging technology, from the basic principles of NOMA, to its combination with simultaneously information and wireless power transfer (SWIPT) technology, to apply in cognitive radio (CR) networks and Heterogeneous networks (HetNets), as well as enhancing the physical layer security and addressing the fairness issue. First, this thesis examines the application of SWIPT to NOMA networks with spatially randomly located users. A new cooperative SWIPT NOMA protocol is proposed, in which near NOMA users that are close to the source act as energy harvesting relays in the aid of far NOMA users. Three user selection schemes are proposed to investigate the e ect of locations on the performance. Besides the closed-form expressions in terms of outage probability and throughput, the diversity gain of the considered networks is determined. Second, when considering NOMA in CR networks, stochastic geometry tools are used to evaluate the outage performance of the considered network. New closed-form expressions are derived for the outage probability. Diversity order of NOMA users has been analyzed based on the derived outage probability, which reveals important design insights regarding the interplay between two power constraints scenarios. Third, a new promising transmission framework is proposed, in which massive multipleinput multiple-output (MIMO) is employed in macro cells and NOMA is adopted in small cells. For maximizing the biased average received power at mobile users, a massive MIMO and NOMA based user association scheme is developed. Analytical expressions for the spectrum e ciency of each tier are derived using stochastic geometry. It is con rmed that NOMA is capable of enhancing the spectrum e ciency of the network compared to the OMA based HetNets. Fourth, this thesis investigates the physical layer security of NOMA in large-scale networks with invoking stochastic geometry. Both single-antenna and multiple-antenna aided transmission scenarios are considered, where the base station (BS) communicates with randomly distributed NOMA users. In addition to the derived exact analytical expressions for each scenario, some important insights such as secrecy diversity order and large antenna array property are obtained by carrying the asymptotic analysis. Fifth and last, the fundamental issues of fairness surrounding the joint power allocation and dynamic user clustering are addressed in MIMO-NOMA systems in this thesis. A two-step optimization approach is proposed to solve the formulated problem. Three e cient suboptimal algorithms are proposed to reduce the computational complexity. To further improve the performance of the worst user in each cluster, power allocation coe cients are optimized by using bi-section search. Important insights are concluded from the generated simulate results.

Device-to-Device (D2D) communication is one of the technologies for next generation communication system. Unlike traditional cellular network, D2D allows proximity users to communicate directly with each other without routing the data through a base station. The main aim of this study is to improve the overall energy efficiency (EE) of D2D communications overlaying cellular system. To reduce the complexity of joint EE optimization, we decompose the main EE problem into two subproblems; resource efficiency (RE) optimization in the first stage and EE optimization for D2D pairs in the second stage. Firstly, we propose an alternative two-stage RE-EE scheme for a single cellular user equipment (CUE) and a D2D pair utilizing uplink spectrum. Later, we extend this work for multiple CUEs and D2D pairs by considering the downlink orthogonal frequency division multiple access (OFDMA). By exploiting a range of optimization tools including the Bisection method, interior point algorithm, fractional programming, Dinkelbach approach, Lagrange dual decomposition, difference of convex functions, and concave-convex procedure, the original non-convex problems are solved and we present iterative two-stage RE-EE solutions. Simulation results demonstrate that the proposed two-stage scheme for uplink scenario outperforms the cellular mode and dedicated mode of communications and the performance is close to the global optimal solution. The results also show that the proposed schemes for downlink resource sharing provide improved system EE performance with significant gain on EE for D2D users compared to a two-stage EE-EE solution, which is obtained numerically. Furthermore, the RE and EE optimization for non-orthogonal multiple access (NOMA) are considered to study the effect of users' access to the whole spectrum. The results indicate that the proposed RE scheme for NOMA with D2D communications achieves higher system EE compared to the OFDMA based schemes.

In wireless networks, the exponentially increasing demands for wireless services are encountered by the scarcity of the available radio resources. More bandwidth is required for not only accommodating the increasing number of users, but also to meet the requirements of the new services such as TV on demand, wireless gaming, and mobile Internet. Non-orthogonal multiple access (NOMA) has attracted a great attention recently due to its superior spectral efficiency (SE) over orthogonal multiple access and could play a vital role in improving the capacity of future networks. In particular, power based NOMA multiplexes the users in power domain via superposition coding (SC) and allows them to access the whole spectrum simultaneously while using successive interference cancellation (SIC) at the receiver side for signal detection. Since NOMA exploits the power domain for multiple access, power allocation is vital to achieve superior SE with NOMA. Resource allocation and its optimization are general methods used to further improve the NOMA based networks performance. In this thesis, the resource allocation in the downlink NOMA system is considered and optimized for different objective functions such as the sum rate and the energy efficiency (EE). In addition, the combination of NOMA and multiple antenna is considered using linear and non-linear precoders. In all the considered cases, suboptimal power allocation schemes are proposed and compared to the numerically obtained optimal one. Results confirm that NOMA outperforms OFDMA. It also support the effectiveness of the proposed schemes as compared to the existing ones and to the optimal one. The results also reveal that using multiple antennas with NOMA can significantly enhance the overall performance. Furthermore, a NOMA-multicell scenario is considered to test the proposed schemes under the effect of intercell interference (ICI). The results prove that the proposed methods effective as compared to the optimal one at a much lower complexity.

Li Xin. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2003. / Includes bibliographical references (leaves 81-86). / Abstracts in English and Chinese. / COHERENT OPTICAL CODE DIVISION MULTIPLE ACCESS BASED ON SUPERSTRUCTURE FIBER BRAGG GRATING ENCODERS AND DECODERS --- p.1 / ACKNOWLEDGEMENT --- p.2 / ABSTRACT --- p.III / 摘要 --- p.V / CONTENTS --- p.VI / LIST OF FIGURES --- p.1 / Chapter CHAPTER 1 --- INTRODUCTION --- p.3 / Chapter 1.1 --- Overview of OCDMA --- p.3 / Chapter 1.2 --- Classification of OCDMA Schemes --- p.6 / Chapter 1.3 --- Introduction of Coherent OCDMA Schemes --- p.9 / Chapter 1.4 --- Introduction of superstructure Fiber Bragg Gratings and Other Encoding and Decoding Components --- p.10 / Chapter 1.5 --- Outline of the Thesis --- p.13 / Chapter CHAPTER 2 --- COUPLED MODE THEORY AND SUPERSTRUCTURE FIBER BRAGG GRATING SIMULATION MODEL --- p.16 / Chapter 2.1 --- Fiber Bragg Grating Model Based on Coupled Mode Theory --- p.16 / Chapter 2.1.1 --- Introduction of FBG and the Coupled Mode Theory --- p.16 / Chapter 2.1.2 --- FBG Model Based on CMT --- p.18 / Chapter 2.1.3 --- FBG Model When there are Phase Discontinuities Between Different Parts --- p.20 / Chapter 2.2 --- Properties of Fiber Bragg Gratings --- p.22 / Chapter 2.3 --- Simulation Model of superstructure Fiber Bragg Gratings --- p.27 / Chapter 2.4 --- Summary --- p.31 / Chapter CHAPTER 3 --- COHERENT OCDMA CODING SCHEME BASED ON THE SUPERSTRUCTURE FIBER BRAGG GRATING ENCODER/DECODER --- p.33 / Chapter 3.1 --- Introduction and Theoretical Derivation of the Coding Scheme --- p.33 / Chapter 3.1.1 --- Introduction of the Coding Scheme --- p.33 / Chapter 3.1.2 --- Derivation of SSFBG Encoder --- p.34 / Chapter 3.1.3 --- Encoding for the SSFBG --- p.39 / Chapter 3.2 --- Introduction of the Simulation Model and the Research on It …… --- p.44 / Chapter 3.3 --- Summary --- p.47 / Chapter CHAPTER 4 --- RESEARCH ON THE SIMULATED COHERENT OCDMA SYSTEM IN IDEAL CASE --- p.48 / Chapter 4.1 --- Introduction of the ideal case and factors that affect the system performance --- p.48 / Chapter 4.2 --- Effects by Refractive Index Modulation of the SSFBG Encoder --- p.49 / Chapter 4.3 --- Effects by Code Type --- p.54 / Chapter 4.4 --- Effect by the Code Length --- p.57 / Chapter 4.5 --- Summary --- p.60 / Chapter CHAPTER 5 --- RESEARCH ON THE SIMULATED COHERENT OCDMA SYSTEM IN PRACTICAL ENVIRONMENT --- p.62 / Chapter 5.1 --- Introduction --- p.62 / Chapter 5.2 --- Comparison of System Performance in Synchronous and Asynchronous Cases --- p.63 / Chapter 5.3 --- Discussion on the System Performance When Users are In Different Power Levels --- p.65 / Chapter 5.4 --- Analysis of Channel Noise In the Coherent OCDMA System --- p.68 / Chapter 5.5 --- Summary --- p.70 / Chapter CHAPTER 6 --- CONCLUSIONS AND FUTURE WORK --- p.72 / Chapter 6.1 --- Conclusions --- p.72 / Chapter 6.2 --- Future Work --- p.75 / APPENDIX A PROOF OF SSFBG THEORETICAL MODEL APPROXIMATION --- p.77 / "APPENDIX B RANDOM SEQUENCE, M-SEQUENCE AND WALSH SEQUENCE" --- p.80 / REFERENCES --- p.81

Huang Yi. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2004. / Includes bibliographical references (leaves 97-98). / Abstracts in English and Chinese. / Abstract --- p.i / 摘要 --- p.iii / Acknowledgments --- p.iv / Contents --- p.v / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- CTDMA for Multicarrier Communication Systems --- p.2 / Chapter 1.2 --- Contributions of This Thesis --- p.4 / Chapter 1.3 --- Outline of This Thesis --- p.6 / Chapter Chapter 2 --- Multicarrier Communication Systems --- p.8 / Chapter 2.1 --- Multicarrier Modulation (MCM) Scheme versus Single Carrier Modulation (SCM) Scheme --- p.9 / Chapter 2.2 --- Orthogonal Frequency Division Multiplexing (OFDM) Systems --- p.12 / Chapter 2.3 --- Multicarrier CDMA --- p.16 / Chapter Chapter 3 --- Data Rate Guaranteed CTDMA for Multicarrier Communication Systems --- p.21 / Chapter 3.1 --- Code Time Division Multiple Access (CTDMA) --- p.22 / Chapter 3.2 --- Mathematical Programming --- p.28 / Chapter 3.3 --- Near Optimal CTDMA Approach --- p.32 / Chapter 3.4 --- Ad Hoc CTDMA Approach --- p.48 / Chapter 3.5 --- Lower Bound on Optimization --- p.61 / Chapter 3.6 --- Performance Evaluation --- p.64 / Chapter Chapter 4 --- Code Assignment for Multicarrier Communication Systems with Quantized Feedback --- p.73 / Chapter 4.1 --- Code Assignment for Fully Loaded Systems --- p.74 / Chapter 4.2 --- Random Orthogonal Codes --- p.76 / Chapter 4.3 --- Wireless Fading Channel Model --- p.78 / Chapter 4.4 --- Performance Evaluation of One-to-one Assignment --- p.80 / Chapter 4.5 --- Code Assignment for Non-fully Loaded Systems --- p.89 / Chapter 4.6 --- Performance Evaluation of Multiple-to-one Assignment --- p.90 / References --- p.97

Wong Chi Sang. / "August 2002." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2002. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

Motivated by the fact that the contention graph associated with ICN is a Markov random field (MRF) with respect to the probability distribution of its system states, and that the belief propagation algorithm (BP) is an efficient way to solve "inference" problems in graphical models such as MRF, we study how to apply BP algorithms to the analysis and control of CSMA wireless networks. We investigate three applications: (1) computation of link throughputs given link access intensities; (2) computation of link access intensities required to meet target link throughputs; and (3) optimization of network utility via the control of link access intensities. We show that BP solves the three problems with exact results in tree networks and has manageable computation errors in a network with loopy contention graph. In particular, we show how a generalized version of BP, GBP, can be designed to solve the three problems above with higher accuracy. Importantly, we show how the BP and GBP algorithms can be implemented in a distributed manner, making them useful in practical CSMA network operation. / The above studies focus on computation and control of "equilibrium" link throughputs. Besides throughputs, an important performance measure in CSMA networks is the propensity for starvation. In this thesis, we show that links in CSMA wireless networks are particularly susceptible to "temporal" starvation. Specifically, certain links may have good equilibrium throughputs, yet they can still receive no throughput for extended periods from time to time. We develop a "trap theory" to analyze temporal throughput fluctuations. The trap theory serves two functions. First, it allows us to derive new mathematical results that shed light on the transient behavior of CSMA networks. Second, we can develop automated analytical tools for computing the "degrees of starvation" for CSMA networks to aid network design. We believe that the ability to identify and characterize temporal starvation as established in this thesis will serve as an important first step toward the design of effective remedies for it. / This thesis investigates the performance and control of CSMA wireless networks. To this end, an analytical model of CSMA wireless networks that captures the essence of their operation is important. We propose an Ideal CSMA Network (ICN) model to characterize the dynamic of the interactions and dependency of links in CSMA wireless networks. This model allows us to address various issues related to performance and control of CSMA networks. / We show that the throughput distributions of links in ICN can be computed from a continuous-time Markov chain and are insensitive to the distributions of the transmission time (packet duration) and the backoff countdown time in the CSMA MAC protocol given the ratio of their means rho, referred to as the access intensity. An outcome of the ICN model is a Back-of-the-Envelope (BoE) approximate computation method that allows us to bypass complicated stochastic analysis to compute link throughputs in many network configurations quickly. The BoE computation method emerges from ICN in the limit rho → infinity. Our results indicate that BoE is a good approximation technique for modest-size networks such as those typically seen in 802.11 deployments. Beyond serving as the foundation for BoE, the theoretical framework of ICN is also a foundation for understanding and optimization of large CSMA networks. / Kai, Caihong. / Adviser: Soung Chang Liew. / Source: Dissertation Abstracts International, Volume: 73-03, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references (leaves 180-183). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [201-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

At last, we focus on the detection problem in the protocol sequence design. The objective is to construct user-detectable sequences that allow any active user be detected by the receiver via some algorithm within some bounded delay if and only if it has become active. / First of all, in order to minimize variation of throughput due to delay offsets, we investigate protocol sequences whose pairwise Hamming cross-correlation is a constant for all possible relative offsets. It can be viewed as a generalization of completely shift-invariant sequences, which can achieve the zero-variation in throughput over a slot-synchronized channel. / Provided that the number of active users is smaller than the number of potential users, strongly conflict-avoiding codes are introduced with the non-blocking property in the asynchronous channel. It can be viewed as an extension of completely irrepressible sequences. / The second one is a non-blocking property which ensures that each active user can successfully transmit information at least once in its each active period. With the assumption that all potential users may be active simultaneously, user-irrepressible sequences and completely irrepressible sequences are studied respectively for different level of synchronization, to support the non-blocking property. / This thesis is based on Massey's model on collision channels without feedback, in which collided packets are considered unrecoverable. A collision occurs if two or more packets are partially or totally overlapped. Each potential user is assigned a deterministic zero-one pattern, called the protocol sequence, and sends a packet if and only if it is active and the value of the sequence is equal to one. Due to lack of feedback, the beginning of the protocol sequences cannot be synchronized and variation in relative offsets is inevitable. It further yields variation in throughput. / We study the design of protocol sequences from three different perspectives. / Zhang, Yijin. / Adviser: Wing Shing Wong. / Source: Dissertation Abstracts International, Volume: 73-03, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references (leaves 1116). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [201-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

Yang Yang. / "July 2002." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2002. / Includes bibliographical references (2nd gr., p. 1-9). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

Kin Kwong Leung. / "August 15, 2003." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2003. / Includes bibliographical references (p. 77-[82]). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.