A fundamental problem in multi-hop wireless networks is to estimate their throughout capacity. The problem can be informally stated as follows: given a multi-hop wireless network and a set of source destination pairs, determine the maximum rate r at which data can be transmitted between each source destination pair. Estimating the capacity of a multi-hop wireless network is practically useful --- it yields insights into the fundamental performance limits of the wireless network and at the same time aids the development of protocols that can utilize the network close to this limit. A goal of this dissertation is to develop rigorous mathematical foundations to compute the capacity of any given multi-hop wireless network with known source-destination pairs. An important factor that affects the capacity of multi-hop wireless networks is radio interference. As a result, researchers have proposed increasingly realistic interference models that aim to capture the physical characteristics of radio signals. Some of the commonly used simple models that capture radio interference are based on geometric disk-graphs. The simplicity of these models facilitate the development of provable and often conceptually simple methods for estimating the capacity of wireless networks. A potential weakness of this class of models is that they oversimplify the physical process by assuming that the signal ends abruptly at the boundary of a geometric region (a disk for omni-directional antennas). A more sophisticated interference model is the physical interference model, also known as the Signal to Interference Plus Noise Ratio (SINR) model. This model is more realistic than disk-graph models as it captures the effects of signal fading and ambient noise. This work considers both disk-graph and SINR interference models. In addition to radio interference, the throughput capacity of a multi-hop wireless network also depends on other factors, including the specific paths selected to route the packets between the source destination pairs (routing), the time at which packets are transmitted (scheduling), the power with which nodes transmit (power control) and the rate at which packets are injected (rate control). In this dissertation, we consider three different problems related to estimating network capacity. We propose an algorithmic approach for solving these problems. We first consider the problem of maximizing throughput with the SINR interference model by jointly considering the effects of routing and scheduling constraints. Second, we consider the problem of maximizing throughput by performing adaptive power control, scheduling and routing for disk-graph interference models. Finally, we examine the problem of minimizing end-to-end latency by performing joint routing, scheduling and power control using the SINR interference model. Recent results have shown that traditional layered networking principles lead to inefficient utilization of resources in multi-hop wireless networks. Motivated by these observations, recent papers have begun investigating cross-layer design approaches. Although our work does not develop new cross-layered protocols, it yields new insights that could contribute to the development of such protocols in the future. Our approach for solving these multi-objective optimization problems is based on combining mathematical programming with randomized rounding to obtain polynomial time approximation algorithms with provable worst case performance ratios. For the problems considered in this work, our results provide the best analytical performance guarantees currently known in the literature. We complement our rigorous theoretical and algorithmic analysis with simulation-based experimental analysis. Our experimental results help us understand the limitations of our approach and assist in identifying certain parameters for improving the performance of our techniques. / Ph. D.

Recently, many new types of wireless networks have emerged for both civil and military applications, such as cognitive radio networks, MIMO networks. There is a strong interest in exploring the optimal performance of these new emerging networks, e.g., maximizing the network throughput, minimizing network energy consumption. Exploring the optimal performance objectives of these new types of wireless networks is both important and intellectual challenging. On one hand, it is important for a network researcher to understand the performance limits of these new wireless networks. Such performance limits are important not only for theoretical understanding, but also in that they can be used as benchmarks for the design of distributed algorithms and protocols. On the other hand, due to some unique characteristics associated with these networks, existing analytic techniques may not be applied directly to obtain the optimal performance. As a result, new theoretical results, along with new mathematical tools, need to be developed. The goal of this dissertation is to make a fundamental advance on network performance optimization via exploring a series of optimization problems. Based on the scale of the underlying wireless network, the works in this dissertation are divided into two parts. In the first part, we study the asymptotic capacity scaling laws of different types of wireless networks. By "asymptotic", we mean that the number of nodes in the network goes to infinity. Such asymptotic capacity scaling laws offer fundamental understandings on the trend of maximum user throughput behavior when the network size increases. In the second part of this dissertation, we study several optimization problems of finite-sized wireless networks. Under a given network size, we accurately characterize some performance limits (e.g., throughput, energy consumption) of wireless networks and provide solutions on how to achieve the optimal objectives. The main contributions of this dissertation can be summarized as follows, where the first three problems are on asymptotic capacity scaling laws and the last three problems are optimization problems of finite-sized wireless networks. <b>1. Capacity Scaling Laws of Cognitive Radio Ad Hoc Networks.</b> We first study the capacity scaling laws for cognitive radio ad hoc networks (CRNs), i.e., how each individual node's maximum throughput scales as the number of nodes in the network increases. This effort is critical to the fundamental understanding of the scalability of such network. However, due to the heterogeneity in available frequency bands at each node, the asymptotic capacity is much more difficult to develop than prior efforts for other types of wireless networks. To overcome this difficulty, we introduce two auxiliary networks ζ and α to analyze the capacity upper and lower bounds. We derive the capacity results under both the protocol model and the physical model. Further, we show that the seminal results developed by Gupta and Kumar for the simple single-channel single-radio (SC-SR) networks are special cases under the results for CRNs. <b>2. Asymptotic Capacity of Multi-hop MIMO Ad Hoc Networks.</b> Multi-input multi-output (MIMO) is a key technology to increase the capacity of wireless networks. Although there has been extensive work on MIMO at the physical and link layers, there has been limited work on MIMO at the network layer (i.e., multi-hop MIMO ad hoc network), particularly results on capacity scaling laws. In this work, we investigate capacity scaling laws for MIMO ad hoc networks. Our goal is to find the achievable throughput of each node as the number of nodes in the network increases. We employ a MIMO network model that captures spatial multiplexing (SM) and interference cancellation (IC). We show that for a MIMO network with n randomly located nodes, each equipped with γ antennas and a rate of W on each data stream, the achievable throughput of each node is Θ(γW/√<span style="text-decoration:overline;"> n ln n</span></span>). <b>3. Toward Simple Criteria for Establishing Capacity Scaling Laws.</b> Capacity scaling laws offer fundamental understanding on the trend of user throughput behavior when the network size increases. Since the seminal work of Gupta and Kumar, there have been tremendous efforts developing capacity scaling laws for ad hoc networks with various advanced physical layer technologies. These efforts led to different custom-designed approaches, most of which were intellectually challenging and lacked universal properties that can be extended to address scaling laws of ad hoc networks with a different physical layer technology. In this work, we present a set of simple yet powerful general criteria that one can apply to quickly determine the capacity scaling laws for various physical layer technologies under the protocol model. We prove the correctness of our proposed criteria and validate them through a number of case studies, such as ad hoc networks with directional antenna, MIMO, cognitive radio, multi-channel and multi-radio, and multiple packet reception. These simple criteria will serve as powerful tools to networking researchers to obtain throughput scaling laws of ad hoc networks under different physical layer technologies, particularly those to appear in the future. <b>4. Exploiting SIC forMulti-hopWireless Networks.</b> There is a growing interest on exploiting interference (rather than avoiding it) to increase network throughput. In particular, the so-called successive interference cancellation (SIC) scheme appears very promising, due to its ability to enable concurrent receptions from multiple transmitters and interference rejection. However, due to some stringent constraints and limit, SIC alone is inadequate to handle all concurrent interference. We advocate a joint interference exploitation and avoidance approach, which combines the best of interference exploitation and interference avoidance, while avoiding each's pitfalls. We discuss the new challenges of such a new approach in a multi-hop wireless network and propose a formal optimization framework, with cross-layer formulation of physical, link, and network layers. This framework offers a rather complete design space for SIC to squeeze the most out of interference. The goal of this effort is to lay a mathematical foundation for modeling and analysis of a joint interference exploitation and avoidance scheme in a multi-hop wireless network. Through modeling and analysis, we develop a tractable model that is suitable for studying a broad class of network throughput optimization problems. To demonstrate the practical utility of our model, we conduct a case study. Our numerical results affirm the validity of our model and give insights on how SIC can optimally interact with an interference avoidance scheme. <b>5. Throughput Optimization with Network-wide Energy Constraint.</b> Conserving network wide energy consumption is becoming an increasingly important concern for network operators. In this work, we study network-wide energy conservation problem which we hope will offer insights to both network operators and users. Specifically, we study how to maximize network throughput under a network-wide energy constraint for a general multi-hop wireless network. We formulate this problem as a mixed-integer nonlinear program (MINLP). We propose a novel piece-wise linear approximation to transform the nonlinear constraints into linear constraints. We prove that the solution developed under this approach is near optimal with guaranteed performance bound. <b>6. Bicriteria Optimization in Multi-hop Wireless Networks.</b> Network throughput and energy consumption are two important performance metrics for a multi-hop wireless network. Current state-of-the-art is limited to either maximizing throughput under some energy constraint or minimizing energy consumption while satisfying some throughput requirement. However, the important problem of how to optimize both objectives simultaneously remains open. In this work, we take a multicriteria optimization approach to offer a systematic study on the relationship between the two performance objectives. We show that the solution to the multicriteria optimization problem characterizes the envelope of the entire throughput energy region, i.e., the so-called optimal throughput-energy curve. We prove some important properties of the optimal throughput-energy curve. For case study, we consider both linear and nonlinear throughput functions. For the linear case, we characterize the optimal throughput-energy curve precisely through parametric analysis, while for the nonlinear case, we use a piece-wise linear approximation to approximate the optimal throughput-energy curve with arbitrary accuracy. Our results offer important insights on exploiting the trade-off between the two performance metrics. / Ph. D.

A critical factor affecting the future prospects of wireless networks for wide-scale deployment is network capacity: the end users wish to have their communication experience over wireless networks to be comparable or similar to that for wireline networks. An effective approach to increase network capacity is to increase spectrum efficiency. Such an approach can be achieved by the use of multiple antenna systems (also known as multiple-input multiple-output (MIMO) technology). The benefits of substantial improvements in capacity at no cost of additional spectrum and power have positioned MIMO as one of the breakthrough technologies in modern wireless communications. As expected, research activities on applying MIMO to a variety of wireless networks have soared in recent years. However, compared with the simple point-to-point MIMO channel, which is relatively well-understood nowadays, network design and performance optimization for MIMO-based wireless networks is considerably more challenging. Many fundamental problems remain unsolved. Due to the complex characteristics of MIMO physical layer technology, it is not only desirable but also necessary to consider models and constraints at multiple layers (e.g., physical, link, and network) jointly. The formulations of these cross-layer problems for MIMO wireless networks, however, are usually mathematically challenging. In this dissertation, we aim to develop some novel algorithmic design and optimization techniques that provide optimal or near-optimal solutions. Based on network structure, this dissertation is organized into two parts. In the first part, we focus on single-hop MIMO wireless networks, while in the second part, we focus on multi-hop MIMO networks. The main results and contributions of this dissertation are summarized as follows. Single-hop MIMO Networks. In the first part of this dissertation, we study three different optimization problems for single-hop MIMO networks. The first problem addresses weighted proportional fair (WPF) scheduling associated with MIMO broadcast channels (Chapter 2). For the WPF scheduling problem in MIMO broadcast channels, we develop two algorithms that can efficiently determine the optimal dirty paper encoding order and power allocation to achieve an optimal WPF performance. To our knowledge, our work is the first that provides solutions to the WPF scheduling problem in MIMO broadcast channels. Our next problem concerns single-hop MIMO ad hoc networks (Chapter 3), which are quite different from the MIMO broadcast channels studied in the previous chapter. Single-hop MIMO ad hoc networks can be simply described as "multiple one-to-one," as compared with MIMO broadcast channels, which are "one-to-many." Performance optimization for such networks is known to be challenging due to the non-convex mathematical structure. Indeed, these networks can be viewed as the general case of interference channels in network information theory context, for which the capacity region remains unknown even under the two-user case. In this chapter, we treat the co-channel interference in the network as noise. We consider the maximum weighted sum rate problem under the single-carrier setting. We propose a global optimization approach that combines branch-and-bound (BB) and the reformulation-linearization technique (RLT). This technique is guaranteed to find a global optimal solution Multi-hop MIMO Networks. In addition to managing resources such as power and scheduling in single-hop networks, routing and end-to-end session rate control need to be considered in multi-hop MIMO networks. Thus, performance optimization problems in multi-hop MIMO networks are more interesting and yet challenging. In Chapter 4, we first consider the problem of jointly optimizing power and bandwidth allocation at each node and multihop/multipath routing in a multi-hop MIMO network that employs orthogonal channels. We show that this problem has some special structure that admits a decomposition into a set of subproblems in its dual domain. Based on this finding, we propose both centralized and distributed optimization algorithms to solve this problem optimally. In Chapter 5, we relax the orthogonal channel assumption. More specifically, we exploit the advantage of "dirty paper coding" (DPC) to allow multiple links originated from the same node to share the same channel media simultaneously. However, the formulation of cross-layer optimization problem with DPC has a non-convex structure and an exponentially large search space inherent in enumerating DPC's encoding orders. To address these difficulties, we propose an approach to reformulate and convexify the original problem. Based on the reformulated problem, we design an efficient solution procedure by exploiting decomposable dual structure. One thing in common in Chapters 4 and 5 is that we adopt the classical matrix-based MIMO channel models at the physical layer. Although this approach has its merit, the complex matrix operations in the classical MIMO models may pose a barrier for researchers in networking research community to gain fundamental understanding on MIMO networks. To bridge this gap between communications and networking communities, in Chapter 6, we propose a simple, accurate, and tractable model to enable the networking community to carry out cross-layer research for multi-hop MIMO networks. At the physical layer, we develop an accurate and simple model for MIMO channel capacity computation that captures the essence of spatial multiplexing and transmit power limit without involving complex matrix operations and the water-filling algorithm. At the link layer, we devise a space-time scheduling scheme called order-based interference cancellation (OBIC) that significantly advances the existing zero-forcing beamforming (ZFBF) to handle interference in a multi-hop network setting. The proposed OBIC scheme employs simple algebraic computation on matrix dimensions to simplify ZFBF in a multi-hop network. Finally, we apply both the new physical and link layer models to study a cross-layer optimization problem for a multi-hop MIMO network. / Ph. D.

Traditionally, achieving good performance for a multi-hop wireless network is known to be difficult. The main approach to control the operation of such a network relies on a distributed paradigm, assuming that a centralized approach is not feasible. Relying on a distributed paradigm could be justified at the time when the basic technical building blocks (e.g., node computational power, communication technology, positioning technology) were the bottlenecks. Recent advances and breakthroughs in these technical areas along with the emergence of programmable networks with softwarized control plane intelligence allow us to consider employing a centralized optimization paradigm to control and manage the operation of a multi-hop wireless network. The programmable control provides a platform on which the centralized global network optimization paradigm can be supported. The benefits of a centralized network optimization lie specially in that a network may be configured in such a way that offers optimal performance, which is hardly possible for a network relying on distributed operation. The objectives of this dissertation are to fully understand the potential benefits of a centralized control plane for a multi-hop wireless network, to identify any new challenges under this new paradigm, and to devise innovative solutions for optimal performance via a centralized control plane. Given that the performance of a wireless network heavily depends on its physical layer capabilities, we will consider a number of advanced wireless technologies, including MIMO, full duplex, and interference cancellation at the physical layer. The focus is on building tractable computational models for these wireless technologies that can be used for modeling, analysis and optimization in the centralized control plane. Problem formulation and efficient solution procedures are developed for various centralized optimization problems across multiple layers. End-to-end throughput maximization is a key objective among these optimization problems on the centralized control plane and is used to demonstrate the superior advantage of this paradigm. We study several problems: • Integration of SIC and MIMO DoF IC. We propose to integrate MIMO Degree-of-Freedom (DoF) interface cancellation (IC) and Successive Interference Cancellation (SIC) in MIMO multi-hop network under DoF protocol model. We show that DoF-based IC and SIC can be jointly integrated to combat the interference more effectively and improve the end-to-end throughput significantly. We develop the necessary mathematical models to realize the idea in a multi-hop wireless network. • Full-Duplex MIMO Wireless Networks Throughput. We investigate the performance of MIMO full-duplex (FD) in a multi-hop network. We show that if IC is exploited, MIMO FD can achieve significant throughput gain over MIMO HD in a multi-hop network, which is contrary to the recent literature suggesting an unexpected marginal gain. Our proposed model handles the additional network interference by joint efficient link scheduling and interference cancellation. • PCP in Tactical Wireless Networking. We propose the idea of the Programmable Control Plane (PCP) for the tactical wireless network under the protocol model. PCP decouples the control and data plane and allows the network control layer functionalities to be dynamically configured to adapt to specific wireless channel conditions, customized applications and/or certain tactical situations. The proposed PCP functionalities are cast into a centralized optimization problem, which can be updated as needed and provide a centralized intelligence to manage the operation of a wireless MIMO multi-hop network under the protocol model. • UPCP in Heterogeneous Wireless Networks. We propose the idea of the Unified Programmable Control Plane (UPCP) for tactical heterogeneous wireless networks with interference management capabilities under the SINR model. The UPCP abstracts the complexity of the underlying network comprised of heterogeneous wireless technologies and provides a centralized intelligence over the network resources. We develop necessary mathematical model to realize the UPCP. / Ph. D.

Les réseaux sans fil multi-saut (WMN : Wireless multi-hop Networks) sont passés du stade de simple curiosité pour revêtir aujourd'hui un intérêt certain aussi bien du point de vue de la communauté de recherche que des opérateurs de réseaux et services. En analysant les services et applications fournis au sein des réseaux WMNs, nous pouvons constater que certaines applications telles que la visioconférence, la VoIP, etc sont sensibles au délai et nécessitent une certaine qualité de service (QoS). D'autres applications telles que le transfert de fichier, le streaming vidéo, etc. sont gourmands en terme d'utilisation de bande passante. Par conséquent, les architectures de communication des réseaux WMNs doivent intégrer des mécanismes de routage efficaces et adaptés pour répondre aux besoins des services et applications envisagés. Dans cette thèse, Nous nous intéressons à la problématique du routage dans les réseaux WMNs. Notre objectif est de proposer une nouvelle approche de routage qui prend en compte différents métriques de coûts. Tout d'abord, nous avons montré que le routage sous contraintes multiples est un problème NP complet et que trois étapes sont nécessaires à la conception d'une nouvelle solution de routage: (i) modélisation de l'interférence, (ii) l'estimation de la de la bande passante restante, (iii) l'estimation du délai à un saut. Suivant cette vision, nous avons proposé deux variantes du protocole de routage OLSR (SP-OLSR, S2P-OLSR) se basant sur la métrique SINR. Les résultats des simulations ont montré l'intérêt de la proposition dans un contexte de communication vocale (VoIP). Ensuite, nous avons proposé un algorithme d'estimation d'interférence à 2 sauts (2-HEAR) afin d'estimer la bande passante disponible. Puis, et sur la base de cet algorithme, nous avons proposé une nouvelle métrique de routage pour les WMNs: Estimated Balanced Capacity (EBC) en vue de parvenir à l'équilibrage de charge entre des différents flux. La dernière question abordée dans cette thèse est celle de l'estimation du délai à un saut. La solution proposée donne une borne du délai en se basant sur un modèle de file d'attente de type G/G/1. Enfin, nous avons englobé toutes les précédentes contributions pour mettre en place une nouvelle approche de routage hybride sous contraintes multiples. Ce protocole comporte une partie proactive utilisant la nouvelle métrique de routage (EBC) et une partie réactive qui permet de prendre en compte le délai relative à une connexion donné. / There is a growing interest in wireless multi-hop networks (WMNs) since there are promising in opening new business opportunity for network operators and service providers. This research field aims at providing wireless communication means to carry different types of applications (FTP, Web browsing, video streaming, in addition to VoIP). Such applications have different constraints and their specific requirements in terms of Quality of Service (QoS) or performance metrics (delay jitter, end-to-end delay). We examine, in this thesis, the problem of routing in WMNs. Our main goal is to propose a new multi-metrics routing capable to fit these particular needs. In this thesis, we make several contributions toward WMN multi-constrained routing. First, we show that the multi-constrained path finding problem is NP-Complete and inherently a cross-layer issue, and that three steps are necessary to design the multi-metric routing protocol: (i) modeling of the inferring signal, (ii) estimation of the remaining bandwidth, (iii) estimation of the one-hop delay. Second, moving in such direction, we propose two enhanced versions of the OLSR routing protocol. The suggested protocols consider the SINR as a routing metric to build a reliable topology graph. Performance evaluation shows that utilizing such routing metric helps to improve significantly the VoIP application quality in the context of ad hoc network while maintaining a reasonable overhead cost. Third, we have proposed a 2-Hop interference Estimation Algorithm (2-HEAR) in order to estimate the available bandwidth. Then, and based on such algorithm, we have proposed a novel routing metric for WMNs: Estimated Balanced Capacity (EBC) in order to achieve load-balancing among the different flows. The next issue tackled in this thesis is the one-hop delay estimation, the one-hop delay is estimated by means of an analytical model based on G/G/1 queue. Finally, we have encompassed all the previous contributions to address our main goal, i.e. the design of a multi-constrained routing protocol for WMNs. A hybrid routing protocol is then proposed. This protocol is a junction of two parts : a proactive part that makes use of the previously estimated constraint, and a reactive part, which is triggered ”on demand” when news applications are expressed.

Fourth Generation (4G) cellular technology Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) offers high data rate capabilities to mobile users; and, operators are trying to deliver a true mobile broadband experience over LTE networks. Mobile TV and Video on Demand (VoD) are expected to be the main revenue generators in the near future [36] and efficient video streaming over wireless is the key to enabling this. 3GPP recommends the use of H.264 baseline profiles for all video based services in Third Generation (3G) Universal Mobile Telecommunication System (UMTS) networks. However, LTE networks need to support mobile devices with different display resolution requirements like small resolution mobile phones and high resolution laptops. Scalable Video Coding (SVC) is required to achieve this goal. Feasibility study of SVC for LTE is one of the main agenda of 3GPP Release10. SVC enhances H.264 with a set of new profiles and encoding tools that may be used to produce scalable bit streams. Efficient adaptation methods for SVC video transmission over LTE networks are proposed in this thesis. Advantages of SVC over H.264 are analyzed using real time use cases of mobile video streaming. Further, we study the cross layer adaptation and scheduling schemes for delivering SVC video streams most efficiently to the users in LTE networks in unicast and multicast transmissions. We propose SVC based video streaming scheme for unicast and multicast transmissions in the downlink direction, with dynamic adaptations and a scheduling scheme based on channel quality information from users. Simulation results indicate improved video quality for more number of users in the coverage area and efficient spectrum usage with the proposed methods.

Fourth Generation (4G) cellular technology Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) offers high data rate capabilities to mobile users; and, operators are trying to deliver a true mobile broadband experience over LTE networks. Mobile TV and Video on Demand (VoD) are expected to be the main revenue generators in the near future [36] and efficient video streaming over wireless is the key to enabling this. 3GPP recommends the use of H.264 baseline profiles for all video based services in Third Generation (3G) Universal Mobile Telecommunication System (UMTS) networks. However, LTE networks need to support mobile devices with different display resolution requirements like small resolution mobile phones and high resolution laptops. Scalable Video Coding (SVC) is required to achieve this goal. Feasibility study of SVC for LTE is one of the main agenda of 3GPP Release10. SVC enhances H.264 with a set of new profiles and encoding tools that may be used to produce scalable bit streams. Efficient adaptation methods for SVC video transmission over LTE networks are proposed in this thesis. Advantages of SVC over H.264 are analyzed using real time use cases of mobile video streaming. Further, we study the cross layer adaptation and scheduling schemes for delivering SVC video streams most efficiently to the users in LTE networks in unicast and multicast transmissions. We propose SVC based video streaming scheme for unicast and multicast transmissions in the downlink direction, with dynamic adaptations and a scheduling scheme based on channel quality information from users. Simulation results indicate improved video quality for more number of users in the coverage area and efficient spectrum usage with the proposed methods.

The current dominate layered networking architecture, in which each layer is designed and operated independently, results in inefficient and inflexible resource use in wireless networks due to the nature of the wireless medium, such as time-varying channel fading, mutual interference, and topology variations. In this thesis, we focus on resource allocation and scheduling in wireless orthogonal frequency division multiplexing (OFDM) networks based on joint physical and medium access control (MAC) layer optimization. To achieve orders of magnitude gains in system performance, we use two major mechanisms in resource management: exploiting the time variance and frequency selectivity of wireless channels through adaptive modulation, coding, as well as packet scheduling and regulating resource allocation through network economics. With the help of utility functions that capture the satisfaction level of users for a given resource assignment, we establish a utility optimization framework for resource allocation in OFDM networks, in which the network utility at the level of applications is maximized subject to the current channel conditions and the modulation and coding techniques employed in the network. Although the nonlinear and combinatorial nature of the cross-layer optimization challenges algorithm development, we propose novel efficient dynamic subcarrier assignment (DSA) and adaptive power allocation (APA) algorithms that are proven to achieve the optimal or near-optimal performance with very low complexity. Based on a holistic design principle, we design max-delay-utility (MDU) scheduling, which senses both channel and queue information. The MDU scheduling can simultaneously improve the spectral efficiency and provide right incentives to ensure that all applications can receive their different required quality of service (QoS). To facilitate the cross-layer design, we also deeply investigate the mechanisms of channel-aware scheduling, such as efficiency, fairness, and stability. First, using extreme value theory, we analyze the impact of multiuser diversity on throughput and packet delay. Second, we reveal a generic relationship between a specific convex utility function and a type of fairness. Third, with rigorous proofs, we provide a method to design cross-layer scheduling algorithms that allow the queueing stability region at the network layer to approach the ergodic capacity region at the physical layer.

With the proliferation of mobile devices and the advance of audio/video coding technologies, there is an increasing demand to provide quality-of-service (QoS) guarantees for multimedia applications. A WLAN (wireless local are network) typically consists of an access point (AP) and a finite set of mobile stations. Since the AP is generally more powerful and less physical constraint than mobile stations, it is of great interest to consider the use of sectorized multi-beam antennas at the AP to boost the network throughput by exploiting the benefit of spatial reuse. IEEE 802.11 is current the de facto standard for WLANs. However, if we directly apply 802.11 to the WLAN with multi-beam AP without any modification, we will encounter many challenging problems. Although existing solutions modify the 802.11 DCF (distributed coordination function) to solve these problems, yet DCF does not provide any QoS support. On the basis of 802.11e HCCA (hybrid channel control access), in this thesis, we propose a novel MAC protocol, named MPCF (multi-beam AP-assisted point coordination function), which is not only backward compatible with DCF, but also supports QoS functionalities, including non-reversal prioritization, time-bounded reservation, admission control, and cross-layer rate adaptation for multimedia streaming. Simulation results show that, in terms of throughput, frame delay dropped rate, and energy throughput, MPCF significantly outperforms existing protocols even in imperfect beam-forming and mobility environments.

Wireless communication is a rapidly growing field with many of its aspects undergoing constant enhancement. The use of cross-layer design (CLD) in current technologies has improved system performance in terms of Quality-of-Services (QoS) guarantees. While multimedia transmission is difficult to achieve, CLD is capable of incorporating techniques to achieve multimedia transmission without high complexity. Many systems have incorporated some form of adaptive transmission when using a cross-layer design approach. Various challenges must be overcome when transmitting multimedia traffic; the main challenge being that each traffic type, namely voice; image; and data, have their own transmission QoS; delay; Symbol Error Rate (SER); throughput; and jitter requirements. Recently cross-layer design has been proposed to exchange information between different layers to optimize the overall system performance. Current literature has shown that the application layer and physical layer can be used to adequately transmit multimedia over fading channels. Using Reed-Solomon coding at the application layer and Rate Adaption at the physical layer allows each media type to achieve its QoS requirement whilst being able to transmit the different media within a single packet. The following dissertation therefore strives to improve traffic through-put by introducing an unconventional rate adaption scheme and by using power adaption to achieve Symbol Error Rate (SER) QoS in multimedia transmission. Firstly, we introduce a system which modulates two separate sets of information with different modulation schemes. These two information sets are then concatenated and transmitted across the fading channel. The receiver uses a technique called Blind Detection to detect the modulation schemes used and then demodulates the information sets accordingly. The system uses an application layer that encodes each media type such that their QoS, in terms of SER, is achieved. Simulated results show an increase in spectral efficiency and the system achieves the required Symbol Error Rate constraint at lower Signal to Noise Ratio (SNR) values. The second approach involves adapting the input power to the system rather than adapting the modulation scheme. The two power adaptive schemes that are discussed are Water- Filling and Channel Inversion. Channel Inversion allows the SER requirement to be maintained for low SNR values, which is not possible with Rate Adaption. Furthermore, the system uses an application layer to encode each media type such that their QoS is achieved. Simulated results using this design show an improvement in through-put and the system achieves the SER constraint at lower SNR values. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2013.