As wireless networks continue streaking through more aspects of our lives, it is seriously constrained by limited network resources, in terms of time, frequency and power. In order to enhance performance for wireless networks, it is of great importance to allocate resources smartly based on the current network scenarios. The focus of this dissertation is to investigate radio resource management algorithms to optimize performance for different types of wireless networks. Firstly, we investigate a joint optimization problem on relay node placement and route assignment for wireless sensor networks. A heuristic binary integer programming algorithm is proposed to maximize the total number of information packets received at the base station during the network lifetime. We then present an optimization algorithm based on binary integer programming for relay node assignment with the current node locations. Subsequently, a heuristic algorithm is applied to move the relay nodes to the locations iteratively to better serve their associated edge nodes. Secondly, as traditional goal of maximizing the total throughput can result in unbalanced use of network resources, we study a joint problem of power control and channel assignment within a wireless mesh network such that the minimal capacity of all links is maximized. This is essentially a fairness problem. We develop an upper bound for the objective by relaxing the integer variables and linearization. Subsequently, we put forward a heuristic approach to approximate the optimal solution, which tries to increase the minimal capacity of all links via setting tighter constraint and solving a binary integer programming problem. Simulation results show that solutions obtained by this algorithm are very close to the upper bounds obtained via relaxation, thus suggesting that the solution produced by the algorithm is near-optimal. Thirdly, we study the topology control of disaster area wireless networks to facilitate mobile nodes communications by deploying a minimum number of relay nodes dynamically. We first put forward a novel mobility model for mobile nodes that describes the movement of first responders within a large disaster area. Secondly, we formulate the square disk cover problem and propose three algorithms to solve it, including the two-vertex square covering algorithm, the circle covering algorithm and the binary integer programming algorithm. Fourthly, we explore the joint problem of power control and channel assignment to maximize cognitive radio network throughput. It is assumed that an overlaid cognitive radio network (CRN) co-exists with a primary network. We model the opportunistic spectrum access for cognitive radio network and formulate the cross-layer optimization problem under the interference constraints imposed by the existing primary network. A distributed greedy algorithm is proposed to seek for larger network throughput. Cross-layer optimization for CRN is often implemented in centralized manner to avoid co-channel interference. The distributed algorithm coordinates the channel assignment with local channel usage information. Thus the computation complexity is greatly reduced. Finally, we study the network throughput optimization problem for a multi-hop wireless network by considering interference alignment at physical layer. We first transform the problem of dividing a set of links into multiple maximal concurrent link sets to the problem of finding the maximal cliques of a graph. Then each concurrent link set is further divided into one or several interference channel networks, on which interference alignment is implemented to guarantee simultaneous transmission. The network throughput optimization problem is then formulated as a non-convex nonlinear programming problem, which is NP-hard generally. Thus we resort to developing a branch-and-bound framework, which guarantees an achievable performance bound.

Master of Philosophy / Wireless technology is experiencing spectacular developments, due to the emergence of interactive and digital multimedia applications as well as rapid advances in the highly integrated systems. For the next-generation mobile communication systems, one can expect wireless connectivity between any devices at any time and anywhere with a range of multimedia contents. A key requirement in such systems is the availability of high-speed and robust communication links. Unfortunately, communications over wireless channels inherently suffer from a number of fundamental physical limitations, such as multipath fading, scarce radio spectrum, and limited battery power supply for mobile devices. Cooperative diversity (CD) technology is a promising solution for future wireless communication systems to achieve broader coverage and to mitigate wireless channels’ impairments without the need to use high power at the transmitter. In general, cooperative relaying systems have a source node multicasting a message to a number of cooperative relays, which in turn resend a processed version message to an intended destination node. The destination node combines the signal received from the relays, and takes into account the source’s original signal to decode the message. The CD communication systems exploit two fundamental features of the wireless medium: its broadcast nature and its ability to achieve diversity through independent channels. A variety of relaying protocols have been considered and utilized in cooperative wireless networks. Amplify and forward (AAF) and decode and forward (DAF) are two popular protocols, frequently used in the cooperative systems. In the AAF mode, the relay amplifies the received signal prior to retransmission. In the DAF mode, the relay fully decodes the received signal, re-encodes and forwards it to the destination. Due to the retransmission without decoding, AAF has the shortcoming that noise accumulated in the received signal is amplified at the transmission. DAF suffers from decoding errors that can lead to severe error propagation. To further enhance the quality of service (QoS) of CD communication systems, hybrid Automatic Repeat-reQuest (HARQ) protocols have been proposed. Thus, if the destination requires an ARQ retransmission, it could come from one of relays rather than the source node. This thesis proposes an improved HARQ scheme with an adaptive relaying protocol (ARP). Focusing on the HARQ as a central theme, we start by introducing the concept of ARP. Then we use it as the basis for designing three types of HARQ schemes, denoted by HARQ I-ARP, HARQ II-ARP and HARQ III-ARP. We describe the relaying protocols, (both AAF and DAF), and their operations, including channel access between the source and relay, the feedback scheme, and the combining methods at the receivers. To investigate the benefits of the proposed HARQ scheme, we analyze its frame error rate (FER) and throughput performance over a quasi-static fading channel. We can compare these with the reference methods, HARQ with AAF (HARQ-AAF) and HARQ with perfect distributed turbo codes (DTC), for which correct decoding is always assumed at the relay (HARQ-perfect DTC). It is shown that the proposed HARQ-ARP scheme can always performs better than the HARQ-AAF scheme. As the signal-to-noise ratio (SNR) of the channel between the source and relay increases, the performance of the proposed HARQ-ARP scheme approaches that of the HARQ-perfect DTC scheme.

Master of Philosophy / Wireless technology is experiencing spectacular developments, due to the emergence of interactive and digital multimedia applications as well as rapid advances in the highly integrated systems. For the next-generation mobile communication systems, one can expect wireless connectivity between any devices at any time and anywhere with a range of multimedia contents. A key requirement in such systems is the availability of high-speed and robust communication links. Unfortunately, communications over wireless channels inherently suffer from a number of fundamental physical limitations, such as multipath fading, scarce radio spectrum, and limited battery power supply for mobile devices. Cooperative diversity (CD) technology is a promising solution for future wireless communication systems to achieve broader coverage and to mitigate wireless channels’ impairments without the need to use high power at the transmitter. In general, cooperative relaying systems have a source node multicasting a message to a number of cooperative relays, which in turn resend a processed version message to an intended destination node. The destination node combines the signal received from the relays, and takes into account the source’s original signal to decode the message. The CD communication systems exploit two fundamental features of the wireless medium: its broadcast nature and its ability to achieve diversity through independent channels. A variety of relaying protocols have been considered and utilized in cooperative wireless networks. Amplify and forward (AAF) and decode and forward (DAF) are two popular protocols, frequently used in the cooperative systems. In the AAF mode, the relay amplifies the received signal prior to retransmission. In the DAF mode, the relay fully decodes the received signal, re-encodes and forwards it to the destination. Due to the retransmission without decoding, AAF has the shortcoming that noise accumulated in the received signal is amplified at the transmission. DAF suffers from decoding errors that can lead to severe error propagation. To further enhance the quality of service (QoS) of CD communication systems, hybrid Automatic Repeat-reQuest (HARQ) protocols have been proposed. Thus, if the destination requires an ARQ retransmission, it could come from one of relays rather than the source node. This thesis proposes an improved HARQ scheme with an adaptive relaying protocol (ARP). Focusing on the HARQ as a central theme, we start by introducing the concept of ARP. Then we use it as the basis for designing three types of HARQ schemes, denoted by HARQ I-ARP, HARQ II-ARP and HARQ III-ARP. We describe the relaying protocols, (both AAF and DAF), and their operations, including channel access between the source and relay, the feedback scheme, and the combining methods at the receivers. To investigate the benefits of the proposed HARQ scheme, we analyze its frame error rate (FER) and throughput performance over a quasi-static fading channel. We can compare these with the reference methods, HARQ with AAF (HARQ-AAF) and HARQ with perfect distributed turbo codes (DTC), for which correct decoding is always assumed at the relay (HARQ-perfect DTC). It is shown that the proposed HARQ-ARP scheme can always performs better than the HARQ-AAF scheme. As the signal-to-noise ratio (SNR) of the channel between the source and relay increases, the performance of the proposed HARQ-ARP scheme approaches that of the HARQ-perfect DTC scheme.

We describe an adaptive, mid-level approach to the wireless device power management problem. Our approach is based on reinforcement learning, a machine learning framework for autonomous agents. We describe how our framework can be applied to the power management problem in both infrastructure and ad~hoc wireless networks. From this thesis we conclude that mid-level power management policies can outperform low-level policies and are more convenient to implement than high-level policies. We also conclude that power management policies need to adapt to the user and network, and that a mid-level power management framework based on reinforcement learning fulfills these requirements.

Many large-scale random graphs (e.g., the Internet) exhibit complex topology, nonhomogeneous spatial node distribution, and preferential attachment of new nodes. Current topology models for ad-hoc networks mostly consider a uniform spatial distribution of nodes and do not capture the dynamics of evolving, real-world graphs, in which nodes "gravitate" toward popular locations and self-organize into non-uniform clusters. In this thesis, we first investigate two constraints on scalability of ad-hoc networks – network reliability and node capacity. Unlike other studies, we analyze network resilience to node and link failure with an emphasis on the growth (i.e., evolution) dynamics of the entire system. Along the way, we also study important graph-theoretic properties of ad-hoc networks (including the clustering coefficient and the expected path length) and strengthen our generic understanding of these systems. Finally, recognizing that under existing uniform models future ad-hoc networks cannot scale beyond trivial sizes, we argue that ad-hoc networks should be modeled from an evolution standpoint, which takes into account the well-known "clustering" phenomena observed in all real-world graphs. This model is likely to describe how future ad-hoc networks will self-organize since it is well documented that information content distribution among end-users (as well as among spatial locations) is non-uniform (often heavy-tailed). Results show that node capacity in the proposed evolution model scales to larger network sizes than in traditional approaches, which suggest that non-uniformly clustered, self-organizing, very large-scale ad-hoc networks may become feasible in the future.

The recent advances in mobile computing devices and wireless networking produced the technical platform for multimedia services over thin mobile devices. Nowadays, we are witnessing an important growth in applications using thin mobile devices, such as social networks, virtual walkthrough, media streaming, and augmented reality (AR), just to mention a few. Most of these applications are based on the client-server architecture, however several studies showed that the client-server architecture suffers from various issues, such as the server bottleneck, latency and the lack of scalability. This led most of the systems to switch to the peer-to-peer (P2P)-like environment for its scalability and potential cost saving. P2P multimedia streaming over thin mobile devices-based classes of applications has known a significant growth during the last years. Although P2P video streaming over thin mobile devices received a great deal of attention, the application of 3D streaming over mobile devices was challenging mainly due to the limited mobile resources and capabilities, as well as the wireless medium limitations. Having 3D streaming over Mobile Ad hoc Networks (MANET) is considered more challenging given that the 3D streaming-based system has to deal with a dynamic environment resulting from nodes mobility, which may lead to route breakages and connection loss. Therefore, one of the major difficulties in 3D streaming over MANET is related to the supplying partner's strategy that aims at determining the most suitable source holding the required 3D data to stream it quickly and efficiently to the requesters. In this thesis, we propose our P2P based 3D streaming system which we refer to as MOSAIC as well as a suite of supplying partner strategy protocols for P2P 3D streaming over thin mobile devices. Our proposed suite of protocols selects the potential sources that have the relevant 3D data, based on a set of criteria such as the source location, the mobile device's available resources as well as its residual energy. We also proposed a multihop supplying partner selection protocol that takes into account the signal strength and the nodes mobility when streaming the relevant 3D data. The performance evaluation obtained to evaluate our MOSAIC system as well as our suite of protocols using an extensive set of NS2 simulation experiments, is then reported.

Multi-hop wireless network are promising techniques in the field of wireless communication. The dynamic topology of the network and the independent selfish participants of the network make it difficult to be modeled by traditional tools. Game theory is one of the most powerful tools for such problems. However, most current works have certain limitations. There has not been widely accepted solution for the problem yet. In this thesis we propose our solutions for the problem of bandwidth sharing in wireless networks. We assume the nodes are rational, selfish but not malicious independent agents in the game. In our model, nodes are trying to send their data to the access point. Some nodes may require others to forward their package to successfully connect to the access point. However, nodes are selfish and do not wish to help others. Therefore it is possible that some nodes may refuse the requirement. In that case, the unpleasant nodes may punish the others by slowing down their traffic, in which case both parties will suffer. Therefore it is non-trivial to find out the Equilibrium for these nodes after the bargain process. What is the proper distribution of resources among these nodes? We propose a solution based on the game theory. Our solution fulfils the goal of fairness and social welfare maximum.

Multi-hop wireless network are promising techniques in the field of wireless communication. The dynamic topology of the network and the independent selfish participants of the network make it difficult to be modeled by traditional tools. Game theory is one of the most powerful tools for such problems. However, most current works have certain limitations. There has not been widely accepted solution for the problem yet. In this thesis we propose our solutions for the problem of bandwidth sharing in wireless networks. We assume the nodes are rational, selfish but not malicious independent agents in the game. In our model, nodes are trying to send their data to the access point. Some nodes may require others to forward their package to successfully connect to the access point. However, nodes are selfish and do not wish to help others. Therefore it is possible that some nodes may refuse the requirement. In that case, the unpleasant nodes may punish the others by slowing down their traffic, in which case both parties will suffer. Therefore it is non-trivial to find out the Equilibrium for these nodes after the bargain process. What is the proper distribution of resources among these nodes? We propose a solution based on the game theory. Our solution fulfils the goal of fairness and social welfare maximum.

The thesis focuses on resource management or sensor allocation when we use bearings-only measurements to track targets in an unattended ground sensor (UGS) network. Intelligent resource management is necessary because each UGS sensor node has limited power and it is desirable that estimation performance not degrade very much when only a few nodes are active to maximize the effective tracking lifetime. For scheduling to prolong the tracking lifetime, a new energy-based (EB) metric is proposed to model the number of snapshots remaining for a hypothesized node set, i.e., the remaining battery energy divided by the energy to sense and share information amongst the node set. Unlike other methods that use the total energy consumed for the given snapshot as the energy-based metric, the new EB metric can achieve load balancing of the nodes without resorting to computationally demanding non-myopic optimization. The metrics to choose nodes at a given snapshot could be geometry-based (GB) to minimize the estimation error, EB, or multiobjective. In determining the active set, each node only knows the existence of itself, the active set of nodes from the previous snapshot and the node's neighbors, i.e., the set of nodes within a distance of r_nei. When measuring the tracking lifetime of the system, we propose an adaptive transmission range control, known as the knowledge pool (KP) where the transmission range is determined by the knowledge of the network and the currently remaining battery level. The KP saves more energy usage than another adaptive transmission range control bounded with the GB metric when the global location information is available. We also provide practical search algorithms to optimize a constraint metric (multiobjective function) using one metric as the optimization metric under the constraint of the other. We also demonstrate the resource management schemes for multitarget tracking with the field data.

Wireless networks are becoming more and more popular. In current wireless network environments, mobile users can use multiple wireless network interfaces built in their mobile devices to roam around the mobile networks. They can scan the wireless spectrums and utilize the network resources extremely, and they can roam into nearby wireless networks due to the mobility capabilities of the powerful mobile devices. Before connecting to an access point, an authentication process is necessary. There are many interactive wireless authentication protocols which have been proposed in the literature. Under the wireless networks, handover is an important property for a mobile user to change her/his position. However, the existing interactive wireless authentication protocols may cause unstable connection. This is because that a mobile user may perform failed authentications with some nearby invalid access points and thus she/he cannot finish handover in time. Hence, we would like to design a mechanism for a mobile user to determine the validity of access points before the interactive authentication, and the mobile user can choose a valid one when making handover. In our proposed scheme, the mobile user can just scan and receive authentication messages from access points without interactions with them while she/he can determine which one of them is valid. We call this cognitive authentication. Besides, we also propose cooperative defense which allows mobile users to exchange their received authentication messages for detecting illegal access points. Finally, we provide security proofs for our proposed scheme.