In this dissertation, adaptive power control for single and multiuser opportunistic systems is investigated. First, a new adaptive power-controlled diversity combining scheme for single user systems is proposed, upon which is extended to the multiusers case. In the multiuser case, we first propose two new threshold based parallel multiuser scheduling schemes without power control. The first scheme is named on-off based scheduling (OOBS) scheme and the second scheme is named switched based scheduling (SBS) scheme. We then propose and study the performance of thresholdbased power allocation algorithms for the SBS scheme. Finally, we introduce a unified analytical framework to determine the joint statistics of partial sums of ordered RVs with i.i.d. and then the impact of interference on the performance of parallel multiuser scheduling is investigated based on our unified analytical framework.

Energy saving, despite recent advances in extending battery life, is still an important issue in wireless ad hoc networks. An often adopted method is power management, which can help in reducing the transmission power consumption and thus can prolong the battery life of mobile nodes. In this paper, we present a new approach of power management for the wireless ad-hoc networks. Firstly, we propose a clustering algorithm. The clustering algorithm is incooperated with power adjustment and energy-efficient routing procedure to achieve the goal of reducing the transmission power. We use clusterheads to monitor a mobile node's transmission power and to conduct the routing path between any source-destination pair. Not only the lifetime of network is increased but also the interference in communication channel is reduced. As a result, the transmission quality is improved and the network throughput is enhanced. By simulation, we showed that our algorithm outperforms the traditional clustering algorithm both in power saving and in throughput.

Energy is a critical resource in the design of wireless networks since wireless devices are usually powered by batteries. Battery capacity is finite and the progress of battery technology is very slow, with capacity expected to make little improvement in the near future. Under these conditions, many techniques for conserving power have been proposed to increase battery life. In this dissertation we consider two approaches to conserving the energy consumed by a wireless network interface. One technique is to use power saving mode, which allows a node to power off its wireless network interface (or enter a doze state) to reduce energy consumption. The other is to use a technique that suitably varies transmission power to reduce energy consumption. These two techniques are closely related to theMAC (Medium Access Control) layer. With respect to power saving mode, we study IEEE 802.11 PSM (Power Saving Mechanism) and propose a scheme that improves its energy efficiency. We also investigate the interaction between power saving mode and TCP (Transport Control Protocol). As a second approach to conserving energy, we investigate a simple power control protocol, called BASIC, which uses the maximum transmission power for RTS-CTS and the minimum necessary power for DATA-ACK. We identify the deficiency of BASIC, which increases collisions and degrades network throughput, and propose a power control protocol that addresses these problems and achieves energy savings. Since energy conservation is not an issue limited to one layer of the protocol stack, we study a cross layer design that combines power control at the MAC layer and power aware routing at the network layer. One poweraware routing metric is minimizing the aggregate transmission power on a path from source to destination. This metric has been used along with BASIC-like power control under the assumption that it can save energy, which we show to be false. Also, we show that the power aware routing metric leads to a lower throughput. We show that using the shortest number of hops in conjunction with BASIC-like power control conserves more energy than power aware routing with BASIC-like power control.

Efficient utilization of the limited wireless spectrum while satisfying applications’ quality of service requirements is an essential design goal of forthcoming wireless networks and a key to their successful deployment. The need for spectrally efficient systems has motivated the development of adaptive transmission techniques. Enabling this adaptation requires protocols for information exchange as well as mathematical tools to optimize the controllable parameters. In this dissertation, we provide insights into such protocols and mathematical tools that target efficient utilization of the wireless spectrum. First, we propose a distributed CDMA-based medium access protocol for mobile ad hoc networks (MANETs). Our approach accounts for multiple access interference at the protocol level, thereby addressing the notorious near-far problem that undermines the throughput performance in MANETs. Second, we present a novel power-controlled MAC protocol, called POWMAC, which enjoys the same single-channel, single-transceiver design of the IEEE 802.11 Ad Hoc MAC protocol, but which achieves a significant throughput improvement over the 802.11 protocol. Third, we consider joint power/rate optimization in the context of orthogonal modulation (OM) and investigate the performance gains achieved through adaptation of the OM order using recently developed optimization techniques. We show that such adaptation can significantly increase network throughput while simultaneously reducing the per-bit energy consumption relative to fixed-order modulation systems. Finally, we determine the maximum achievable “performance” of a wireless CDMA network that employs a conventional matched filter receiver and that operates under optimal link-layer adaptation where each user individually achieves the Shannon capacity. The derived bounds serve as benchmarks against which adaptive CDMA systems can be compared.

Transmission power control (TPC) has been used in wireless networks to improve channel reuse and/or reduce energy consumption. It has been mainly applied to single-input single-output (SISO) systems. Significant improvement in performancecan be achieved by employing multi-input multi-output (MIMO) techniques. In this dissertation, we propose adaptive medium-access control (MAC) protocols for power-controlled MIMO-capable wireless networks. In these protocols, we adapt the number of transmit/receive antennas, along with the transmission powers/rates, for the purpose of minimizing total energy consumption and/or maximizing network throughput. Our first protocol, called E-BASIC, exploits the diversity gain of MIMO by adapting the transmission mode, transmission power, and modulation order so as to minimize the total energy consumption. We incorporate E-BASIC in the design of an energy-efficient routing (EER) scheme that selects the least-energy end-to-end path. We then propose two MAC protocols that exploit the multiplexing gain of MIMO, and consider their integration into legacy systems. We alsopropose a combined energy/throughput MAC protocol, called CMAC, which dynamically switches between diversity and multiplexing modes so as to maximize a utility function that depends on both energy consumption and throughput. Finally, we consider employing "virtual" MIMO capability into single-antenna wireless sensor networks (WSNs). We propose a distributed MIMO-adaptive energy-efficient clustering/routing protocol, coined CMIMO, which aims at reducing energy consumption in multi-hop WSNs. In CMIMO, each cluster has up to two cluster heads (CHs), which are responsible for routing traffic between clusters. Simulation results indicate that our proposed protocols achieve significant energy/throughput improvement compared with non-adaptive protocols.

This dissertation examines the design and application of network coding (NC) strategies to enhance the performance of communication networks. With its ability to combine information packets from different, previously independent data flows, NC has the potential to improve the throughput, reduce delay and increase the power efficiency of communication systems in ways that have not yet been fully utilized given the current lack of processing power at relay nodes. With these motivations in mind, this dissertation presents three main contributions that employ NC to improve the efficiency of practical communication systems. First, the integration of NC and erasure coding (EC) is presented in the context of wired networks. While the throughput gains from utilizing NC have been demonstrated, and EC has been shown to be an efficient means of reducing packet loss, these have generally been done independently. This dissertation presents innovative methods to combine these two techniques through cross-layer design methodologies. Second, three methods to reduce or limit the delay introduced by NC when deployed in networks with asynchronous traffic are developed. Also, a novel opportunistic approach of applying EC for improved data reliability is designed to take advantage of unused opportunities introduced by the delay reduction methods proposed. Finally, computationally efficient methods for the selection of relay nodes and the assignment of transmit power values to minimize the total transmit power consumed in cooperative relay networks with NC are developed. Adaptive power allocation is utilized to control the formation of the network topology to maximize the efficiency of the NC algorithm. This dissertation advances the efficient deployment of NC through its integration with other algorithms and techniques in cooperative communication systems within the framework of cross-layer protocol design. The motivation is that to improve the performance of communication systems, relay nodes will need to perform more intelligent processing of data units than traditional routing. The results presented in this work are applicable to both wireless and wired networks with real-time traffic which exist in such systems ranging from cellular and ad-hoc networks to fixed optical networks.

abstract: The rapid advancement of wireless technology has instigated the broad deployment of wireless networks. Different types of networks have been developed, including wireless sensor networks, mobile ad hoc networks, wireless local area networks, and cellular networks. These networks have different structures and applications, and require different control algorithms. The focus of this thesis is to design scheduling and power control algorithms in wireless networks, and analyze their performances. In this thesis, we first study the multicast capacity of wireless ad hoc networks. Gupta and Kumar studied the scaling law of the unicast capacity of wireless ad hoc networks. They derived the order of the unicast throughput, as the number of nodes in the network goes to infinity. In our work, we characterize the scaling of the multicast capacity of large-scale MANETs under a delay constraint D. We first derive an upper bound on the multicast throughput, and then propose a lower bound on the multicast capacity by proposing a joint coding-scheduling algorithm that achieves a throughput within logarithmic factor of the upper bound. We then study the power control problem in ad-hoc wireless networks. We propose a distributed power control algorithm based on the Gibbs sampler, and prove that the algorithm is throughput optimal. Finally, we consider the scheduling algorithm in collocated wireless networks with flow-level dynamics. Specifically, we study the delay performance of workload-based scheduling algorithm with SRPT as a tie-breaking rule. We demonstrate the superior flow-level delay performance of the proposed algorithm using simulations. / Dissertation/Thesis / Ph.D. Electrical Engineering 2013

Due to the increasing integration of renewable energy generations, the overvoltage and overload issues in transmission networks have become more significant, and they may occur at various locations. To mitigate the overvoltage issues, traditional solutions which often consider the installation of reactive power compensators such as shunt reactors, SVC, STATCOM may not be cost-effective. To mitigate the overload issues, traditional methods using direct or price-based demand control will affect customers’ electrical experience in that they are inconvenienced greatly. This thesis discusses the flexible tap changing techniques that utilise existing parallel transformers in distribution networks to provide reactive power absorption and demand response services for transmission systems. Among them, the tap stagger technique operates parallel transformers in small different tap positions, i.e. staggered taps, to result in more reactive power absorption from upstream networks. In addition, the tap changing technique changes voltages in the range of statutory limits through the adjustment of tap positions in order to change network demands without directly affecting customers. The aggregated reactive power absorption or demand response from many pairs of parallel transformers in distribution networks could be sufficient to provide VAr or demand support to transmission networks. Network capability studies have been carried out in OpenDSS simulation software to investigate the VAr absorption capability by using tap staggering technique and the demand reduction capability by using tap changing technique. The studies are based on two UK HV distribution networks (132-33kV) with 11 and 28 primary substations (33/11 or 6.6 kV) respectively, and the techniques are applied to parallel transformers in primary substations. Based on the results of the two networks, the capabilities of the whole ENW and the UK distribution networks have been estimated respectively by using linear estimation method. In addition, the VAr absorption capability of the tap stagger technique has been validated by using site trial data. The results show an average VAr absorption capability of 0.89MVAr for a primary substation, 315MVAr for ENW networks and about 2500MVAr for the UK at stagger level 4 and show an average demand reduction capability of 3.1% of the original demand at tap down level 3. The results of capability studies together with the validations results confirm that the flexible tap changing techniques are able to provide transmission networks with effective VAr support and demand response services. To assess network VAr absorption and demand response capability more precisely, this thesis also proposes an online load profile estimation method to estimate the load profiles of the network more accurately if not all substations in the network are monitored. The method uses Peak Load Share values, Euclidean Distance, and some load measurements to estimate load profiles. The method has been validated and compared with a traditional aggregation-based method. The results show an average estimation error of 13% ~ 23% in different conditions using the proposed method, and show an average estimation error reduction from about 47% (using the traditional method) to about 13% (using the proposed method). The results indicate that the developed method has a considerable improvement on the accuracy of load profile estimation.

There has been a rapid growth in the data rate carried by cellular services, and this increase along with the emergence of new multimedia applications have motivated the 3rd Generation Partnership (3GPP) Project to launch Long-Term Evolution (LTE) [1]. LTE is the latest standard in the mobile network technology and is designed to meet the ubiquitous demands of next-generation mobile networks. LTE assures significant spectral and energy efficiency gains in both the uplink and down- link with low latency. Multiple access schemes such as Orthogonal Frequency Division Aultiple Access (OFDMA) and Single Carrier Frequency Division Multiple Access (SC-FDMA) which is a modified version of OFDMA have been recently adopted in 3GPP LTE downlink and uplink, respectively [1]. A typical feature of OFDMA is the decomposition of available bandwidth into multiple narrow orthogonal subcarriers. The orthogonality among subcarriers causes minimal intra-cell interference, however, the inter-cell interference (ICI) incurred on a given subcarrier is relatively impulsive and poses a fundamental challenge for the network designers. Moreover, as the number of interferers on a given subcarrier can be relatively limited it may not be accurate to model ICI as a Gaussian random variable by invoking the central limit theorem. The nature of ICI relies on a variety of indeterministic parameters which include frequency reuse factor, channel conditions, scheduling decisions, transmit power, and location of the interferers. This thesis presents a combination of algorithmic and theoretical studies for efficient modeling and management of ICI via radio resource management. In the preliminary phase, we focus on developing and analyzing the performance of several centralized and distributed interference mitigation and rate maximization algorithms. These algorithms relies on optimizing the spectrum allocation and user’s transmission powers to maximize the system capacity. Even though, the developed algorithms possesses low complexity, the simulation run-time may become challenging in the practical scenarios with very large number of users and subcarriers. Motivated by this fact, we then develop several statistical models that can accurately capture the dynamics of interference with distinct applications in the performance analysis of single carrier and multicarrier future wireless networks. The developed models can be customized for (i) various state-of-the-art coordinated and uncoordinated scheduling algorithms; (ii) slow and fast power control mechanisms; (iii) partial and fractional frequency reuse systems; and (iv) various composite fading distributions. The developed framework is useful in evaluating important system performance metrics such as outage probability, ergodic capacity, and average fairness numerically without the need of time consuming Monte-Carlo simulations. The theoretical framework is expected to enhance the planning tools for OFDMA based wireless networks by providing fast estimates of the typical performance metrics. Finally, we investigate and quantify the spectral and energy efficiency of two tier heterogeneous networks (HetNets) by employing power-control based interference mitigation technique. In particular, we analyze the performance of two tier HetNets deployment by deriving the theoretical bounds on the area spectral efficiency and exact analytical expressions for the energy efficiency by considering slow and fast power control mechanisms. The derived expressions are expected to be useful in providing insights for the design of efficient HetNet deployments.

Modern hybrid electric and pure electric vehicles are highly dependent on control algorithms to provide seamless safe and reliable operation under any driving condition, regardless of driver behavior. Three unique and independently operating supervisory control algorithms are introduced to improve reliability and vehicle performance on a series-hybrid electric vehicle with an all-wheel drive all-electric drivetrain. All three algorithms dynamically control or limit the amount of torque that can be delivered to the wheels through an all-electric drivetrain, consisting of two independently controlled brushless-direct current (BLDC) electric machines. Each algorithm was developed and validated following a standard iterative engineering development process which places a heavy emphasis on modeling and simulation to validate the algorithms before they are tested on the physical system. A comparison of simulated and in-vehicle test results is presented, emphasizing the importance of modeling and simulation in the design process.