No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

<p> Energy and security are becoming increasingly important in the design of future wireless communication systems. This thesis focuses on these two main aspects of wireless networks and studies their tradeoffs with other performance metrics such as throughput and delay.</p><p> The first part of the thesis deals with the energy aspect of wireless networks in which we present several novel joint-physical network layer techniques and either evaluate their energy efficiency or study the energy/delay/throughput tradeoffs. First, we study the energy/delay tradeoffs for the problem of reliable packet transmission over a wireless time-varying fading link and also investigate the effect of having Channel State Information on the resulting tradeoff . Then, we extend the model to a single-hop multicast time varying wireless network. We address energy/delay/throughput tradeoffs by considering the problem of streaming a real time file with a fixed delay and energy constraints where the objective is to maximize the number of packets received by the destinations. Again, the effect of having Channel State Information is studied. Also, the effect of using Random Network Coding as a transmission scheme is studied and compared to traditional transmission schemes such as simple ARQ. Next, we consider the effect of cooperation on the energy efficiency of wireless transmissions in which we propose several joint physical-network layer cooperation techniques. Also, the effect of Random Network Coding is investigated in the context of cooperation in which Random Network Coding based cooperation techniques are investigated and compared to cooperation techniques that rely on simple ARQ solely or combined with superposition Alamouti space-time codes. We then consider the particular case of cellular systems in which we design rate allocation technique that minimizes the consumption energy in a Macro cell. This technique takes into account sleep mode configuration of current base stations.</p><p> In the second part of the thesis, we focus on security and in particular on privacy. We also study the tradeoff between securing wireless transmissions and the energy/delay overhead due to security by considering the problem of information exchange among adjacent wireless node in the presence of an eavesdropper. The nodes are required to exchange their information while keeping it secret from the eavesdropper. The nodes can choose to transmit either through public channel or though more costly private channels. We express the cost of using the private channels in terms of the extra energy or delay required to transmit through the private channel. We then minimize the security cost subject to a target security level. Also this part presents a deterministic Network Coding based transmission scheme and investigates its effect on the achieved performance.</p><p> Last, we introduce the problem of minimum energy scheduling of a group of base stations and compare this problem to the standard minimum length scheduling problem. We also discuss the complications and the challenges associated with solving the minimum energy scheduling problem.</p>

This thesis presents new control approaches for improving the performance, stability, and efficiency of a single-phase grid-connected voltage source inverter (VSI) with an LCL filter that is used in renewable energy power conditioning applications. There are two main controllers that need to be designed: an external DC-bus voltage controller to balance the power flow coming into the VSI, and an internal current controller to control the current injected by the VSI into the utility grid. This thesis aims to find well-tailored control approaches for the aforementioned control loops. First, the stability and behavioral characteristics of the open-loop VSI with an LCL filter are explored using a Poincaré map, and the open-loop system is found to have marginal stability. A current control method is proposed, called composite nonlinear feedback (CNF), which offers significantly improved overall performance compared to the state-of-the-art proportional resonant (PR) controller with state feedback. To reduce the overall number of sensors in the system, two different observers are implemented to estimate the VSI state variables: (1) the Luenberger observer (LO), and (2) the sliding mode observer (SMO). To balance the system power flow, a new DC-bus voltage droop control method is proposed, that provides fast performance during transients. This control approach includes a novel discrete DC-bus voltage sensing technique, which effectively removes the double frequency ripple from the DC-bus voltage signal and prevents it from propagating into the current control loop. A variant on the DC-bus voltage droop control method, called adaptive droop control is proposed, which adaptively changes the droop gains in order to regulate the DC-bus voltage to a constant value. Finally, another variant on the DC-bus voltage droop control method is proposed, called optimized adaptive droop control, which adaptively changes the gains of the controller in order to minimize the overall system power losses. A stability analysis is conducted using the singular perturbation control theory, which allows a nonlinear dynamical system to be broken down into subsystems with different time scales. The results of the stability analysis confirm that the proposed closed-loop grid-connected VSI with an LCL filter is locally stable. / Thesis (Ph.D, Electrical & Computer Engineering) -- Queen's University, 2013-09-30 13:47:56.337