Performance of the Generalized Minimum Residual (GMRES) Iterative Solution for the Magnetic Field Integral Equation

The paper discusses a generalized minimum residual (GMRES) iterative solution of the magnetic field integral equation (MFIE) applied to frequency domain scattering problems at medium and high frequencies. First, the performance of the original MFIE is studied, for the perfectly electrically conducting (PEC) sphere. It is shown that the residual error and the solution error do not correlate with each other. Whereas the solution error has already reached a limiting value or even increases, the residual error continues to decrease very fast, typically exponentially. Second, the MFIE is combined with the normal projection of the primary integral equation for the surface magnetic field. Such a technique does not increase the computational complexity of the MFIE. At the same time, it gives a termination criterion for GMRES iterations since the residual error of the combined equation has a typical saturation behavior. In the saturation zone, the residual error and the solution error have approximately the same small value (a typical relative RMS error for the sphere is 1%). A very similar saturation behavior of the residual error has been observed for other tested PEC scatterers including a cube, a cylinder, and a sphere with one segment cut off (the so-called cat eye) at different frequencies

Energy-Efficient Network Protocols for Wireless Sensor and Actor Networks

Wireless sensor networks (WSNs) have a wide variety of applications in civilian, medical and military applications. However, the nodes in such a network are limited to one type of action: sensing the environment. With increasing requirements for intelligent interaction with the environment, there is a need to not only perceive but also control the monitored environment. This has led to the emergence of a new class of networks, referred to as wireless sensor and actor networks (WSANs), capable of performing both sensing and acting tasks on the environment. The evolution from WSNs, which can be thought of as performing only read operations, to WSANs, which can perform both read and write operations, introduces unique and new challenges that need to be addressed. In this research, the fundamental challenges required for effective operation of WSANs are analyzed from the following three different perspectives: (i) operation correctness, (ii) resource optimality, and (iii) operation performance. The solutions proposed to address the challenges are evaluated with the optimal solution and other competing approaches through analytical and simulation results. The feasibility of the proposed solutions is demonstrated through a testbed implementation.Ph.D.Committee Chair: Sivakumar, Raghupathy; Committee Member: Beyah, Raheem; Committee Member: Copeland, John; Committee Member: Ji, Chuanyi; Committee Member: Riley, Georg

Component based channel assignment in single radio, multi-channel ad hoc networks

In this paper, we consider the channel assignment problem in single radio multi-channel mobile ad-hoc networks. Specifically, we investigate the granularity of channel assignment decisions that gives the best trade-off in terms of performance and complexity. We present a new granularity for channel assignment that we refer to as component level channel assignment. The strategy is relatively simple, and is characterized by several impressive practical advantages. We also show that the theoretical performance of the component based channel assignment strategy does not lag significantly behind the optimal possible performance, and perhaps more importantly we show that when coupled with its several practical advantages, it significantly outperforms other strategies under most network conditions