Virtual multiple input multiple output (MIMO) techniques are used for energy efficient communication in wireless sensor networks. In this paper, we propose energy efficient routing based on virtual MIMO. We investigate virtual MIMO for both fixed and variable rates. We use a cluster based virtual MIMO cognitive model with the aim of changing operational parameters (constellation size) to provide energy efficient communication. We determine the routing path based on the virtual MIMO communication cost to delay the first node death. For larger distances, the simulation results show that virtual MIMO (2×2) based routing is more energy efficient than SISO (single input single output) and other MIMO variations.

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Abstract-In recent years, monopole antennas have become one of the vital components of cellular mobile communications and internet networks across the globe. Their relatively easy and low fabrication cost and faster installation makes them an obvious choice for developing countries. The most common form is the quarter-wave monopole, in which the antenna is approximately 1/4 of a wavelength of the radio waves. In this paper, we present the analytical treatment of a quarter-wave monopole antenna above virtual ground. Virtual ground is realized by using bent radials around the vertical monopole element. Radiation resistance and gain of the quarter-wave monopole are mathematically derived and three-dimensional radiation patterns are simulated using sinusoidal current distribution. It is observed that for the case of the quarter-wave monopole, we achieve twice the gain of a dipole antenna of half-wave-length long. As the radiated power is limited to upper hemisphere of the ground plane, the total radiated power of the quarter-wave monopole is half of that of a dipole. Hence, the value of radiation resistance of the monopole is half of that of a dipole.Index Terms-Ground plane, radiation pattern, directivity, half-wave dipole, monopole antenna.

In this paper, an intuitive comparison of the computational performance of orthogonal frequency division multiplexing (OFDM) system has been made in terms of complex calculations required using different Fourier transform techniques. The different transform techniques are introduced such as discrete Fourier transform (DFT) and various types of fast Fourier transform (FFT) as 2-radix FFT, 4-radix FFT etc. and the very recent very fast Fourier transform (VFFT). With intuitive mathematical analysis, it has been shown that with the reduced complexity that VFFT can offer, OFDM performance can be greatly improved in terms of calculations needed.

Keywords:1 Degree of freedom Platform, Backlash Removal, System Modelling. Abstract:In electromechanical drives, there is always a backlash between any pair of gears. Because of this, it is almost impossible to realize a high accuracy and high performance drive. However such drives are crucial in today's modern electromechanical systems. A high performance drive/anti-drive servo mechanism is developed to eliminate the effect of backlash. The concept utilizes redundant unidirectional drives to assure positive coupling of gear meshes at all times. Based on this concept, a methodology for enumeration of admissible redundant-drive backlash free mechanism has been established. The angular displacement is achieved as a difference of two torques. These torques can be controlled by a high performance control system. A controller model will be designed to move a single degree of freedom platform up to a desired span with a payload.

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