welcome

JECEI is devoted to the research in Electrical and Computer Engineering. The editors would like to welcome you to the fifth issue that contains six papers focusing on research works in Laser beam reflection, Add-drop filters, Nonlinearity in fibre systems, Biding strategy in power market, PAPR reduction in OFDM systems, and TDL-based wideband beamforming. The article “ABCD Matrix for Reflection and Refraction of Laser Beam at Tilted Concave and Convex Elliptic Paraboloid Interfaces and Studying Laser Beam Reflection from a Tilted Concave Parabola of Revolution,” by M. Mansour Abadi et al., deals with an extension to the previous research works. A general scheme that the incident beam is oblique is discussed here and the full analysis of the reflection and refraction of a Gaussian beam at the surface of a tilted concave/convex elliptic paraboloid surface is addressed. Based on the optical phase matching, analytic mathematical equations are derived for the spot size and the wavefront radius of a beam. Expressions are converted into the ABCD matrices, which are more convenient and practical to use. Finally, a practical case is analyzed by applying the obtained formulas. In the next article, entitled “FSR Decrement and Coupling Coefficient Increment in Add-Drop Filters,” by E. Rafiee and F. Emami, the effects of the structural parameters such as, MRR radius, the width of MRR and waveguide and the gap between MRR and waveguide on the optical characteristics (i.e., free spectral range and coupling coefficient) of an add-drop filter, consisting of two straight waveguides and a micro-ring resonator (MRR), are investigated. By enhancing the gap and width, it is found that coupling coefficient would be increased at first but after a while it would be decreased. It is also shown that increasing the radius and width would decrease FSR. The main goal of this research is to decrease FSR and increase the coupling coefficient of add-drop filters. Third article, entitled “Effect of Nonlinear Phase Variation in Optical Millimetre Wave Radio over Fibre Systems,” by A. Bahrami et al., proposes an optical millimetre wave radio-over-fibre (mm-wave RoF) system that uses a dual drive Mach Zehnder modulator (DD-MZM), which is biased at the maximum transmission biasing point, to generate an optical double sideband-suppressed carrier. The inputs to the DD-MZM are BPSK, QPSK, 8-PSK and 16-QAM schemes at a carrier frequency of 5 GHz with a rate of 2 Gsym/s and a local oscillator of 15 GHz obtain an mm-wave RoF signal at 30 GHz. Impairments including the self-phase modulation, chromatic dispersion and attenuation are considered when modelling the single mode fibre (SMF) based on the symmetrical split step Fourier method. It is shown that the power efficiency improves in the optimum region on average by ~11 dB, ~11 dB, ~12 dB and ~18 dB for BPSK, QPSK, 8-PSK and 16-QAM, respectively for the same optical launch power over 10, 30 and 50 km of SMF compared to the linear and non-linear regions. The article “Bidding Strategy in Restructured Environment of Power Market Using Game Theory,” by J. Shadmani et al., considers a one way auction in the electricity market for the generator companies in both perfect and imperfect competition cases. A new model is provided to use the historical data of power market in the state of competition with imperfect information in which two probability functions were simultaneously used for the estimation of required information about each generator company. Nash equilibrium in the game theory is used to find the stability point in the biding strategy of generator companies. The effect of network conditions like limitation of transmission lines, network load, maximum generation of each generator company and the imperfect estimation of information about other competitors is investigated In the fifth article, entitled “Analysis and Comparison of PAPR Reduction Techniques in OFDM Systems,” by M. B. Noori Shirazi et al., the PAPR and its reduction methods in OFDM signals are investigated. These techniques can be classified into two main categories, signal distortion techniques, and multiple signaling and probabilistic techniques. The advantages and disadvantages of each technique are derived from different prospectives. Moreover, the numerical results of the first class techniques from BER prospective demonstrate that for changing the parameters respected to each technique, its performance can be changed sharply. In addition, computational complexity of the second class techniques are compared to each other which their results show that TR and TI techniques are much more complex than the others. Finally, in the last article (sixth one),“TDL-based Wideband Beamforming for Radio Sources Close to the Array Endfire,” by N. Solgi, author proposes a new approach which offers higher performance and desired beamforming on TDL structure when the wideband uncorrelated radio sources are close to the array endfire. This new TDL structure is based on Shirvani-Akbari array (SAA). Numerical results of this investigation show that both ULA-based and SAA-based TDL structures have the same performance where the signals of interest located at the middle angles. In copntrast, where the signals are close to the array endfire, the SAA-based TDL structure has much higher performance. The editors of JECEI wish to take this opportunity to thank the scientists and reviewers around the world who have contributed their time and expertise in the preparation of the fifth issue of the journal.