The main challenge faced in today's telecommunication is the ever increasing demand for bandwidth and data rates. The desire to expand the capacity of fiber optic communication to accommodate this demand accelerated the development of high capacity Dense Wavelength Division Multiplexing (DWDM) transmission equipment. However, nonlinear impairments are the fundamental limiting mechanisms to the amount of data that can be transmitted in DWDM. In DWDM, Four Wave Mixing is the most critical of nonlinear effects in fibre optics communication. This effect limits the DWDM’s channel capacity. There are numerous researches on nonlinear impairments that show the intricacy of FWM phenomena in DWDM system. This article present review of the several measures which have been carried out by researchers to overcome nonlinear effects in DWDM. Such measures include Modulation Formats, Channel Spacing, Channel Shuffling Algorithm and Electro-Optic Phase Modulation. The review provides insight into the methods, parameters and approaches used by other researchers. This will pave way for can thus lead to significant improvement in the design of DWDM system.
Optimal performance of the Brushless Direct Current (BLDC) motor is to be realized using an efficient Proportional Integral Derivative (PID) controller. However, conventional tuning technique fails to perform satisfactorily under parameter variations, nonlinear conditions and time delay. Also using conventional technique to tune the parameters gain of the PID controller is a difficult task. To overcome these difficulties, modern heuristic optimization technique are required to optimally tune the Proportional, Integral, Derivative of the controller for optimal speed control of three phase BLDC motor. Thus, genetic algorithm (GA) based PID controller was used to achieve a high dynamic control performance. The Brushless DC Motor mathematical equation which describes the voltage and corresponding rotational angular speed and torque of the brushless DC motor was employed using electrical DC Machines theorem. The Genetic algorithm was further analyzed by adopting the three common performance indices i.e. Integral Time Absolute Error (ITAE), Integral Square Error (ISE) and Integral Absolute Error (IAE) in order to capture and compare the most suitable BLDC Motor speed and torque control characteristics. All simulations were done using MATLAB (R2018a). The simulation result showed that the system with GA-PID controller had the better system response when compared with the existing technique of ZN-PID controller.
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