PARTICLE SWARM OPTIMIZATION BASED OPTIMIZED CNR PENALTY OF RADIO OVER FIBER SYSTEM INCLUDING THE EFFECTS OF PHASE NOISE FROM LASER AND RF OSCILLATOR by Sarpreet Kaur
Abstract
Radio over fiber systems have been gaining popularity since the beginning of this century due to crowded frequency spectrum and demand for high data rates. It provides the benefits of both optical fiber technology and wireless techniques. Optical fiber systems provide higher data rates and very less attenuation whereas wireless technology has an edge over long distance transmissions. Nature based algorithms have become very famous to optimize certain values to achieve the desired results. However while focusing on the wired part there are some inherent deteriorating factors which does not let the system utilize its full potential. Especially during the electrical to optical conversion in the central office, phase noise processes play a dominant role leading to the deterioration of the signal. Phase noise is also knows as phase jitter. In a radio system it can severely damage the performance of the communication system making it very sensitive. Basically phase noise is a representation in the frequency domain which shows the sudden fluctuation in the frequency waveform of the signal. In radio over fiber system, phase noise processes are related to the line widths of laser diode and RF Oscillator used in signal generation process. The previous studies have analyzed the effect of line widths of both the components on the output of the system graphically. However, no concrete values were considered and the inputs were more of the random nature and the work is carried out on a single length of fiber. In this work, an efficient PSO algorithm has been applied to optimize CNR penalty of Radio over Fiber system including the effects of phase noise from laser and RF oscillator within predefined ranges of 100 to 624 MHz and 0.1 to 10 Hz respectively. The changes in the optimization function are observed along with the fiber length of 2 Km, 10 Km and 30 Km. Particle swarm optimization provides an optimum platform to get specific values of line width of RF oscillator to be around 0.1 Hz and that of laser diode around 620 MHz giving a minimized error and an efficient RoF system. The proposed algorithm provided the optimized value of 0.1001107 Hz, 0.1002415 Hz and 0.1002619 Hz for RF linewidth and the values of linewidth of laser (571.2951 MHz, 421.1735 MHz and 410.7692 MHz) for 2 Km, 10 Km and 30 Km respectively. It has been observed that carrier to noise ratio penalty responds very sensitively to a minor change in line width of radio frequency oscillator whereas the change in line width of laser diode produces a meager penalty on the output of the system. It is further observed that a small change in RF line width leads to high phase noise and changes in laser line causes a minimum effect on the same output. Radio over fiber technology opens a wide arena for various possible, probable and preferable technologies. It has a vast potential and the work for its enhancement has already started. It can be further used in satellite communications, fiber to home systems, eco friendly technology and other millimeter wave regime systems. The proposed work can be further extended to uncrowd the spectrum by making it less susceptible to noise floors and focusing more on the component enhancement even a minor degradation can be worked out.
