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Title: Performance Evaluation of High Data Rate Transmission for Microwave Communication System Over Fiber Link
Authors: Rakesh
Supervisor: Kaler, R. S.
Keywords: Microwave, FOC
Issue Date: 20-Aug-2009
Abstract: The optical communication system has many advantages over conventional radio systems. The numbers of users of microwave communication are increasing day by day. But the bandwidth is limited for microwave transmission. The wide-bandwidth capability and very low attenuation in fibers of optical transmission systems makes them attractive for the transmission and processing of microwave signals. This strand has led to the development of the research area of microwave photonics. For transmitting microwave signal over fiber, there is a need to convert radio signal into optical form at the transmitter end and a reverse process at the receiver side. In this thesis, we have developed two types of techniques for transmitting radio frequency signal over fiber channel. First technique is based upon intensity modulation direct detection. In first technique, a laser is used to convert radio signal into optical signal. In the second, an external modulator (Mach–Zehnder modulator) with laser is used for the same purpose in the second technique (coherent system). Firstly, the rate equation laser is operated in a dynamic state, where its intensity oscillates at a microwave frequency that varies with the input signal fed by wave generator. This system can also use for two modulating tones. The frequency of the first tone is varied from 1 to 20 GHz and second is set at 5 GHz. A data signal of 10 Gbps is transmitted over long haul single mode fiber by single tone system. A very good bit error rate (BER) 〖10〗^(-40) performances in a 100 Km and 25 Km fiber link is achieved for both single tone and two tones respectively in proposed microwave over fiber communication system. Secondly, The Lorentzian laser is used with Mach–Zehnder modulator (MZM) to achieve a conversion of microwave band into baseband at which fiber operates. The key device in the coherent system is a Mach-Zehnder modulator which performs all-optical microwave mixing with semiconductor laser. The single pole low pass filter is realized by passing the microwave signals, acting as a dispersive device. An optically converted signal is obtained at the end of laser and this signal passes through a single mode fiber. In multi tone coherent system, the frequency of the first tone is varied from 1 to 20 GHz and second is set at 5 GHz. A data signal of 18 Gbps is transmitted over long haul single mode fiber by coherent system. A soliton is a self-reinforcing solitary wave of permanent form which does not change its shape while travelling at constant speed. A dispersion compensated fiber and a periodical amplification is done to increase the efficiency of the soliton. To achieve a lossless soliton, the group velocity dispersion (GVD) parameter β_2 is required to be constant along the fiber length. But it is difficult to achieve a constant GVD parameter, so dispersion compensated fiber is used for increasing the efficiency of the soliton fiber link. A circulating loop is used which is consist of three regular fiber spans, one dispersion-compensating fiber (DCF) span, optical filter and EDFA optical amplifier. The system transmits the data up to 9000 km. It is shown that the pulse spectrum is broadening due to the high-order soliton effect and third- order dispersion near the zero dispersion wavelength, the spectrum begin to be shaped by optical filter installed at the end of the loop. Thus the thesis investigates high data rate transmission for microwave communication system over fiber link.
Appears in Collections:Masters Theses@ECED

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