Analyzing And Comparing Of Multiplexing Technology In The Radio-Over-Fiber System

Radio-over-fiber system combines radio communication and fiber communication, making it characteristic of the low consumption and high capacity of wire communication and the mobility of wireless communication. Therefore, it draws more and more attention.In this paper, simulation of each system and data testing are accomplished by applying Optiwave Optisystem.In this paper, firstly, the working principle of Radio-over-fiber is introduced, two conditions of modulating one radio sub-carrier and two radio sub-carriers are analyzed, three intensity modulations of Single-Sideband modulation, Double-Sideband modulation and Optical-Carrier-Suppression modulation are compared by applying spectrograms and the corresponding demodulation methods are explained. Secondly, this paper briefly discusses the Wavelength Division Multiplexing methods when the channel spacing is more than two times radio sub-carrier bandwidth and the channel spacing is less than one time radio sub-carrier bandwidth. As for the case of channel spacing between one and two times radio sub-carrier bandwidth—crossing Wavelength Division Multiplexing, through doing research on corresponding performance parameters, the advantages and disadvantages of the three systems, that is, Wavelength Division Multiplexing system of Single-Sideband modulation, Wavelength Division Multiplexing system of Double-Sideband modulation and Optical-Carrier-Suppression modulation of Double-Sideband modulation are compared and explicated. Lastly, by integrating Subcarrier Multiplexing and Wavelength Division Multiplexing, a Radio-over-fiber transmission scheme based on Optical-Carrier-Suppression modulation is designed. By comparing the other three systems which are Optical-Carrier-Suppression modulation transmission system, Optical-Carrier-Suppression modulation of Subcarrier Multiplexing transmission system and Optical-Carrier-Suppression modulation of Wavelength Division Multiplexing transmission system, corresponding performance parameters are discussed and the feasibility of this design scheme is analyzed.The results demonstrate as follows. First, as far as crossing Wavelength Division Multiplexing is concerned, the bit error rate has the same capability characteristics as the system before multiplexing, which means the system has steady performance within a certain range, and attenuation of the system increases as the fiber transmission distance increases. Compared with the system before multiplexing, the overall performance of the multiplexing system deteriorates, and is influenced by the extinction ratio to a larger degree. Second, with regard to the crossing Wavelength Division Multiplexing system of Double-Sideband modulation, the filters used in demodulation process can improve the deterioration of the system performance which is caused by two side bands having different transmission rate in fiber. At the same time, the system after multiplexing is influenced by the extinction ratio to a smaller degree. Third, as for Optical-Carrier-Suppression modulation of Wavelength Division Multiplexing transmission system, the stability of the multiplexing system gets more weakened than before, its overall attenuation is enhanced, and it is influenced by the extinction ratio to a larger extent. Fourth, Optical-Carrier-Suppression modulation of Subcarrier Multiplexing transmission system has the same characteristics with the system before multiplexing; in terms of power of the receiving end, the best is Optical-Carrier-Suppression modulation transmission system and the poorest is Optical-Carrier-Suppression modulation of Subcarrier Multiplexing transmission system; in terms of the stability of system, Optical-Carrier-Suppression modulation transmission system and the design scheme are both stable, and the former is better; in consideration of the degree to which the system is influenced by the extinction ratio, the influence to Optical-Carrier-Suppression modulation of Wavelength Division Multiplexing transmission system is minimal and the influence to the design scheme is the most. Thus it can be concluded that the design scheme possesses certain advantages on power of the receiving end and stability of the system and the design scheme is feasible.