Research On ROF System Based On Sixfold Millimeter Wave Generation Technology

Fiber wireless communication system ROF(Radio-over-Fiber) is a product which combines optical fiber communication with wireless communication. It not only has the advantages of large capacity and strong anti-interference ability of optical fiber communication, but also has the characteristics of flexibility and mobility of wireless communication.It will become one of the ideal ways of the broadband access in the future.In ROF system,it needs millimeter-wave signals as carriers to deliver information, so millimeter-wave generation and transmission are critical to maintain stability of the system and improve the transmission performance,it is also one of the key technologies in ROF system and an important research direction.Therefore,this thesis is mainly focused on the research of some key technologies of ROF system which is based on the six frequency doubling millimeter-wave generation in the following aspects:(1)The basic theories, characteristics and key technologies of ROF system are analysed,then the existing methods of millimeter-wave generation and their research status are summarized in ROF system. The three major generation technologies in the optical domain which include direct modulation method,external modulation method and optical heterodyne detection method are studied, their advantages and disadvantages are compared.(2)A six frequency doubling millimeter-wave generation approach which is based on the OPM(Optical Phase Modulators) is proposed.At the central station,the phase modulation index and the drivers of the initial phase signal of the two parallel OPMs are regulated.The modulation signals which one and two order sidebands are suppressed after through a coupler can be producted,the frequency difference between the positive third-order sideband and the negative third-order sideband is 6REf after filters the center carrier sideband.The millimeter-wave frequency which is six times of the RF signal can be obtained at the base station. A bidirectional ROF transmission system based on Optisystem11 is established. The simulation results show that:thefrequency of 10 GHz RF signal can product 60 GHz millimeter-wave;the structure and design of the bidirectional transmission system can greatly simplify the base station.When the BER(Bit Error Rate) is under the 10-9,the power loss of the uplink and the downlink are both less than 2d B.This approach compares with the four frequency doubling millimeter-wave generation approach, when under the same BER requirements of the situation, the power loss reduces 0.6d B.This proves that the transmission system can produce six frequency doubling millimeter-wave signal and realize the long-distance transmission.(3)The technology why OFDM(Orthogonal Frequency Division Multiplexing)can effectively overcome the dispersion is analysed.The OFDM technology is added into the ROF system.An optimization scheme based on the six frequency doubling millimeter-wave generation approach which was proposed before is designed. The optimization model of the system based on Optisystem11 is established.The transmission performance in cases of different transmission and coding mode is analysed and compared,the capability of anti interference of dispersion is optimized and the impact of different coding methods on the transmission performance of the system is summarized. The simulation results show that: the transmission distance of the 2.5Gbit/s signal of the single-mode fiber can increase to 60 km by using4 QAM.Under the same BER,when the transmission distance is more than 30 km,the transmission performance and distance of 4QAM system is more better than16 QAM system,the 4QAM system is about twice the 16 QAM in transmission distance.