Research On The Technology Of Millimeter-wave Modulation And Passive Base-station Design In Radio-over-Fiber System

Radio-over-fiber(ROF)is a technique which integrates wireless transmission and fiber wired transmission. As a powerful solution for increasing the capacity and decreasing cost,ROF can meet with the needs of mobility and bandwidth, so it has become a current research hotspot of correspondence domain. Both millimeter-wave modulation and passive base station designs are two important key techniques to make ROF system practical. The two key techniques in radio-over-fiber system are investigated by numerical simulation and experiment in this paper. The main research results are listed below.Firstly,a novel scheme with optical millimeter-wave generation based on double sideband (DSB) modulation by external modulator in radio-over-fiber system is proposed. The results by simulation and experiment show that the generated optical millimeter-wave by proposed method can effectively reduce baseband signal degeneration caused by the time shift of the code edges because of fiber dispersion, it is suitable for long distance transmission. Two sideband signals are directly generated by DSB modulation and filtering. An optical interleaver is employed to separate the spectrum of the upper sideband and the lower sideband. Only one sideband is used to modulate baseband data,and then is recombined with the unmodulated sideband to generate optical mm-wave. So it can restrain the time shift of the code edges. The dispersion performance of the generated mm-wave is theoretically analysed, it can immune the fading effect. We confirm the theoretical results and compare the power penalty and eye diagrams of mm-wave by simulation and experiment. The results show that the downlink data signals can transmit longer distance without dispersion compensation, and BER is low.Secondly, a full-duplex radio-over-fiber system with passive base station based on optical carrier reuse is proposed and experimently demonstrated. This system has simple and cost-efficient configuration, the optical power is effectively utilized. An optical phase modulator and optical interleaver are used to generate DWDM optical mm-wave for carrying downstream data and wavelength reuse for uplink connection. We compare the power penalty and eye diagrams after the signal transmitting different distance by numerical simulation. The results show the limitation of chromatic dispersion is greatly reduced due to avoiding the generation of higher order sidebands via driving the phase modulator with optimized RF signal. We evaluate the BER performance for downlink and uplink, the power penalty after transmission over 40km are both less than 2dB.