Research About The Full-Duplex System And Peak-to-Average Power Ratio Performance Of OFDM-ROF

There is a greater demand of broadband and flexible service with the development of multimedia technology. The radio over fiber (ROF) technology is a combination of wireless communication and optical communication. It has many advantages such as full of flexibility, wide bandwidth, low loss and so on. It has been actively investigated recently. The orthogonal frequency division multiplexing (OFDM) technique has been considered as the core technology of 4G because it has offered higher channel efficiency, greater capability, and increased robustness against both frequency selective fading and narrow band interference. Thus, both ROF and OFDM become the hotspots of next generation communication system. In this paper, we primarily investigated the full-duplex OFDM-ROF system and researches concentrating on the high peak-to-average power ration (PAPR) of the OFDM signal have been made. And we have obtained several positive outcomes:Firstly, a novel scheme to generate 40GHz optical millimeter-wave based on optical carrier suppression (OCS) and a full-duplex OFDM-ROF system by using one single-arm Mach-Zehnder intensity modulator were investigated and experimentally demonstrated. The experiment investigates the up-link of full-duplex OFDM-ROF system. The method of using subcarrier modulation at the central station has many advantages compared to the conventional single-carrier modulation. It could increase the robustness against fiber chromatic dispersion and because the downstream data was not modulated to the optical carrier, the interference between up-link and down-link data was reduced. Moreover, the base station made use of optical circulator and Fiber Bragg Grating (FBG) to reuse the optical carrier that avoided overusing of coupler and simplified the system. The 2.5-Gb/s OFDM signal of the downstream data was up-converted with the 20GHz RF sine-wave signal by an electrical mixer. The optical carrier was modulated via an intensity modulator driven by the up-converted signal. Then the generated optical millimeter-wave was transmitted to the base station in a single-mode fiber (SMF); The optical carrier was reused to carry 2.5-Gb/s OOK signal of the upstream data and delivered to the central station. The experiment results show that both 2.5-Gb/s downstream and upstream data can be transmitted over 50km SMF with the power penalty lower than 1dB and 0.5dB respectively.Secondly, we have theoretically and experimentally investigated the impact of high PAPR of the OFDM signal on the optical OFDM-ROF system. In the optical communication system, properly increasing the transmission power can improve the signal noise ratio (SNR) of the receiver and increase the transmission distance. However, the nonlinearity of the optical fiber will appear and even greatly affect the system's performance if the transmission power is too high, The nonlinearity of fiber mainly derives from high PAPR. So the selective mapping (SLM) was introduced to reduce the impact of high PAPR on the performance of the system. We set up the optical link model based on scrambling code technology, and the simulation and experiment both testified the practical value of SLM in improving the performance of the optical OFDM-ROF system.