Research On Some Influences About OFDM Optical Wireless Transmission System

Radio-over-Fiber(ROF)technology，which combined the advantage of opticalcommunication and wireless communication, become the main direction ofcommunication development.Meanwhile, because of its resistance to multipath effects and the advantages ofnarrow-band interference, the orthogonal frequency division multiplexing (OFDM)technology has been widely used in various wireless standards. Therefore, the OFDMoptical transmission system which combined the OFDM and the ROF system canprovide high-speed, high-capacity, high-quality communications services to meet thegrowing needs of people.We investigated server key techniques which revolve around how to improve theperformance of OFDM signal optical transmission. The main contents include:1.The influence of modulation depth in OFDM optical transmission is investigated.In order to explore the influence of the modulation depth in subcarrier OFDM opticaltransmission system. The bit error ratio responses of subcarrier OFDM optical systems inintensity modulator (IM) is investigated by simulation and experiment when themodulation depth is changing. Simulation and experimental results show that there isan optimum Carrier Sideband Ratio (CSR),which is about20,when subcarrier OFDMsignal transporting through optical fiber. Too large or too small Carrier Sideband Ratiowill cause the system’s bit error ratio performance decrease. we verified that the PMsystem has a good transmission characteristics because the sidebands is suitable andchange less with the modulation depth2.The influence of wireless RF front-end instability in OFDM optical-wirelesstransmission is studied.60GHz wireless transmission has become the academic andcommercial research focus. However, there is great attenuation in free spacetransmission and impact of RF front-end no-idealities. we uses optical wirelesstechnology to solve the long-distance transmission problems, and combined with theADS(advanced design system) software analyzes the impact of radio frequencyreceiver. By simulation, we reach50km in optical wireless transmission and get theconclusion that the system will significant deterioration when Wireless terminal phasemismatch is greater than40°or phase noise performance is greater than10MHz.3.The influence of training sequence structure in OFDM optical transmission is studied. We proposed use of the training sequence as part of pilot estimates to estimatethe signal, and compare the receiving performance of OFDM signal which has differenttraining sequences. Finally, we get the conclusion that the OFDM signal which has thetraining sequence of each ones zero-signal insert in two real signals has the bestreceiving performance, because this kind of OFDM signal can resist the subcarrierbeating during the direct detection...