Radio Over Fiber Communication System Based On Subcarrier Index Modulation

Recently,the emerging technologies such as "Internet of Everything","HD Video Streaming" and "Virtual Reality/Augmented Reality" have been requested higher demands on the bandwidth and capacity of communication systems.At the same time,radio-over-fiber(RoF)technology with large bandwidth of optical communication and flexible access of wireless communication is considered as one of the effective solutions.Orthogonal frequency division multiplexing(OFDM)technology has high robustness to optical dispersion effects and wireless multipath fading effects,as well as the advantages of high spectral efficiency and flexible allocation bandwidth.Combining OFDM technology with RoF technology can achieve doubled advantages,resulting in better performance of the RoF system.Subcarrier index modulation(SIM)technology is a technology related to OFDM subcarrier mapping,which can improve the spectral efficiency and energy efficiency of the system.Therefore,the combination of SIM technology and RoF technology is a significant research topic.This thesis firstly summarizes the significance and advantages of RoF system and the research frontier of SIM technology.Then,some key technologies in the OFDM-RoF system are analyzed in detail,including sampling,shaping filtering,equalization,carrier phase recovery in OFDM,three transmission schemes of RoF system,and two detection structures of OFDM-RoF.On this basis,the experiments verified that the application of SIM technology in the RoF system can improve the spectral efficiency and energy efficiency of the RoF system.In the first step,a high spectral efficiency QPSK-SIM-OFDM RoF scheme was studied.It uses less silent subcarriers in the OFDM subcarrier mapping,to enable the carrier to carry more bit information,thereby improving spectral efficiency.At the same time,within a certain range,the spectral efficiency increases as the number of silent subcarriers increases.In this thesis,a verification experiment is carried out to estimate the performance of the system,and clear constellation diagrams and bit error rates are obtained.Experimental results show that compared with the conventional QPSK-OFDM,QPSK-SIM-OFDM using 128 subcarriers with 2 silent subcarriers can enhance the spectral efficiency by 3.1%,and 128 subcarriers with 21 silent subcarriers by up to 4.5%.With 512 subcarriers,the spectral efficiency can be increased up to 15.6%.In the second step,a high energy efficiency QPSK-SIM-OFDM RoF scheme was studied.It uses the power of the OFDM subcarrier to carry on-off keying(OOK)information,where the high-power subcarriers carry high-order modulation information and the low-power subcarriers carry no modulation information.The power of the SIM-OFDM signal is reduced while maintaining a stable bit error rate.Since the addition of OOK information will reduce the spectral efficiency of the signal,it is necessary to increase the bit rate of the signal to remain the given throughput.Experiment results show that the 800 Mbps QPSK-SIM-OFDM has an energy efficiency improvement of 30% over the 500 Mbps conventional QPSK-OFDM-RoF,while maintaining the equivalent throughput.