Research On Transmission Characteristics Of OFDM-RoF System Based On 5G Coding Technology

With the rapid development of communication technology and the emergence of applications such as big data,the Internet of Things,and cloud computing,mobile users have an increasing demand for high-speed,large-capacity communication.The 5G communication system proposes to use carrier resources of higher frequency bands to improve the transmission rate of the system.In the face of problems such as the limited transmission distance of highfrequency carriers in wireless channels and the dense cellular structure of base stations,Radioover-Fiber(RoF)technology has the advantages of large bandwidth,low loss and strong antiinterference ability.It has become an effective technical means to achieve long-distance reliable fronthaul and low-cost dense coverage of 5G high-frequency signals.Since the dispersion and attenuation effects in the optical fiber link will affect the transmission reliability of the radio frequency signal,research on the transmission characteristics of the Orthogonal Frequency Division Multiplexing(OFDM)signal with different coding schemes in the 5G system in the RoF system is carried out,which has important application value for the rapid and low-cost deployment of 5G high-band systems in the future.The specific research contents of this thsis are as follows:Firstly,three methods of optically generating millimeter-wave commonly used in RoF systems are introduced,and the principle of the external modulator method based on MachZehnder modulator is mainly analyzed,and three different sideband modulation methods are simulated and realized.Based on the co-simulation of Matlab and Optisystem,a traditional OFDM-RoF transmission system is established,and the effects of fiber dispersion,transmission rate,number of fast Fourier transform points and different received optical powers on the transmission characteristics of OFDM-RoF system are analyzed respectively.Subsequently,for Low Density Parity Check Code(LDPC),a probability shaping OFDMRoF system model based on LDPC is proposed.Based on the co-simulation system constructed by Matlab and Optisystem,the transmission performance of the system is evaluated.Under the condition of the same received bit error rate,the transmission power threshold of the probability-shaped OFDM signal is raised by about 1.10 d Bm compared with the traditional OFDM signal,and the peak-to-average power ratio is reduced by about 0.6d B.When the baseband data rate is 2.5Gbps and the RF carrier frequency is 25 GHz,the transmission bit error rate is tested under different fiber lengths,the results indicate that the proposed LDPC-based probability shaping OFDM-RoF system can effectively enhance the sensitivity of the receiver,and enhance the reliable transmission distance of the system.Finally,for Polar code,the optimization of transmission characteristics of OFDM-RoF system is studied.The transmission characteristics of Polar-Sparse Code Multiple Access(SCMA)signal in OFDM-RoF system are studied by simulation.The results show that when transmitting in a long-distance RoF system,the longer the code length of the Polar code is,the better the transmission performance is.And based on the constructed Polar-SCMA RoF cosimulation system.The transmission performances of Polar codes and LDPC codes under the same parameters,SCMA and probability shaping,are compared and evaluated.Lastly,the simulation analysis of the transmission bit error rate of the RoF system based on the PolarSCMA signal under different fiber lengths is carried out.The results show that the Polar-SCMA signal can further enhance the transmission performance of the OFDM-RoF system.