Research On AD Hoc Network Synchronization Technology Based On OFDM System

Wireless communication system will be subject to noise,frequency selective fading and multipath interference in the actual transmission process,so that in such an environment,the transmission of information will be seriously affected.Orthogonal Frequency Division Multiplexing(OFDM)technology is widely used in orthogonal frequency division multiplexing(OFDM)due to its advantages of anti-multipath delay expansion and high bandwidth utilization.In the synchronization problem,the orthogonality between each subcarrier is broken,which will have a great negative effect on the operation of the system.Therefore,it is necessary to use AD hoc synchronization algorithm to improve the performance of OFDM systems.This paper researches ad-hoc network synchronization technology based on OFDM and realizes it with Field Programmable Gate Array(FPGA).The main contents are as follows:(1)Aiming at the problem that signal transmission in the wireless system is out of sync due to noise interference,a training sequence is generated by MATLAB at the transmitter terminal.The sequence is converted into leading data through channel coding,series parallel conversion and adding cycle prefix.The frame header of the signal at the transmitter is found through frame synchronization of the leading data at the receiving end.The problem of signal asynchronism is solved by using symbol synchronization to recover data signal,using sampling frequency synchronization to complete clock frequency synchronization of signal data,and using channel estimation to minimize data error.(2)In view of the high complexity of hardware implementation of wireless communication system,MATLAB is used for simulation and performance comparison of two traditional AD hoc network synchronization algorithms to determine the synchronization algorithm suitable for this paper.After improving the algorithm,a new synchronization algorithm is proposed as the synchronization algorithm of OFDM AD hoc network.(3)Based on the basic architecture and working principle of FPGA,implement the loop prefix and leader generated by the transmitter on FPGA,implement the frame synchronization,symbol synchronization and sampling frequency synchronization on the receiving end on FPGA,and implement the ad-hoc network synchronization algorithm on FPGA.(4)The OFDM ad-hoc synchronization technology is applied to practical engineering projects.XC7V690 T and AD9361 are used to realize fast parallel processing.MATLAB and VIVADO are used for co-simulation to verify the correctness of OFDM ad-hoc synchronization algorithm on FPGA.The software design realizes the function of frame grouping,spread spectrum and modulation.The functions of down-conversion,synchronous capture,synchronous identification and de-expansion,differential demodulation of the receiver software verify the feasibility of the design in this paper.(5)An experimental platform was built to verify the transmitting and receiving capabilities and AD hoc network performance of the OFDM system at the board level.The correctness and reliability of the system are verified by the test of transmitting power,sensitivity,networking delay and other parameters,as well as the comparison of the upper computer and the simulation diagram.