Research On Synchronization Technology Of Communication Module In Ad Hoc Network Based On OFDM

Orthogonal frequency division multiplexing(OFDM)technology is widely used in wireless communication because of its high frequency band utilization and antimultipath delay expansion.If the orthogonality between subcarriers is destroyed due to synchronization problems,the system performance will be seriously affected.Therefore,it is very important to find symbol timing and carrier frequency offset at the receiver for signal recovery.This paper introduces the advantages of OFDM Technology in the application of wireless ad hoc network,describes the basic principle of communication module based on OFDM and the design of system parameters in detail,and analyzes the influence of symbol synchronization deviation and frequency deviation on synchronization performance.In this paper,Schmidl algorithm,Minn algorithm,park algorithm and CAZAC sequence synchronization algorithm are introduced in detail.The frame error rate of the four algorithms is calculated by MATLAB,and the performance of the algorithm is compared.On this basis,an improved PN sequence based on QPSK is proposed to solve the problems of high PAPR of traditional PN sequence and band limit of filter.By comparing the autocorrelation and low-pass characteristics of scrambling codes,a set of suitable scrambling codes combined with PN sequences is selected as the training sequence of the algorithm.A synchronization algorithm anti large frequency offset based on ad hoc network UAV patrol is designed: coarse synchronization based on scrambling code matching and fine synchronization based on normalized local sequence matching.Because the length of PN sequence is reduced,the estimation range of frequency offset is larger,and the integer frequency offset correction is not needed.By using the normalized matching scheme,the complexity of hardware implementation and the consumption of hardware resources are greatly reduced.The simulation of synchronization performance is analyzed and compared under different frequency offset.The results show that the PN sequence designed in this paper has better synchronization performance in terms of frame error rate and frequency offset estimation.The hardware implementation of the algorithm is based on FPGA chip: coarse synchronization module,frequency offset calculation module and fine synchronization module are designed.Through the joint simulation of Matlab and Modelsim,it shows that the algorithm can complete the synchronization and frequency offset estimation well in hardware implementation,and gives the resource consumption report of the whole synchronization algorithm.A set of FPGA and AD9361 experimental verification platform based on XC7Z035 is built to test the board level synchronous transmission performance.When the signal-to-noise ratio is 0d B ? 20 d B,the synchronous frame error rate is 0,which meets the design requirements.