Research And Implementation Of Synchronization Technology In NC-OFDM Communication System

In the context of cognitive radio,NC-OFDM communication system has become the most promising communication system.It not only has the advantages of the traditional OFDM communication system,but also has the characteristics of integrating discontinuous spectrum resources for data transmission,which makes it become an effective means of anti-jamming.This article focuses on the synchronization technology in the NC-OFDM system.In order to perform normal data transmission when part of the subbands are available in the interference environment,a synchronization algorithm based on non-continuous ZC sequences is proposed,and it is implemented on the NI USRP platform using Lab VIEW FPGA programming technology.In the second chapter,we introduce the channel model and some typical jamming modes,such as Aiming Narrowband Jamming,Partial Band Noise Jamming and Multi-Tone Jamming;The principle of NC-OFDM system is described,and the system parameters and frame format are designed.A synchronization scheme based on the non-continuous ZC sequence is proposed,the selection method of the synchronization sequence is analyzed,and the structure design of the synchronization sequence is given.The third chapter of this paper studies the synchronization technology of NC-OFDM system based on non-continuous ZC sequence,aiming to meet the reliable synchronization performance of the system when 90%of the subbands in the NC-OFDM system are interfered.Firstly,a timing synchronization algorithm based on non-continuous ZC sequence is proposed,and its synchronization acquisition and timing estimation principles are given.The synchronization acquisition performance and timing synchronization performance are analyzed.The simulation results show that in the AWGN channel and EVA fading channel,when 90%of the subbands are interfered,the acquisition probability is greater than 99%when E_s N₀ is 3d B and 14d B,and the false alarm probability is less than 10^-3.This chapter also studies the frequency offset estimation algorithm based on DFT interpolation,which can effectively estimate the frequency offset in the range of(7)-f_s 2,f _s2(8).The simulation results under the AWGN channel show that the NRMSE performance of the frequency offset estimation is almost close to the Cramereau bound in a non-interference environment.When 90%of the subbands are interfered,the NRMSE performance of the frequency offset estimation is about 1d B away from the Cramereau bound.They are both at SNR32d B,NRMSE<10^-3.The fourth chapter of this paper presents the NC-OFDM synchronization link implementation scheme based on the NI USRP platform.First,it introduces the FPGA internal structure and resources of the XC7K410T chip in the USRP platform,and briefly describes the way to develop it using Lab VIEW.Then it gives the implementation schemes of the studied synchronization algorithms.For timing synchronization,it mainly introduces the realization method of sliding correlation calculation,average power calculation,peak capture and timing output.For frequency synchronization,it mainly gives the realization method of finding the maximum frequency point,calculating the interpolator and using the DDS IP core for frequency offset compensation.Finally,the acquisition performance of the synchronization algorithm is actually tested based on the USRP platform.The experimental results show that the synchronization acquisition performance in a non-interference environment differs by about 1d B from the simulation performance,and the frequency offset estimation performance differs by 0.6d B.In an interference environment,the synchronization acquisition performance is about 1?2d B between the actual measurement and the simulation,and the frequency offset estimation performance is about 1d B away.The reason is the difference in accuracy between floating point and fixed point and the error caused by the device.