Design And Analysis Of High-speed Frequency Hopping System Based On OFDM

With the rapid development of modern science and technology,the density of communication equipment is increasing year by year,resulting in large-scale electromagnetic interference between communication equipment.So,it is very important for transmission equipment to have anti-interference capability.Because of its strong antiinterference performance,Frequency Hopping(FH)technology has been applied in many fields,especially the transmission between ground base station and aircraft.At the same time,Because of its strong resistance to multipath fading,Orthogonal Frequency Division Multiplexing(OFDM)technology is widely used in ground-air transmission.Therefore,in order to solve the problems of multipath fading and artificial electromagnetic interference in the ground-air communication transmission,this thesis designed the FH-OFDM system combining high-speed FH and OFDM,studied the anti-interference performance and frequency hopping synchronization of the FH-OFDM,and completed the hardware implementation at the same time.This thesis specifically includes:1.Firstly,according to the index requirements of air-ground transmission,the frame format of system synchronization head and OFDM data block is designed in this thesis.Then,combining DQPSK modulation and demodulation technology,OFDM peak reduction equalratio technology and Minimum Mean Square Error(MMSE)signal to noise ratio estimation technique,the model of FH-OFDM system with high frequency hopping rate is established.Finally,The FH-OFDM system model is simulated by MATLAB.The simulation results show that the FH-OFDM system can work normally in both gaussian channel and multipath channel,and the performance indexes meet the design requirements.2.Aiming at the established FH-OFDM system,according to the self-synchronization method of fast scan type and synchronization method based on TOD,a new synchronization scheme is proposed: scanning resident method.This method completes frequency hopping synchronization in two stages.In the coarse synchronization stage,the frequency hop generator uses the scanning rate to scan the coarse synchronous frequency hop set to solve the capture problem of the FH-OFDM system with 30% multi-tone interference.In the precise synchronization stage,the frequency hopping generator uses the frequency hopping operating rate to scan the frequency hopping set of the precise synchronization and complete the precise synchronization of the receiving and receiving ends.MATLAB simulation results show that FH synchronization can capture almost without error within the range of theoretical signal to noise ratio,which is consistent with the theoretical analysis results.Finally,the hardware design and implementation of the FH-OFDM system are completed,and the synchronization scheme is implemented in FPGA.The simulation results show that the synchronization time of the scanning resident method is 3.8ms,which is lower than the minimum synchronization time required by the system,and the feasibility of the FH synchronization scheme is verified.3.Aiming at the established FH-OFDM system,on the basis of analyzing the performance of the theoretical FH system against wideband interference and multi-frequency continuous wave interference,the communication capability of the FH-OFDM system under wideband interference,narrowband gaussian interference,single-tone interference and multi-tone interference is studied.The results of MMSE signal to noise ratio estimation are used to identify the interference in the FH sub-channel,and different signal to interference ratio are used to simulate the interference power.The simulation results show that the FH-OFDM system has a strong capability to resist human interference in gaussian channel and multipath channel.Single-tone interference almost has no influence on the FH-OFDM system,while the influence of multi-tone interference on the FH-OFDM system is weaker than that of broadband interference and narrowband noise interference.