Study On The Technique Of OFDM And Turbo Codes In Short-Wave Frequency Hopping Systems

Since DFT was proposed as a part of the modulation and de-modulation in the multi-carrier transportation systems by 1971,OFDM(Orthogonal Frequency Division Multiplexing) has been applicated in many fields.OFDM is expecially applicable in wireless high information transportation with multi-path and Doppler shift.However,the speed of the information transportation of ordinary short-wave frequency hopping systems is quite low.generally at 2.4kbit/s,and only tongue can be transported.Information transporting speed must be enhanced so that data can be transported.considering the characters and requirements of short-wave frequency hopping systems and based on the short-wave frequency systems with the hopping speed is 20hop/s,We introduced a technique which applicates OFDM and Turbo codes to the short-wave frequency hopping systems,so that the information transporting speed can reach 20.48kbit/s,including 5.12kbit/s pilot information and 15.36kbit/s data information.The short-wave channel was briefly introduced,and the theory of OFDM was also briefly introduced.The characters of OFDM in short-wave frequency hopping systems was analyzed.The reason that cuases high PAPR was stressed analyzed and a new way to reduce PAPR was presented based on the three ordinary ways.The pilot channel estimation and other channels insertion and equalization is focoused on,and the value was simulated.Turbo codes was inducted as a channel coding.Finally,the curve of the system's error performance was presented.The main points of this paper are:(1)Based on the short-wave frequency hopping system with 20hop/s,we presented a technique with OFDM and Turbo codes,which can improve informations' transporting speed and depress the bit error rate. On the assumption that the synchronization of the frequency hopping system can be utility,the system with these techniques is more suitful for application in short-wave Reyleigh channel by simulation.(2) For the sake of realization of the system,a upswing method for reducing the PAPR of the OFDM systems was presented.And simulation results shows that this method is effective for BPSK and QPSK mapping in OFDM modulation.At the end of this thesis,the matter of this thesis is presented and new hopes are brought forward. Frequency hopping speed can be improved since the short-wave frequency domain can be used,which can improve data transportation speed and improve the system's anti-jamming performance.At the same time,M-QAM mapping can be used in OFDM for improving data transportation speed.