Channel Equalization Algorithm About Shortwave High-speed Data Transmission In Fixed Frequency And Frequency Hopping System Based On 3KHz Bandwidth

Shortwave communication is an important way in the wireless communication.However,the existence of fading,multipath interference and Doppler shift and other unfavorable factors in channel affects the reliability of data transmission.For this reason,channel estimation and equalization algorithm about shortwave high-speed data transmission in fixed frequency and frequency hopping system based on 3KHz bandwidth are studied in this thesis,which can improve the system performance by reducing the inter-symbol interference caused by multipath propagation.Firstly,channel estimation and equalization algorithm in frequency hopping system are studied in this thesis.Equalization usually requires channel information,so channel estimation can play an important role on the performance of equalization algorithm.According to the characteristics of the frequency hopping system,two typical channel estimation algorithm based on LMS（Least Mean Square）and RLS（Recursive Least Squares）are mainly introduced and simulated.Then,the basic equalization algorithms about DFE（Decision Feedback Equalizer）,DDE（Data Directed Estimation）,NDDE（Nonlinear Data Directed Estimation）and Turbo equalization are analyzed.The block turbo equalization algorithm based on NDDE algorithm is given.According to the simulation,to achieve the BER（Bit Error Rate）of10^-5,the SNR（Signal to Noise Ratio）of the given algorithm is 0.5dB less than that of NDDE algorithm.Then,channel estimation and equalization algorithm in fixed frequency system are studied.A Simple and practical autocorrelation channel estimation algorithm with low complexity and two interpolation algorithms are analyzed and simulated.Equalizer performance is very sensitive to the choice of sampling points in high-speed data transmission system.Sampling points offset caused by multipath delay affects the system performance.So the Fractional Space Equalizer（FSE）based on MMSE（Minimum Mean Square Error）criterion is given.Simulation results show that the FSE is not sensitive to the choice of sampling points and outperforms the symbol rate equalizer when the latter was optimized at the best sampling time.Finally,channel estimation and equalization algorithm in fixed frequency system are implemented on DSP（Digital Signal Processor）platform.The capacity of DSP on-chip RAM（Random Access Memory）is limited.Considering that the real-time requirement of system is quite high,with the help of SDRAM（Synchronous Dynamic Random Access Memory）and FPGA（Field Programmable Gate Array）,not only P-E-W-D pipelining structure is implemented but also the dynamic memory management and Ping-Pong Buffer are used.According to the simulation,to achieve the BER of10^-5,the SNR of FSE is 1dB less than that of symbol rate equalizer.