Soft Information Extraction For 64 QAM And Data Detection In Frequency-hopping About HF Communication

HF Communication plays an important role in wireless communication. However, the performance of the transmission system is badly influenced by the inter-symbol interference resulted from the multipath propagation and channel distortion. With the development of electronic information technology, HF communication is widely used. It’s more important to improve reliability of the system by eliminating the inter-symbol interference. So time-domain equalization technology and block data detection technology are given in this thesis.In this thesis, the characteristics of HF communication are described firstly. Since the channel is time-varying, an adaptive channel estimation algorithm is needed to track accurately the channel change. Four adaptive channel estimation algorithms are introduced in this thesis. The most applicable condition for each algorithm comparing with the other algorithms is analyzed. Then soft information based on soft decision is studied. Three methods to get soft information are derived in this thesis, namely accurately log-likelihood ratio algorithm, approximately log-likelihood ratio algorithm and simplified algorithm. For square 64 QAM modulation constellation, the calculation formula of simplified algorithm is given. The performance of three algorithms is simulated and analyzed. Simulation results show that the performance of those three algorithms is almost equal, but the computational complexity for simplified algorithm is greatly reduced. Turbo equalization is an iterative equalization, it is used to eliminate inter-symbol interference and improve system performance through passing soft information between equalizer and decoder. According to MIL-STD-188-110 C, using 256/32 data block structure, 64 QAM modulation, LDPC coding in 3 4 coding rate, the time-domain Turbo equalization based on linear MMSE criterion and soft interference cancellation criteria is simulated. Finally, non-iterative block data detection technology is presented, including linear block data detection and nonlinear data detection. Training data and unknown data are sent alternately and inter-symbol interference is eliminated with decision feedback. Nonlinear block data detection algorithm is simulated based on frequency-hopping communication. The simulation results show the system can reach the requirements.