Research Of Channel Estimation And Equalization In Single-carrier And Multi-carrier Communication Systems

As an important part of the communication systems, the channel estimation(CE) and equalization can determine the whole system performance. It has been a hot research topic in communication systems. Wireless channels have some inherent characteristics, such as the multipath effect and the Doppler shift, which can lead to inter-symbol interference. The well-designed channel estimator and equalizer can effectively resist the inter-symbol interference and reduce the symbol error rate(SER) of the system. Focusing on the different properties of the commonly used single carrier satellite communication system and the second generation of terrestrial digital video broadcasting(DVB-T2) system, the thesis studies the channel estimation and equalization algorithms in the two kinds of systems. The work in the thesis can be concluded as follows:Firstly, the thesis introduces the basic principle, frame structure and the pilot modes of single carrier satellite communication system and DVB-T2 system. Then, the thesis analyzes the influence of multipath fading and Doppler shift on the property of the wireless channels.Secondly, the thesis studies the technology of channel estimation and frequency domain equalization in the low SNR case for the single carrier satellite communication system. The thesis analyzes the characteristics of pilot-aided channel estimation and frequency domain equalization algorithm and complete their FPGA(Field Programmable Gate Array) hardware implementation. For the implemented channel estimation scheme, an significant channel tap detection algorithm which is used in OFDM system with adaptive threshold is adopted, where the threshold is determined by a noise power estimator. Then it is confirmed that the scheme can solve the problem of large noise interference for the system in the low SNR case. The thesis analyzes the hardware cost and tests the Bit Error Rate(BER) performance of the downloaded realization. It has been shown that:(1) adaptive threshold scheme can improve 0.9 d B, compared with the fixed threshold scheme with BER= 1e-6.(2) Considering the BPSK and the 1/3 rate mode with the minimum Signal to Noise Ratio(SNR) threshold, the BER of the system can reach to 1e-6 in the AWGN channel when SNR is-2.42 d B and in the double equal gain fading channel when SNR is-0.27 d B.Lastly, the thesis studies the technology of channel estimation for the DVB-T2 system. The thesis analyzes the conventional channel estimation algorithms, such as the Least Square(LS) algorithm, Pilot-Block Averaging noise-reduction algorithm, the Adaptive Averaging Channel Estimator-LS algorithm, the two-dimensional(2-D) interpolation method and the double one-dimensional(2×1D) interpolation method. Based on 2×1D interpolation method, the thesis proposes a new time-frequency weighted channel estimation method at data subcarriers in this thesis. The proposed algorithm computes the channel frequency response(CFR) at the virtual pilots with a weighted factor, which is determined by constructing a cost function related with the Doppler shift and the maximum multipath delay. Simulations show that by adjusting the weighted factor of CFR calculated through time-direction interpolation(TDI) and frequency-direction interpolation(FDI), the proposed time-frequency weighted method can significantly improve the accuracy of channel estimation and has a 1 d B performance gain compared with the conventional 2×1D interpolation method when BER=1e-4.