Channel Estimation In OFDM-based Power Line Communication System

Power line communication(PLC)is a communication method that uses power line as the medium for data transmission.It has the advantages of low cost and convenient networking,but also has much inherent problem such as large signal attenuation,multi-path effect and impulse interference.Orthogonal frequency division multiplexing(OFDM)is considered as a technology that can effectively resist various unfavorable factors on power line channel,and channel estimation is one of the key technologies to ensure reliable transmission for OFDM system.Therefore,the channel estimation algorithm in OFDM power line communication system is studied in this thesis.The details are as follows:1.Channel estimation is studied in the conventional scenes where the PLC system does not suffer from impulse interference.Firstly,for the problem that carrier shielding of PLC system causes the performance degradation of traditional DFT channel estimation algorithm,an improved DFT channel estimation algorithm is proposed.In this algorithm the frequency response of masked subcarriers is estimated so the energy leakage of the channel impulse response(CIR)is reduced.The “floor effect” of traditional DFT channel estimation algorithm in PLC system is solved and the robustness to symbol timing synchronization errors is enhanced.Then,a fast real-time LMMSE channel estimation algorithm is designed to solve the problem that traditional LMMSE channel estimation algorithm has high complexity and requires prior information such as second-order statistics of the power line channel and SNR.In this algorithm the improved DFT channel estimation algorithm is firstly used to estimate the CIR and the SNR in real time,and then the solution of the LMMSE filter matrix is simplified by using the Kumar fast algorithm and the transform relationship between the frequency domain channel correlation matrix and the CIR.With a small loss of performance,the complexity of LMMSE algorithm is greatly reduced.2.Channel estimation is studied in the bad scenes where the PLC system suffers from impulse interference.Firstly,aiming at the influence of non-linear impulse interference cancellation technology on channel estimation,a channel estimation algorithm that uses the preamble of PLC system for iterative cancellation of nonlinear distortion interference is designed,and the simulation results prove that the nonlineardistortion interference is handeled well in this algorithm.Then,aiming at the problem that the impact of the impulse interference can not be eliminated completely in above algorithm,a channel estimation algorithm eliminating the impulse interference iteratively in time-frequency domain is designed.The impulse interference and nonlinear distortion interference are simultaneously reconstructed in this algorithm and the performance of channel estimation under bad scenes is greatly improved.3.PLC system channel estimation scheme design.Firstly,the performace in different scenes and the complexity of various channel estimation algorithms are compared.Then,a suitable algorithm is selected to design robust channel estimation scheme.Finally,simulation results show that this scheme can adapt to various scenes and has steady performance in the bad scenes of different impulse interference intensity.