Application Research Of OFDM Based On Orthogonal Wavelet Transform In G3-PLC

Orthogonal Frequency Division Multiplexing(OFDM)is a multi-carrier modulation technique.Classic OFDM use the Fast Fourier Transform(FFT)as the core technic,which is sensitive to frequency offset and timing deviation,and has poor anti-interference ability and high peak-to-average ratio.Wavelet transform has strong detection ability for transient information,and reasonable basis function can guarantee good orthogonality.Therefore,the discrete wavelet transform(DWT)is used to replace FFT algorithm.The algorithm of OFDM communication system based on wavelet transform is studied and will be formed.The DWT-OFDM algorithm is used in G3 standard power carrier communication(PLC)to improve the communication performance of G3-PLC in terms of communication reliability,communication efficiency and peak-to-average ratio characteristics.Firstly,the thesis analyzes the theory of wavelet analysis,the wavelet basis function,the principle and key technology of classical system.For the shortcomings of FFT-OFDM system,wavelet transform is used instead of FFT to establish DWT-OFDM system.The good orthogonality and time-frequency locality of wavelet function are used to improve system performance and improve the defects of multi-carrier modulation system.At the same time,according to the orthogonality requirement of OFDM,the biorthogonal wavelet is applied to the system to improve the reliability.On this basis,the DWT-OFDM algorithm is applied to the G3-PLC.By analyzing the G3-PLC physical layer model and frame structure,Physical layer model of the G3-PLC based on DWT-OFDM is designed.In the Gaussian,multipath and measured power line channel environment,the communication performance of the transmission model is simulated and analyzed from the aspects of wavelet base,wavelet decomposition layer and window function type.Finally,combined with the analysis of bi-orthogonal wavelet transform and simulation experiment,the reliability,efficiency and peak-to-average ratio characteristics are optimized and studied.The theoretical analysis and simulation experiments based on the measured power line channel show that the DWT-OFDM system has stronger anti-interference ability in the low SNR environment,and the bior6.8 has the best BER performance when performing the two-layer decomposition.When the bit error rate is 10-3,the performance is improved by about 8 dB,and the communication efficiency is improved while ensuring reliability,which can be increased from about 40%to about 54%.At the same time,the application of the soft limit method is adopted.The peak-to-average ratio can be reduced from approximately 9 dB to approximately 8 dB.