Research On The Key Technology Of Multicarrier System Based On Complex Wavelet Analysis In

In this paper, combined with other key technologies in 4G, orthogonal multi-carriers modulation based on complex wavelet analysis is researched to improve communication system performance.The coefficients in filter bank of Approximately Linear Phase Orthogonal Complex Wavelet Transform (ALPOCWT) are derived from that of orthogonal real wavelet, and OFDM is improved into ALP-OCWDM through replacing the transform key IFFT and FFT of OFDM by ALPOCWT. The bandwidth of modulation symbol in ALP-OCWDM is narrower than that of OFDM and OWDM, so it owns the highest spectral efficiency. In Gaussian channel, Rayleigh channel and Multipath channel, Bit Error Rate (BER) performance of ALP-OCWDM is better than OFDM’s and OWDM’s. According to the feature of wavelet transform concentrating signal and dispersing noise, Gaussian noise can be suppressed by wavelet transform. Thus an improved system based on ALP-OCWDM called De-ALP-OCWDM is proposed. Simulation has proved that the improved De-ALP-OCWDM system features better BER performance and reliability.The modulation of Complex-valued filter involves complex operation, so it has quite high computational complexity. Dual-tree Complex Wavelet Transform (DTCWT) as discrete realization of complex wavelet is used to replace the transform key of OFDM. The improved system called Orthogonal Complex Wavelet Division Multiplexing is based on Dual-tree Complex Transform (DT-OCWDM). The bandwidth in modulation symbol of DT-OCWDM is narrower than OFDM’s and ALP-OCWDM’s, so spectral efficiency of DT-OCWDM is the highest of all. There is a difference of 20dB between main lobe and the first side lobe in modulation signal of DT-OCWDM, so signal energy is more concentrated. In Gaussian channel, Rayleigh channel and Multipath channel, the BER performance of DT-OCWDM is better than that of OFDM and OWDM. DT-OCWDM is applied to DVB-T and simulation has confirmed its usefulness.Under the influence of attenuation and delay in channel, so channel equalization is needed for received signal. The channel estimation methods based on pilot in DT-OCWDM are researched and comparisons are made among LS channel estimation method, MMSE channel estimation method and LMS channel. Theory and simulation analysis have proved Mean Square Error (MSE) of LMS channel estimation in DT-OCWDM is far less than the other two channel estimation method in DT-OCWDM. ZF equalization, MMSE equalization, and joint equalization are done according to the estimation of channel characteristics. Simulation results show that ZF equalization is better than MMSE equalization, and joint equalization method can get the best equalization effect.When OFDM in MIMO-OFDM is replaced by DT-OCWDM, the improved system is called MIMO-DT-OCWDM. It not only expands capacity but also further improves the anti-multipath and anti-noise characteristics. Improved systems called STBC-DT-OCWDM and VBLAST-DT-OCWDM are proposed in this paper on the basic of STBC diversity system and VBLAST multiplexing system, respectively. In Gaussian channel, the BER performance of STBC-DT-OCWDM is better than that of STBC-OFDM. In Gaussian channel with spatial correlation, the BER performance of VBLAST-DT-OCWDM is better than that of STBC-OFDM.DTCWT is applied to MC-CDMA, and the improved system called DTCWT-CDMA is gained through substituting WALSH spreading code group in MC-CDMA for another code group, which is obtained from Quasi-orthogonal matrix and characterizes good correlation performance. This DTCWT-CDMA system features not only high-speed data transform, effective bandwidth utilization rate, but also high gain of frequency diversity and good BER performance in Gaussian channel.