| Meeting the need of real time multimedia and Internet access services for the coming wireless communication,whenever and wherever wireless data can be transmitted with high speed and great quality,which is the main advancing direction of the fourth generation wireless communication technique.Multi-carrier modulation has become the pivotal technique for its favorable validity and reliability.OFDM system as the more representative of the multi-carrier transmission technology has been widely studied,but because of its existence of some shortcomings to be improved such as the peak-to-average ratio ad soon on.In this thesis,a multi-carrier transmission system using wavelet is compared and a Comprehensive Wavelet Packet Modulation technique which using different wavelets is proposed.Firstly,the basic Wavelet Packet theory is introduced which are the important base of Wavelet Packet transform based multi-carrier modulation theory and algorithm.And then the main purpose of this thesis is to study the effects of different wavelet functions on the performance of wavelet packet modulation.The performance of the system is compared with the frequency spectral efficiency,peak-to-average ratio,anti-multipath fading and corresponding time offset and frequency offset.According to the simulation,in the aspect of frequency spectral efficiency,WPM is better than OFDM and the performance of WPM has been shown to be identical to OFDM in several reference wireless channels,though at a higher cost of equalization in multipath channels.WPM is slightly more sensitive than OFDM to the corresponding time offset and frequency offset.Finally a comparison of the core transforms has shown the low complexity potential of WPM based systems.According to the simulation,the suitable wavelet is selected for multicarrier transmission.However,due to the wavelet that has the ability to achieve better performance is much more complex in realistic use,it will increase the complexity of the system.In order to solve this problem,a Comprehensive Wavelet Packet Modulation(CWPM)scheme is proposed and the performance analysis is also been made by the Matlab software simulation.Through the experimental results and theoretical analysis,by measuring the factor of frequency spectral utilization,OFDM suffers from quite large side lobes.And in the aspect of peak-to-average ratio,CWPM has about 1d B improvement than OFDM.Compared with the WPM under the same performance,the CWPM has a good performance in reducing the implementation complexity.Considering the simulation above,and the factors of the ability of anti-additive Gaussian white noise and the anti-multipath fading,proves that the use of comprehensive wavelet packet modulation is effective than the conventional wavelet packet modulation. |
