The Research On Some Problems Of Wavelet Packet Based Multi-carrier Modulation System

Wavelet packet based multi-carrier modulation system not only has some advantages eg. anti-jamming which made from multi-path or inter-symbols, and high efficience of spectrum, but also takes some advantages to OFDM in arbitrary pilling of signal channels. So, people pay more and more attention on it. Whereas, multi-carrier modulation has some inherent disadvantages, such as the PAPR (ratio of peek power to average power) is too great and synchronization is difficult. These limit its development and application. People have done many works in sovling these problems of OFDM, but few in WPM. The thesis is just about PAPR and synchronization of WPM.Multi-carrier modulation system, wavelet & wavelet packet theory and WPM systems are orderly introduced firstly. Especially, we illustrate kinds of WPM systems and their characteristics. Good application prospect of WPM is presented. Then, we will study the statistical property of transmitted signals from theory aspect. After some mathmatical infers, we find the amplitude in each time of a WPM symbol period obeys the normal distribution, and the convarince is detemined by corresponding filter coefficients. We also examinze the conclusion through numerical calculations, and compare the performances in PAPR of kinds of wavelet filters. At last we propose a companding technique to better the great PAPR.And we pay much attention in analyzing and solving symbol synchronization using analogous methods of OFDM. When pulse forming function is db5 or db5's corresponding scale function, their autocorrelation function which can be used to describle WPM systms's ability in symbol synchronization are illustrated. And WPM has the ability to apply in wireless networks, so, the effect of kinds of grouping examination is presented. At last, a thickly estimates of symbol timing method using maximum likely function is also presented.