Research On Optimization For Wavelet Packet Modulation Structure

With the development of broadband wireless communications technology, mobile users have imperious demand for high-speed mobile data service and multimedia service, the multi-carrier modulation technique comes into being. As a new technology of multi-carrier modulation, the wavelet packet modulation (WPM) is concerned with people greatly for its good property of anti-inter-symbol interference, anti-inter-channel interference, high spectral efficiency and so on. However WPM has the problem of peak-to-average power ratio (PAPR) inevitably. We all know that the number of WPM's tree structure increases in the form of 2 times power when the modulation levels increases, this provide the condition for the optimization of the wavelet packet modulation structure. Combined the telecommunication feature, from the points of PAPR reduction and lower complexity, this thesis discusses the optimization of the wavelet packet modulation structure.1. The tree structure of wavelet packet modulation is analyzed. Based on the node classification of wavelet packet tree, the PAPR performances of 3-level wavelet packet modulation about different inner-node number and same inner-node number are simulated separately, and PAPR performances for the same kind pruning tree with different wavelet packet basic function are simulated.2. According to the distribution feature of tree node and statistical selection frequency,using the pruning technique of full tree, the pruning method for the partition and update of wavelet packet tree node is discussed, which realizing the pruning of full tree and improves PAPR. Simulation results show that the pruning structures have same PAPR performance when close to the end node, and they are poor for reducing the PAPR; the pruning structures have good performance for reducing PAPR. Also the pruning tree structure is better than the full tree structure in reducing complexity.3. The method for improving the PAPR of OFDM is introduced into WPM. With the selective mapping (SLM) technique, the method which combined the SLM and pruning techniques for improving PAPR is discussed. Based on the pruning and merging for full tree WPM, the SLM technique is introduced for further optimization of WPM system. Simulation results indicate that the SLM technique is effective for reducing PAPR of WPM system, and the pruned trees have better performance than the traditional full tree.