Research On Wavelet Packet-Division Multiplexing System Oriented Graded Multi-Service

Today, with the development of mobile communication, users press for the services of high speed data and multimedia more and more. The new need bring forward challenges for the transmission ability of wireless link and net form, while OFDM is hopeful to become a key technology for next generation mobile communication system because of its high spectrum efficiency and good capability of decreasing multipath interference.In the paper, we introduce a substitution of OFDM——wavelet packet modulation which abbreviation is WPM. Theoretical background on this odulation scheme is first recalled. Specific issues of using such sets of waveforms for multicarrier communication systems are underlined, and an exhaustive comparison with OFDM is made. Special emphasis on the flexibility of this scheme is given. Then we simulate WPM in several typical wireless channel models. 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. Additional results taking into consideration effects of some non-ideal elements of the system have shown that WPM is slightly more sensitive than OFDM to these commonly encountered types of distortion. A comparison of the core transforms has shown the low complexity potential of WPM based systems.WPM uses an arbitrary timefrequency plane tiling to create orthogonal subchannels of different bandwidths and symbol rates in a multichannel system. The nonuniform-bandwidth multichannel schemes as implemented by wavelet packet modulation can be optimized for a given communication channel. In this paper we derive operating conditions for the optimal wavelet packet tree, subject to a budget on both power and complexity. Furthermore, we present a fast tree-selection algorithm which will achieve this optimum. Comparison of our modulation scheme with a DWMT scheme of equal complexity shows that optimal-WPM offers significantly improved capacities for ISI channels, and fares no worse than DWMT in more benign environments.At last, we illustrate a recently proposed wavelet-based method for estimating signals from noisy 2-D multichannel observations. This method exploits both the intrachannel and interchannel signal correlations using a discrete Fourier transform (DFT) and 2-D discrete wavelet transform (DWT) to approximate the optimal data...