| Recent years Multicarrier Modulation (MCM) is among the most popular concepts for wide-band data transmission over dispersive communication channels. In MCM, the data stream is split into several independent substreams with lower data rate to modulate the corresponding subcarriers. Orthogonal Frequency Division Multiplexing (OFDM) is such kind of typical implementation of MCM, and has been employed in some wirelss standards and protocols. Besides OFDM, this paper has proposed wavelet basis over MCM system, and done more research about Wavelet Packet Multicarrier Modulation (WP-MCM) system. In the structure of MCM, this two different basis schemes, i.e. Fourier and Wavelet, are compared and analysed over different channels. Finally the application of MCM over multi-antennas is researched. The main work includes:1. According to the analysis of Fourier basis in OFDM, the disadvantage of sensibility of frequency offset is found to be so serious especially over interchannel interference (LCI) channels. Therefore, the concept to introduce the wavelet to be the subcarrier function comes into being. The system is referred as WP-MCM. Relative work has been done, including the mathematical model, definition and computation of wavelet packet, function space comprehension and fast discrete wavelet packet transform (DWPT). The features of WP-MCM are concluded.2. Dual-way filter bank is the key part during DWPT. In this paper three sorts of wavelet series and the properties of the corresponding filter bank are illustrated. In WP-MCM with fixed-scale wavelet packet decomposition, the different effects of this three wavelet series on system reliability are discussed and the way how to choose the appropriate wavelet is given as last.3. In the structure of MCM, Fourier basis and orthogonal wavelet basis is debated to show the BER performance, computation complexity of OFDM and WP-MCM system respectively over different channel scenarios.4. When the image is employed as the source, multilevel coding (MLC) is introduced into WP-MCM system. A new data division scheme is proposed after the theoretical analysis of PSNR value. The combination of these two methods provides an adaptive image transmission scheme. Simulation results demonstrated theefficiency well. In addition, the algorithm of optimal wavelet packet is explained to optimize the channel fading and wavelet packet decomposion so as to reduce the power of wireless channel interference.5. Due to the wide application of OFDM and multi-input multi-output (MIMO), MIMO-OFDM system is depicted after describing the basic techniques when using multi-antennas. Closed-loop MIMO-OFDM is focused on with the singular value decomposition (SVD) as the key part. The inherent unequal error protection (UEP) ability during the equivalent space suchannels is found, and then the idea is to utilize (not balance) this property and extend it to the application of hierarchical data transmission scheme. Detailed simulation results show the UEP clearly and the surprising wonderful performance. |
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