Wavelet Theory Is Applied Research In Wireless Communications, Multi-carrier Modulation System

The bandwidth efficiency and ability to combat the effects of frequency selective channels are critical issues in the design of wideband wireless digital communications system. The frequency selective channel effects, in wireless communications the multi-path fading is caused by the signals from different paths exhibits time variability. To improve the bandwidth utilization and to avoid the inter symbol interference (ISI) caused by the time dispersion in the channel, the methods we used includes adopting equalization techniques in the receiver in 2G cellular system, or considering Rake combination techniques in DS-CDMA in 3G cellular system. However, with increasing need of high speed transmission, the above two methods are no more omnipotent. In recent years Multicarrier Modulation (MCM), especially Orthogonal Frequency Division Multiplexing (OFDM) is among the most popular concepts for wide-band data transmission over dispersive communication channels. In MCM, the data stream is divided into a set of orthogonal subchannels which is narrow enough to be considered as a flat channel. A typical and most widely applied multicarrier modulation is OFDM, a simple computation of fast Fourier transform makes OFDM and its variants practically applicable in real systems and variants practically applicable in various wireless standards and protocols. Besides OFDM, this paper has further research on wavelet packet MCM system and proposed multi-wavelet packet MCM system, which is a multi-band multi dimensional modulation scheme with a flexible dyadic time-frequency tiling. In MCM system, these basis schemes, i.e. Fourier, Wavelet and multi-wavelet, are compared and analyzed over different channel environments. In this thesis, wavelet packet Multicarrier CDMA is also researched to compare with DFT-MC-CDMA system. The main work includes:First of all, characteristics of wireless channels are reviewed. The channel is of course not ideal, effects in wireless applications and characteristics of electric waves impose problems to correctly demodulate the incoming signal. It is necessary to pay full...