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الثلاثاء، 5 أغسطس، 2014

Wavelet Domain Processing and Beamforming for OFDM Based 4G System

Author        : Mohamed Shokry Eid Heakle
Degree        : Ph.D. Electric Communication
Title: Wavelet Domain Processing and Beamforming for OFDM Based 4G System

Abstract
The increasing demand for high data rate services, as in 4G, requires the transmission of wideband waveforms and due to the frequency selective nature of the fading communication channel, this requires complex and highly cost receivers to mitigate intersymbol interference (lSI). In Orthogonal Frequency Division Multiplexing (OFDM) the bandwidth of the data symbols are modulated with low data rates and simultaneously transmitted on separate (orthogonal) subcarriers. In this way, the transmitted data is not affected by the frequency selective nature of the fading communication channel. In addition. by using cyclic prefix (CP) with length longer than the channel delay spread, OFDM based systems can mitigate lSI effects. By combining OFDM with Adaptive Antenna Arrays (AAA), the system capacity can be increased and the performance is further improved due to the capability of AAA to cancel interference effects and to improve the performance in fading environment. Non-blind algorithms, such as the Least Mean Square (LMS) algorithm, as well as blind algorithms, such as the Constant Modulus Algorithm (CMA), for AAA processing are considered in this thesis.
In this thesis, the application of wavelet domain processing in OFDM systems is considered. By using Orthogonal Wavelet Division Multiplexing (OWDM) where FFT in conventional OFDM is replaced by the Discrete Wavelet transform (DWT), the CP is no longer needed and hence the spectral efficiency is highly improved. Wavelet domain processing also allows multi-rate and multi-user transmission 1I1 OWDMA system with improved performance in different channel environment.
Another contribution in this thesis is the use of wavelet domain processing in blind and non-blind adaptive antenna arrays; it is shown that the characteristics of V,3VC[etS such as dimension reduction of signal space, denoising effect as well as the multi¬resolution processing result in a highly improved performance in different channel and users environment. The application of wavelet domain processing to )01111 OFDM-AAA systems is also considered. This combination results in great performance improvement in different channel conditions.
As a final contribution in this thesis, MIMO antenna techniques with wavelet based OFDM is investigated. Such enhancement of modulation and multiplexing processing techniques is recommended for future implementation of 4G system.

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