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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