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PhD ThesisOrthogonal frequency division multiplexing (OFDM) is a multicarrier
modulation technique that has become a viable method for wireless
communication systems due to the high spectral efficiency, immunity
to multipath distortion, and being flexible to integrate with other techniques.
However, the high-peak-to-average power ratio and sensitivity
to synchronization errors are the major drawbacks for OFDM systems.
The algorithms and architectures for symbol timing and frequency synchronization
have been addressed in this thesis because of their critical
requirements in the development and implementation of wireless
OFDM systems. For the frequency synchronization, two efficient carrier
frequency offset (CFO) estimation methods based on the power and
phase difference measurements between the subcarriers in consecutive
OFDM symbols have been presented and the power difference measurement
technique is mapped onto reconfigurable hardware architecture.
The performance of the considered CFO estimators is investigated in
the presence of timing uncertainty conditions. The power difference measurements
approach is further investigated for timing synchronization in
OFDM systems with constant modulus constellation. A new symbol
timing estimator has been proposed by measuring the power difference
either between adjacent subcarriers or the same subcarrier in consecutive
OFDM symbols. The proposed timing metric has been realized
in feedforward and feedback configurations, and different implementation
strategies have been considered to enhance the performance and reduce
the complexity. Recently, multiple-input multiple-output (MIMO)
wireless communication systems have received considerable attention.
Therefore, the proposed algorithms have also been extended for timing
recovery and frequency synchronization in MIMO-OFDM systems.
Unlike other techniques, the proposed timing and frequency synchronization
architectures are totally blind in the sense that they do not
require any information about the transmitted data, the channel state
or the signal-to-noise-ratio (SNR). The proposed frequency synchronization
architecture has low complexity because it can be implemented efficiently
using the three points parameter estimation approach. The
simulation results confirmed that the proposed algorithms provide accurate
estimates for the synchronization parameters using a short observation
window. In addition, the proposed synchronization techniques have
demonstrated robust performance over frequency selective fading channels
that significantly outperform other well-established methods which
will in turn benefit the overall OFDM system performance.
Furthermore, an architectural exploration for mapping the proposed frequency
synchronization algorithm, in particular the CFO estimation
based on the power difference measurements, on reconfigurable computing
architecture has been investigated. The proposed reconfigurable
parallel and multiplexed-stream architectures with different implementation
alternatives have been simulated, verified and compared for field
programmable gate array (FPGA) implementation using the Xilinx’s
DSP design flow.Ministry
of Higher Education and Scientific Research (MOHSR) of Ira
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