Novi pristup rešavanju problema frekvencijskog ofseta kod sistema sa ortogonalnim frekvencijskim multipleksom
Author
Stošović, SlavimirMentor
Nikolić, ZoricaCommittee members
Stefanović, MihajloPerić, Zoran

Milošević, Vladimir
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In this dissertation, principles of orthogonal frequency division multiplex (OFDM), a
method of encoding digital data on multiple carrier frequencies, are given. After theoretical
basics of wireless channel and discrete adaptive filters, advantages and disadvantages of this
kind of transfer are presented. Also, basic blocks of classical OFDM system are described,
with comments on how behavior and implementation of each of them can be improved.
OFDM systems with MDPSK modulation and differential detection in receiver are
considered. Performances for different values of modulation levels and different OFDM
parameter values are analyzed, in accordance with existing standards and OFDM systems that
do not belong to certain standard classification. For this purpose, a modular simulation
environment is developed, in which a universal model of the OFDM system with possibility
of all OFDM parameters adjustment and wireless channel parameters is possible.
The main OFDM system disadvan...tage is frequency offset sensitivity, which destroys
subcarrier orthogonality and produces intercarrier interference. Hence, frequency offset is the
main factor which limits the subcarrier bandwidth and increase of system bitrate.
In order to resolve frequency offset problem, we analyze OFDM receivers with
different configuration and complexity. Proposed receivers are designed by modifying
existing differential detection algorithms, such as double differential detection, multisymbol
differential detection and decision differential detection algorithm.
The new approach to the frequency offset problem solving in system with orthogonal
frequency division multiplex is based on adaptive transversal filter application. We proposed
optimal OFDM receivers with good performance in wide frequency offset range in the Rician
and Rayleigh fading channel. Proposed receivers significantly improve the quality of the
received signal and can be applied in modern wireless telecommunication systems.