Channel Modelling and Estimation in Multiple-Input Multiple-Output Orthogonal Frequency Division Multiplexing Wireless Communication Systems
In wireless communications, the demands for high data rates, enhanced mobility, improved coverage, and link reliability have enormously increased in recent years and are expected to further increase in the near future. To meet these requirements, new concepts and technologies are needed. Theoreti...
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| Format: | Thesis |
| Language: | English English |
| Published: |
2008
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| Subjects: | |
| Online Access: | http://psasir.upm.edu.my/id/eprint/7794/1/FK_2008_63A.pdf |
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| Summary: | In wireless communications, the demands for high data rates, enhanced mobility,
improved coverage, and link reliability have enormously increased in recent years
and are expected to further increase in the near future. To meet these requirements,
new concepts and technologies are needed. Theoretical studies have shown that using
multiple antennas at the transmitter and receiver, known as multiple-input multipleoutput
(MIMO) technology, can dramatically increase the capacity, coverage, and
link reliability of a communication system. Orthogonal frequency-division
multiplexing (OFDM) is an attractive technique for high data rates transmission over
frequency-selective fading channels, due to its capability in combating the
intersymbol interference (ISI). The combination of MIMO and OFDM results in a
powerful technique that incorporates the advantages of both MIMO and OFDM, and
is a strong candidate for fourth generation (4G) wireless communication systems.
In this thesis, two issues related to realizing practical mobile MIMO OFDM
communication systems are addressed. The first issue is about MIMO channel modeling and effect of realistic channels on the theoretical capacity. For this target, a
geometrically-based three-dimensional (3-D) scattering MIMO channel model is
developed. The correlation expressions are derived and analytically evaluated. The
impact of spatial correlation on MIMO channel capacity is investigated under
different antenna array configurations, angular energy distributions, and parameters.
Analytical and numerical results have shown that the elevation angle has
considerable effect on the spatial correlation and consequently on the MIMO channel
capacity for the case when the antenna array of the mobile station (MS) is vertically
oriented. This has led to a conclusion that 3-D scattering MIMO channel modeling is
necessary for accurate prediction of MIMO system performance.
The second issue addressed in this thesis is the channel estimation in MIMO OFDM
systems. New time-domain (TD) adaptive estimation methods based on recursive
least squares (RLS) and normalized least-mean squares (NLMS) algorithms are
proposed. These estimators are then extended to blindly track the time-variations of
the channel in the decision-directed (DD) mode. Simulation results have shown that
TD adaptive channel estimation and tracking in MIMO OFDM systems is very
effective in slow to moderate time-varying fading channels. It was observed that the
performance of the DD RLS-based estimator always outperform that of the DD
NLMS estimator at low mobility and low SNR. In contrast, it was found that the DD
NLMS estimator gives better tracking performance at moderate mobility and higher
SNR. However, as the training rate is reduced, comparable performance with both
estimators is obtained at high SNR. Finally, it has been shown that channel
estimation in TD is more accurate with less complexity compared to its counterpart
in frequency-domain (FD). |
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