Characterization of the equatorial F2-region plasma drift using doppler interferometry at Parit Raja
The ionosphere has long been used as a medium for long-distance transmission before the advent of satellites. There has now been a resurgence in its research after events that have occured in Iraq and Aceh where, ground-based infrastructures are destroyed from the effects of war or natural disast...
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| Format: | Thesis |
| Language: | English English English |
| Published: |
2013
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| Subjects: | |
| Online Access: | http://eprints.uthm.edu.my/2182/1/24p%20ABDULL%20ZUBI%20AHMAD.pdf http://eprints.uthm.edu.my/2182/2/ABDULL%20ZUBI%20AHMAD%20COPYRIGHT%20DECLARATION.pdf http://eprints.uthm.edu.my/2182/3/ABDULL%20ZUBI%20AHMAD%20WATERMARK.pdf |
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| Summary: | The ionosphere has long been used as a medium for long-distance transmission
before the advent of satellites. There has now been a resurgence in its research after
events that have occured in Iraq and Aceh where, ground-based infrastructures are
destroyed from the effects of war or natural disasters. The bulk of research work in
this area of study which uses the ionosphere as a channel medium comes from
advanced countries representing the midlatitude regions of the world. It is therefore
the objective of this thesis to characterize the behaviour of the ionosphere which is
more representative of the equatorial regions. This work presents the measurements
of plasma drifts from the ionospheric F2-layer at the equatorial station of Parit Raja
(1° 52' N and 103° 48' E) using the technique of Doppler interferometry. Analysis is
carried out from data gathered during periods of low solar and geomagnetic activities
of 2005 with a view to statistically model or characterize its properties. As a result of
plasma drift, Doppler effects are observed on the reflected echoes due to scattering
from the irregular and non-uniform reflection layer. An approximation for the
ionospheric F2-layer as a non-selective flat Rayleigh channel is first developed using
an FIR filter that follows a Jakes’ Doppler channel response with the assumptions
that multipaths are not resolvable and appear as one at the receiver with uniform
Doppler rate. Since the actual ionosphere is non-flat with frequency-selectivity and
also exhibits time-variability, a more realistic modelling of the ionospheric structure
is needed. This is achieved by subdividing the operating bandwidth of the
ionospheric medium into an aggregate of narrowband and orthogonal subchannels,
where each is narrowband enough to possess flat Rayleigh fading. By adopting this
technique of multicarrier transmission, each subchannel can be considered as flat and
uniformly time-varying, which can be practically implemented using an IIR filter.
The effect of variable Doppler rates is addressed by employing the techniques of
upsampling and interpolation. The channel modelling is based on the Jakes Doppler
response for 35 KHz in bandwidth which is more appropriate for equatorial region as
opposed to ITU-R F.1487 that adopts the Gaussian spectral response with 10 KHz of
bandwidth for midlatitude regions. Empirical simulation of results for the developed
models using measured data and the performance measures have been reasonably
accurate in characterizing the channel as having a Jakes Doppler response with
Rayleigh fading within limits of +/-2 Hz Doppler shifts or +/-100 m/s plasma drifts. |
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