الفهرس 
Overview of Multipath Mitigation TechniquesOnly 14 pages are availabe for public view
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Abstract
Global positioning system (GPS) is well known as a versatile global tool for
positioning and navigation. Now, it has also become the primary tool for time and
frequency adjustment all over the world, especially after the deactivation of selective
availability (SA). There are several sources of error that severely degrade the accuracy
of all forms of GPS measurements. After the deactivation of SA, multipath can be
considered the most severe error source in GPS measurements for both standalone and
differential modes. Therefore, there are many multipath mitigation techniques in the
literature have been proposed to eliminate or reduce its effects. These techniques
range from antenna design to receiver architecture design and post-processing of
observables.
The work in this thesis can be divided into four main parts. The first part gives a
detailed overview of the GPS basics. This is followed by an overview of the time and
frequency measurements using the GPS. Then, we discuss the different error sources
that constitute the GPS error budget. This is followed by an overview of the generic
GPS receiver block diagram, carrier and code tracking loops. At the end of this part,
we discuss the receiver correlation/ discrimination model built around a variable delay
lock loop (DLL) implementation. Finally, we use this model to investigate and
illustrate multipath effects on the code-phase tracking of the ranging signal and
pseudorange measurement.
In the second part, we propose a modified short-multipath-insensitive code loop
discriminator (MSMICLD) using a non-coherent dot-product power discriminator
function. The proposed discriminator is insensitive to short multipath that has
relative delays of less than 0.5 chips (146.6 m). The MSMICLD is modeled using
MATLAB and its performance is evaluated with and without multipath for three
different types of receivers; unlimited pre-correlation (front-end) bandwidth (BW),
2 MHz pre-correlation BW and 8 MHz pre-correlation BW. The code loop tracking
errors due to multipath for the proposed discriminator and the narrow correlator
(NC) loop are determined and compared for the three cases. Moreover, the
performance of the proposed MSMICLD is compared with the conventional shortmultipath
insensitive code loop discriminator (SMICLD) in the three cases.
In the third part, we propose a new discriminator function, namely all multipaths
insensitive code loop discriminator (AMICLD), which is insensitive to the multipaths
regardless of their relative delays. The proposed discriminator is implemented using a noncoherent
dot-product power (DPP) discriminator function. The performance of the proposed
discriminator is validated with and without multipaths for three different types of receivers;
infinite pre-correlation BW, 2 MHz pre-correlation BW and 8 MHz pre-correlation BW.
Moreover, the performance of the proposed AMICLD is compared with that of the
conventional multipath insensitive delay lock loop (MIDLL) discriminator.
In the fourth part, we validate the performance of the AMICLD against that of the
MIDLL discriminator in the presence of multipaths with practical scenario.