الفهرس | Only 14 pages are availabe for public view |
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. |