Abstract-Low

The use of GPS is becoming increasingly popular for real-time navigation systems. To ensure that satellite failures are detected and excluded at the receiver is of high importance for the integrity of the satellite navigation system. The focus of this paper is to implement a fault detection and exclusion algorithm in a software GPS receiver in order to provide timely warnings to the user when it is not advisable to use the GPS system for navigation. The GPS system currently provides some basic integrity information to users via the navigation message, but it is not timely enough for safetycritical applications. RAIM is a means of providing integrity with the capability of detecting when a satellite failure or a measurement error has occurred. It is the simplest and most cost effective technique for integrity monitoring. After applying the iterative fault detection and the exclusion algorithm, a significant improvement in positioning accuracy is achieved.

No abstract

Abstract-This paper evaluates the positioning performance of a single-frequency software GPS receiver using Ionospheric and Tropospheric corrections. While a dual-frequency user has the ability to eliminate the ionosphere error by taking a linear combination of observables, a single-frequency user must remove or calibrate this error by other means. To remove the ionosphere error we take advantage of the Klobuchar correction model, while for troposphere error mitigation the Hopfield correction model is used. Real GPS measurements were gathered using a single frequency receiver and post-processed by our proposed adaptive positioning algorithm. The integrated Klobuchar and Hopfield error correction models yeild a considerable reduction of the vertical error. The positioning algorithm automatically combines all available GPS pseudorange measurements when more than four satellites are in use. Experimental results show that improved standard positioning is achieved after error mitigation.

Ground stations are part of any satellite network, providing communication with satellites. Low Earth Orbit (LEO) satellites are used for public communication and for scientific purposes. The communication quality depends on the performance of the satellite ground station, in addition to that of the satellite. Usually, LEO satellites communicate with ground stations at S-band. Ground stations can communicate with LEO satellites only when the satellite is in their visibility region. The duration of the visibility and so the communication duration vary for each LEO satellite pass over the ground station, since LEO satellites move too fast over the Earth. The range over the same satellite path depends on the look elevation angle from the ground station. The shortest range is achieved under maximal elevation of satellite's path above the ground station. The range variation causes the free space loss changes impacting on link budget. For the downlink performance, of the greatest interest is receiving system signal to noise ratio (S/N) or (S/N 0 ). (S/N) depends on the last end receiving device bandwidth. In order to avoid the effect of the last end receiving device bandwidth, within this paper only the impact of elevation on signal to spectral noise density ratio (S/N 0 ) is considered. Keywords-LEO; satellite; signal to noise ratio; ground stationI.