Evaluation of indoor location based on combination of AGPS/ HSGPS

Abstract

In this paper, the proposed system depends on the assist GPS (AGPS) idea in order to calculate the user position inside a building by using a roof-antenna (at known position) that has LOS with satellites. The antenna receives navigation data and sends it to the user using a wireless network. The distance between the user and the roof antenna is assumed less than 300m. In this case, the time delay between them is approximately equal to 1 Clear/Acquisition (C/A) code chip period, and it is detected by using autocorrelation with error in cm. In the simulations, real data from a GPS receiver were used. The effect of Geometric Dilution Of Precision (GDOP) on user position calculation is discussed for different GPS times, satellite numbers and combinations of them. The error in user position calculation is directly proportional to GDOP, which is decreased when the number of satellites is increased. GDOP also increases when the user clock bias error is increased, especially when the number of satellites is less than 5; yet, it is not affected by the user position. Generally, the error in user position estimation using this method is small and acceptable for most indoor applications.