Analyses of Mobile Satellite Signal Performance in the Presence of Ground Blockage: A GPS Approach

Abstract

The presence of ground blockages such as buildings or multi-level highways play a very important role in determining the quality of service perceived by the mobile satellite (MS) users. Not only the MS users will experience signal fluctuations, in some cases signal lost might occur. Raw MS propagation data would be able to provide the insight into these crucial problems. The availability of the MS propagation data would enable the effects of ground blockages to be extensively studied and understood in order to minimize them and to provide real-time knowledge about the received signal performance. This paper presents the analyses of the MS propagation data obtained using the cost effective, portable and commercial GPS receiver. The analyses results will show the relationship between the MS received signal performance and the ground blockages. The feasibility of using GPS in the study of MS link performance will also be validated. The outcome of this research work will be useful for MS service providers and network developers to find the optimum methods that can mitigate problems faced by MS users. This paper discusses the MS signal quality problems caused by the presence of ground blockage based on empirical data measured using a cheap but effective portable GPS receiver. MS signal is so sensitive that small changes in the geographical environment can disrupt their signal performance. Two main sources of signal degradation for the MS users are shadowing effect and multipath fading. The shadowing is caused by the presence of obstacles that impedes the line-of-sight (LOS) signal such as building and trees which degrades the received signal quality. Multipath effect is due to the arrival of the reflected LOS signals of different amplitude and phase which can cause signal fluctuations. These reflections are due to the surrounding environment such as buildings, trees and electric poles. Common methods used to study signal performance of the MS system have been done using the existing geo-satellite system or airborne platform [1] - [4]. These methods are complex and costly which limit the number of important propagation data representing many geographical areas to be available to the MS service provider and network developer. Recently, the use of GPS as an alternative to the common method of existing geo-satellite system or airborne platform has been proposed [5] - [6]. Portable GPS receiver imitates the mobile phone. Therefore, the propagation data from the GPS is important and can be useful in the study of the MS signal quality. The GPS system which has a constellation of 21 Medium-Earth-Orbit (MEO) satellites transmitting at L–band (1575.42MHz) provides a cheaper and simpler alternative to obtain MS propagation data. Since GPS receivers are readily available and also able to provide information about signal strength intensity of many satellites at the same time, the current work concentrates on the signal intensity measurement using the portable GPS receiver. This measurement technique allows propagation data for real operating condition to be recorded simultaneously from different satellites at any instant of time for different number of propagation environments (urban, suburban, rural) with different elevations.