System-Level Considerations for Signal-of-Opportunity Positioning

Abstract This paper presents a review of four types of signal of opportunity (analogue/digital television - TV, analogue/digital audio, Global System for Mobile Communications - GSM, and Wi-Fi signals) and the implications of using these signals for navigation in terms of: i) problems that affect positioning, ii) exploiting them in dissimilar geographical regions of the world, and iii) positioning techniques and related problems. Deployment in Sydney, Australia is investigated, including Dilution of Precision (DOP) predictions of accuracy. Key words Signals of opportunity, indoor positioning, DOP 1. INTRODUCTION The Global Positioning System (GPS) and Global Navigation Satellite Systems (GNSS) in general are adopted as a de facto positioning technology because of the highly accurate location information they provide; however, this technology fails in particular environments such as indoors or urban canyons, despite increasing demand and commercial potential in these areas. These failures of GNSS are mainly due to the low received signal power and low visibility of satellites in urban/indoor areas. Therefore, non-GNSS navigation technologies are essential for such regions [1]. Utilizing signals of opportunity is a promising alternative navigation means of providing adequate geolocation [2]. Signals of opportunity are existing radio frequency (RF) signals around us, which tend to have much higher power levels and wider coverage in urban/indoor environments than GNSS signals. Furthermore, they can penetrate buildings due to their lower frequencies [3]. While using signals of opportunity also costs less in terms of system implementation than GNSS [4], there are significant problems that need to be considered in employing each of them for positioning, owing to the fact that such terrestrial signals were not designed for location estimation. Signals of opportunity in previous research include analogue/digital television and analogue/digital audio signals transmitted from commercial radio and television broadcasting towers [3]. They also include GSM signals from mobile telephone base stations [3]. Other types of signals of opportunity are ultra-wide band (UWB), ZigBee, and wireless local area networks (WLAN) such as Wi-Fi and Bluetooth [2]. The critical challenge of using signals of opportunity as ranging signals is synchronization. Some signals of opportunity such as Digital Video Broadcasting (DVB), Digital Audio Broadcasting (DAB), WLAN, and Fourth-Generation Communications System 4G use OFDM modulation [5], because of its low sensitivity to radio channel quality, multipath propagation, etc. The big advantage of the OFDM signal is orthogonality between known and random part of the OFDM symbol, so that a known part of the signal can be deployed for ranging without impact of the random part [5]. However, a crucial problem of OFDM is its vulnerability to synchronization errors [6]. In this study, we focus on four major types of signals of opportunity: analogue/digital television, analogue/ digital radio, GSM, and Wi-Fi signals. The aim is to examine these signals from three different points of view: •