Indoor positioning using FM radio signals

Location based services are becoming an indispensable part of the life. Wide adoption of the Global Positioning System in mobile devices, combined with Wi-Fi and cellular networks, have practically solved the problem of outdoor localization and opened a new market. This, however, is the case only for outdoors. There are numerous areas of ubiquitous computing, which require the knowledge of user position indoors. Awareness of user's location is important in such areas as smart environments, assisted daily living, behaviour analysis studies. Over the past years, a significant effort has been dedicated to development of indoor localization systems. The results vary in characteristics, performance, and cost. Despite the effort, the existing indoor positioning systems are still limited: they either require expensive infrastructure (UWB, ultrasound), have limited coverage (Wi-Fi, Bluetooth, RFID, DECT) or low accuracy (cellular networks). The cost of commercial systems is prohibitive for their wide adoption (Ubisense). The main objective of this thesis was to determine the feasibility of indoor positioning using FM radio signals, generated either by local transmitters or by broadcasting FM stations. The performance of FM localization cannot be simply predicted from other technologies, such as Wi-Fi or GSM, due to significantly lower frequencies (around 100~MHz vs. units of GHz) leading to differences in signal propagation. Moreover, FM represents a popular and well-established technology, readily available in many mobile devices. At the infrastructure side, broadcasting FM stations provide almost ubiquitous coverage, while short-range FM transmitters are available license-free from conventional electronics markets. The results indicate that indoor positioning using broadcasting FM stations outperforms in terms of accuracy both Wi-Fi and GSM indoor localization systems (for confidence levels up to 90% and in all cases, respectively). Due to the passive nature of the client devices, the system can be used in sensitive areas where local radio transmission, such as Wi-Fi or GSM, is prohibited for safety or security reasons. Finally, an FM receiver has significantly lower power consumption than a Wi-Fi module and provides 2.6 to 5.5 times longer battery life in localization mode.