OFDM Symbol Timing Acquisition for Collaborative WLAN-based Assisted GPS in Weak Signal Environments
Mahsa Shafiee, Kyle O’Keefe, Gérard Lachapelle · 2012
Due to the ever-growing coverage of WLAN networks, the integration of these networks and GPS has become a promising approach to solving the problems encountered in indoor GPS positioning. 802.11 networks, known by the trade name WiFi, can be employed in several different ways as a complementary positioning technology for GPS navigation and the two can be used in an integrated framework to provide a continuous and robust positioning service. With WiFi becoming more and more ubiquitous, there are many WiFi-enabled devices, which have access to GPS but are not necessarily enabled for GSM/CDMA2000/WiMAX services. In this paper, the concept of WiFi-based A-GPS as a promising approach for receiver-level integration of WiFi and GPS is presented. Although research has been dedicated to accomplish A-GPS systems using assistance information from wireless networks (such as cellular networks), no scheme has yet been published to use 802.11 WLAN signals to provide complete assistance information including frequency, approximate user position and fine time assistance. This paper presents a method of relative time estimation sufficient to enable an effective and complete WiFi-based A-GPS. The proposed system can be deployed in places where WiFi coverage is available and where there is no or limited access to other synchronized systems based on the existing infrastructure. Examples include WiFi enabled mobile devices deployed on university campuses, hospitals and shopping malls, where there may be a need for providing A-GPS services to WiFi users that cannot access other networks.