Synchronising WiFi access points with GPS time obtained from smartphones to aid localisation

WiFi Access Points (W APs) are readily available everywhere for access to the Internet. Unless specifically designed for localisation applications and their position accurately calibrated, W APs do not offer accurate position calculation and do not know their geographic position. However, Smartphones, with the aid of onboard GPS and WiFi will know their location to within few meters when outdoors. This paper proposes to utilise Smartphones, while outdoors, to sync the clock-time and define the location of any W AP within reach. This is achieved by using Trilateration techniques where the Smartphones become reference stations at several instances in time as they approach available W APs. Also, any W AP position is continuously updated as other Smartphones approach them. Such W APs can later be used as reference stations to aid indoors localisation. Simulation scenarios based on MATLAB implementation has proved the viability of this scheme.