Date Added: Jul 2012
Mobile phones are increasingly being equipped with hardware and software services that allow them to determine their locations; however, support for building location-based applications remains a challenging problem. The most widely used localization technology in smart phones is GPS, but it rarely works indoors and provides low energy efficiency. Cell tower-based localization is widely available, but can provide very poor accuracy without a fingerprint profile. WiFi localization, when available, provides reasonable accuracy, but is also much less effective in other areas. Constandache et al. proposed an Escort system to assist in localizing and tracking others in a public place without requiring either GPS, WiFi, war-driving, maps, or floor plans.