The fast growing popularity of smartphones and tablets enables us to use various intelligent mobile applications. As many of\r\nthose applications require position information, smart mobile devices provide positioning methods such as Global Positioning\r\nSystem (GPS),WiFi-based positioning system (WPS), or Cell-ID-based positioning service. However, those positioning methods\r\nhave different characteristics of energy-efficiency, accuracy, and service availability. In this paper, we present an Energy-Efficient\r\nCollaborative and Opportunistic Positioning System (ECOPS) for heterogeneous mobile devices. ECOPS facilitates a collaborative\r\nenvironment where many mobile devices can opportunistically receive position information over energy-efficient and prevalent\r\nWiFi, broadcasted from a few other devices in the communication range. The position-broadcasting devices in ECOPS have\r\nsufficient battery power and up-to-date location information obtained fromaccurate but energy-inefficient GPS.Aposition receiver\r\nin ECOPS estimates its location using a combination of methods including received signal strength indicators and 2D trilateration.\r\nOur field experiments showthat ECOPS significantly reduces the total energy consumption of deviceswhile achieving an acceptable\r\nlevel of location accuracy. ECOPS can be especially useful for unique resource scarce, infrastructureless, and mission critical\r\nscenarios such as battlefields, border patrol, mountaineering expeditions, and disaster area assistance.
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