NDOOR positioning using smartphones has attracted tremendous
interests in recent years due to an increasing
number of location-based applications that require accurate
positioning or continuous tracking in buildings. The Wi-Fi
fingerprinting based approach has become popular due to
its simplicity and leveraging on the widely available Wi-Fi
infrastructure. This approach does not require any specialized
hardware or additional infrastructure support. However,
tracking the location of a mobile user requires frequent
Wi-Fi scanning which is known to be power-hungry for
smartphones. In addition, the accuracy of Wi-Fi fingerprinting
depends on a number of key factors including the number
of Wi-Fi access points deployed, spatial differentiability,
and temporal stability of the radio environment [1].