Location awareness is an important capability for mobile
computing. Yet inexpensive, pervasive positioning -- a requirement for
wide-scale adoption of location-aware computing -- has been
elusive. We demonstrate a radio beacon-based approach to location,
called Place Lab, that can overcome the lack of ubiquity and high-cost
found in existing location sensing approaches. Using Place Lab,
commodity laptops, PDAs and cell phones estimate their position by
listening for the cell IDs of fixed radio beacons, such as wireless
access points, and referencing the beacons’ positions in a cached
database. We present experimental results showing that 802.11 and GSM
beacons are sufficiently pervasive in the greater Seattle area to
achieve 20-30 meter median accuracy with nearly 100% coverage measured
by availability in people’s daily lives.