Silent whistle: Effective indoor positioning with assistance from acoustic sensing on smartphones

Indoor positioning systems provide location information without the ability to use GPS. Indoor positioning faces challenges of accuracies and pervasiveness. In this paper, we present SilentWhistle, a mobile system that incorporates acoustic information and motion traces on smart phones to locate users. SilentWhistle does not expose the identity of a mobile device as does Bluetooth or Wi-Fi communications. By detecting and filtering the received audio frequencies, we encode the frequencies to location information. When users encounter each other or related beacons, by measuring the relation between sound strength and distance, the initial location information obtained by dead reckoning can be enhanced by triangulations transferred from sound strength. Centralized and distributed models of SilentWhistle can avoid the spreading of incorrect location messages. Our case studies agree on SilentWhistle is capable of obtaining location with error of less than 1.25m.