Accessible Ultrasonic Positioning
IEEE Pervasive Computing
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Particle filters for position sensing with asynchronous ultrasonic beacons
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ALO: An ultrasound system for localization and orientation based on angles
Microelectronics Journal
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All wearable centric location sensing technologies mustaddress the issue of clock synchronisation between signaltransmitting systems and signal receiving systems. GPS receivers,for example, compensate for synchronisation errorsby incorporating a model of the receiver clock offsetin the navigation solution. Drift between satellite clocks isalso monitored to keep signal data in synch with GPS time.Most ultrasonic positioning systems solve the synchronisationproblem by using a second medium for communicationbetween transmitter and receiver devices. The transmittersin these systems emit RF signals (pings) to indicatethe transmission of subsequent ultrasound signals (chirps).By subtracting the arrival time of the ping from that of thechirps, the receiver is able to compute the distance to eachtransmitter.In this paper, we describe an ultrasonic positioning systemthat does not use RF signals to achieve synchronisation.Instead, it exploits a periodic chirp transmission pattern tomodel the receiver's position using chirp reception timesexclusively. Not only does the system improve on the accuracyof previous technologies but it also eliminates bulky RFcircuitry - a definite advantage for wearable applicationswhere component size and weight are critical for usability.