Indoors Data Communications using Airborne Ultrasound

Abstract

We have tested an indoor data communications system based on ultrasound which is the core of an indoor positioning system. Unlike most other such systems, it relies on ultrasound alone. No radio or infrared channel nor any tether is used for the communications. The main hardware components are a tag and a detector. The detector has an Ethernet interface and uses digital signal processing to cope with the acoustic environment and its noise, reverberations and Doppler shift. The attainable range is 10-20 meters and by making a comparison with the range for speech, we find that the range predictions are consistent with our experience. The channel efficiency of the system is found to be somewhat less than for human speech which also has to deal with a similar environment. This comparison is done by using the Shannon channel capacity theorem.

Hybrid ultrasound-RFID indoor positioning: Combining the best of both worlds

“…The papers [5], [6] describe what may be the first successful ultrasound room-level positioning system. The core of the positioning system is a multi-user 40 kHz ultrasound communications system which works fairly consistently over ranges of 10 meters and more.…”

“…This can also be called positioning by confinement. Based on the analysis of [5], [6], it is shown here that this makes the system much more robust as time-delay estimation is no longer needed. Instead one needs to establish communications and transfer a short message with identity information.…”

“…One of the main differences from the ultrasound indoor positioning system of [5], [6] is that the direction of flow of ultrasound is reversed, so the need for humans to wear an ultrasound transmitter is eliminated. This makes it possible to increase the distance between humans and the high-level ultrasound transmitter to several meters.…”

Accuracy of Spread Spectrum Techniques for Ultrasonic Indoor Location

“…The accuracy of the systems deteriorates rapidly in noise. It has been reported that ultrasonic noise in typical office environments is less than 40db/Hz dB [15] so this measure was done within industrial environment. The update rate of the systems is limited since time must be allowed for the reverberation of the pulses to decay before re-sending.…”

Indoor Granular Presence Sensing and Control Messaging With an Ultrasonic Circular Array Sensor

“…A high rate ultrasonic communication system was designed to operate in frequencies in the order of hundreds of kHz [13], [14], while in [15] a bandwidth between 50-110 kHz was used for transmission. In [16] and [17], the feasibility of ultrasonic communications at frequencies in the order of tens of kHz was investigated.…”