P8.5 - Ultrasonic Indoor Positioning for Umpteen Static and Mobile Devices

SENSOR+TEST Conferences 2011
2011-06-07 - 2011-06-09
Proceedings SENSOR 2011
P8 - Mechanical
H. Schweinzer - Vienna University of Technology (Austria)
859 - 864


Indoor ultrasonic (US) systems for locating mobile devices are presented since years differing in operating modes and various parameters. This paper depicts the alternatives and derives a positioning system, called LOSNUS (Locating of Sensor Nodes by UltraSound), which is directed at supporting the locating of umpteen static devices together with mobile nodes.
In factory and building automation numerous sensor and actuator devices are often deployed which are connected to a control network or a wireless sensor network (WSN). Primarily being crucial parameters for application tasks, device positions can support important service functions. They are especially useful in repetitively performed locating processes, e.g. maintenance in case of dislocated devices, device integration in a WSN on base of the position, and network security.
Mainly directed towards low-cost realization, LOSNUS is realized as a centralized system. Only one control unit per room is used for sequentially activating US transmitters installed at known static positions in the room via individual cables. All localized devices receive the transmitted signals in parallel. Beside of eventually local pre-processing, the minimal reactions of devices are storing received US data and transferring it via e.g. WSN to the location server. This server is the only unit which has full information enabling to compute device positions. The used method of calculating the positions is Time-Difference-of-Arrival (TDoA).
The locating process delivers a high position accuracy of ~10mm. The locating sequence uses exactly defined delays between signal transmissions which are sufficient that the received Line-of-Sight signals of consecutive transmitters are not overlapping. Nevertheless, broadband transmitters are used for sending coded signals which result in a typical locating rate of 10 cycles per second. A test system was set up to show the functionality of the locating system.
Only a few additional components within a device are necessary for US signal receiving that can be realized cost efficiently: a microphone, analog amplifying and filtering, and a comparator for 1-bit (polarity) conversion of the signal. With a sampling rate of 1 MS/s distances are measured with accuracy better than 1mm.