Real Time Location Systems (RTLS)
Real Time Location Systems (RTLS) describe a class of Systems that provides information in Real-Time about the location of objects, animals, people and goods.
The five key criteria for indoor location systems are:
- Accuracy and confidence in the localisation results. With openRTLS UWB solution 1 to 30cm accuracy (1cm level with oversampling, multiple nodes and fine-calibration). According to EU commision research(1) and practical experience only wideband system deliver reliable accurate results indoor. How about accuracy of other systems? Many non-UWB systems eq Bluetooth low energy and Wifi claim sub meter performance in the lab at fixed local condition and at close range to the reference points. In practical real life application, the reference points are many meters away, variations in the amount of people and objects degrades the system performance to many meters accuracy. UWB based RTLS systems degrades in centimeters in simular situations.
- Range. Indoor ~30meter and outdoor ~800m (LOS=line of sight, 6.8Mbps using long range antenna)
- Density. The amount of mobile tags which can be tracked. Limits are ~80000 node's per 200m2
- Cost of hardware and installation. Decawave/openRTLS: 1 to 6 usd/m2 including installation, depending on type of building
- Power consumption. With the world lowest power consumption for UWB tags can last for more then 9 years on one charge. The idle/sleep current is 65nA which provides a lifespan of 8 years on a coincell. With a position update rate of one per 10 seconds using a common 600mAh battery the tags last 5 years.
note1: CEPT EU commision report 34 on UWB
Outdoor use of UWB anchors (the fixed reference points) is permitted for sites who register ECC Report 167 . Tags used outdoor do not need registration because they are not seen as a fixed outdoor installation. Outdoor use requires a special version of the proprietary TDOA.
Standard out of the box system perform at sub 10cm accuracy in LOS condition. Anchors setup using autopositioning to have the system define anchors positions by itself. For higher accuracy use a total station like sokkia CX105 to measure anchor/reference position with mm accuracy. Below a IEEE report on accuracy of the openRTLS system versus Decawave standard firmware and bespoon factory firmware. For example the circle of the bespoon looks round because of averaging the measurements. This results in a smaller circle compared to the realworld. The system will continuously provide an additional position error. When averaging 2 points on a circle the average is 0. Using averaging to improve accuracy is not a good way when motion of the target is nonlinear. OpenRTLS use more expensive electronics around the chip to improve accuracy, signal steepness and filter out of band signals.
Decawave versus Bespoon versus openRTLS accuracy.
IEEE 12th international conference on Ubiquitous Intelligence and Computing [J. Wang, A. K. Raja, and Z. Pang] “Prototyping and Experimental
Comparison of IR-UWB Based High Precision Localization
Technologies” ABB corporate research team
Real Time: Information on the location of the relevant object / person is available now or with a very short latency.
Location: The system provides information on the position of an object / person in a form that can be used to relate them to their environment:
- as a symbol overlaid on a map or a floor plan
- as a audible tone that indicates the proximity to the object
- some other method that provides meaningful information to the users of the system
System: This information is gathered, processed and delivered using a collection of hardware and software technologies in an organized and structured way
The most pervasive example of an RTLS is GPS. The problems begin when you go indoors however. GPS doesn't work indoors so all the tracking and location functionality that GPS provides suddenly disappears. But long before the advent of GPS people across a broad range of industries were examining their business processes and they began to realize that with accurate location information they could, in many cases, transform those businesses or at the very least make considerable improvements in costs, service and profits. Since then people have been searching for reliable, accurate location technology that could be applied to their business process. The advent of cost-effective wireless technology has led to many attempts to apply it to RTLS some more successful than others.
The problems with the existing solutions and restrictions on mass adoption were:
- Location precision
- Power consumption
- Interference and multi-path
- Environment dependent tailor-made systems
Decawave, a pioneering fabless semiconductor company from Ireland, solved all these problems by developing the DW1000; a complete, single chip CMOS Ultra-Wideband IC based on the IEEE 802.15.4a UWB standard.
OpenRTLS uses 2 different type of technologies to determine both position, orientation and movement.
- UWB (ultrawide band) radio for accurate indoor & outdoor localisation
- MEMS sensors measuring acceleration, rotation, changes in magnetic field and pressure for localisation, orientation and movement characteristics
UWB is also used for (secure) datacommunication.
The device to be tracked is reffered to as 'tag'. Tags can have a wide variety of additional features like button's, display, haptic feedback, speakers and or microphones beside one or 2 radio chips and mems sensors. On request and depending on the requirements a custom made tag can be created in 3 to 10 weeks period. Standard tags are available in the store.
Most projects are installed in and around existing buildings. Easy installation, autocalibration and cost effective reference points called 'anchors' are key benefits of openRTLS. Most projects require TDOA (time difference of arrival). In a TDOA configuration the 'tag' transmit for a very short period (approx. 77 micro second). all anchors in reach receive the signal and forward the information to the IT-network. The forwarding of the position and other relevant tag information can be forwarded wirelessly or via standard IT-network infrastructure. Because of the very short transmit time battery operated tags can last for years and many tags can be tracked with a high position update rate (100 times a second to one time per 24 hours).