Time for RTLS? Real-Time Location Systems
Gaining Ground in Healthcare
By Adrian Jennings
The Time Domain PLUS™ Ultra Wideband RTLS line brings 12"-36" location accuracy to healthcare and other verticals.
If you've ever misplaced your keys or tried to locate a package lost in shipment, you already understand some of the benefits of Real-Time Location Systems (RTLS). In healthcare in particular, RTLS that continually monitor the locations of assets, personnel, and patients are gaining traction.
Several factors are driving wider adoption of RTLS. There is a proven return on investment for the technology because it significantly improves the management of assets. Accurate real-time monitoring and location information can increase asset utilization, staff efficiency, and workflow; definitively link an asset to a business process for auditing or compliance; improve billing accuracy; and reduce leasing, service, and capital equipment expenses.
RTLS systems have matured to the point where they provide consistent levels of location accuracy and performance. Costs are continuing to decline and systems are easier to install, therefore driving down the total cost of ownership and the cost per item being located. In addition, software applications are evolving from point-based location and management to robust enterprise-wide standards-based solutions that service multiple departments within a healthcare facility.
Real-Time Location System technologies
The basis of any RTLS system is a tag, which can emit a signal through the air, and a network of receivers, which can locate the tag based on an indication of how far the tag is from at least three receivers (for 2D location). The readers achieve this either by measuring the signal strength of the emitted tag signal (louder means closer) or measuring the time of arrival of the signal (sooner means closer). Of the two methods, the timing method provides better accuracy.
A tag can emit a signal through the air using one of three different methods: either optically (infrared), acoustically (ultrasound), or using radio waves (RF). The pros and cons of each of these approaches are discussed below and the key technical characteristics of each are summarized in Table 1.
Infrared: IR systems can be configured to provide a hyper accurate RTLS solution, but suffer from the serious drawback that the signal does not penetrate walls. A true 2D tracking system would therefore require three receivers in every room, which is usually not attempted due to the high cost. Instead, IR systems are used in a proximity mode, with each receiver indicating which tags it can see. In this way an IR system can provide room level accuracy (since tags in neighboring rooms are not seen), but with a dense deployment of receivers (one per room).
Ultrasound: Ultrasonic systems use very short pulses of ultrasound in order to locate tags. Since ultrasonic signals do not penetrate walls either, the exact same pros and cons that apply to IR systems apply to ultrasonic systems. Additionally, however, a great deal of ultrasonic "noise" in the environment causes interference concerns.
Radio Frequency: Radio Frequency (RF) systems are by far the most widely deployed RTLS systems in use today. The key differentiating feature is that RF signals penetrate walls and allow a significant reduction in infrastructure density compared to IR and ultrasonic systems. There are, however, multiple types of RF RTLS systems: Ultra-High Frequency (UHF), 2.4 GHz, and Ultra Wideband (UWB).
UHF: UHF systems are those with frequency of operation in the hundreds of MHz (typically 433 MHz or 915 MHz). Although these systems are useful for tag detection because they operate over long ranges, they suffer from a major drawback as an RTLS technology: the accuracy of a RF RTLS technology is a function of the frequency bandwidth (the swath of spectrum occupied). In the case of UHF systems, the bandwidth is rather narrow and the accuracy rather poor.
2.4 GHz: Systems that operate in the 2.4 GHz band are called "spread spectrum" because they occupy a wide swath of frequencies. In this way they provide much better accuracy than UHF systems, sometimes even as good as room level.
There are two main classes of 2.4 GHz RTLS: those that conform to the WiFi standard, and those that do not. Those that conform to the WiFi standard allow the reuse of existing WiFi infrastructure. For this reason WiFi RTLS is gaining good momentum on the basis of reduced cost of ownership. Generally speaking, those that do not conform to the WiFi standard provide slightly better accuracy.
WiFi RTLS itself is split onto two main classes: signal strength and time of arrival. As mentioned earlier in this article, time of arrival systems provide better accuracy, but suffer from degraded performance in densely walled buildings. Most time of arrival WiFi systems are therefore deployed outdoors or in wide open spaces. Conversely, although signal strength WiFi suffers from poorer location accuracy, it works well in densely walled environments, and almost not at all outside or in wide open spaces.
Ultra Wideband: As the name implies, ultra wideband (often abbreviated to "UWB") systems occupy the widest swath of spectrum of any of the RTLS technologies, and consequently offer the best accuracy. Like WiFi, a UWB system can operate in signal strength or time of arrival modes, with the time of arrival mode providing location as accurately as 12".
UWB systems have the added advantage of maintaining good time of arrival performance on densely walled environments which make it a popular choice for providing bed-level accuracy in healthcare environments. Its ability to simultaneously locate many thousands of tags is also beneficial for some applications.
Choosing the correct RTLS technology
The task of choosing the correct RTLS technology is mostly one of defining the problems that it will be required to solve. Since each problem has its own set of RTLS requirements, matching the correct technology becomes a task of selecting the system with the best match of capabilities.
The first step is to define the set of problems at hand, and then to pick one of the following attributes that best describes what you are trying to achieve. Each of these applies equally to caregivers, patients, and equipment.
Presence: This is literally "accounting" for people and equipment. The location accuracy required is minimal, with the emphasis on long range coverage:
"Is Doctor D somewhere in the building?"
Whereabouts: The next level of accuracy offers the whereabouts of people and equipment. This is the lowest accuracy version of RTLS:
"In which part of the hospital is Patient P currently undergoing treatment?"
"Is Nurse N still down in the ED?"
Vicinity: RTLS installations really start to show their value when there is a desire to find people and equipment. "Vicinity" here means finding a person or object to within a few rooms, or even the exact room.
"Where is a spare IV pump?"
"Where is the nearest nurse?"
"Why has Patient P been in the waiting room for so long?"
Activity: Understanding the activity of people and equipment enables a large number of applications, but requires the best location accuracy in order to assess activities and interactions.
"For how long has IV pump 32 been in use by Patient P?"
"Has Patient P been seen by Doctor D yet?"
"Has Alzheimer Patient A been bathed with the
required frequency this week?"
"Has Anesthetist A seen Patient P yet, or should Surgeon S be directed to a different operating room? "
"Is the Drug D being administered to the correct patient and by a qualified staff member? "
"Why are all the crash carts in the same equipment closet and not distributed about the ED? "
It's clear from this list that as location accuracy increases, so too does the granularity of information provided, as well as the number of problems solved. It is often the case, however, that the total cost of ownership also increases with fidelity, so a balance must be struck to find the correct choice.
Table 2 summarizes these applications (presence, whereabouts, vicinity, and activity) and rates whether each technology is the best choice, a good choice (although a better one exists), a poor choice (it will do the job, but not reliably), or the wrong choice (it simply won't work) in an indoor healthcare environment with many walls. Remember, a technology can be a poor choice either because its location accuracy is poor, or so good that it's overkill.
In the table at right, note that UHF wins the presence category because it has the best wall penetration and therefore the widest coverage area per infrastructure node. If a very high density of tags exists (thousands per node), UWB becomes the best solution. Signal strength WiFi wins in the whereabouts and vicinity categories chiefly because it is possible to reuse existing WiFi infrastructure in order to enable this level of RTLS. UWB wins the activity category since it is the only technology able to deliver the precision required.
No matter what type of RTLS serves your needs, there's a right combination that can help you better monitor both equipment and personnel to significantly improve how you manage your assets.
Adrian Jennings is Chief Technology Officer at Time Domain Corporation. He leads R &D for Time Domain's UWB products and is responsible for defining the company's technology, product strategy and product development road map to meet worldwide market demand. He can be reached at adrian.jennings@timedomain.com.
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