Fellow connectologist, Dave Hoglund, has written an interesting white paper on the physics behind indoor positioning systems (IPS). Before your eyes roll up into your head, you shouldn't miss this opportunity to really understand the reasons behind why different real time location systems (RTLS) work better for some applications than others. As I've said before, there is no "best" RFID system.

As with many new technologies, there is a lot of loose usage of terms that vendors employ to describe their system's capabilities. The following excerpt describes the difference between "tracking" and "locating." This may seem like splitting hairs, but as you will see, difference in system capabilities is significant. (Emphasis in the original.)

In the world of indoor positioning systems the term tracking has become somewhat overstated, and overused marketing jargon. The reality is that most companies offering RFLS [radio frequency location system] tracking systems are actually offering locating systems. The distinction between the two should not be lost on those charged with implementing such systems into the facility. Tracking is knowing the full history of the item, as well as its current location. Tracking also provides full insight as to the item's duty cycle as it is being tracked, its status at every step in the duty cycle, and its interaction to other assets or people in the clinical environment. A valid tracking system should be capable of conveying in real-time the assets in-use status, its state of cleanliness, and its operating health as well as maintaining an accurate history of each of these elements. A well designed tracking system goes far beyond the limited capability of locating or providing location knowledge, which merely provides answer to the basic questions of where is my asset, or where is my patient?

If your end goal is simple asset tracking, then a locating system is sufficient. But if you hope to create what IPS vendor Radianse calls "context sensitive medicine" you must have true tracking capabilities (among other things). One of the biggest mistakes I see with RFID (and wireless LANs) is the selection, design and deployment of technology that only meets the immediate need. As a buyer, if you want to leverage an infrastructure investment over multiple applications, you must assess your needs and develop requirements for each of those applications at the beginning. Otherwise you end up re-selecting, re-designing, and re-deploying the same (or different) technology as you address each application in turn. Also note that it is not necessarily a good thing to put everything on the same infrastructure - whether it's a positioning system or a wireless network - when that infrastructure fails everything on it fails too.

The common WLAN re-work scenario starts with wireless (but static) data communications deployed with a rudimentary site survey and throwing access points (APs) up about every 100 meters. When you add a wireless medical device, say an infusion pump that moves with ambulating patients, another site survey and network re-design is required to fill in coverage gaps and ensure successful roaming across APs and subnets. When wireless voice over IP (VoIP) is adopted the process is repeated again, with a new set of requirements around latency, jitter and quality of service. Finally, adding life critical alarms to your WLAN introduces yet another set of requirements and re-work. If you add an RTLS to this WLAN nightmare scenario you re-work the network 5 times - a considerable hidden cost to leverage a common infrastructure.

Like most new technologies, digging down to the really important requirements are self evident after you've deployed an application the first time. The key is how much re-work (and the associated costs) will be required to get it right the first time. Hoglund goes on to describe some of the important requirements for more advanced positioning applications. (Again, emphasis in the original.)

Beyond reporting tag accuracy, there is the tenability of data that must be considered. Aside from reporting the tag's location, how repeatable is the data, and is it accurate and can it be trusted? It is also meaningful to once again note that any worthwhile tracking system should be measured against the number of applications served. This requires pushing concepts beyond location knowledge while providing the passive collection of data for the benefit of tag-to-tag relationships, or tag-to-environment relationships, in effect, creating smart clinical environments. When certain conditions are present, i.e., when a tag enters or exits a predefined area, or as tags come into contact with other tags, certain events may be triggered automatically. For example a tag-to-tag example can be made for proper pairing of mother and infant in the newborn nursery. In another situation a triggering alert could be automatically communicated to Central Supply staff when a piece of medical equipment separates from the patient indicating its out-of-use status while at the same time noting its soiled condition thus preventing further use of the equipment until it is once again cleaned. In all of these situations, the collection of data is made passively without any additional demands placed upon the caregiver.

While this paper was written for Parco Wireless, it is educational in nature. If you want to know the reasons behind tag battery life, positioning accuracy and repeatability, why different systems have different costs and more, be sure to read this white paper.

Pictured right is Parco's ultra wideband tag, which is about the size of a quarter.