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.)
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.)
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.