RFID: 802.11 vs. Dedicated Receivers
The RFID news from last week prompted some thoughts on this important enabling technology for improved patient flow. One way to differentiate indoor positioning systems (IPS) is whether they use dedicated (and proprietary0 receivers or garden variety 802.11 access points (APs).
There are some fine 802.11-based indoor positioning systems on the market, but they frequently make too much out of the fact that they use 802.11 APs as receivers rather than dedicated receivers. They imply that using 802.11 APs (which they refer to as “existing infrastructure”) is considerably more cost effective than dedicated solutions (Radianse). As usual, things are a bit more complicated than that. Let's look at the infrastructure question first.
All wireless APs or receivers connect to the hospital local area network (LAN), so all positioning technologies leverage the most expensive infrastructure that's required. It is true that solutions like Ekahau or PanGo use APs that might already be deployed for other purposes, and any investment in wireless LANs, can be leveraged by adding IPS to the other tasks required of that network. The rub is the intended use of your WLAN and how it is designed. Coverage (how much of a facility is covered by APs) and capacity (the maximum number of wireless devices that can connect to APs in a given location) are two key variables in WLAN design.
The key variable for an IPS design is resolution, the ability to indicate the location of an asset or patient within a certain distance (typically 1 to 3 meters). Regardless of technology, in order to provide adequate resolution consistently and reliably, a site survey must be done. This almost always results in adding additional 802.11 APs. And it could mean adding a lot more APs, depending on the original design criteria for the WLAN. The cost of APs is an obvious variable; “thin” APs (like those from AireSpace, Aruba, Symbol and others) can cost as little as a few hundred dollars, an 802.11a AP from Cisco will run you more than $2,000.00.
If you're contemplating using a distributed passive antenna system like InnerWireless, you will have to use dedicated receivers. An IPS system is dependant on multiple antennas so that relative signals can be analyzed to calculate position. The relative location feature of Vocera is also dependent on multiple individual antennas.
Evaluating the total cost of a solution is critical. The advantage of solutions that use dedicated receivers is the ability to optimize a dedicated design for IPS. Systems using 802.11 APs must create a symbiotic relationship with an infrastructure that was not originally intended as an IPS.
An IPS requires RFID tags that are low cost, small in size, and have a long battery life. The kind of communications between a tag and receiver required to accurately determine location is highly specialized. Tags and receivers based on dedicated designs are not encumbered with all the additional capabilities that a system based on 802.11. Dedicated systems can be more easily optimized because there are few constraints to conform to standards. Consequently, dedicated solutions currently produce RFID tags that are smaller and less expensive than those based on 802.11. Receiver units are currently within the price range of 802.11 APs.
Along with infrastructure cost and performance (resolution, tag size, battery life) a key consideration is the tracking application driven by the infrastructure. Suitability to task, usability and reliability are more important to the success of an implementation than almost any other factor (unless it's too expensive to buy). Many IPS are intended to be used with other applciations. This is especially true for patient flow applications and biomed asset management. Integration tools on both sides, the IPS and your target application (say a patient flow app), are critical. Any integration must be timely, reliable and low cost. And of course of ther are lots of questions to be asked and criteria to evaluate.
As with any other recent technology, let the buyer beware.