This is part 1 of 2 on RTLS. The idea is to give an introductory to RTLS and follow up with the pros and cons of RTLS in relation to an actual implementation.

Since the rise of RFID, everyone has something they want to track. From the big boys in the ranks of Wal-Mart, Metro AG, to small-mid-size inventory based setups, are quickly harvesting every RFID feature to reap its benefits. We have received some enquiries from tagging jewellery (*obviously*) , to producing RFID labels for medical bottles, tracking WIP items on manufacturing floor, to keeping tabs on people/patients real time. So the question is, can “one size” fit all?

Certainly not. RFID comes in several types and each may likely be more suitable for specific applications - (1) Passive based RFID (2) Semi-Passive RFID and (3) Active based RFID. For passive based RFID, they are further sub divided into LF, HF, UHF.

What I hope to share is on the practicality of Active RFID, or the term coined “Real Time Location Systems”. First to explain what it is. Real Time Locations Systems, commonly abbreviated RTLS generally falls into two implementation groups. The first uses RFID technology while the second approach adopts Wireless LAN, specifically what is commonly known as WIFI. It is debatable which technology was first used in RTLS; some say RFID and the other camp claims WIFI.

It was 2002 when we started working on RTLS based projects. Since that time, I have consulted in several projects that make use of RTLS. Our team has also developed several mobile applications using engines such as Ekahau Positioning Engine and Placelab.

Now, there are several options available in the market for RTLS. This is a list of WIFI based RTLS products, and you will notice one on the list is based on open source :

• Ekahau
• AeroScouts
• Radianse
• Pango Networks
• Placelab (open source, active tags not available)
• NIST
• RFIND ( thanks Marilyn!)

At the time of this writing, RTLS systems have also been implemented using Ultrawide Band (UWB) technology. RTLS setup at its basic, consists of a battery operated tag/badge that communicates with readers/beacons strategically placed within a building, park etc. In WIFI based RTLS, the active tag wireless transmits RSSI data to the location engine server on the wireless network. The location engine acts on the Received Signal Strength Indicator (RSSI) information for each device and calculates the coordinates which represent the device’s location on the map.

Not to be confused with passive based RFID, RTLS serves specific usage scenarios which cannot handled well (or efficiently) by HF or UHF RFID systems.

RTLS Use Case : In general RTLS use case will have a specific requirement to track assets or people whose locations are arbitrary at any point of time. For example, in a hospital there is an increasing requirement to track hospital mobile assets such as infusion pumps, beds, wheelchairs. With these assets, there are no associated planned routes that can suggest strategic placements of HF/UHF RFID readers. It is almost impractical to plant RFID interrogators at every corner, on every floor of a facility. Because of the short reading distance of passived based RFID systems, you will need at least one RFID reader every 3 - 5 metres (for HF systems every 1.5 metres) !!

In relation to this, a typical RTLS use case will require the future system in providing very fine granular localized information of its asset. Engines such as those from Ekahau, AeroScouts and NIST can provide tracking average accuracy of mere metres. Walking along corridors, Ekahau Positioning Engine in particular performs localization on average accuracy of one to two metres.

A key deciding factor on using RTLS, as the name implies concerns timing. Active tags being powered by batteries can be programmed to repeatedly send out signals (packets) in very short intervals of time. The location engine consumes these packets calculates the device’s approximate location. Typically active tags is able to “contact” a nearby beacon or access point in distances ranging from 25 metres to 100 metres, depending on the grade of access points used. In stark contrast, passive tags relies fully on RFID readers to power itself. With the uncertainty that a passive tag may be sufficiently close enough to a reader, there is considerably low chances the tag can even be detected to begin with.

In summary a typical RTLS use case will have at least one of the following requirements :

1. No pre-determined path. Need to “find” assets or people who can be anywhere at any point of time.
2. Application needs to track the exact position of an asset or person down to mere metres within the facility
3. The word is real-time. Use case requires real-time monitoring and reporting of the asset or person’s locality, in very short intervals of time (seconds or minutes)
4. Reading distances further than 3 -5 metres on average

Share This

This entry was posted on Saturday, September 8th, 2007 at 4:11 pm and is filed under RTLS, RFID, Learn RFID . You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.