Radio Frequency Identification (RFID) has been in existence for several decades and is only now obtaining wide spread adoption in the marketplace; though there is still confusion about the different types and how they are used. Added to this confusion is a new term, Real Time Locating System (RTLS). It substitutes for GPS indoors where it doesn’t function well. Using active RFID, RTLS provides a precise x, y coordinate location; and accurately answers the question, “Where”?
Aside from presence detection and identification of tags, RFID is able to perform various types of locating. Both passive and active technologies are capable of performing basic chokepoint locating while the RTLS technology, which is built upon active RFID technology, is capable of performing more sophisticated precision locating, such as triangulation.
See the Technology Comparison diagram alongside.
In chokepoint locating there are a series of radio frequency (RF) coverage areas or zones of coverage, established by the presence of an RFID reader and its associated antenna within a defined space. (See figure below) The actual size of a chokepoint area can be varied based on the vendor hardware being used and/or parameter settings in the system. (The circles C1 to C13 represent the chokepoints).
As tagged objects move through a chokepoint they are recorded, typically in a software database. The location of an object is determined by looking at the historical path created by the records of 2 or 3 chokepoints through which an object has passed (point to point locating). Resolution is increased by adding more chokepoints to the environment. This method of locating has its limitations:
- Not true real-time location information
- location finding is down to the last choke point passed
- chokepoints can cause bottlenecks in processes
- if ‘holes’ exist allowing chokepoints to be bypassed, data becomes inaccurate
However, chokepoints are ideal for capturing when items arrive or depart a site, building, or work area if that is simply what needs to be achieved.
Triangulated / Trilaterated Location
RTLS provides precise and current real time locating,and functions by using the signal from a tag to triangulate in 2D (trilaterate) its position. The locating accuracy is determined by the density of the triangulation points in the system. The device used as the triangulation point depends on the type of RTLS technology being utilized. Conventional RTLS uses access points or sensors for the triangulation points. These devices are anywhere from $1000-$5000 and require power and/or network connectivity. Like chokepoints, each access point will cost approximately $8,000 or $9,000 to deploy.
This method provides a less precise identification of asset location in an RTLS. In this method, assets are located to within a room or defined area (zone), but not to where exactly within that zone. Typically one or more access points or sensors will define each zone, with tags located to a zone by their proximity to the nearest sensor. RFind allows for zones to be logically defined within a trilateral location area, allowing for this simpler method to be employed wherever it is appropriate.
RFind offers a unique extension of trilateral locating: ‘Slot & Sequencing‘. This method employs additional algorithms to work out the sequence of assets – either while moving along a path or while stationary – in a defined parking area or lay-down yard. Each ‘slot’ / parking bay / asset location is logically defined and only one asset or vehicle can occupy a slot at a time.
RFind’s Tag to Tag™ communication technology uses the inexpensive active tags that are present in the environment as the triangulation or reference points for the system.
These tags, which average in price around $50, are fully self-contained and do not require any cabling and even light up as a visual guide to the asset. They are capable of performing the same duty as a triangulation engine in the traditional RTLS systems and require little infrastructure in the environment. The tags blanket even heavy metallic environments with assured signal integrity for low-cost RFID coverage and increased reliability.
Chokepoints and triangulation using access points is a very costly approach to locating. Increasing the accuracy of these two approaches presents an exponential increase in the overall cost of the infrastructure. By attacking the traditional high infrastructure cost associated with these methods, trilateral targeting using RFind’s Tag to Tag™ communication technology, makes RTLS truly affordable and offers the promise for ubiquitous use and deployment. As a side benefit, RFind’s technology provides the lowest cost vs. location granularity of all the locating approaches — as granular as 15 feet (5 meters) or even less in some applications.
An RFind system can perform simple presence detection, identification, chokepoint / point to point locating and RTLS, bringing all key location methods together in one system. RFind’s Tag to Tag™ communication technology offers the best option for users with a need for precise GPS type asset locating ability, indoors or outdoors. With RFind, the most pragmatic and appropriate combination of locating techniques for your needs can be delivered with the same basic hardware, in one simple, highly cost-effective system.