|RTLS is used to identify and locate objects, assets or individuals automatically in real time. The goal of RTLS is to continuously track the location of the targets. It works with the help of a tag that is attached to the target from which wireless signals are sent and received by the readers. The readers are usually fixed at predetermined positions and they transmit the location data to the software, which then interprets the exact location visually to the end user. Examples of real-time locating systems include tracking automobiles through an assembly line, locating pallets of merchandise in a warehouse, or finding medical equipment in a hospital.
The physical layer of RTLS technology is usually some form of radio frequency (RF) communication, but some systems use optical (usually infrared) or acoustic (usually ultrasound) technology instead of or in addition to RF. Tags and fixed reference points can be transmitters, receivers, or both, resulting in numerous possible technology combinations. RTLS can be used numerous logistical or operational areas such as: locating and managing assets in a facility, sending location triggered alerts, maintaining proper staffing levels in operational areas.
RTLS are generally used in indoor and/or confined areas, such as buildings, and do not provide global coverage like GPS. RTLS tags are affixed to mobile items to be tracked or managed. RTLS reference points, which can be either transmitters or receivers, are spaced throughout a building (or similar area of interest) to provide the desired tag coverage. In most cases, the more RTLS reference points that are installed, the better the location accuracy, until the technology limitations are reached.
A number of disparate system designs are all referred to as "real-time locating systems", but there are two primary system design elements:
Locating at choke points:
The simplest form of choke point locating is where short range ID signals from a moving tag are received by a single fixed reader in a sensory network, thus indicating the location coincidence of reader and tag. Alternately, a choke point identifier can be received by the moving tag, and then relayed, usually via a second wireless channel, to a location processor. Accuracy is usually defined by the sphere spanned with the reach of the choke point transmitter or receiver. The use of directional antennas, or technologies such as infrared or ultrasound that are blocked by room partitions, can support choke points of various geometries.
Locating in relative coordinates:
ID signals from a tag is received by a multiplicity of readers in a sensory network, and a position is estimated using one or more locating algorithms, such as trilateration, multilateration, or triangulation. Equivalently, ID signals from several RTLS reference points can be received by a tag, and relayed back to a location processor. Localization with multiple reference points requires that distances between reference points in the sensory network be known in order to precisely locate a tag, and the determination of distances is called ranging.
Another way to calculate relative location is if mobile tags communicate directly with each other, then relay this information to a location processor.
RF trilateration uses estimated ranges from multiple receivers to estimate the location of a tag. RF triangulation uses the angles at which the RF signals arrive at multiple receivers to estimate the location of a tag. Many obstructions, such as walls or furniture, can distort the estimated range and angle readings leading to varied qualities of location estimate. Estimation-based locating is often measured in accuracy for a given distance, such as 90% accurate for 10 meter range.
Systems that use locating technologies that do not go through walls, such as infrared or ultrasound, tend to be more accurate in an indoor environment because only tags and receivers that have line of sight (or near line of sight) can communicate.
RTLS can be used numerous logistical or operational areas such as:
- locate and manage assets within a facility, such as finding a misplaced tool cart in a warehouse or medical equipment
- notification of new locations, such as an alert if a tool cart improperly has left the facility
- to combine identity of multiple items placed in a single location, such as on a pallet
- to locate customers, for example in a restaurant, for delivery of food or service
- to maintain proper staffing levels of operational areas, such as ensuring guards are in the proper locations in a correctional facility
- to quickly and automatically account for all staff after or during an emergency evacuation
- to automatically track and time stamp the progress of people or assets through a process, such as following a patient's - emergency room wait time, time spent in the operating room, and total time until discharge. Such a system can be used for process improvement
- clinical-grade locating to support acute care capacity management
Types of technologies used:
- There is a wide variety of systems concepts and designs to provide real-time locating.
- Active radio frequency identification (Active RFID)
- Active radio frequency identification - infrared hybrid (Active RFID-IR)
- Infrared (IR)
- Optical locating
- Low-frequency signpost identification
- Semi-active radio frequency identification (semi-active RFID)
- Passive RFID RTLS locating via Steerable Phased Array Antennae
- Radio beacon,
- Ultrasound Identification (US-ID)
- Ultrasonic ranging (US-RTLS)
- Ultra-wideband (UWB)
- Wide-over-narrow band
- Wireless Local Area Network (WLAN, Wi-Fi)
- Clustering in noisy ambience,
- Bivalent systems
A general model for selection of the best solution for a locating problem has been constructed at the Radboud University of Nijmegen. Many of these references do not comply with the definitions given in international standardization with ISO/IEC 19762-5 and ISO/IEC 24730-1. However, some aspects of real-time performance are served and aspects of locating are addressed in context of absolute coordinates.
Key vendors: AeroScout, Ekahau, TeleTracking Technologies