Information technology -- Real-time locating systems (RTLS) -- Part 2: 2,4 GHz air interface protocol
ISO/IEC 24730 defines two air interface protocols and a single application program interface (API) for real-time locating systems (RTLS) for use in asset management and is intended to allow for compatibility and to encourage interoperability of products for the growing RTLS market.
ISO/IEC 24730-2:2006, the 2,4 GHz air interface protocol, establishes a technical standard for real-time locating systems that operate at an internationally available 2,4 GHz frequency band and that are intended to provide approximate location with frequent updates (for example, several times a minute). In order to be compliant with this standard, compliance with ISO/IEC 24730-2:2006 and ISO/IEC 24730-1 is required.
Real time locating systems are wireless systems with the ability to locate the position of an item anywhere in a defined space (local/campus, wide area/regional, global) at a point in time that is, or is close to, real time. Position is derived by measurements of the physical properties of the radio link.
ISO/IEC 24730-2:2006 specifies the air interface for a system that locates an asset in a controlled area, e.g. warehouse, campus, airport (area of interest is instrumented) - accuracy to 3 m.
There are a further two methods of locating an object which are really RFID rather than RTLS:
- Locating an asset by virtue of the fact that the asset has passed point A at a certain time and has not passed point B.
- Locating an asset by virtue of providing a homing beacon whereby a person with a handheld can find an asset.
The method of location is through identification and location, generally through multi-lateration. The different types are
- Time of Flight Ranging Systems,
- Amplitude Triangulation,
- Time Difference of Arrival (TDOA),
- Angle of Arrival.
ISO/IEC 24730-2:2006 defines the air interface protocol needed for the creation of an RTLS system. There are many types of location algorithms that could be used. An example of a location algorithm is given in Annex A.
ISO/IEC 24730-2:2006 defines a networked location system that provides X-Y coordinates and data telemetry. The system utilizes RTLS transmitters that autonomously generate a direct-sequence spread spectrum radio frequency beacon. These devices may be field programmable and support an optional exciter mode that allows modification of the rate of location update and location of the RTLS device. ISO/IEC 24730 also defines these modes, but does not define the means by which they are accomplished.