RTLS (Real time location system) standards

A Real Time Location System (as defined in ISO/IEC 19762-5) is of a combination of wireless hardware and real time software that is used to continuously determine and provide the real time position of assets and resources equipped with services designed to operate with the system.

A number of fixed location nodes are used to determine the relative location of the RTLS tags attached to the assets whose location is being determined. One of various techniques is used to achieve this, including: time travel, differential time travel, and time travel triangulation.

Key relationships with other components

There is some possible overlap and ambiguity with RFID active tags. The main differences are:

  • In an RTLS system, all the items that are being tracked are generally known to the application and are expected to remain within the physical bounds of the RTLS system. This is often a building such as a hospital, office, factory, warehouse, or storage yard with all the capture points connected on a local network. As such the position of RTLS tags is monitored continuously.
  • In an active RFID system, the tags are only read when they come within appropriate communication range, and transmit their identity and other data when within the reading zone. Between reading zones the only "active" function is to maintain any sensor process, if included.

The differences are fairly subtle, and there are likely to be RTLS systems that make use of RFID tags in the following way. If once an RFID tag is within a clearly physically bounded site and its presence is exposed to the entire space domain of that site, then RFID tags and the system might be able to provide some degree of location using basic RTLS techniques.

Equally, RTLS systems might be capable of providing some of the same functionality of active RFID tags. If a limited number of sites are involved in an application, then each site can be set up with an RTLS system. As long as the data that is transferred between sites includes a constant identifier, then each site is capable of tracking the location of the item when within its zone. The extent to which RTLS might encroach on RFID is determined by the fact that there are proposals to extend some of the ISO standards to support the sensors.

Standards

The main ISO standards that have been developed for RTLS have been the work of JTC1 SC31 WG5. The standards cover: application program interface, various short-range (as opposed to radar and satellite-based systems) and conformance and performance methods for systems operating at 2.4 GHz.

Significant development areas

A review of news in the technology press and company product information indicates a trend to overlap applications in the marketplace between active RFID and RTLS. However, from a standardisation point of view, there appears to be no convergence given the fundamentally different air interface protocols and preferred frequencies. Most active tag technologies operate at 433 MHz, while most RTLS systems operate at 2.4 GHz.

Some RFID vendors are adopting or adapting RTLS concepts to provide additional functionality for their products. This is even extending to claimed developments in passive back-scatter RFID tags. Such developments will probably remain proprietary or, if not covered by IP, will still result in product differentiation. Again, this is unlikely to have a direct impact on the standardisation effort other than being an indicator that some RFID features that bring benefits to end users are beyond the scope of the standardisation process. However, the biggest concern is the potential confusion about RTLS and RFID among those developing application standards.