Technologies based on assessing position relative to a number of "beacons" formed by routers and hubs using standard WiFi technologies. A particularly lightweight and innovative approach from the SCYP project makes use of purely signal strength information from unauthenticated beacons. Commercially, Nokia has been working on this technology, demo video here, useful for illustrating the concept.
Pluses of this scheme:
- WiFi antennae are common and will become even more widespread amongst personal mobile devices - no need to distribute additional sensors
- Very low cost to deploying beacon grid - may even be part of an existing WiFi provision
- Fairly cheap requirements for calibration - a few sweeps of the area suffice - FAQ
It is unclear the number of RFID masts would be required to give a decent granularity of location coverage across an institution, or the cost of such a solution. The "Mojix eLocation Solution" is a recent commercial system which insists that it is the "market's first UHF passive RFID Real Time Location System" - which suggests that affordances for any form of fine-grained location over RFID (above simple "swipes" at specially positioned kiosks) may be crude and/or expensive. However, another promising report of passive RFID in a museum context (Skyetek sensors - 1m range) is by Baldwin & Kuriakose at Melbourne.
Hybrid RFID and WiFI positioning
This is a commercial system for location of objects, which seems to be used most in hospitals at the present time. Here's a video demonstration of the tech.
A recent publication on Local positioning systems (Google books link - Kolodziej & Hjelm) surveys the overall accuracies possible with the radio technologies. The following verdict: (p.121) "Most systems using radio technologies such as Bluetooth or Wi-Fi can only pinpoint an item within about 10 to 16 ft (3 ft with site surveying) in an indoor environment. With UWB, Ubisense is able to track to an accuracy of 6in."