Ekahau, a Saratoga company that offers a WiFi-based real time locater system, has raised $16 million in financing.

Ekahau’s technology, called RTLS (for Real Time Location Systems), can be considered a competitor to the better known Active Radio Frequency ID (RFID) technology.

Ekahau uses a WiFi location tag, which communicates over the popular 802.11 radio frequency. When a piece of emergency equipment in a hospital is tagged with passive radio tags for identification, Ekahau’s RTLS system can provide the real time location of the patient that is using that equipment.

The $16 million includes $12 million in a second round of funding and $4 million of venture loans and government funding. New investors include several undisclosed investors, with founding investor Nexit Ventures participating.

Competitors in the RTLS area include Aeroscout and Pango.

Here’s Ekahau’s description of why RTLS is better than active RFID:

Passive RFID tags are used primarily for asset identification purposes, as a replacement for bar codes, and they do not provide real time location information. The position of the tag can be captured only when the RFID tag is read either manually or by a fixed reader, at a gate for instance. RFID can be used for location tracking, but only as long as it is feasible to install and wire RFID readers inside buildings. A typical enterprise real-time tracking application however calls for room-level accuracy, and a passive RFID-based solution with a reader at every door would be too expensive. Some active RFID tags can hold real-time location information as well, but they require installation of a costly and proprietary antenna infrastructure. The Ekahau Wi-Fi tag, on the other hand, in addition to ID information also provides reliable real-time location information. This information is based on Wi-Fi access point signals, and is therefore the most cost effective RTLS solution for any enterprise.”