User's Manual

©WhereNet Corp. June 2001 TFF-1015-000-4589_UserMan_rev_08_30_05 Page 4
Introduction
This User Guide describes the features, communication formats, configuration, and operation of the WhereTag. It includes
everything needed to be able to configure the tag and the communications between the tag and a host system.
Appendix A is a complete description of all the WhereTag commands together with examples of how they are
used to set up and operate the WhereTag. Appendix B is a physical description of the tag.
This chapter briefly describes the major features and components of the Real Time Location System.
The Real Time Location System
The WhereNet system tracks and locates items tagged with a WhereTag. Each tag emits short, low power bursts of widely
spread spectrum radio energy. These bursts are received by the system infrastructure. The infrastructure calculates the
location of the tagged item based on the different arrival times of the burst.
The WhereTag III HO or ST is a compact battery operated radio frequency device. It is a component of the
WhereNet Real Time Location System.
The WhereNet Real Time Locating System (RTLS) is a precise local locating system with robust wireless
telemetry capabilities. Its integrated architecture meets all the requirements for an enterprise-wide wireless infrastructure
including locating, telemetry, and high-speed wireless communications.
WhereTags
WhereTags are attached to assets whose status must be quickly and accurately monitored. Examples are the
movement of a shipping container through a loading yard or a trailer through a warehousing facility.
RTLS uses DSSS RF technology to determine the location of WhereTag transmitting beacons. These
transmissions are extremely low power, about
2 mW (high output options increase this to 54 mW). The transmissions can be received at distances in excess of
1,000 meters outdoors (high output tags operate at up to 3,000 meters).
Because the transmissions are low power and spread across 60 MHz they add almost no RF pollution to
the environment. They can be readily used with wireless LANs and Blue Tooth devices without adversely
affecting the throughput of those systems.
The transmissions from the WhereTags are very resistant to interference because of the large amount of
processing gain. The system is able to receive signals that are below the RF noise floor of the surrounding
environment.
WhereTags are located by measuring the difference in the arrival time of a signal at a minimum of three
fixed-position Location Sensors (the reliability increases if more than three sensors receive the signal). The
WhereTags transmit their keep alive signal at a programmable interval. The Location Sensors are in a grid
formation that ensures that at least three antennas can receive a blink from any place within the site. By
comparing the difference in the arrival time of the beacon signal at each of the receiving antennas the system can
determine the location of the transmitting WhereTag. This type of location determination is called TDOA (Time
Difference Of Arrival). Tags are located to an accuracy of less than ten feet in virtually all environments, indoors
and out. The accuracy can be affected by environmental factors such as concentrations of large metal objects.
Location Sensors
The Location Sensors are interconnected using standard Ethernet or connected wirelessly using 802.11b/g WiFi
compliant communications. One type of Location Sensor, called a Locating Access Point, (LAP) includes a full
802.11b/g Access Point (AP). These integrated APs are from manufacturers such as Cisco, Symbol, and Intermec.