CSI Wireless©2004
Specifications subject to change without notice
Page 3
Company Confidential – Limited Distribution
Whenever the Location Tag locator has a new position or status to report, it
contacts the network and transmits the message regardless of roaming status.
Global Positioning System
The Global Positioning System (GPS) is a satellite-based navigation system
operated and maintained by the U.S. Department of Defense. GPS consists of a
constellation of 24 satellites providing worldwide, 24-hour, three-dimensional
(3D) coverage. Although originally conceived for military needs, GPS has a broad
array of civilian applications including timing, surveying, fleet management,
marine, land, aviation, and vehicle navigation. GPS is the most accurate
technology available for navigation. As a satellite-based system, GPS is immune
from the limitations of land-based systems, which have limited coverage and
whose accuracy varies with geographic location and, even under ideal conditions,
cannot compare with GPS. By computing the distance to GPS satellites orbiting
the earth, a GPS receiver can calculate an accurate position. This process is called
satellite ranging. GPS receivers can also provide precise time, speed, and course
measurements that are important for vehicle mobile positioning and
communications applications.
The Location Tag locator includes an advanced eGPS receiver, which provides
the position, course, speed and time information required for asset management
applications and more. The Location Tag’s eGPS receiver features a twelve-
channel digital signal processor (DSP) which operates at the GPS L1 frequency
(1575.42 MHz) and processes the Coarse/Acquisition (C/A) code portion of the
GPS signal and integrates that information with network data.
How does it work? Upon activation, the GPS receiver scans for GPS satellite
signals. The Location Tag must locate and receive signals from at least four
satellites to be able to determine its location. Without eGPS, this process of
locating the satellites, receiving the data and achieving a position fix can take
several minutes. This delay can be problematic for many users and, in some cases,
would make the Location Tag impossible to use.
With eGPS, the wireless network fills in the missing information for the GPS
receiver. This can occur when GPS satellite transmissions are blocked by
buildings or natural obstructions such as heavy tree cover. eGPS allows Location
Tag to operate more quickly and under adverse RF conditions. A network of GPS
receivers across the United States is used to obtain the most up-to-date ephemeris
data from all which allows the receiver to quickly locate the four satellites and
process the data contained in their signals.
The most obvious advantage of eGPS is the significant improvement in battery
life that is achieved. Where normal GPS receivers would last hours, the eGPS
receiver in the Location Tag can last for days. Most users will find they only need
to recharge the Location Tag about every 12 days.
