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To access the contents, click the chapter and section titles.
Wireless Networking Handbook
Combining Location Devices with Wireless WANsLocation devices identify your position on the Earths surface in terms of latitude and longitude. Traditionally, products that provide this type of information have been relatively expensive; therefore, they have mainly been used for providing navigation information to aircraft and ships. In the last few years, however, the size and cost of location devices have shrunk dramatically. Location devices are based on Global Positioning System (GPS) technologya worldwide, satellite-based radio navigation system providing three-dimensional position, velocity, and time information to users having GPS receivers anywhere on or near the surface of the Earth. Today, you can purchase a handheld position indicator for several hundred dollars. With this device and a good map, youre unlikely to get lost. GPS devices tell you your position on earth within a few meters. Plus, many products, such as mapping software, are starting to incorporate GPS technology. The GPS was developed by the U.S. Department of Defense and provides two levels of servicea Standard Positioning Service (SPS) and a Precise Positioning Service (PPS). SPS is a positioning and timing service available to all GPS users as a continuous, worldwide service with no direct charge. SPS provides the capability to obtain horizontal positioning accuracy within 100 meters and vertical positioning accuracy within 140 meters. The PPS is a highly accurate service used by the military to obtain positioning, velocity, and timing information. The GPS satellites operate on two L-band frequencies: L1 (1575.42 MHz) for SPS and L2 (1227.6 MHz) for PPS. The system uses spread spectrum modulation and provides a great deal of resistance to interference. Each satellite transmits a navigation message containing its orbital elements, clock behavior, system time, and status messages. A users GPS receiver can determine its position by obtaining time information from three satellites. Altitude determinations require more than three satellites.
GPS/Wireless ApplicationsThe combination of wireless WAN technologies and location devices offer some interesting applications. The joining of these technologies makes it possible for a mobile element to communicate its exact location to other elements. Many companies are combining CDPD and paging with the Global Positioning System (GPS) in their products, mainly for vehicle tracking. ETEs MobileTrakETE has a product, MobileTrak, which is a portable, low-cost, Automatic Vehicle Locating (AVL) system that works with ETEs line of wireless communications products. MobileTrak combines wireless, two-way packet data communications with GPS to create a low cost, off-the-shelf, AVL system. The MobileTrak system depicts vehicle location on a full color map on either a laptop, desktop PC, or Macintosh that can be integrated with wireless dispatch products from ETE and other companies. The MobileTrak system consists of the following three main components:
In the United States, the MobileTrak Wireless Agent supports both RAM Mobile Data and ARDIS wireless WAN services. Internationally, the MobileTrak Wireless Agent supports DataTAC and Mobitex wireless networks.
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