28-05-2013, 03:29 PM
Wide Area Wireless Data Services
Wide area wireless data services provide wireless data to high-mobility users over a very large coverage area. In these systems a given geographical region is serviced by base stations mounted on towers, rooftops, or mountains.
The base stations can be connected to a backbone wired network or form a multihop ad hoc wireless network. Initial wide area wireless data services had very low data rates, below 10 Kbps, which gradually increased to 20 Kbps. There were two main players providing this service: Motient and Bell South Mobile Data (formerly
RAM Mobile Data). Metricom provided a similar service with a network architecture consisting of a large network of small inexpensive base stations with small coverage areas. The increased efficiency of the small coverage areas
allowed for higher data rates in Metricom, 76 Kbps, than in the other wide-area wireless data systems. However, the high infrastructure cost for Metricom eventually forced it into bankruptcy, and the system was shut down. Some of the infrastructure was bought and is operating in a few areas as Ricochet.The cellular digital packet data (CDPD) system is a wide area wireless data service overlayed on the analog ellular telephone network. CDPD shares the FDMA voice channels of the analog systems, since many of these
channels are idle due to the growth of digital cellular. The CDPD service provides packet data transmission at rates of 19.2 Kbps, and is available throughout the U.S. However, since newer generations of cellular systems also provide data services, CDPD is mostly being replaced by these newer services. Thus, wide ara wireless data services have not been very successful, although emerging systems that offer broadband access may