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Unit 12: Space-based Wireless WANs

of our daily lives. We see and recognize their use in weather reports, television transmission Notes
by DIRECTV and the DISH Network, and everyday telephone calls. In many other instances,
satellites play a background role that escapes our notice:

z z Some newspapers and magazines are more timely because they transmit their text and
images to multiple printing sites via satellite to speed local distribution.
z z Before sending signals down the wire into our houses, cable television depends on satellites
to distribute its transmissions.

z z The most reliable taxi and limousine drivers are sometimes using the satellite-based Global
Positioning System (GPS) to take us to the proper destination.

z z The goods we buy often reach distributors and retailers more efficiently and safely because
trucking firms track the progress of their vehicles with the same GPS. Sometimes firms will
even tell their drivers that they are driving too fast.

z z Emergency radio beacons from downed aircraft and distressed ships may reach search-
and-rescue teams when satellites relay the signal

Did u know? Business radio and TV
Narrowcasting or business TV and radio is a term used for satellite broadcasters who
use transmission time to reach a very specific audience. Technically speaking, there is
no difference with broadcast satellite TV applications described in the previous section.
Digital television has made it possible to distribute information within organisations and
companies that are geographically dispersed, or to deliver distance education. Similarly,
digital radio allows for the delivery of radio services to relatively small closed user groups.
MPEG-2/DVB technology is the dominant standard for digital television, but other
computer-based media coding techniques (such as MPEG-1, Real Video, etc) are also used
to embed video and/or audio into data streams, often integrated with other multimedia or
Internet services. Transmission via satellite requires there to be digital receivers available
at relatively low prices on the consumer market. The advantage is that more advanced or
popular audio coding techniques (for example MP3) can also be used and that the same
stream can be used for other applications, such as data distribution, outside broadcast
hours.

12.1.3 Satellite Applications

Advances in satellite technology have given rise to a healthy satellite services sector that
provides various services to broadcasters, Internet service providers(ISPs), governments, the
military, and other sectors. There are three types of communication services that satellites
provide: telecommunications, broadcasting, and data communications. Telecommunication
services include telephone calls and services provided totelephone companies, as well as wireless,
mobile, and cellular network providers.
Broadcasting services include radio and television delivered directly to the consumer and mobile
broadcasting services. DTH, or satellite television, services (such as the DirecTV and DISH
Network services in the United States) are received directly by households. Cable and network
programming is delivered to local stations and affiliates largely via satellite. Satellites also play
an important role in delivering programming to cell phones and other mobile devices, such as
personal digital assistants and laptops.
Data communications involve the transfer of data from one point to another. Corporations and
organizations that require financial and other information to be exchanged between their various
locations use satellites to facilitate the transfer of data through the use of very small-aperture
terminal (VSAT) networks. With the growth of the Internet, a significant amount ofInternet traffic
goes through satellites, making ISPs one of the largest customers for satellite services.

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