1. SATELLITE AND MOBILE NETWORK COMMUNICATION

2. INTRODUCTION
Three applications which make use of satellite technology:
Mobile phone networks
Embedded web technology ( EWT )
Global positioning system ( GPS )

3. MOBILE PHONE NETWORKS
Mobile phone communicate by using towers inside many cells networked together to cover large areas. The towers allow the transmission of data throughout the mobile phone network.

4. Each tower transmits its own cell
Each tower transmits its own cell. If you are driving a car and get to the edge of a cell the mobile phone signal starts to weaken. This is recognized by network and the mobile phone then picks up the signal in one of the adjacent cells. If a person is making a call or sending a text to somebody in a different country then satellite technology is used to enable the communication to take place.

5. Mobile phone technology can now be used by computers
Mobile phone technology can now be used by computers. A plug-in device allows the computer to connect to the mobile provided network, which then allows access to the internet. This service is usually provided through a monthly contract which gives a download limit.

7. Embedded web technology

8. Introduction
Embedded web technology ( EWT ) is a relatively new development that uses the internet in real time to control or interact with a device in the home or a device which is part of an industrial application. The device must contain an embedded microprocessor for this system to work.

9. The device can be controlled by an authorized user from a computer anywhere on a network or from a web-enabled mobile phone.

10. Example
Consider the scenario of an oven equipped with an embedded processor. An authorized person can use their web-enabled mobile phone, for example, to send instructions to control the oven remotely ( e.g. switch it on at a given time, set the timings and set the temperature) from their office before setting off for home. Any device with an embedded microprocessor can be controlled in this way;

11. Examples include a DVD recorder, a washing machine, a central heating system or even a scientific experiment in some remote location ( e.g. in outer space or under the sea).

12. GLOBAL POSITIONING SATELLITE SYSTEMS (GPS)

13. INTRODUCTION
Global Positioning Satellite ( GPS ) systems are used to determine the exact location of a number of modes of transport (e.g. airplanes, cars, ships, etc.). Cars usually refer to GPS as satellite navigation systems ( sat navs).

14. How it works
Satellite surrounds the earth transmit signals to the surface. Computers installed in the mode of transport receive and interpret these signals. Knowing their position on the earth depends on very accurate timing – atomic clocks are used in the satellites which are accurate to within a fraction of a second per day. Each satellite transmits data indicating its position and time. The computer on board the mode of transport calculates its exact position based on the information from at least three satellites

15. In cars, the on-board computer contains pre-stored road maps
In cars, the on-board computer contains pre-stored road maps. With these sat nav systems the car’s exact location, based on satellite positioning, cab be shown on map and the driver can also be given verbal instructions such as: ‘ after 100 meters, take the next left turn onto the A1234’. A screen on the sat nav device will also show the car’s position in relation to the road network.

16. Advantages
The driver does not have to consult paper maps while driving, so it is far safer.
It removes errors, as it can warn drivers about one way streets, streets closures, etc.
The system can warn the driver about the location of speed cameras, again aiding safety.
The system can estimate the time of arrival.

17. 5. It is also possible to program in the fastest route to avoid towns, etc. 6. The system can give useful information such as the location of petrol stations.

18. Disadvantage
If the maps are not kept up to date, they can give incorrect instructions.
Unless the system is sophisticated, road closures, doe to accidents or road works, can cause problems.
Loss of satellite signals can cause problems.
If an incorrect start point or end point is keyed in, the system will give incorrect information.