Satellite Communication Methods

1. Satellite Communication Methods Chapter 3

2. This presentation will: • Help you understand how satellites are used in the following areas: • Global Positioning (GPS) • Weather • Data transfer systems • Television • You should be able to explain the advantages and disadvantages of using satellites for these applications.

3. Introduction • The first artificial satellite, Sputnik 1, was launched by the Soviet Union in 1957. • By 2009 thousands of satellites had been launched into orbit around the Earth. • These originate from more than 50 countries and have used the satellite launching capabilities of ten nations. • A few hundred satellites are currently operational, whereas thousands of unused satellites and satellite fragments orbit the Earth as space debris.

4. Global Positioning (GPS) • GPS was first used by the US military to locate ground troops. • It was then released to civilians in 1983. • Russia has its own service (GLONASS) and India plans to launch its IRNSS service in 2012 with the European service (Galileo) launching in 2013.

5. Global Positioning - Uses • One of the most common use of GPS technology is in satnav systems found in cars. • However, it is also used in map making, navigation for ships and aeroplanes and also by the military. • Smart phones are also making use of it and apps such as Gowalla are allowing people to ‘tag’ places of interest and mark them onto Google Maps.

6. Global Positioning – How it works • The GPS service makes use of 24 satellites which orbit Earth twice a day. • At any one point there should be at least 4 satellites in line of sight with a GPS device. • The GPS device will attempt to communicate with at least 3 of the devices. • It then uses a method known as trilateration to determine its current location. The green dot represents your current location. This is determined by the location where all three circles cross over each other. The more satellites connected the better the accuracy of the location result.

7. Global Positioning – Pros and Cons

8. Activity • Describe the term: • Global Positioning Remember: Identify, Amplify and Exemplify • Complete the following table in terms of GPS and SatNav systems: (think of at least 3 more for each column)

9. Weather - uses • These satellites are used to monitor weather formations. • They take images of cloud formations which are then analysed. • They are also able to gather data on pollution, ice cover, water temperature and sea levels.

10. Weather – how it works • Weather satellites are either in geostationary orbit or polar orbit. • Geostationary means that the satellite is in a fixed location above the equator. • Polar orbiting means the satellites orbit from north to south and then south to north.

11. Weather– Pros and Cons

12. Activity • Describe what weather satellites are used for. Remember: Identify, Amplify and Exemplify • Describe the differences between a geostationary orbit and a polar orbit.

13. Data transfer • All satellites transfer data. • The type of data that is transmitted varies but essentially they all pass data using the same types of methods. • For more information please refer to the presentation covering Wireless Communications.

14. Television - uses • Because satellites have a high bandwidth more data can be transmitted compared to a regular aerial. • This means a viewer can receive many more channels. • Set-top boxes allow you to view information about the programme you are watching and also provide you with a list of what programmes are currently on and will be broadcast in the future. • Some boxes also allow you to record and now receive Hi-definition television. • Sky Digital are planning on releasing a new 3D service in 2010.

15. Television – how it works • Sky Digital makes use of the Astra satellite system. • You can see the satellites and their coverage below. • The larger the dish you have the more channels you can receive. The following link will allow you to see where all the satellites are in terms of their location and their orbit. http://science.nasa.gov/RealTime/jtrack/3d/JTrack3D.html Please note: Java needs to be installed and enabled on your web browser for this to work.

16. Television – how it works • Television shows were traditionally broadcast via radio waves which came from television masts. • These masts only provided a limited number of frequencies which meant that not many channels could be broadcast. • They also required line of sight meaning they had to be positioned high up on hills or built very tall. • The UK Government are phasing out this type of transmission and replacing with a completely digitalised service which will provide people with more channels at a better quality.

17. Television – how stuff works • The satellites used for broadcasting television signals are in geosynchronous orbit meaning they remain in one place relative to the Earth. • Their orbit is about 35,000 km above the Earth. • This high orbit means they have a better line of sight compared to traditional aerials. This is a nice little web page that explains how it works in more detail: http://streamsurfers.netfirms.com/faq/faq0001_how_it_works.htm

18. Television – how it works • The satellites receive the transmissions from the ground and then broadcast them out to the receiving dish. • It uses a system called Direct Broadcast Satellite (DBS). • The signals are encrypted so that channels can be subscribed to. This allows companies to charge customers extra for pay-per-view programmes. This is a nice little web page that explains how it works in more detail: http://streamsurfers.netfirms.com/faq/faq0001_how_it_works.htm

19. Television – how it works • Satellite dishes are designed to receive the encrypted broadcast signal but it is the job of the set-top box to decode the data. • The box receives the encryption key which allows it to decode subscribed channels.

20. Television – how it works • Broadcast signals are also compressed so that more channels can fit onto one frequency. • The set-top box will also un-compress the signal so that channels can be watched. • A misconception is that data can be sent via the satellite dish. This is untrue – data is sent via the telephone cable (look at the back of your sky box!)

21. Television – pros and cons

22. Activity • Describe how a television is able to receive digital television broadcasts. Remember: Identify, Amplify and Exemplify • Why do you think a television satellite needs to be in geosynchronous orbit?

23. Example exam questions • Describe three features of navigation software. • Why will the location on a map be lost when travelling through a tunnel? • How can driving be made safer using GPS devices such as SatNavs? • State four types of data that can be collected by weather satellites. • Why are photographs collected by polar orbiting satellites much higher in quality compared to photographs collected by satellites in geostationary orbit?

24. Example exam questions • Why are more channels available through satellite television that terrestrial television? • List the equipment required to receive satellite television in the home. • How are signals broadcast using DBS?