Communication Systems Part 9: Wireless Transmission

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Questions and Answers

What is the expected lifetime of a communication satellite?

10 years (correct)

20 years

5 years

15 years

What is required to avoid interference between pairs of transponders?

At least 1 degree

At least 10 degrees

At least 5 degrees

At least 2 degrees (correct)

How many GPS satellites are typically in orbit for the Global Positioning System?

24 (correct)

Which of the following offers the fastest round trip delay?

Low-Earth Orbit Satellites Signup and view all the answers

Which technology is NOT currently suitable for communication?

Medium-Earth Orbit Satellites Signup and view all the answers

What effect do ground stations experience with Low-Earth Orbit Satellites?

They need less power Signup and view all the answers

What is a major benefit of satellite communication in relation to phone call costs?

It remains unaffected by distance Signup and view all the answers

What is essential for the proper functioning of Medium-Earth Orbit Satellites?

Tracking Signup and view all the answers

Which satellite system was an initiative by Motorola for voice communication?

Iridium Signup and view all the answers

What frequency band allocation is performed by the ITU to satellite users primarily aimed at?

Preventing downlink interference with microwave users Signup and view all the answers

What characteristic of radio waves allows them to travel long distances and penetrate buildings?

They are easily generated. Signup and view all the answers

Why might microwave transmissions experience multipath fading?

Delayed waves may cancel the signal. Signup and view all the answers

Which statement accurately describes the behavior of infrared waves?

They do not pass through objects, limiting their use. Signup and view all the answers

What is a disadvantage of using microwave transmission?

They do not penetrate buildings well. Signup and view all the answers

In which frequency band do radio waves bounce off the ionosphere?

HF band Signup and view all the answers

Which feature of microwave transmission makes it easier to manage compared to fiber optics?

It uses only antennas and repeaters. Signup and view all the answers

What is a primary component used in lightwave transmission?

LASER beams Signup and view all the answers

What is a characteristic of very low frequency (VLF) radio waves?

They follow the curvature of the earth. Signup and view all the answers

Which environmental condition does NOT affect laser communication?

High winds Signup and view all the answers

What is a significant limitation of infrared (IR) waves in communication?

They cannot penetrate solid objects. Signup and view all the answers

What type of satellite appears motionless in the sky?

Geostationary satellites Signup and view all the answers

How do radio waves perform in the presence of electrical interference?

Their performance decreases significantly. Signup and view all the answers

Which of the following is a disadvantage of lightwave transmission?

Limited by weather conditions Signup and view all the answers

What advantage do microwave transmissions have over fiber optic technology?

Less need for a right-of-way. Signup and view all the answers

What is a key function of a satellite's transponder?

Listen and amplify signals Signup and view all the answers

At what altitude do geostationary satellites orbit the Earth?

35,800 km Signup and view all the answers

Which phenomenon limits certain altitudes for satellite placement?

Van Allen belts Signup and view all the answers

Which type of orbit is NOT typically associated with geostationary satellites?

High polar orbit Signup and view all the answers

What is the primary role of communication satellites?

To amplify and relay signals Signup and view all the answers

What was one of the first methods used for long-distance signal transmission before modern satellites?

Bouncing signals off the moon Signup and view all the answers

What is the main purpose of Iridium satellites?

To support voice, data, paging, fax, and navigation services Signup and view all the answers

Which characteristic defines Starlink's planned satellite deployment?

Over 5,000 satellites already in orbit as of November 2023 Signup and view all the answers

What issue nearly resulted in the bankruptcy of Iridium?

The launch of mobile phones Signup and view all the answers

What is a significant advantage of using satellites over fiber optics according to the content?

Satellites can be rapidly deployed in critical situations Signup and view all the answers

What latitude coverage strategy is employed by Iridium satellites?

One satellite every 32 degrees latitude Signup and view all the answers

How many necklaces do Iridium satellites form around the Earth?

Six Signup and view all the answers

What is the total planned deployment of Starlink satellites?

12,000 with a possible extension to 42,000 Signup and view all the answers

In what year did Iridium restart its operations to support handheld devices?

2001 Signup and view all the answers

What is one reason why many people may prefer mobile communication over satellite services?

People often have more access to mobile devices than satellite services Signup and view all the answers

Which service is NOT provided by the Iridium satellites?

Weather forecasting Signup and view all the answers

Study Notes

Communication Systems and Computer Networks

Course code: 1404703
Prepared by: Prof. Shawkat K. Guirguis
Part 9
Date: 2024-12-03

Wireless Transmission

Keywords: Electromagnetic Spectrum, Radio Transmission, Microwave Transmission, Infrared and Millimeter Waves, Lightwave Transmission

The Electromagnetic Spectrum

The electromagnetic spectrum shows different frequencies and their corresponding uses in communication.
Radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays are part of the spectrum.
Different communication technologies utilize different parts of the spectrum.
Example technologies associated with frequency ranges include: Twisted pair(LF,MF,HF), Coaxial(AM,FM radio), Satellite(VHF,UHF,SHF,EHF), Terrestrial microwave(VHF,UHF,SHF,EHF), Fiber Optics(VHF,UHF,SHF,EHF)

Radio Transmission

Radio waves can travel long distances and penetrate buildings.
In the VLF, LF, and MF bands, radio waves follow the curvature of the earth.
In the HF band, radio waves bounce off the ionosphere.
Transmitters and receivers don't need to be aligned.
Signals can travel through obstacles, but signal strength decreases with obstacles
Subject to interference from motors and other electrical equipment

Microwave Transmission

Microwaves travel in nearly straight lines and can be focused.
Parabolic antennas are used to increase signal to noise ratios.
Microwaves do not penetrate buildings.
Microwaves can be refracted by the atmosphere.
Delayed signals can arrive out of phase, causing signal cancellation (multipath fading).
Water absorbs microwaves at 4GHz.
Easier to manage than fiber (only towers and repeaters needed), no right of way needed as in fiber

Infrared and Millimeter Waves

Unguided waves are used for short-range applications like remote controls, VCRs, and mice.
Infrared waves do not pass through objects.
There is no interference between rooms when using infrared.

Lightwave Transmission

Primarily uses laser beams.
Requires precise alignment.
Cannot penetrate rain or thick fog.
Heat convection currents can deflect the beam.

Communication Satellites

Types: Geostationary, Polar Orbiting (medium-earth orbit, low-earth orbit)
Satellites are mainly microwave repeaters in the sky.
Satellites use transponders to receive, amplify and retransmit signals
Altitude of satellites determines coverage and duration.
Van Allen belts (highly charged particles) prohibit certain altitudes.

Geostationary Satellites

Orbit at 35,800 km.
Appear stationary.
At least 2 degrees between each pair to avoid interference.
Many transponders use many different frequencies for compensation.
Satellite slot allocation is done through ITU.

Medium/Low-Earth Orbit Satellites

Medium-Earth orbit takes about 6 hours to circle the earth
Low-Earth orbit has a large number of satellites needed for wide coverage.
Ground stations don't need high power.
Round-trip delay is a few milliseconds.
Examples include: Iridium, Globalstar, Teledesic

Other

Starlink is a satellite Internet constellation by SpaceX.
It provides internet coverage to over 60 countries and global mobile phone service in the future.
Starlink has over 5000 satellites in low earth orbit with a goal of 12,000 plus.

Comparing Satellites vs Fiber

Fiber optic cables have greater bandwidth potential than current satellite technology.
Fiber optic cables require more infrastructure
Satellites are often cheaper for initial deployment in situations requesting fast deployment.

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Description

Explore the principles of wireless transmission in this quiz based on Communication Systems Part 9. Learn about the electromagnetic spectrum and its various applications in communication technologies. Test your knowledge on radio transmission and the different frequency ranges utilized in the field.