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Questions and Answers
What are the frequency ranges covered by VHF and UHF bands?
What are the frequency ranges covered by VHF and UHF bands?
30 MHz to 1 GHz.
What advantages does multiplexing provide in telecommunications?
What advantages does multiplexing provide in telecommunications?
It efficiently carries multiple signals over a single medium, reducing transmission costs and making better use of bandwidth.
Define Frequency-Division Multiplexing (FDM) and its principle.
Define Frequency-Division Multiplexing (FDM) and its principle.
FDM assigns different frequency bands to multiple signals, utilizing the fact that the useful bandwidth of the medium exceeds the required bandwidth for a given signal.
What is the main limitation of infrared communication?
What is the main limitation of infrared communication?
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Explain the concept of Synchronous Time-Division Multiplexing (STDM).
Explain the concept of Synchronous Time-Division Multiplexing (STDM).
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What are the two main types of microwave systems?
What are the two main types of microwave systems?
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What are the frequency ranges for microwave and radio communications?
What are the frequency ranges for microwave and radio communications?
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What is the primary function of a parabolic microwave antenna?
What is the primary function of a parabolic microwave antenna?
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How do satellite microwave systems function in terms of frequency bands?
How do satellite microwave systems function in terms of frequency bands?
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Identify one application for terrestrial microwave systems.
Identify one application for terrestrial microwave systems.
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In what frequency range does infrared communication operate?
In what frequency range does infrared communication operate?
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What transmission method is suitable for omnidirectional applications?
What transmission method is suitable for omnidirectional applications?
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What is an example of a communication application for satellites?
What is an example of a communication application for satellites?
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What is the primary characteristic of asynchronous transmission?
What is the primary characteristic of asynchronous transmission?
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Describe the difference in EMI sensitivity between radio and infrared transmission media.
Describe the difference in EMI sensitivity between radio and infrared transmission media.
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What is the advantage of synchronous transmission over asynchronous transmission?
What is the advantage of synchronous transmission over asynchronous transmission?
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In the context of media comparison, what does 'omnidirectional' mean?
In the context of media comparison, what does 'omnidirectional' mean?
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What role do start and stop bits play in asynchronous transmission?
What role do start and stop bits play in asynchronous transmission?
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How does the area of coverage differ for terrestrial microwave and satellite microwave transmission?
How does the area of coverage differ for terrestrial microwave and satellite microwave transmission?
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Why might infrared transmission be preferred in certain applications?
Why might infrared transmission be preferred in certain applications?
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What must be synchronized in synchronous transmission to ensure accurate data transfer?
What must be synchronized in synchronous transmission to ensure accurate data transfer?
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Study Notes
Transmission Fundamentals, Lecture 2
-
Objectives:
- Explain the fundamentals of logical media: Microwave, Satellite Radio, and Infrared communications.
- Discuss asynchronous and synchronous transmission operations.
Unguided Media
- Transmission and reception accomplished by antennas.
- Configurations for wireless transmission include:
- Directional
- Omnidirectional
Microwave
- Microwave data communication exists in two forms:
- Terrestrial (earth-based) systems
- Satellite systems
- Functionally similar but with different capabilities.
General Frequency Ranges
-
Microwave: 1 GHz to 40 GHz
- Directional beams possible
- Suitable for point-to-point transmission
- Used for satellite communications
-
Radio: 30 MHz to 1 GHz
- Suitable for omnidirectional applications
-
Infrared: 3 × 1011 to 2 × 1014 Hz
- Useful for local point-to-point/multipoint applications in confined areas
Terrestrial Microwave
- Description: Common microwave antennae (parabolic dish, 3 meters in diameter).
- Fixed rigidly to focus a narrow beam.
- Achieves line-of-sight transmission between antennas.
- Located at heights above ground level.
-
Applications:
- Long-haul telecommunications service
- Short point-to-point links between buildings
Satellite Microwave
- Description: Microwave relay station.
- Links two or more ground-based microwave transmitter/receiver stations.
- Receives transmissions on one frequency band (uplink), amplifies, and transmits on another (downlink) frequency.
-
Applications:
- Television distribution
- Long-distance telephone transmission
- Private business networks
Broadcast Radio
- Radio frequency: 3 kHz to 300 GHz (part of the VHF and UHF bands).
- Applications: FM radio, UHF and VHF TV.
- Coverage: Omnidirectional.
- Sensitivity: Less sensitive to attenuation from rainfall.
- Issues: Multipath interference (reflection from land, water, etc., causing ghosting on TV pictures).
Multiplexing
- Capacity: Transmission medium capacity usually exceeds capacity needed for a single signal.
- Multiplexing: Multiplexing carries multiple signals on a single medium (using a multiplexer).
- Efficiency: More efficient use of the transmission medium.
Reasons for Multiplexing
- Cost per kbps of transmission facility declines with increasing data rates.
- Cost of transmission/receiving equipment declines with increasing data rates.
- Most individual data communication devices require relatively modest data rate support.
Multiplexing Techniques
- Frequency-division multiplexing (FDM): Exploits that the useful bandwidth of the medium exceeds the required bandwidth of a signal.
- Time-division multiplexing (TDM): Leverages the achievable bit rate of the medium exceeding the required data rate of a digital signal.
- Synchronous Time-division multiplexing (STDM): A specific type of TDM.
Infrared
- Uses infrared light.
- Transceivers must be in line of sight.
- Infrared does not penetrate walls.
- No frequency allocation issue (no licensing required).
- Typical uses: TV remote control, IR port.
Unbounded (Unguided) Media Comparison
- Table comparing terrestrial microwave, satellite microwave, infrared, and radio based on coverage area and EMI sensitivity.
Asynchronous and Synchronous Transmission
-
Asynchronous:
- Transmission of a stream of bits between devices.
- Cooperation and agreement between devices is needed.
- Receiver must know bit rate for sampling intervals
- Two types: Asynchronous and Synchronous.
-
Asynchronous (behaviour):
- Each character is treated independently.
- Transmitted one character at a time.
- Each character starts with a start bit for receiver detection.
- Receiver samples each bit to determine character value.
- Used for long data blocks.
- Simple and cheap, but requires a small overhead (2-3 bits per character).
-
Synchronous:
- Used for large blocks of data
- Data formatted into frames with start and stop flags (Preamble and Postamble)
- Stream of bits without start and stop codes.
- To prevent timing drift, the sender and receiver's clocks must be synchronized.
- More efficient (lower overhead) than asynchronous.
References
- "Computer Networks and Internets" by Douglas E. Comer (Prentice Hall, 3rd edition)
- "Data and Computer Communications" by William Stallings (8th edition)
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Description
Explore the key concepts of logical media in this quiz focusing on microwave, satellite radio, and infrared communications. Understand the differences between asynchronous and synchronous transmission operations, as well as various configurations for wireless transmission using antennas. Test your knowledge of unguided media fundamentals.
