1. Transmission Medias
2nd semester

2. Outline Transmission Media Guided Media Wireless Transmission
Antennas and Antenna Gain
Wireless Propagation
Electromagnetic Spectrum

3. Transmission Medias A transmission media is the channel that
provides the connection between the transmitter and the receiver.
moves electromagnetic energy from one or more source to one or more receiver.
Which medium should be used?
Maximize data rate
Maximize distance
Minimize transmission impairments
Minimize cost

4. Types of Transmission Medias
The Transmission media or channels can be classified as :
Bounded (guided) medias : signals are confined to the medium and do not leave it
Unbounded (unguided) medias : the signals originated by the source travel freely into the medium and spread throughout the medium. (Antenna)
Analog Channels: These channels can carry analog signals.
Digital Channels: These channels can carry digital signals.
Examples: electrical cables: twisted pair and coaxial cable and optical fiber
Unguided media employ an antenna for transmitting through air or water

5. Outline Transmission Media Guided Media Wireless Transmission
Antennas and Antenna Gain
Wireless Propagation
Electromagnetic Spectrum

6. Electrical Cables
Transmit electrical signals on a conductor, e.g. copper
Cable carrying electrical current radiates energy, and can pick- up energy from other sources
Can cause interference on other cables
Other sources can cause interference on the cable
Interference results in poor quality signals being received.
To minimize interference:
Keep the cables away from other sources
Design the cables to minimize radiation and pick-up
To minimize interference:
Keep the cable lengths short
Keep the cables away from other sources
Design the cables to minimize radiation and pick-up
Use materials to shield from interference
Organize multiple wires so they do not interfere with each other

7. Twisted Pair Cable
A twisted pair consists of two insulated copper wires twisted together in a helical form.
Two varieties of twisted pair: shielded (STP) and unshielded (UTP); also multiple categories (CAT5)
Most commonly used and least expensive medium
Used in telephone networks and in-building communications
Telephone networks designed for analog signaling (but supporting digital data)
Also used for digital signaling

8. Coaxial Cable
Coaxial cable consists of two conductors. The inner conductor is held inside an insulator with the other conductor woven around it providing a shield. An insulating protective coating called a jacket covers the outer conductor.

9. Coaxial Cable
Provide much more shielding from interference than twisted pair: Higher data rates; more devices on a shared line; Longer distances.
Widely used for cable TV, as well as other audio/video cabling.
Used in long-distance telecommunications, although optical fiber is more relevant now

10. Fiber Optic Cables
These cables carry the transmitted information in the form of a fluctuating beam of light in a glass fiber.

11. Fiber Optic Cables
Used in long-distance telecommunications, as well as telephone systems, LANs, and city-wide networks
Advantages of optical fiber over electrical cables:
1. Lower loss: can transfer larger distances
2. Higher bandwidth: a single fiber is equivalent to 10's or 100's of electrical cables
3. Small size, light weight: lowers cost of installation
4. Electromagnetic isolation

12. Comparison of Guided Media
Electrical Cables
Moderate data rates: 1Gb/s
Maximum distance: 2km (twisted pair); 10km (coaxial)
Cheapest for low data rates
UTP: easy to install, susceptible to interference
STP, Coaxial Cable: rigid, protection against interference
Optical Cables
Very high data rates: 100Gb/s+
Maximum distance: 40km
Expensive equipment, but cost effective for high data rates
Difficult to install

13. Outline Transmission Media Guided Media Wireless Transmission
Antennas and Antenna Gain
Wireless Propagation
Electromagnetic Spectrum

14. Wireless Transmission Model
Common wireless systems for communications include:
Terrestrial microwave, e.g. television transmission
Satellite microwave, e.g. IP star
Broadcast radio, e.g. IEEE WiFi (wireless LAN)
Infrared, e.g. in-home communications

15. Wireless Transmission Model
Transmit electrical signal with power Pt
Tx antenna converts to electromagnetic wave; introduces a gain Gt
Signal loses strength as it propagates; loss L
Rx antenna converts back to electrical signal, gain Gr
Receive signal with power Pr

16. Wireless Transmission Issues
What is the role of an antenna?
What is antenna gain?
How does the signal propagate in different environments?
How much power is lost when it propagates?

17. Outline Transmission Media Guided Media Wireless Transmission
Antennas and Antenna Gain
Wireless Propagation
Electromagnetic Spectrum

18. Antenna
An antenna can be defined as an electrical conductor or system of conductors used either for radiating electromagnetic energy or for collecting electromagnetic energy.
For transmission of a signal, electrical energy  electromagnetic energy
For reception of a signal, electromagnetic energy  electrical energy
For transmission of a signal, electrical energy from the transmitter is converted into electromagnetic energy by the antenna and radiated into the surrounding environment (atmosphere, space, water)
For reception of a signal, electromagnetic energy impinging on the antenna is converted into electrical energy and fed into the receiver.
Waves are within the Radio and Microwave bands of 3kHz to 300 GHz
Antenna characteristics are same for sending or receiving
Direction and propagation of a wave depends on antenna type: Isotropic, Omni-directional , and Directional.

19. Antenna Types
Isotropic antenna radiates power in all directions equally. The actual radiation pattern for the isotropic antenna is a sphere with the antenna at the center. (ideal)
Omni-directional antenna radiates power in all directions on one plane (circle , donut).
Directional antenna: radiates power in particular direction. Dish and Yagi are two common types.

20. Antenna Patterns

21. Antenna Gain
In a transmitting antenna, the gain describes how well the antenna converts electrical power into electromagnetic waves headed in a specified direction.
In a receiving antenna, the gain describes how well the antenna converts electromagnetic waves arriving from a specified direction into electrical power.
The gain of an antenna (in any given direction) is defined as the ratio of the antenna power in a given direction to the power of a isotropic antenna in the same direction.
In a transmitting antenna, the gain describes how well the antenna converts input power into radio waves headed in a specified direction. In a receiving antenna, the gain describes how well the antenna converts radio waves arriving from a specified direction into electrical power.
Gain. The gain of an antenna (in any given direction) is defined as the ratio of the power gain in a given direction to the power gain of a reference antenna in the same direction. It is standard practice to use an isotropic radiator as the reference antenna in this definition. Note that an isotropic radiator would be lossless and that it would radiate its energy equally in all directions. That means that the gain of an isotropic radiator is G = 1 (or 0 dB). It is customary to use the unit dBi (decibels relative to an isotropic radiator) for gain with respect to an isotropic radiator. Gain expressed in dBi is computed using the following formula:
GdBi = 10*Log (GNumeric/GIsotropic) = 10*Log (GNumeric)
Occasionally, a theoretical dipole is used as the reference, so the unit dBd (decibels relative to a dipole) will be used to describe the gain with respect to a dipole. This unit tends to be used when referring to the gain of omnidirectional antennas of higher gain. In the case of these higher gain omnidirectional antennas, their gain in dBd would be an expression of their gain above 2.2 dBi. So if an antenna has a gain of 3 dBd it also has a gain of 5.2 dBi.

22. Isotropic Antenna (2D)
Directional Antenna (2D)
Transmit with same power Pt
Blue shape: at each point, received power is Pr
Measure received power 1m away to be Px
Gain of antenna (compared to isotropic) is Px/Pr
Transmit with power Pt
Measure received power 1m away to be Pr
Received power is same at any point equidistant from transmitter (black circle)

24. Outline Transmission Media Guided Media Wireless Transmission
Antennas and Antenna Gain
Wireless Propagation
Electromagnetic Spectrum

25. Wireless Propagation
A signal radiated from an antenna travels along one of three routes: ground wave, sky wave, or line of sight (LOS).

26. Wireless Propagation
Ground Propagation: The signal travel through the lowest portion of the atmosphere, hugging the earth. , e.g. AM radio.
Sky Propagation: The signal bounces back and forth between the earth’s surface and the earth’s ionosphere (for the higher HF frequencies), e.g. amateur radio, international radio stations.
Because it depends on the Earth's ionosphere, it changes with the weather and time of day.
I Frequency of signals affect how signal propagates
I Different frequencies impacted by water, atmospheric
noise, cosmic noise, temperature
In ground propagation, radio waves follows the curvature of the earth’s surface
Sky waves higher-frequency radio waves radiate upward into the ionosphere (the layer of atmosphere) where they are reflected back to earth.

27. Wireless Propagation
Line of sight propagation transmits exactly in the line of sight. The receive station must be in the view of the transmit station.
It is limited by the curvature of the Earth for ground-based stations (100 km, from horizon to horizon).
To facilitate beyond-the-horizon propagation, satellite or terrestrial repeaters are used
I Increased frequency, increased attenuation
I Obstacles affect signals differently
I Signals may reflect o obstacles, multiple copies of same
source signal received at dierent times (multipath)
In line-or-sight propagation, very high-frequency signals are transmitted in straight lines directly from antenna to antenna.

28. Multipath Propagation
In unguided channels, signals are not only transmitted directly from source to destination but also a lot of paths from source to destination by reflection, diffraction , …etc.
So the receiver receive multiple copies (components) of transmitted signal.
Line of sight (LOS) is the fastest component reaching to destination.

30. Outline Transmission Media Guided Media Wireless Transmission
Antennas and Antenna Gain
Wireless Propagation
Electromagnetic Spectrum

31. Electromagnetic Spectrum
It is the range of frequencies (the spectrum) of electromagnetic radiation and their respective wavelengths
Electromagnetic spectrum is used by many applications
International and national authorities regulate usage of spectrum
The electromagnetic spectrum is the range of frequencies (the spectrum) of electromagnetic radiation and their respective wavelengths and photon energies.
We will talk about two ranges of frequencies: microwave range and radio range
Aim: minimize interference between applications/users, while allowing many applications/users

32. Microwave and Radio Wave
Microwave signals are higher frequency signals used for unicast communication such as cellular telephones, satellite networks, and wireless LANs.
Higher frequency  carry large quantities of information.
The required antenna is smaller due to shorter wavelength (due to higher frequencies)
( the size of the antenna required to transmit a signal is proportional to the wavelength (λ) of the signal).

33. Microwave and Radio Waves
Radio wave is lower frequency signals suitable for omnidirectional applications, such as radio and television.
Infrared waves can be used for short-range communication in a closed area using line-of-sight propagation

34. Any Questions ?