1. Group Research Assignment 2
Due: Friday, 2/13 at 11:59pm
Use Friday’s class time to work on it

2. Transmission Media

3. Classification of Transmission Media
Type of path
Guided
Copper wiring, optical fibers, etc.
Unguided
Radio transmission, etc. .

4. A Taxonomy by Forms of Energy
Copper based .

5. Why Twisted Pair? .

6. Radiation And Electrical Noise
Facts:
“Random” electromagnetic radiation, called noise, is everywhere.
Light bulbs, electrical motors, paper shredders,…
When it hits metal, electromagnetic radiation induces a small signal.
“Random” noise can interfere with signals used for communication
How to prevent signals from being interfered? .

7. Noise induced is related to the spatial location of wires.
Altering the spatial locations of the pair can cancel out the noise.
Twisting two wires makes them less susceptible to electrical noise than leaving them parallel.

8. Which wire is used for phone lines and which is for computer networks?.

9. Shielded vs. Unshielded Twisted Pair
Unshielded Twisted Pair (UTP)
Used in transmission where
Low-frequency signals are dominant.
Electrical noise are not very strong.
Wires are far away the source of noise.
Phone lines
Shielded Twisted Pair (STP)
Computer networks
Requiring high reliability

10. .

11. Categories of Twisted Pair Cable.

12. Coaxial Cable
Twisted pair, even shielded, tends to have problems with:
Very strong electrical noise
Close physical proximity to the source of noise
Close to a factory that uses electric arc welding equipment
Close to a transmission tower
High frequency signals
A fluorescent light fixture can interference signals.
We need something more resistant to electrical noise.

13. Coaxial Cable .

14. A Taxonomy by Forms of Energy.

15. Optical Fibers Most popular type of media that uses light
Thin strand glass or transparent plastic encased in a plastic cover .

16. .

17. Fiber optic transmission
Transmission: Laser or Light Emitting Diode (LED)
Reception: photo-sensitive cell or photodiode

18. The Nobel Prize in Physics 2014
“for the invention of efficient blue light-emitting diodes which has enabled bright and energy-saving white light sources".

19. Signal Transmission with Optical Fibers
Basic optics
angle of incidence < critical angle: refraction
angle of incidence < critical angle: reflection
Which travel mode do we want in signal transmission? .

20. Reflection in An Optical Fiber Is Not Perfect!
Reflection absorbs a small amount of energy
The result is that a pulse of light sent at one end of a fiber emerges with less energy and is dispersed (i.e., stretched) over time .

21. Types of Fiber Optics High dispersion Least expensive Less dispersion
Slightly more expensive
Least dispersion
Most expensive .

22. Light and Equipment Must Match
Transmission: LED (light emitting diode) or ILD (injection laser diode)
LEDs
Short distances
Slower bit rates
Multimode fibers
ILDs
Single mode fibers
Long distance with high bit rates .

23. Submarine Cable Map .

24. Interruption of Submarine Cable: 01/30/2008.

25. .

26. Optical Fiber Compared To Copper Wiring
Optical fiber is more desirable than copper wiring.
Optical fiber
Immune to electrical noise
Higher bandwidth
Light traveling across a fiber does not attenuate as much as electrical signals traveling across copper.
Copper
Less expensive
No need special treatment on wires
Ends of an optical fiber must be polished before being used.
Installation is easy.
Less likely to break if accidentally pulled or bent .

27. Other media types that use light
InfraRed (IR)
Dispersing quickly
Easily be blocked
Hard to penetrate the wall.
Commonly suitable for close communications
Used in TV remote
Point-To-Point Laser Communication
Two devices communicate with a laser beam
Cannot be obstructed
Can achieve very high bandwidth
Multi-Gigabit per second .

28. A Taxonomy by Forms of Energy.

29. Electromagnetic (Radio) Communication
Unguided
In the Radio Frequency (RF) range
RF transmission offers advantages over light
Longer distance
Penetrate objects
RF: 3KHz – 300 GHz .

30. What frequency do the following techniques use?
Radio broadcasting
87.5MHz – 108.0MHz
Example: Majic 99  99.5MHz
Wi-Fi
2.4GHz or 5GHz
Global Positioning System (GPS)
MHz

31. Communication Satellites
High-frequency signals must go direct.
Cellular towers
Satellites .

32. GEO (Geostationary Earth Orbit) Communication Satellites.
Transmission delay at the speed of light: sec

33. Low Earth Orbit (LEO) Satellites And Clusters
Low delay
The disadvantage of LEO is that the orbit of a satellite does not match the rotation of the earth
Adjusting the orientation of transmitters and receivers .

34. How to Choose Appropriate Media?
The choice of medium is complex
Cost
materials, installation, operation, and maintenance
Data rate
number of bits per second that can be sent
Delay
time required for signal propagation or processing
Affect on signal
attenuation and distortion
Environment
susceptibility to interference and electrical noise
Security
susceptibility to eavesdropping .

35. Some Examples Landline phones vs. cellular phones
Mature markets vs. emerging markets
Satellite vs. cable communications
Urban vs. suburb
Last mile
Copper vs. Fiber
Comcast XFINITY vs. AT&T U-Verse and Verizon FiOS .

36. How fast can we send information over a link?
Key channel properties: The bandwidth (B), single strength (S), and noise strength (N)
B limits the rate of transmissions
S and N limit how many signal levels we can distinguish
Bandwidth B
Signal S,
Noise N

37. Nyquist Theorem The maximum symbol rate is 2B
Thus, if there are K signal levels, ignoring noise, the maximum bit rate is:

38. The Effect of Noise on Communication
In practice, the signal levels we can distinguish depends on S/N
Or SNR, the Signal-to-Noise Ratio
SNR often given on a log-scale in deciBels:
dB = 10log10(S/N)
Shannon’s Theorem

39. Calculate Channel Capacity with S/N in dB
The voice telephone system:
Signal-to-noise ratio: about 30 dB
An analog bandwidth: about 3 kHz
Calculation
Step 1: Converting the S/N in dB into a simple fraction: S/N = 10(dB/10)
30dB  1000
Step 2: Applying Shannon's Theorem
about 30,000 bps
dB = 10log10(S/N)

40. Exercise
If two signal levels are used, what is the data rate that can be sent over a coaxial cable that has an analog bandwidth of 6.2 MHz?
If a system has an average power level of 100, an average noise level of 33.33, and a bandwidth of 100 MHz, what is the effective limit on channel capacity?
If a telephone system can be created with a signal-to-noise ratio of 40 dB and an analog bandwidth of 3000 Hz, how many bits per second could be transmitted?

41. The Significance of Channel Capacity
Nyquist's work has provided an incentive to explore complex ways to encode bits on signals.
Shannon's Theorem is more fundamental because it represents an absolute limit derived from the laws of physics.
Engineers recognize that faster transmission speeds will only be possible if the signal-to-noise ratio can be improved.