1. Optical Fiber Advantages: Disadvantages Noise resistance
Less signal attenuation
Higher bandwidth
Disadvantages
Cost
Installation/maintenance
Fragility

2. Topics discussed in this section:
7-2 UNGUIDED MEDIA: WIRELESS
Unguided media transport electromagnetic waves without using a physical conductor. This type of communication is often referred to as wireless communication.
Topics discussed in this section:
Radio Waves
Microwaves
Infrared

3. Figure 7.17 Electromagnetic spectrum for wireless communication

4. Figure 7.18 Propagation methods

5. Table 7.4 Bands

6. Figure 7.19 Wireless transmission waves

7. Figure 7.20 Omnidirectional antenna

8. Note
Radio waves are used for multicast communications, such as radio and television, and paging systems.

9. Figure 7.21 Unidirectional antennas

10. Note
Microwaves are used for unicast communication such as cellular telephones, satellite networks, and wireless LANs.

11. Note
Infrared signals can be used for short-range communication in a closed area using line-of-sight propagation.

12. TRANSMISSION IMPAIRMENT

13. Impairment types
Impairment
Attenuation
Distortion
Noise

14. Impairment types (Contd.)
Attenuation
Loss of energy
Attenuated signal is amplified
Distortion
Signal changes its form or shape
Noise
Ex: thermal noise, induced noise, crosstalk etc

15. Decibel
Decibel measures the relative strengths of two signals or a signal at two different points.
dB is negative if a signal is attenuated
dB is positive if a signal is amplified.
dB = 10 log10 (P2/P1)
Where P1 and P2 are the power of a signal at points 1 and 2.

16. Imagine a signal travels through a transmission medium and its power is reduced to half. Calculate its attenuation.

17. Imagine a signal travels through a transmission medium and its power is reduced to half. Calculate its attenuation.
Ans: dB = 10 log10 (P2/P1) = 10 log10 (0.5*P1/P1) = 10 log10 (-0.3) = -3 dB.

18. PERFORMANCE

19. PERFORMANCE Throughput Propagation speed Propagation Time
Measurement of how fast data can pass through a point.
Propagation speed
measures the distance a signal or bit can travel through a medium in one second.
Propagation Time
Measures the time required for a signal to travel from one point of the transmission medium to another.
Propagation time = Distance / Propagation speed.