1. Bandwidth Utilization: Multiplexing and Spreading
Chapter 6

2. Bandwidth Utilization
It is the wise use of available bandwidth to achieve specific goals.
Categories of Bandwidth utilization:
Multiplexing
Spreading
Multiplexing:
It is used to enhance the efficiency of transmission system by combining several low bandwidth channels to make one channel with larger bandwidth.
Spreading:
Expansion of bandwidth used to achieve Privacy and anti-jamming.

3. Multiplexing Multiplexing: One Link Many Channels
It is the set of techniques that allows the simultaneous transmission of multiple signals across a single data link.
Used when the bandwidth of a medium linking two devices is greater than their requirement.
One Link Many Channels
Link: Physical Path
Channel: Portion of link, that carries a transmission.

4. Multiplexing
At sender end, multiplexer (MUX) collects and combines the lines into a single stream (Many to One).
At receiving end, demultiplexer (DEMUX) separate the stream back into the component transmission (One to many).

5. Multiplexing

6. Categories of multiplexing

7. 1. Frequency Division Multiplexing
FDM is an analog multiplexing technique that combines analog signals.

8. 1. Frequency Division Multiplexing
Frequency Division Multiplexing (FDM)
It is used when the bandwidth of the link is greater than the combined bandwidth of the signals to be transmitted.
In FDM, signals generated by each sending device modulate different carrier frequencies.
These modulated signals are combined into a single composite signal that can be transported by a single link.

9. 1. Frequency Division Multiplexing
Channel:
Bandwidth range to accommodate a modulated signal.
Channels can be separated by strips of unused bandwidth (guard band) to prevent overlapping.
Filters: Separate different signals from modulated signal.
Modulator: Perform the function of combining carrier signals with data signals.
De-modulator: Separate data signals with carrier signals.

10. 1. Frequency Division Multiplexing (Multiplexing)

11. Analog Hierarchy
In analog hierarchy, 12 voice channels are multiplexed onto a higher-bandwidth line to create a group. Further grouped as a super- group, master group and jumbo group.

12. 1. Frequency Division Multiplexing (Applications)
AM (530 to 1700KHz)
Each channel needs 10 KHz of Bandwidth
FM Radio (88 to 108 MHz)
Each channel needs 200 KHz of Bandwidth
Television Broadcasting
Each TV channel has its own bandwidth of 6MHz
First Generation Cellular Telephones
Each user is assigned by two 30 KHz channels
(one  sending, one  Receiving)

13. 1. Frequency Division Multiplexing (Guard Bands)
Channels can be separated by strips of unused bandwidth called as Guard Bands.

14. 2. Wavelength Division Multiplexing
Wave-Division Multiplexing [WDM] is an analog multiplexing technique to combine optical signals
Optical fiber data rate is higher than the data rate of metallic transmission cable.
Using a fiber-optic cable for one single line wastes the available bandwidth.

15. 2. Wavelength Division Multiplexing

16. 2. Wavelength Division Multiplexing
Multiple light signals are combined at sender side and separated at receiver end.
The combining and splitting of light source are easily handled by a prism, which bends a beam of light.
Multiplexer combine different beams of light having small band and form a wider band of frequencies.
Demultiplexer do the reverse job.

17. 3. Time Division Multiplexing
TDM is a digital multiplexing technique to combine data
Instead of sharing a portion of the bandwidth, time is shared.
Each connection occupies a portion of time in the link.

18. 3. Time Division Multiplexing