Multiplexing and Data Rate
Multiplexing
CHAPTER 4
Outline * Frequency Division Multiplexing(FDM) * Synchronous Time Division Multiplexing * Statistical Time Division Multiplexing * Asymmetric Digital Subscriber Line(ADSL)
Multiplexing * Set of techniques that allows the simultaneous transmission of multiple signals across a single link * allows several transmission sources to share a larger transmission capacity
Link = physical path
Channel = portion of a link that carries a transmission between a given pairs of lines
2 CATEGORY OF MULTIPLEXING
WDM FDM TDM ADSL
Frequency Division Multiplexing
* FDM – numerous signals are combined for transmission on a single communications line or channel. Each signal is assigned a different frequency (subchannel) within the main channel. * Useful bandwidth of medium exceeds required bandwidth of channel * e.g. broadcast radio and cable television * Channel allocated even if no data
Frequency Division Multiplexing Diagram
* Each signal is modulated to a different carrier frequency * Carrier frequencies separated by guard bands (unused bandwidth) – to prevent interference so signals do not overlap.
3
FDM System
FDM is an analog multiplexing technique that combines signals.
FDM process
FDM Demultiplexing
Example 1
Assume that a voice channel occupies a bandwidth of
4 KHz. We need to combine three voice channels into a link with a bandwidth of 12 KHz, from 20 to 32 KHz. Show the configuration using the frequency domain without the use of guard bands.
Solution
Shift (modulate) each of the three voice channels to a different bandwidth, as shown in next figure
Example 2
Five channels, each with a 100-KHz bandwidth, are to be multiplexed together. What is the minimum bandwidth of the link if there is a need for a guard band of 10 KHz between the channels to prevent interference? Solution
For five channels, we need at least four guard bands.
This
CHAPTER 4
Outline * Frequency Division Multiplexing(FDM) * Synchronous Time Division Multiplexing * Statistical Time Division Multiplexing * Asymmetric Digital Subscriber Line(ADSL)
Multiplexing * Set of techniques that allows the simultaneous transmission of multiple signals across a single link * allows several transmission sources to share a larger transmission capacity
Link = physical path
Channel = portion of a link that carries a transmission between a given pairs of lines
2 CATEGORY OF MULTIPLEXING
WDM FDM TDM ADSL
Frequency Division Multiplexing
* FDM – numerous signals are combined for transmission on a single communications line or channel. Each signal is assigned a different frequency (subchannel) within the main channel. * Useful bandwidth of medium exceeds required bandwidth of channel * e.g. broadcast radio and cable television * Channel allocated even if no data
Frequency Division Multiplexing Diagram
* Each signal is modulated to a different carrier frequency * Carrier frequencies separated by guard bands (unused bandwidth) – to prevent interference so signals do not overlap.
3
FDM System
FDM is an analog multiplexing technique that combines signals.
FDM process
FDM Demultiplexing
Example 1
Assume that a voice channel occupies a bandwidth of
4 KHz. We need to combine three voice channels into a link with a bandwidth of 12 KHz, from 20 to 32 KHz. Show the configuration using the frequency domain without the use of guard bands.
Solution
Shift (modulate) each of the three voice channels to a different bandwidth, as shown in next figure
Example 2
Five channels, each with a 100-KHz bandwidth, are to be multiplexed together. What is the minimum bandwidth of the link if there is a need for a guard band of 10 KHz between the channels to prevent interference? Solution
For five channels, we need at least four guard bands.
This