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# Copy of Copy of Time-Division Multiplexing

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## Khristine Teves

on 1 March 2015

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#### Transcript of Copy of Copy of Time-Division Multiplexing

A digital process that allows several connections to share the high bandwidth of a link
Time-Division Multiplexing
Synchronous TDM
Two Types of TDM
Remember this formulas!
Multiplexed Data Rate:
Formulas for Synchronous TDM
In synchronous TDM, the data flow of each
connection is divided into units, where each
input occupies one input time slot.
Synchronous TDM
Multiplexing
TDM, FDM, WDM
Illustration of TDM
Figure 1
Always Solve!
A multiplexer combines three 200kbps data channels using a times slot of 2 bits per slot. What is the frame rate, frame duration, data rate and slot duration? Note: f/s=40k
Problem Solving
Asynchronous TDM
Channel Rate x No. of Channels
Frame Duration:
Channel Bit Duration x No.of Bits per Slot
Frame Rate:
Channel Data Rate x No. of Bits per Slot
Switching Rate:
Frames per Second x No. of Channels
Full available channel bandwidth can be utilized for each channel.
lntermodulation distortion is absent.
TDM circuitry is not very complex.
The problem of crosstalk is not severe.
If any device does not have data to send then
its time slot remains empty.
Solution:
Data rate = 200 kbps x 3 = 600 kbps
Frame rate = 600 kbps/6bpf = 100 kbps
Frame Duration = 1/40k = 25us
Slot Duration = 25us/3 = 8.33us
The channel capacity cannot be fully used. Some of the slots go empty in certain frames.
The capacity of single communication line that is used to carry the various transmission should be greater than the total speed of input lines.
Multiplexing in STDM
Every device is given the opportunity
to transmit a specific amount of data onto the link.
The interleaved units are of same size.
CPE - ECE Dept. DLSU
Khristine Shara Lee M. Teves, David Miguel B. dela Cruz
A technique that separates each channel by putting them in different bandwidth frequencies within the bandwidth of the medium.
Frequency-Division Multiplexing
Frequency-Division Multiplexing
A channel occupies a fraction of the
bandwidth and each channel is
modulated into a Carrier Frequency

Diagram of FDM
Figure 2
Figure 3
Diagram of FDM
Figure 3
Data 1
Data 2
Data 3
Filter 2
Filter 3
Filter 1
Data 1
Data 2
Data 3
Uses of FDM
Mainly used for analog transmissions. It can be used over both wired and wireless mediums.
An example of an application that uses FDM is FM radio. FM is a band that occupies the frequency range from 88 MHz to 108 MHz within the larger radio frequency spectrum. Each radio station transmits at the frequency assigned to its channel.
Same goes with cable television, The TV transmission cable carries all available channels at their assigned frequencies.
The communication channel must have a very large bandwidth.
Intermodulation distortion takes place.
All the FDM channels get affected due to wideband fading.
A large number of signals (channels) can be transmitted simultaneously.
FDM does not need synchronization between its transmitter and receiver for proper operation.
Demodulation of FDM is easy.
Large number of modulators and filters are required.
FDM suffers from the problem of crosstalk.
A method by which multiple analog message signals or digital data streams are combined into one signal over a shared medium.
Multiplexing
Types of Multiplexing
Time-Division Multiplexing
Frequency-Division Multiplexing
Wavelength-Division Multiplexing
A technique where optical signals with different wavelengths are combined, transmitted together, and separated again.
Wavelength-Division Multiplexing
Expensive and probably less reliable.
Uses of WDM
Used for optical fiber communications to transmit data in several (or even many) channels with slightly different wavelengths
Also used for interrogating multiple fiber-optic sensors within a single fiber
Coarse WDM
Two Types of WDM
Dense WDM
A more flexible method of TDM. With this the
length of time allocated is not fixed for each
device but time is given to devices that have
data to transmit.
Asynchronous TDM
This works by tagging each frame with an
identification number to note which device it
belongs to.
Time-Division Multiplexing
Require more processing by the multiplexor and take longer than STDM.
Efficient and effective bandwidth utilization saves time.
Frames can have different sizes.
Allows more devices than there is physical bandwidth for.
Good utilization of trunk.
Multiplexing in ATDM
The number of time slots in a frame is based on a statistical analysis of number of input lines.
Slots are not predefined and are allocated to any of the device that has data to send.
The multiplexer scans the various input lines, accepts the data from the lines that have data to send, fills the frame and then sends the frame across the link