1. Quaid-e-Awam University of Engineering, Science & Technology Nawabshah
Department of Electronic Engineering
Multiplexing
ASSIGNED BY : DR. NADEEM BHATTI
PRESENTED BY: UMM-E-HANI KHAN (19ES49)
2. What is multiplexing?
Multiplexing is the set of techniques that allows the simultaneous transmission of multiple signals
across a single data link. As data and telecommunications use increases, so does traffic.
Multiple users share a medium with minimum or no interference.
Example of interference: two people talking at the same time.
In a multiplexed system, n lines share the bandwidth of one link.
The lines on the left direct their transmission streams to a multiplexer (MUX), which combines
them into a single stream (many-to- one).
3. There are three basic multiplexing techniques:
frequency-division multiplexing
wavelength-division multiplexing
time-division multiplexing.
The first two are techniques designed for analog signals,
the third, for digital signals
Multiplexing
4. Frequency-division multiplexing (FDM)
Frequency-division multiplexing (FDM) is an analog technique that can be applied when the
bandwidth of a link (in hertz) is greater than the combined bandwidths of the signals to be
transmitted.
Signals of different frequencies are combined into a composite signal and is transmitted on the
single link.
Bandwidth of a link should be greater than the combined bandwidths of the various channels.
Each signal is having different frequency.
Channels are separated by the strips of unused bandwidth called Guard Bands (to prevent
overlapping).
5. Advantages of FDM:
It does not need synchronization between its transmitter as well as receiver
FDM is simpler and easy demodulation
FDM system does not need synchronization but TDM needs synchronization. It is an advantage
of FDM over TDM
FDM provides more latency than TDM
Using FDM system multimedia data can be transferred with very high efficiency and low noise
and distortion
FDM system has high reliability
In this system due to slow narrowband fading, only one channel gets affected
A large number of the signal can be transmitted simultaneously
6. Disadvantages of FDM:
It is suffering the problem of cross talk
FDM is only used only when a few low-speed channels are desired
Intermodulation distortion takes place
The circuitry for FDM is complex than TDM
FDM requires more hardware than TDM
FDM system extremely expensive
FDM provides less throughput
The full bandwidth of the channel cannot be used on the FDM system
The communication must have very large bandwidth
7. Applications of FDM
FDM is used for FM & AM radio broadcasting.
AM frequency = 530 to 1700 KHz.
FM frequency = 88 to 108 MHz.
FDM is used in television broadcasting.
First generation cellular telephone also uses FDM.
8. Time Division Multiplexing
It is the digital multiplexing technique.
Channel/Link is not divided on the basis of frequency but on the basis of time.
Total time available in the channel is divided between several users.
Each user is allotted a particular time interval called time slot or slice.
In TDM the data rate capacity of the transmission medium should be greater than the data rate
required by sending of receiving devices.
10. Synchronous TDM
Each device is given same Time Slot to transmit the data over the link, whether the device has any
data to transmit or not.
Each device places its data onto the link when its Time Slot arrives, each device is given the
possession of line turn by turn.
If any device does not have data to send then its time slot remains empty.
Time slots are organized into Frames and each frame consists of one or more time slots.
If there are n sending devices there will be n slots in frame.
11. Synchronous TDM
In STDM every device is given opportunity to transmit a
specific amount of data onto the link.
Each device gets its turn in fixed order and for fixed
amount of time = INTERLEAVING.
Interleaving is done by a character (one byte).
Each frame consist of four slots as there are four input
devices.
Slots of some devices go empty if they do not have any
data to send
12. Asynchronous TDM
Also known as Statistical Time Division multiplexing.
In this time slots are not Fixed i.e. slots are Flexible.
Total speed of the input lines can be greater than the capacity of the path.
In ASTDM we have n input lines and m slots i.e. m less than n (m<n).
Slots are not predefined rather slots are allocated to any of the device that has data to send.
14. Advantages of Time-division Multiplexing
Easy adaptation: TDMA can surely adapt to the transport of information in the very same
fashion that voice communication does.
Fairly high transmission speed: It can transport messages at speeds spanning from 64 kbps to
120 Mbps.
Absence of external impedance: The synchronous transmission has no impedance.
Digitization potential: TDMA is a sophisticated way to transform a simple framework into a
digitized one.
Bandwidth efficiency: The signal is conveyed using the maximum channel bandwidth.
15. Disadvantages of Time-division Multiplexing
There is a problem with memory space distribution: Every client creates a designated memory
space, so clients who move from one unit to the next do not automatically receive a planned
opening. A cell could be disconnected if, all of the time, allotments in the succeeding cell are now
engaged. Similarly to the way, if all of the time allotments in the cell where a customer ultimately
ended up are now occupied, the customer will not receive a phone line.
Need for major modifications: Increased data rates necessitated adjustment.
The effort required for Synchronization: The synchronization burden is substantial. To
maintain adequate signal transmission and reception, the transmitter and receiver components
must be correctly and consistently synced.
16. Applications of Time-Division Multiplexing
It is used in a type of telephone line that uses ISDN (Integrated Services Digital Network)
technology.
It is deployed in PSTN (public switched telephone network).
It’s a significant component of a telephone system.
It’s actually found in telephone wire lines.
In a digital audio mixing system, TDM is implemented.
In SONET, time-division multiplexing, or TDM, is applied (Synchronous Optical Networking).
TDM, or Time Division Multiplexing, is employed in a half-duplex communication system.
TDM is a technique utilized in GSM or Global System for Mobile Communication.
