Multiplexer concept

1. DISCOVER . LEARN . EMPOWER
Multiple Access Techniques
University Institute of
Engineering
Electronics &
Communication Engineering
Bachelor of Engineering (Electronics &
Communication Engineering)
Foundation of Wireless Mobile
Communication (ECO-404)
Prepared By: Priya Rana
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2. • Is the technique of transmission of information from
one or more source to one or more destination over
a same transmission medium i.e. Multiple users share
a same channel simultaneously.
• The process of combining the data streams is known
as multiplexing and hardware used for multiplexing is
known as a multiplexer.

4. • Frequency Division Multiplexing is a technique in which the available
bandwidth of a single transmission medium is subdivided into several
channels.
• a single transmission medium is subdivided into several frequency channels,
and each frequency channel is given to different signals.
• the bandwidth of the communication channel should be greater than the
combined bandwidth of individual signals.
• Each logical sub-channel is separated by an unused bandwidth called Guard
Band to prevent overlapping of signals.

5. • FREQUENCY DIVISION MULTIPLE ACCESS
• FDMA (frequency division multiple access) is the division of the frequency band allocated
for wireless cellular telephone communication into number of channels, each of which can carry a
voice conversation or, with digital service, carry digital data.
• FDMA is the division of the frequency band allocated for wireless cellular telephone communication
into channels
• FDMA in analogue advanced mobile phone system (AMPS)
• Each channel can be assigned to only one user at A time.

6. • FDMA IS A METHOD THAT
LETS MORE THAN ONE
USER TO SHARE A SINGLE
RADIO FREQUENCY
SPECTRUM.
• THIS IS DONE BY ASSIGNING
ACTIVE USERS A DIFFERENT
FREQUENCY CHANNEL.
• FDMA PUTS EACH CALL ON
A SEPARATE FREQUENCY.

7. Frequency division multiplexing

8. GUARD BANDS
• Between the different used frequency channels is a
small amount of bandwidth not used. This space is
called a guard band.
• This bandwidth is necessary to cater for instability of
the sender, frequency shifts due to movement (the
Doppler effect) and no-ideal filtering.

9. MAIN FEATURES
• Continuous transmission
• Narrow bandwidth
• Simple hardware at mobile unit and BS : (1) no digital processing needed (2)
ease of framing and synchronization.
• FDMA can be used with both analogue and digital signal.
• FDMA requires high-performing filters in the radio hardware
• Due to the frequency filtering, FDMA is not sensitive to near-far problem.

10. • In TDM all the signals operate with same
frequencies are transmitted at different time and
data signals were transmitted serially from the
users.
• The bandwidth requirement of communication
channel should be greater than maximum
bandwidth occupied by channel

11. TDMA
• TDMA : TIME DIVISION MULTIPLE ACCESS.
• TDMA IS DIGITAL TRANSMISSION TECHNOLOGY THAT
ALLOWS A NUMBER OF USERS TO ACCESS A SINGLE RADIO-
FREQUENCY (RF) CHANNEL WITHOUT INTERFERENCE BY
ALLOCATING UNIQUE TIME SLOTS TO EACH USER WITHIN
EACH CHANNEL.
• TDMA DIVIDES EACH CELLULAR CHANNEL INTO THREE
TIME SLOTS IN ORDER TO INCREASE THE AMOUNT OF DATA
THAT CAN BE CARRIED.

12. • THE REASON FOR CHOOSING TDMA
FOR ALL STANDARDS WAS THAT IT
ENABLES SOME VITAL FEATURES FOR
SYSTEM OPERATION IN AN ADVANCED
CELLULAR OR PCS ENVIRONMENT.
• TDMA RELIES UPON THE FACT THAT
THE AUDIO SIGNAL HAS BEEN
DIGITIZED I-E DIVIDED INTO A NUMBER
OF MILLISECONDS-LONG PACKETS. IT
ALLOCATES A SINGLE FREQUENCY
CHANNEL FOR A SHORT TIME AND THEN
MOVES TO ANOTHER CHANNEL.

13. SYNCHRONIZATION IN TDMA
• “CLOCK” IS REQUIRED FOR TDMA.
• ALL TRANSMITTERS AND RECEIVERS MUST BE AWARE OF THIS
``CLOCK'' TO SCHEDULE THEIR TRANSMISSIONS AND RECEPTIONS
AND TRANSMISSIONS ARE SYNCHRONIZED.
• IN CELLULAR TELEPHONE SYSTEMS A CLOCK SIGNAL INDICATES
THE BEGINNING OF TIME-SLOTS IS TRANSMITTED BY THE BASE
STATIONS. FROM THIS SIGNALS, MOBILE STATIONS CAN
DETERMINE WHEN THEIR TURN COMES UP.

14. • A frequency filter or also known as a frequency
selective circuit is a special type of a circuit,
which is used for filtering out some of the input
signals on the basis of their frequencies.
• A filter is a circuit capable of passing (or
amplifying) certain frequencies while
attenuating other frequencies. Thus, a filter can
extract important frequencies from signals that
also contain undesirable or irrelevant
frequencies.

15. • Passband
The band of frequencies of the input signal that pass
through the filter without any attenuation is
called Passband.
• Stopband
The band of frequencies of the input signal that are blocked
or attenuated in the filter is called Stopband.
• Cutoff Frequency
The passband & stopband are distinguished from each
other by the cutoff frequency or corner frequency.

18. Low Pass Filter
• Low Pass filter allow low-frequency signals
without any attenuation (decrease in power)
but it rejects any high-frequency signals.
High Pass Filter
• The type of filter that allows the high-frequency
signals to pass without any attenuation in its
amplitude & blocks (rejects) any low-frequency
signal is called high pass filter.

19. Band Pass Filter
• This type of filter allows a specific band of
frequencies & blocks any other frequencies
lower or higher than its passband frequencies.
Band Reject Filter or notch filter:
• This type of filter attenuates the signal whose
frequencies lies in a fixed band of frequencies.

20. 1. Theodore S. Rappaport, “Wireless
Communication: Principles and Practices”,
Pearson Education India, 2009
2. T. L. Singhal, “Wireless Communications”,
TMH
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21. THANK YOU
For queries
Email: priya.e12225@cumail.in
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