This document discusses multiple access techniques used in wireless communication. It focuses on frequency division multiple access (FDMA) which allows multiple users to share the same frequency channel by assigning different, non-overlapping frequency sub-bands to each user. FDMA divides the available bandwidth into separate channels, with each user assigned their own channel containing a narrow frequency band. Guard bands are left between channels to prevent overlap and interference. The document provides examples of FDMA used in analog cellular systems and describes its advantages, including continuous transmission and simple hardware requirements.

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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