This document provides an overview of three multiple access technologies: TDMA, FDMA, and CDMA, detailing their operations, specifications, advantages, and disadvantages. TDMA allocates specific time slots for each channel, FDMA assigns different frequency bands to signals, and CDMA uses unique codes to distinguish channels. The document compares these technologies in terms of efficiency, flexibility, and application in telecommunications.

1. GANDHINAGAR INSTITUTE OF
TECHNOLOGY
CDMA/FDMA/TDMA
Active Learning Assignment
Communication
7th Sem. EC, A1
Name: Keerthana Nambiar(140120111012)
Faculty Guide: Prof. Hardik Bhatt

2. CDMA/FDMA/TDMA
Which telecommunication service is
better for you?

3. International Cocktail Party
• FDMA – Large room divided up into small rooms.
Each pair of people takes turns speaking.
• TDMA – Large room divided up into small rooms.
Three pairs of people per room, however, each pair
gets 20 seconds to speak.
• CDMA – No small rooms. Everyone is speaking in
different languages. If voice volume is minimized,
the number of people is maximized.

5. Definitions
• TDMA – Time Division Multiple Access
• FDMA – Frequency Division Multiple Access
• CDMA – Code Division Multiple Access

6. TDMA
• Here, we give certain time frame to each channel.
Within that time frame, the channel can access the
entire spectrum bandwidth
• Each station got a fixed length or slot. The slots,
which are unused will remain in idle stage.

7. Time Division

8. General Specification of TDMA
• Rx: 869-894MHz Tx: 824-849MHz
• 832 Channels spaced 30kHz apart
(3 users/channel)
• DQPSK modulation scheme
• 48.6kbps bit rate
• Interim Standard (IS) – 54
• Digital AMPS (Advanced Mobile Phone System)
• Uses Time Division Duplexing (TDD) usually

9. TDMA Operation
• Efficiency of TDMA frame:
- overhead bits per frame
- number of reference bursts per frame
- number of traffic bursts per frame
- number of overhead bits per reference burst
- number of overhead bits per preamble p
OH
r
t
r
p
b
N
N
b
b
 
er slot
- number of equivalent bits in each guard time interval
- frame duration
- bit rate of the radio-frequency channel
1 100%
g
f
rf
OH r r t p t r g
total f rf
OH
f
total
b
T
R
b N b N b N N b
b T R
b
b

   
 
 
  
 
 

10. Advantages of TDMA
• Flexible bit rate
• No frequency guard band required
• No need for precise narrowband filters
• Easy for mobile or base stations to initiate and
execute hands off
• Extended battery life
• TDMA installations offer savings in base station
equipment, space and maintenance
• The most cost-effective technology for upgrading a
current analog system to digital

11. Disadvantages to using TDMA
• Requires network-wide timing synchronization
• Requires signal processing fro matched filtering and
correlation detection
• Demands high peak power on uplink in transient
mode
• Multipath distortion

12. Application

13. FDMA
• In this type of multiple access, we assign each signal
a different type of frequency band (range).
• So, any two signals should not have same type of
frequency range.
• Hence, there won’t be any interference between them,
even if we send those signals in one channel.

14. Frequency Division

15. General Specification of FDMA
• Rx: 869-894MHz Tx: 824-849MHz
• 832 Channels spaced 30kHz apart
(3 users/channel)
• DQPSK modulation scheme
• 48.6kbps bit rate
• Used in analog cellular phone systems (i.e. AMPS)
• Uses Frequency Division Duplexing (FDD)
• ISI (Intersymbol Interference) is low

16. FDMA Operation
• Number of FDMA Channels
• In the U.S. each cellular carrier is allocated
416 channels where:
2
- total spectrum
- guard band
- channel bandwidth
f guard
c
f
guard
c
N
 




 

12.5
10
30
12.5 2 10
416
30
f
guard
c
MHz
kHz
kHz
MHz kHz
N
kHz






 
 

17. Advantages of FDMA
• If channel is not in use, it sits idle
• Channel bandwidth is relatively narrow (30kHz)
• Simple algorithmically, and from a hardware standpoint
• Fairly efficient when the number of stations is small and the
traffic is uniformly constant
• Capacity increase can be obtained by reducing the information
bit rate and using efficient digital code
• No need for network timing
• No restriction regarding the type of baseband or type of
modulation

18. Disadvantages to using FDMA
• The presence of guard bands
• Requires right RF filtering to minimize adjacent
channel interference
• Maximum bit rate per channel is fixed
• Small inhibiting flexibility in bit rate capability
• Does not differ significantly from analog system

19. Application

20. CDMA
• In CDMA technique, a unique code has been assigned
to each channel to distinguish from each other.
• A perfect example of this type of multiple access is
our cellular system. We can see that no two persons’
mobile number match with each other although they
are same X or Y mobile service providing company’s
customers using the same bandwidth.

21. Code Division
Code

22. General Specification of CDMA
• Rx: 869-894MHz Tx: 824-849MHz
• 20 Channels spaced 1250kHz apart
(798users/channel)
• QPSK/(Offset) OQPSK modulation scheme
• 1.2288Mbps bit rate
• IS-95 standard
• Operates at both 800 and 1900 MHz frequency bands

23. CDMA Operation
• Spread Spectrum Multiple Access Technologies

24. Advantages of CDMA
• Many users of CDMA use the same frequency, TDD
or FDD may be used
• Multipath fading may be substantially reduced
because of large signal bandwidth
• No absolute limit on the number of users
• Easy addition of more users
• Impossible for hackers to decipher the code sent
• Better signal quality
• No sense of handoff when changing cells

25. Disadvantages to using CDMA
• As the number of users increases, the overall quality
of service decreases
• Self-jamming
• Near- Far- problem arises

26. Application

27. Thank You