CDMA (Code Division Multiple Access) is a cellular technology where each user is assigned a unique code and all users transmit over the same frequency at the same time. It utilizes spread spectrum technology where the message signal is multiplied by a pseudo-random noise code before transmission. This allows all users to be identified by their unique code despite sharing the same frequency band. Some key advantages are high security, lower signal-to-noise ratio requirements, frequency reuse between cells, and entire spectrum availability to each user. However, quality of service can decrease as more users are added due to issues like self-jamming and the near-far problem where distant signals can drown out closer ones.

1. CDMA
Code Division Multiple Access

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

3. CDMA
Technology
A cellular system based on code division
multiple access (CDMA) has been developed
by Qualcomm, Inc. and standardized by the
Thlecommunications Industry Association
(TIA) as an Interim Standard (15-95).
Spread Spectrum technology of channel
access used in 3G Comm. N/Ws.
Each user uses the same frequency
spectrum at the same time

4. CDMA Access
method
Accessing to the transmission
channel at same frequency
and same time
Unique Code is assigned to
each user for communication
by pseudorandom generator
Utilization of the B.W of the
transmission channel
efficiently

5. CDMA operation
• Message Signal
• Pseudo random noise code
• XOR operation
• Orthogonality helps identifying
the individual users
CDMA in which each channel is assigned a unique PN code which is
orthogona' to PN codes used by other users.

6. CDMA
Operation
Spread Spectrum Multiple
Access Technologies

7. CDMA Advantages
High security due to
encryption provided
with random codes
1
The ability of CDMA to
operate with a much
smaller signal-to-noise
ratio than conventional
narrowband FM
techniques
2
CDMA systems to use
the same set of
frequencies in every
cell, which provides a
large improvement in
capacity
3
Each users is available
with entire spectrum
hence high voice
quality
4

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

9. Near- Far- problem in CDMA

10. Thank you