CDMA uses direct sequence spread spectrum technology where each user is assigned a unique pseudorandom noise (PN) code and spreads their data signal using this code. Users transmit simultaneously over the same frequency band and are separated by their unique PN codes. CDMA capacity depends on factors like processing gain, signal-to-noise ratio, and voice activity. The network architecture includes mobile stations, base stations, base station controllers, mobile switching centers, and various registers for authentication, location, and equipment identification. Spread spectrum techniques like CDMA and FHSS provide advantages such as reduced interference, better quality voice/data, security, and resistance to jamming.

1. CDMA & SPREAD
SPECTRUM
COMMUNICATION
PRESENTED BY: PRITISH KUMAWAT(01116414219)
NEDA(00216414219)
VIJAY PAL SINGH(00416414219)

2. Multiple Access Techniques
Frequency Division Multiple Access (FDMA)
Time Division Multiple Access (TDMA)
Code Division Multiple Access (CDMA)

3. CDMA
• Each user is assigned a unique PN code.
• Each user transmits its information by spreading with
unique code.
• Direct Sequence spread spectrum is used.
• Users are separated by code not by time slot and frequency
slot.
• Users share same bandwidth
• User axis shows cumulative signal strength of all users

4. Working of CDMA

5. CDMA capacity
Factors deciding the CDMA capacity:
• Processing gain
• Signal to noise ratio
• Voice Activity Factor
• Frequency reuse efficiency

6. Architecture of CDMA

7. Mobile Station (MS):
Two Blocks
1) Mobile Equipment (ME)
2) Subscribers Identity Module (SIM)
Function of Mobile Station:
1. Personal Mobility
2. IMEI (International Mobile Equipment Identity)
3. IMSI (International Mobile Subscriber Identity)

8. Base Station Subsystem (BSS)
1) Base Transceiver Station (BTS)
2) Base Station Controller (BSC)
BTS : Base Transceiver station
1. It defines the cell .
2. It handles the radio link protocol with the mobile station
BSC: Base station Controller
1. It manages radio resources for one or more BTS.
2. Allocation and Deallocation of channels.
3. Transmitter power control.
4. Handoff control

9. Network Subsystem
MSC: Mobile Switching Center
HLR: Home Location Register
VLR: Visitor Location register
AuC: Authentication Centre
EIR: Equipment Identity Register

10. Network subsystem
Home Location
Register (HLR)
1 One HLR per CDMA
operator
2 Contains permanent
Mobile database of all the
subscribers in the network
3 Contains MSRN(mobile
station routing no.)
4 It is referred for every
incoming call
Mobile Switching
centre:(MSC)
1 Call set
up/supervision/release
2 Call routing
3 Billing information collection
4 Mobility management
5 Paging, Echo cancellation
connection to BSC, other MSC
and other local exchange
networks
6 Access to HLR and VLR

11. Network Subsystem
Visitor Location Register(VLR)
1. Temporary visitors database
2. One VLR per MSC
Authentication Centre (AuC)
1. Provides security
2. Authentication and encryption
Equipment Identity Register:
1. Contains IMEI

12. Advantages
• Increased security.
• Soft handoff
• Increased efficiency.
• Extended reach - beneficial to rural users situated
far from cells
• Multipath reception improves voice clarity

13. Disadvantages
• Time synchronization is required.
• Near far problem.
• CDMA is relatively low, and the network is not
as mature as GSM.
• CDMA can not offer international roaming, a
large GSM advantage

14. SPREAD SPECTRUM
OUTLINE:
• Basic of spread spectrum
• Need of spread spectrum
• Block diagram
• Working
• significance

15. 4
Introduction of Spread
Spectrum Communications
• Spread Spectrum is a means of transmission in which
the data sequence occupies a bandwidth in excess of the
minimum bandwidth necessary to send it.
Effectively the signal is mapped to a higher dimension signal
space
• Signal spreading is done before transmission by using a
spreading sequence. The same sequence is used at the
receiver to retrieve the signal
• Spread Spectrum is most effective against interference
(intentional or non-intentional) with fixed energy.
• Main commercial applications in wireless and GPS.

16. r
NEED FOR SPREAD SPECTRUM
• SECURITY
• Safeguards for
physical security must be
even greater in wireless
communications
• Encryption: intercepted
communications must not
be easily interpreted
• Authentication: is the

17. BLOCK DIGRAM SPREAD
SPECTRUM COMMUNICATION
Spread-spectrum radio communications is a favorite technology of the
military because it resists jamming and is hard for an enemy to intercept, Just
as they are unlikely to be intercepted by a military opponent

18. How Spread Spectrum Works
• Spread Spectrum uses wide band, noise-like signals. Because
Spread Spectrum signals are noise-like, they are hard to detect.
• Spread Spectrum signals are also hard to Intercept
or demodulate.
• Further, Spread Spectrum signals are harder to jam
(interfere with) than narrowband signals.
• These Low Probability of Intercept (LPI) and anti-jam
(AJ) features are why the military has used Spread Spectrum
for so many years.
.

19. PN Sequences
• PN generator produces periodic sequence that appears to
be random
• PN Sequences
▫ Generated by an algorithm using initialseed
▫ Sequence isn’t statistically random but will pass many test
of randomness
▫ Sequences referred to as pseudorandom numbers or
pseudonoise sequences
▫ Unless algorithm and seed are known, the sequence is impractical
to predict

20. Important PN Properties
• Randomness
▫ Uniform distribution
▫ Independence
• Unpredictability

21. Spreading Codes
• A noise-like and random signal has to be
generated at the transmitter.
• The same signal must be generated at the receiver
in synchronization.
• We limit the complexity by specifying only one bit
per sample, i.e., a binary sequence.
9

22. • Spread Spectrum signals use fast codes that
run many times the information bandwidth or
data rate.
These special "Spreading" codes are
called "Pseudo Random" or "Pseudo Noise"
codes. They are called "Pseudo" because they
are not real Gaussian noise.

23. Why Spread Spectrum?
• Spread spectrum signals are distributed over
a wide range of frequencies and then
collected back at the receiver
▫ These wideband signals are noise-like and
hence difficult to detect or interfere with.
• Initially adopted in military applications, for
its resistance to jamming and difficulty
of interception
• More recently, adopted in commercial
wireless communications

24. SIGNIFICANCE
• Immunity to jamming
• Low interference
• High processing gain
• Easy encryption
• Multiple access

25. SPREAD SPECTRUM TECHNIQUES
• THE MAJOR SPREAD SPECTRUM
TECHNIQUES ARE
• DSSS
• FHSS

26. Frequency Hopping Spread Spectrum
(FHSS)
• Data signal is modulated with a narrowband
signal that hops from frequency band to
frequency band, over time
• The transmission frequencies are determined by
a spreading, or hopping code (a pseudo-random
sequence)
WirelessEnvironment
and WirelessLANs
18

27. WirelessNetworks
Spring2005
Frequency Hoping Spread Spectrum

28. Frequency Hopping
the carrier frequency is 'hopping' according to a
unique sequence

29. Direct Sequence Spread Spectrum
• Data signal is multiplied by a spreading code,
and resulting signal occupies a much higher
frequency band
• Spreading code is a pseudo-random sequence
WirelessEnvironment
and WirelessLANs
15
(DSSS)
11010111010100100001101010010011111010100100111
Information after spreadingUser data
1101010010011
Spreading code 11010111010100100001101010010011111010100100111(…)

30. Processing Gain (spreading factor)
Period of
one chip
Period of one
data bit
PG = SF = Tb / Tc

31. DSSS Example
WirelessEnvironment
and WirelessLANs
17

32. Advantages of Spread Spectrum
1. Reduced crosstalk interference:
2. Better voice quality/data integrity and less static noise
3. Lowered susceptibility to multipath fading
4. Inherent security:
5. Co-existence:
6. Longer operating distances
7. Hard to detect:
8. Hard to intercept or demodulate:
9. Harder to jam

33. Conclusion
Spread spectrum promises several benefits such as
higher capacity and ability to resist multipath propagation.
Spread spectrum signals are difficult to intercept for an
unauthorized person, they are easily hidden. For an
unauthorized person, it is difficult to even detect their presence
in many cases. They are resistant to jamming. They provide a
measure of immunity to distortion due to multipath
•
propagation. They have multiple access capability
• .
telephones, personal communications and position location.
For example, DS/SS is used in electronic Industries
Association’s Interim Standard IS-95 for cellular telephones,
as
well as wide range of position location systems such as the
global position location and other vehicle location
and messaging systems.