1. GSM and CDMA
What is it all about ?
By
Manjit Chandel

2. Marketing
You can change your GSM SIM card to
get rid of your girlfriend….
Shewag ki Maa ka phone CDMA pe
aaya tha…

3. Questions ???
How is one better than the other ???
Which one is cheaper ???
Which one is more reliable ???
What is the difference in technology ….if
any ???

4. More Questions….
Is there a single
security code that
will permit me to
make changes to
my phone ???
What role does
bandwidth play ???
What provides
protection from
eavesdropper ???
How a mobile
subscriber on one
network access his
home network ???

5. What is the underlying
Difference ??
TDMA
FDMA
CDMA
Layman’s view…
Are all different versions of digital
technology…

6. Time Division Multiple
Access
Users separated in
time
Requires digital
transmission
Normally wider
bandwidth
compared to FDMA
Used for GSM

7. Frequency Division
Multiple Access(FDMA)
Users separated in
frequency
Only possible in
analog system

8. Code Division Multiple
Access
Users separated by
code
Requires digital
transmission
Wider bandwidth
compared to TDMA

9. Time for History….
GSM originated in Europe…
GSM earlier known as Group Special
Mobile, a study group appointed to
study and develop European public
land mobile system
One important criteria that the proposed
system had to meet was ISDN
compatibility..

10. And now CDMA…
Introduced in 1980
IN North America….
Purpose…. What else
……but Military usage
Used in Cellular Communication
System , in the early 90’s

11. Finally ….What is
CDMA? …..
A way to transmit bits of information through
wideband, spread spectrum radio interface.
IS-95 is the transmission protocol that
employs CDMA.
Evolution from IS-95A to IS-95B to
CDMA2000
Better utilization of radio spectrum by allowing
multiple users to access the same physical
channel.

12. How CDMA Works?
Generating a CDMA signal
1.analog to digital conversion
2.vocoding
3.encoding and interleaving
4.channelizing the signals
5.conversion of the digital signal to a Radio
Frequency (RF) signal

13. How does it works……

14. Code GeneratorClock Multiplier
FilterModulator
Data Clock
Data
Carrier
Transmit
Signal
Working of CDMA Channel Establishment

15. Voice Compression
..How is it
accomplished??
CDMA uses a device called a vocoder
to accomplish voice compression.
The term "vocoder" is a contraction of
the words "voice" and "code."
Vocoders are located in the phone.

16. Channelizing
The encoded voice data is further encoded to
separate it from other encoded voice data.
The encoded symbols are then spread over
the entire bandwidth of the CDMA channel.
This process is called channelization.
The receiver knows the code and uses it to
recover the voice data.

17. Codes…
CDMA uses two important types of
codes to channelize users.
Walsh codes channelize users on the
forward link (BTS to mobile).
Pseudorandom Noise (PN) codes
channelize users on the reverse link
(mobile to BTS).

18. CDMA Call Processing State
System Idle State
System Initialization State
System Access State
Traffic Channel State

19. Hand Off ???
Advantage of CDMA is the ability to
communicate with more than one base
station at one time during a call
This functionality allows the CDMA
network to perform soft handoff
How does it all HAPPEN ?

20. Soft Handover…

21. MS BSC/MSCSecondary BS ‘B’Primary BS ‘A’
Pilot Strength Measurement
Pilot Measurement Request
Pilot Strength Measurement
Handoff Request
Handoff Direction
ACK
Handoff Information
ACK
ACK
ACK
Frame Selector Join

22. Roaming in CDMA
Mobile
Station
Base Station Visited MSC VLR Home MSC HLR Originating Switch
User
Dials CallIAM
HLR Query
HLR Response
SS7 IAM
Normal Call Processing Continues

23. Why is roaming charged
more ???
The Directory number of the MS is
dialed
Originating Switch sends an ss7 initial
address message (IAM) to home MSC
MSC queries the HLR for the location of
the MS
The HLR returns the locations of the
visited System

24. Roaming Contd..
The MSC invokes call forwarding to the
MSC in the visited system..
The forwarding MSC switch send an
SS7 IAM to the visited MSC
Call processing……

25. Call Waiting….
Base Station MSC VLR Home MSC HLR Originating Switch
User
Dials CallIAM
VLR Query
VLR Response
Mobile
Station
ISDN Hold Ack
MSC Applies Call waitingFlash
ISDN Hold
MSC puts Call1 on Hold connects call2

26. GSM
NSS
BSS
MS
OSS
UsersExternal
Networks
Operators
GSM Subsystems

27. Entities
MS:
Physical equipment used by the
subscribers
BSS:
Physical equipment that provides radio
coverage
NSS:
Switching functions of GSM
Databases required for subscribers
Done through MSC

28. When an MS is switched
on…What happens??
• It first has to determine if it has access
to PLMN
• It does a location update for the same
informing its PLMN about its location
• Location of an MS is stored in a central
database

29. MS MSCBSS PSTNVLR
GSM
CALL
FLOW
Setup
Send info for outgoing signal
Complete Call
Call Proceeding
Assignment
Assignment
Assignment Complete
Assignment Complete
IAM
Assignment Complete
(ACM)
Alerting
Answer
Connect
Connect Acknowledge

30. Privacy and Security in
GSM
Each subscriber is identified using a
cryptographic security mechanism
Subscriber security information is stored
in the SIM Card
The algorithm are stored in the SIM
card and in the authentication center.

31. Security Algorithms for
GSM
1.Authentication Algorithm(A3)
• Used by handset to compute a
signed response to a
random number transmitted by BS
2.Private key generation(A8)
•Uses the same random number and
K(i) to generate a private
key(K©)that is used for voice and
data privacy
A3 A8
K(I) on SIM Card
RAND(from BS)
SRES to BS K© privacy mask

32. Generation Next…
3G
No boundary between telephony,
information and entertainment services
It will range from voice only to voice,
data, and other multimedia application
Wireless users will be able to make
video conference calls and surf the
internet simultaneously
WHAT IS ALL THIS

33. How is it related to my
topic….
People demand access for information
and services wherever they are
GSM should provide this connectivity.
Internet access and a whole range of
mobile multimedia capability.
Thus GPRS in GSM

34. Pay for what you use…
GPRS enhances GSM data services
There is no end to end connection to be
established, so setting up a GPRS call
is almost instantaneous and users can
be continuously online
And users pay for the actual data
transmitted, rather than for connection
time

35. A GPRS architecture in GSM
BSS
EIR
SGSN
MSC/VLR
SMS-GMSC
GGSNTE
HLR
MT PDN TE
GGSN
Other PLMN
SM-SC

36. Finally Everything Together
GSM
CDMAone
PDC
TDMA
CDMA2000 IX
GPRS
CDMA200 IXEV
WCDMA
EDGE