- GSM is a standard for 2G digital cellular networks that uses narrowband TDMA. It describes protocols for features like GPRS, EDGE, authentication, encryption, and more. - The GSM architecture consists of mobile equipment (handsets), a base station subsystem for radio network management, a network switching subsystem for call routing, and a network management subsystem. - Key aspects include the SIM card for user identification, base transceiver stations for radio signals, transcoding between speech formats, home and visitor location registers for subscriber data, and authentication centers for security.

1. GSM Architecture
By:
•Hassan Amjad
•Bilal Waheed
•Mohsin Amin

2. Intro to GSM:
• GSM (Global System for Mobile
Communication)
• It is a standard set developed by the ETSI.
• It describe protocols for 2G digital cellular
networks.
• Full duplex.
• GPRS & EDGE facilities.

3. GSM Variants :
Variant Uplink Downlink Total Duplex- Channels
(MHz) (MHz) Bandwidth frequency
GSM-400 451-458 and 461-468 and Twice 14 MHz 10 MHz Twice 72
479-486 489-496
GSM-900 890-915 935-960 Twice 25 MHz 45 MHz Twice 124
(primary
band)
Extended 880-915 925-960 Twice 35 MHz 45 MHz Twice 174
GSM-900
GSM-R 876-880 921-925 Twice 4 MHz 45 MHz Twice 19
DCS-1800 1,710-1,785 1,805-1,880 Twice 75 MHz 95 MHz Twice 373
PCS-1900 1,850-1,910 1,930-1,990 Twice 60 MHz 80 MHz Twice 300

4. GSM Architecture
What so ever the variants are the basic architecture
of GSM network remains the same as elaborated
below:
• BSS (Base Station Subsystem)
• NSS ( Network Switching Subsystem )
• NMS ( Network Management Subsystem )

5. Architecture Diagram :

6. ME:
• Mobile equipment
• Handset + SIM
+

7. Handset:
• is a device that can make and
receive telephone calls
• over a radio link
• Can moving around a wide
geographic area.

8. SIM:
Subscriber identification module
It contains
• IMSI ( international mobile subscriber identity )
• PIN (personal identification number )
• PUK ( personal un blocking code )
• ICCID ( integrated circuit card identification )

9. • IMSI ( used by operators to identify user)
• IMSI = MCC+MNC+MSIN
i. MCC ( mobile country code)
ii. MNC ( mobile network code)
iii. MSIN ( mobile user identification number )
• ICCID (SIM is internationally recognized by this
number )
• Usually printed on SIM

10. Base Station Subsystem:
• The Base Station Subsystem is responsible for
managing the radio network, and it is controlled
by an MSC.
• A BSS itself may cover a considerably large
geographical area consisting of many cells (a cell
refers to an area covered by one or more
frequency resources).

11. BSS consists of three element
• BTS ( Base transceiver station)
• BSC ( Base station controller )
• TC ( Tran coder)

12. Base transceiver station:
• Encoding, encrypting, multiplexing,
modulating, and feeding the RF
signals to the antenna.
• Time and frequency synchronizing
• Decoding, decrypting, and equalizing
received signals
• Random access detection
• Uplink channel measurements

13. Base station controller :
• The BSC manages the radio resources for
one or more BTSs. It handles radio channel
setup, frequency hopping, and handovers.
• The BSC is the connection between the
mobile and the MSC.
• Control of frequency hopping
• Performing traffic concentration to reduce
the number of lines from the MSC
• Reallocation of frequencies among BTSs
• Time and frequency synchronization
• Power management

14. Transcoder:
• In the air interface (between MS and BTS), the
media carrying the traffic is a radio frequency.
• To enable an efficient transmission of digital
speech information over the air interface, the
digital speech signal is compressed.
• We must however also be able to communicate
with and through the fixed network, where the
speech compression format is different.
• Somewhere between the BTS and the fixed
network, we therefore have to convert from one
speech compression format to another, and this
is where the Transcoder comes in.

15. • For transmission over the air interface, the speech
signal is compressed by the mobile station to
• 13 k bit/s (Full Rate and Enhanced Full Rate),
• 5.6 k bit/s (Half Rate),
• 12.2 k bit/s (Enhanced Full Rate).
• AMR (Adaptive Multirate Coding) which is more
flexible since it produces speech with bitrates
similar to older solutions but adapted to link
conditions.
• However, the standard bit rate for speech in the
PSTN is 64 Kbits/s. The modulation technique is
called "Pulse Code Modulation" (PCM). This
requires the GSM network to perform bit rate
adaptation of speech.

16. Network switching subsystem (NSS)
NSS typically consists of following
elements
• MSC (Mobile switching center)
• HLR (Home location register )
• VLR ( visitor location register )
• AUC (Authentication center )
• EIR ( Equipment identity register)
• GMSC ( Gate way mobile switching
center )

17. HLR:
• centralized network database
• stores and manages all mobile
subscriptions belonging to a specific
operator.
• a permanent store for subscriber until
that subscription is canceled.
It stores
1. Subscriber identity
2. Subscriber supplementary services
3. Subscriber location information
4. Subscriber authentication information

18. VLR :
• It is a temporary database .
• Stores only information of subscriber
those are in that MSC.
• Every MSC has its own VLR
• When a subscriber roams into a new
MSC service area, the VLR connected to
that MSC requests information about
the subscriber from the subscriber's
HLR.

19. EIR :
• Data base used to store mobile identity
• Help us blocking calls from stolen MS

20. AUC:
• AUC is a database connected to the HLR
• Function is to authenticate the subscribers
attempting to use a network.

21. MSC & GMSC:
• MSC performs the telephony switching functions
for the mobile network.
• controls calls to and from other telephony and
data systems, such as the Public Switched
Telephone Network (PSTN), Integrated Services
Digital Network (ISDN).
• In GMSC Gateway functionality enables an MSC
to interrogate a network's HLR in order to route
a call to a Mobile Station (MS).
• Any MSC can be GMSC

22. NMS:
NMS consists of two element
1. OMC ( Operation and maintenance center )
2. NMC (Network management center )

23. OMC & NMC
• OMC a computerized monitoring & maintenance
center which is connected MSCs and BSCs.
• OMC is local.
• In NMC centralized control of a network is done.
• One NMC per network to control many OMCs.
• OMC and NMC functionality can be combined in
the same physical network node.

24. GSM GEOGRAPHICAL NETWORK
STRUCTURE
Local area (LA)
• LA is as a group of cells.
• Within the network, a subscriber’s location is
known by the LA.
• The identity of the LA in which an MS is
currently located is stored in the VLR.

25. MSC SERVICE AREA
• An MSC service area is made up of a number of
LAs and
• MSC use LA to route a call to MS

26. Hardware view of a sample network

27. Software view of a sample network

28. GMSK:
• Gaussian Minimum Shift Keying.
• Gaussian Minimum Shift Keying (GMSK) is a
form of continuous-phase FSK in which the
phase change is changed between symbols to
provide a constant envelope. Consequently it is a
popular alternative to QPSK.
• The RF bandwidth is controlled by the Gaussian
low-pass filter.

29. continuous-phase :
continuous-phase
• In CPM the carrier phase is modulated in a
continuous manner in contrast to QPSK .

30. • CPM is typically implemented as a constant-
envelope waveform.
• QPSK requires a relatively large percentage of
the power to occur outside of the intended band.
• CPM is attractive because the phase continuity
yields high spectral efficiency.
• The primary drawback is the high
implementation complexity required for an
optimal receiver.

31. MSK:
• Minimum shifting keying .
• It is similar to OQPSK
• OQPSK gives us square wave which is difficult to
handle.
• MSK gives us half cycle sinusoidal wave for a symbol

32. GMSK:
• Gaussian minimum shifting keying
• MSK with Gaussian filter.
•

33. Gaussian filter
• Gaussian filters are designed to give no
overshoot to a step function input while
minimizing the rise and fall time.
• Gaussian filter has the minimum possible time
delay

34. Example
The filter smoothes the binary pulses

35. signal is integrated over time to obtain a continuous
waveform which captures the bit transition information

36. • Send this wave to IQ modulator .
• Integrate out put and send it

37. ADVANTAGES DISADVANTAGES
• High spectral efficiency. • Higher power level than
• Reducing sideband QPSK.
power. • Requiring more complex
• Excellent power channel equalization
efficiency due to constant algorithms such as an
envelope. adaptive equalizer at the
• Good choice for voice receiver.
modulation. • Inter symbol interference

38. Interleaving
• Interleaving rearranges a group of bits in a parti
cular way.
• Improve the performance of the error correction
mechanisms
• The interleaving decreases the possibility of
losing whole bursts during the transmission.

39. Interleaving