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1. 10/2/2020 1
GSM Fundamentals
Presentation By:
ABDULELLAH QASIM

2. Page 2
Chapter 1 GSM System Overview
Chapter 2 GSM Network Structure
Chapter 3 Service Area and Number Planning
Chapter 4 Channels on the Wireless Interface
Chapter 5 Radio Techniques
Chapter 6 GPRS & EDGE Introduction

3. GSM system overview
• The GSM system is a frequency- and time-division cellular system,
each physical channel is characterized by a carrier frequency and a
time slot number
• Cellular systems are designed to operate with groups of low-power
radios spread out over the geographical service area. Each group of
radios serve MSs presently located near them. The area served by
each group of radios is called a CELL
• Uplink and downlink signals for one user are assigned different
frequencies, this kind of technique is called Frequency Division
Duplex (FDD)
• Data for different users is conveyed in time intervals called slots ,
several slots make up a frame. This kind of technique is called Time
Division Multiple Access (TDMA)
Page 3

4. GSM Development
Page 4
Standard Protocol for GSM take effect
System was named as Global System for
Mobile Communication
GSM system began to provide service in Europe(2G)
Provide services for the whole world
Micro Cell Technique is used in GSM system
1989
1991
1992
1994
1996

5. Cell Technique
• A certain radio coverage area formed by a set of transceivers that
connected to a set of antennas is called a CELL.
• Macro Cell
• In the beginning , High-Power BTSs are adopted to provide services. The BTS
covers a wider area , but its frequency utilization is not efficient. So , it can
only provide a few channels for subscribers.
• Micro Cell
• Later the Low-Power BTS joins the system for getting a better service area with
high capacity . At the same time it adopts the frequency reuse technique to
improve the efficiency of the frequency utilization and also the whole capacity
of the network.
Page 5
Macro Cell and Micro Cell

6. Multiple Access Technique
• Multiple Access Technique allows many subscribers to use
the same communication medium.
• There are three kinds of basic Multiple Access Technique :
FDMA , TDMA and CDMA.
• GSM system adopt FDD-TDMA (FDMA and TDMA together).
Page 6

7. FDMA
• FDMA uses different frequency
channels to accomplish
communication.
• The whole frequency spectrum
available is divided into many
individual channels (for
transmitting and receiving)，
every channel can support the
traffic for one subscriber or some
control information.
Page 7
Frequency
Time

8. TDMA
• TDMA accomplishes the
communication in different
timeslot.
• A carrier is divided into
channels based on time.
Different signals occupy
different timeslots in
certain sequence , that is ,
many signals are
transmitted on the same
frequency in different time.
Page 8
Time
Frequency

9. The Frequency Spectrum
Page 9
GSM 900
Duplex Separation: 45MHz
Channel Bandwidth: 200KHz
Uplink
890 915 935 960MHz
Downlink

10. The Frequency Spectrum
Page 10
Duplex Separation: 95MHz
Channel Bandwidth: 200KHz
Base Station Receive
1710 1785 1805 1880MHz
Base Station Transmit
DCS 1800

11. The Frequency Spectrum
Page 11
Frequency
Spectrum
Range (MHz) Uplink Frequency
Frequency
Point
Available
Downlink
Frequency
GSM 450
450.4~457.6
460.4~467.6
Fu(n)=450.6+0.2(n-259) 259<=n<=293 Fd(n)=Fu(n)+10
GSM 480
478.8~486
488.8~496
Fu(n)=479+0.2(n-306) 306<=n<=340 Fd(n)=Fu(n)+10
GSM 850
824~849
869~894
Fu(n)=824.2+0.2(n-128) 128<=n<=251 Fd(n)=Fu(n)+45
E-GSM 900
880~915
925~960
Fu(n)=890+0.2n
Fu(n)=890+0.2(n-1024)
0<=n<=124
975<=n<=1023
Fd(n)=Fu(n)+45
R-GSM 900
876~915
921~960
Fu(n)=890+0.2n
Fu(n)=890+0.2(n-1024)
0<=n<=124
955<=n<=1023
Fd(n)=Fu(n)+45
PCS 1900
1850~1910
1930~1990
Fu(n)=1850.2+0.2(n-512) 512<=n<=810 Fd(n)=Fu(n)+80

12. Frequency Reuse
• The frequency resource of mobile system is very limited.
• The different Subscribers can use the same frequency in
different places.
• The quality of communication must be ensured.
Page 12
7(Site)X 1(Cell) reuse
2
R
4 site X 3 cells reuse

13. Cell Types
Page 13
120 Degree Cell
Omni
1
120
degree
1
2
3
Omni-directional Cell

14. GSM-GPRS Network Component
Page 14
GSM /GPRS BSS
BTS
BSC
BTS
BSC
PCU
SS7
SMS system
PSTN
ISDN
Internet,
Intranet
MSC/VLR GMSC
HLR/AUC
SGSN
CG BG
GGSN
GPRS Backbone
Other PLMN
MS
MS
OMC

15. Interface Between Different Entities
Page 15
GSM /GPRS BSS
BTS
BSC
BTS
BSC
PCU
SS7
SMS system
PSTN
ISDN
Internet,
Intranet
MSC/VLR GMSC
HLR/AUC
SGSN
CG BG
GGSN
GPRS backbone
Other PLMN
A
Gb
Gi
Gp
C/D/Gs
Gr/Gs/Gd/Ge Gc
Ga
Abis
Um
MS
MS
OMC

16. Mobile Station—MS
Page 16
International Mobile Equipment Identity (IMEI)
– Mobile Equipment
MS=ME+SIM
International Mobile Subscriber Identity (IMSI)
– Subscriber Identity Module

17. Subscriber Identity Module – SIM
Page 17
• International Mobile Subscriber Identity (IMSI)
• Temporary Mobile Subscriber Identity (TMSI)
• Location Area Identity (LAI)
• Subscriber Authentication Key (Ki)
SIM

18. Base Station Subsystem – BSS
• The Base Station Controller –
BSC
• The Base Transceiver Station
– BTS
• The Trans-coder – TC and Sub
multiplexer (SM)
Page 18
BTS
BSC
TC/SM
BSS
MSC

19. Packet Control Unit-----PCU
Page 19
• Packet data
switching
• Bridge between
SGSN and BSC
• Provide Pb and Gb
interface
BTS
BSC
TC/SM
BSS
MSC
GPRS
Backbone
PCU SGSN

20. The Network Switching System
Page 20
Mobile-service Switching Center – MSC
Home Location Register – HLR
Visitor Location Register – VLR
Equipment Identity Register – EIR
Authentication Center – AUC
Echo Cancellor – EC
AUC
HLR
MSC/VLR
PSTN
NSS
EIROMC
BSS
EC

21. Mobile-service Switching Center – MSC
Page 21
• Call Processing
• Operations and Maintenance Support
• Interface management
• Inter-network & Inter-working
• Billing
Home Location Register – HLR
• Subscriber ID (IMSI and MSISDN)
• Current subscriber VLR (current location)
• Supplementary service information
• Subscriber status (registered/deregistered)
• Authentication key and AuC functionality
Visitor Location Register – VLR
• Mobile Status (IMSI attached / detached / busy / idle etc.)
• Location Area Identity(LAI)
• Temporary Mobile Subscriber Identity(TMSI)
• Allocating the Roaming Number

22. Equipment Identity Register – EIR
• White List
• Black List
• Grey List
Page 22
IMEI is Checked In White List
IMEI is Checked in Black/Grey List
If NOT found
EIR focus on the
equipment , not the
subscriber!!

23. OMC Functional Architecture
Page 23
OS
MMI
DB
Event/Alarm
Management
Security
Management
Configuration
Management
Performance
Management
Fault
Management

24. Service Area
Page 24
PLMN service area
......
Service Area
MSC service area...
Location area...
cell
PLMN service area PLMN service area
MSC service area...
Location area...
cell

25. LAI
Page 25
Location Area Identification
The LAI is the international code for a location area.
MCC: Mobile Country Code，It consists of 3 digits .
For example: The MCC of China is "460"
MNC: Mobile Network Code，It consists of 2 digits .
For example: The MNC of China Mobile is "00"
LAC: Location Area Code，It is a two bytes hex code.
The value 0000 and FFFF is invalid.
For example: 460-00-0011
MCC MNC LAC

26. CGI
Page 26
The CGI is a unique international identification for a cell
The format is LAI+CI
LAI: Location Area Identification
CI: Cell Identity. This code uses two bytes hex code to
identify the cells within an LAI.
For example : 460-00-0011-0001
CGI: Cell Global Identification

27. BSIC
Page 27
NCC: PLMN network color code. It comprises 3 bit. It
allows various neighboring PLMNs to be
distinguished.
BCC: BTS color code. It comprises 3 bit, used to
distinguish different cells assigned the same
frequency!
NCC BCC
BSIC
BSIC（Base Station Identification Color Code)

28. MSISDN
Page 28
CC: Country Code. For example: The CC of China is "86".
NDC: National Destination Code. For example: The NDC of
China Telecom is 139, 138, 137, 136, 135.
SN: Subscriber Number. Format:H0 H1 H2 H3 ABCD
Example: 86-139-0666-1234
CC NDC SN
National (significant)
Mobile number
Mobile station international
ISDN number

29. IMSI
Page 29
MCC: Mobile Country Code，It consists of 3 digits .
For example: The MCC of China is "460"。
MNC: Mobile Network Code，It consists of 2 digits .
For example: The MNC of China Telecom is "00"。
MSIN: Mobile Subscriber Identification Number. H1H2H3 S ABCDEF
For example: 666-9777001
NMSI: National Mobile Subscriber Identification，MNC and MSIN
form it together.
For Example of IMSI : 460-00-666-9777001
Not more than 15 digits
3 digits 2 digits
IMSI
MCC MNC MSIN
NMSI

30. TMSI
• The TMSI is assigned only after successful subscriber authentication.
• The VLR controls the allocation of new TMSI numbers and notifies them
to the HLR.
• TMSI is used to ensure that the identity of the mobile subscriber on the
air interface is kept secret.
• The TMSI consists of 4 bytes( 8 HEX numbers) and determined by the
operator.
Page 30
TMSI: Temporary Mobile Subscriber Identification)

31. IMEI
Page 31
TAC FAC SNR SP
IMEI
IMEI: International Mobile Station Equipment Identification
TAC: Type approval code, 6 bit, determined by the type approval center
FAC: Final assembly code, 2 bit, It is determined by the manufacturer.
SNR: Serial number, 6 bits, It is issued by the manufacturer of the MS.
SP: 1 bit , Not used.
Check the IMEI in your MS : *#06#

32. Physical Channel and Logical Channel
Page 32
2 30 16 74 52 3
The physical channel is the medium over which the
information is carried: 200KHz and 0.577ms
0 1
TDMA FRAME
Timeslot The information carried in one time
slot is called a “burst”
The logical channel consists of the information carried
over the physical channels
TDMA FRAME

33. Two types of Logical Channel
Page 33
Traffic Channel (TCH) :
Transmits traffic information, include data
and speech.
Control Channel (CCH) :
Or Signaling Channel, transmits all kinds of
control information.

34. Traffic Channel (TCH)
Page 34
TCH
Traffic Channels
Speech
TCH/FS
Data
TCH/HS
TCH/9.6 TCH/2.4
TCH/4.8
TCH Traffic Channel
TCH/FS Full rate Speech Channel
TCH/HS Half rate Speech Channel
TCH/9.6 Data Channel 9.6kb/s
TCH/4.8 Data Channel 4.8kb/s
TCH/2.4 Data Channel 2.4Kb/s

35. Control Channel (CCH)
Page 35
FCCHSCH
CCH (Control Channels)
DCCH
SDCCH
BCH
BCCH Synch. CH.
ACCH
SACCHFACCH CCCH
RACH CBCH
PCH/AGCH
Broadcast Control Channel – BCCH
Common Control Channel – CCCH
Dedicated Control Channel – DCCH
Associated Control Channel – ACCH

36. Broadcast Control Channel – BCCH
Page 36
CCH
BCH
BCCH
Synch.
Channels
SCH FCCH
The information carried on the BCCH
is monitored by the MS
periodically when it is in idle mode
BCCH: Broadcast Control Channel
FCCH: Frequency Correction Channel
SCH: Synchronization Channel

37. Common Control Channel – CCCH
Page 37
CCH
CCCH
RACH
uplink
CBCH
downlink
PCH/AGCH
downlink
The CCCH is responsible for
transferring control information
between all mobiles and the
network.
RACH: Random Access Channel
PCH: Paging Channel
AGCH: Access Granted Channel
CBCH: Cell Broadcast Channel

38. Dedicated Control Channel – DCCH
Page 38
CCH
DCCH
SDCCH
FACCH SACCH
DCCH is assigned to a single
wireless connection for
measurement and handover
purpose.
SDCCH: Stand-alone Dedicated
Control Channel
ACCH: Associated Control Channel
SACCH: Slow Associated
Control Channel
FACCH: Fast Associated Control
Channel
ACCH

39. Uplink Logical channel
Page 39
RACH CCCH
CCH
SDCCH
SACCH
FACCH
TCH/F
TCH/H
DCCH
TCH
DCH

40. Downlink Logical channel
Page 40
FCCH
SCH
BCCH
PCH
AGCH
BCCH
CCCH
CCH
SDCCH
SACCH
FACCH
TCH/F
TCH/H
DCCH
TCH
DCH

41. How to use these channels?
Page 41
Allocate signaling channel
FCCH
SCH
BCCH
PCH
RACH
AGCH
SDCCH
SDCCH
TCH
FACCH
Power-off
Idle mode
Dedicated mode
Idle mode
Search for frequency correction burst
Search for synchronous burst
Extract system information
Monitor paging message
Send access burst
Set up the call
Allocate voice channel
Conversation
Release the call

42. Packet logic channel
• Packet data channel (PDCH)
• Comprising packet service channel and packet control channel
• Packet service channel (PDTCH)
• Combined into the single-directional service channel
• Packet control channel
• Broadcast control channel: PBCCH
• Public control channel: PPCH, PRACH, PAGCH
• Private control channel: PACCH, PTCCH
Page 42
TCH
BCCH
SACCH
CCCH
TCH

43. GSM Logical Channel Combination
Page 43
Main BCCH combination – FCCH + SCH + BCCH + CCCH
SDCCH combination – SDCCH/8 + SACCH/8
Combined BCCH – BCCH + CCCH +SDCCH/4 + SACCH/4
TCH/FR combination – TCH/F + FACCH/F + SACCH/F
TCH/HR combination – TCH/H + FACCH/H + SACCH/H

44. Combination of packet logic channel
• Packet logic channels (PDCH) can be combined via the following three modes
• Mode 1: PBCCH+PCCCH+PDTCH+PACCH+PTCCH;
• Mode 2: PCCCH+PDTCH+PACCH+PTCCH;
• Mode 3: PDTCH+PACCH+PTCCH
• In case of small GPRS traffic, GPRS and circuit services use the same BCCH and CCCH in
the cell. In this case, only combination mode 3 is needed in the cell
• With the increase of traffic, the packet public channel should be configured in the cell.
Channel combination mode 1 and mode 2 should be adopted
Page 44

45. GSM Multi-frames
Page 45
TDMA Frames
0 1
0 1 2 43 46 47 48 5049
51 – Frame Multi-frames
0 1 10
CONTROL
CHANNELS
2 3 4 5 6 7 2 3 5 764

46. GSM Multi-frames
Page 46
TDMA Frames
0 1
0 1 2 43 21 22 23 2524
26 – Frame Multi-frames
0 1 10
TRAFFIC
CHANNELS
2 3 4 5 6 7 2 3 5 764

47. Power Control
Page 47
Saves battery power
Reduces co-channel and
adjacent channel interference
8W
0.8W
5W
Both Uplink and Downlink
power settings can be
controlled independently
and individually.
BCCH -------
Does not attend Power control

48. DTX and VAD
Page 48
Voice Activity Detection – VAD
Discontinuous Transmission – DTX
Battery Saving
Interference reduction

49. Timing Advance (TA)
Page 49
Transmission delay t
Transmission delay t
TA
The mobile phone should
send the signal in advance!

50. Multi-path Fading
Page 50
• Diversity
• Frequency Hopping
Time Dispersion

51. Diversity – What’s Diversity?
Page 51
⚫ Receive diversity provides an effective technique for both
overcoming the impact of fading across the radio channel and
increasing the received signal to interference ratio.
⚫ The former is achieved by ensuring “uncorrelated” (i.e. low
enough correlated) fading between antenna branches i.e. not
all antennas experience fades at the same time.

52. Kinds of Diversity
Page 52
⚫ Time diversity
Coding, interleaving
⚫ Frequency diversity
Frequency hopping
⚫ Space diversity
Multiple antennas
⚫ Polarization diversity
Dual-polarized antennas
⚫ Multi-path diversity
Equalizer
t
f

53. Frequency Hopping
Page 53
Frequency
f 0
Frame
f 1
f 2
f 3
f 4
Time

54. GSM Development Evolution
Page 54
57.6 kbps
115 kbps
384kbps
2Mbps
GSM
HSCSD
GPRS
EDGE
IMT-2000
9.6 kbps
2G
2.5G
3G

55. Data rate of EDGE and GPRS
Page 55
8PSKGMSK
9.0
13.4
15.6
21.4
8.8
11.2
14.8
17.6
22.4
29.6
44.8
54.4
59.2
0.0
10.0
20.0
30.0
40.0
50.0
60.0
CS-1 CS-2 CS-3 CS-4 MCS-1 MCS-2 MCS-3 MCS-4 MCS-5 MCS-6 MCS-7 MCS-8 MCS-9
Kbps
GPRS
EGPRS

56. 56
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