1. GSM System Architecture1

2. GSM interface 2

3. GSM Network Structure OMC MSC/VLR BSC E BIE PSTN A Abis ISDN PSPDN
BTS
BSS C Um F H
HLR/
AUC
EIR
SC/VM MS
MSS 3

4. Mobile Station ( MS )
Equipment used by mobile service subscribers for access to services.
Mobile Equipment
Subscriber Identity Module (SIM)
Mobile stations are not fixed to one subscriber. A subscriber is identified with the SIM card. 4

5. Base Transceiver Station ( BTS )
Wireless transmission
Wireless diversity
Wireless channel encryption
Conversion between wired and wireless signals
Frequency Hopping
BaseBand Unit:
voice and data speed adapting and channel coding
RF Unit:
modulating/demodulating, transmitter and receiver
Common Control Unit:
BTS operation and maintenance 5

6. Base Station Controller ( BSC )
Managing Wireless network-BSS
Monitoring BTS
Controls:
Wireless link distribution between MS and BTS
Communication connection and disconnection
MS location, handover and paging
Voice encoding, transecoding (TC), rate, adaptation,
The operation and maintenance functions of BSS. 6

7. Mobile Service Switching Center ( MSC )
holds all the switching functions
manages the necessary radio resources,
updating the location registration
carrying out the inter-BSC and inter-MSC tender
Inter-working with other networks (IWF). 7

8. Home Location Register ( HLR )
Manages the mobile subscribers database
subscriber information
part of the mobile location information
3 identities essential
the International Mobile subscriber Identity
the Mobile station ISDN Number
the visitor location register (VLR) address 8

9. Visitor Location Register ( VLR )
Dynamically stores subscriber information needed to handle incoming/outgoing calls
Mobile Station Roaming Number
When a roaming mobile enters an MSC area. This MSC warns the associated VLR of this situation; the mobile enters a registration procedure through which it is assigned a mobile subscriber roaming number (MSRN)
Temporary Mobile Subscriber Identity, if applicable
The location area in which the mobile has been registered
Data related to supplementary service parameters 9

10. AUC/EIR Authentication Center(s) (AUC)
Providing the authentication key used for authorizing the subscriber access to the associated GSM PLMN.
Equipment Identity Register(s) (EIR)
Handling Mobile Station Equipment Identity 10

11. Overview: Function Layers of GSM-111

12. Protocol Stack Structure of GSM12

13. TDMA
Concept:
channel is composed of a series of timeslots of periodicity. Different signal energies are distributed into different timeslots. The adjacent channel interference is restricted by connection choosing from time to time. So the useful signal is passed only in the specified timeslot.
GSM adopts TDMA/FDMA mode
channel width: 200KHz,
each channel has 8 timeslots
time
User 3
User 2
User 1
Frequency 13

14. GSM Timeslot and Frame structure
Frequency
200KHz
time BP
15/26ms
interval 14

15. GSM Spec 15

16. Frequency Resource EGSM900 : up: 880~890MHz down: 925~935MHz
duplex interval: 45MHz
bandwidth: 10MHz，
frequency interval: 200KHz
GSM900 :
up: 890~915MHz
down: 935~960MHz
duplex interval: 45MHz
bandwidth: 25MHz，
frequency interval: 200KHz
GSM1800 :
up: MHz down: MHz
duplex interval: 95MHz， working bandwidth: 75MHz，
frequency interval: 200KHz
GSM1900MHz:
up:1850~1910MHz
down:1930~1990MHz
duplex interval: 80MHz， working bandwidth: 60MHz，
frequency interval: 200KHz 16

17. Frequency Resource General Priority Single Band Network 900MHz High
Which one?
900MHz
High
1800MHz
Low
1900MHz
New Operator
Reason
Propagation Characteristic
For Operator
For Subscriber 17

18. Single Band Network Single Band 900MHz Dual Band 1800MHz Triple Band
In a sense, the network determines the handsets can be selected.
But nowadays, most handsets support dual band. 18

19. Single Band Network The higher the propagation frequency 900MHz
Cell coverage radius :
We know
Propagation characteristic
The higher the propagation frequency
The higher the propagation loss
The smaller the cell coverage radius.
900MHz
1800MHz
1900MHz 19

20. Timeslot and Frame structure
1 super high frame = 2048 super frame = TDMA frame
2045
2046
2047 3 2 1
2044 49 47 48 50 24 25
BCCH
1 super frame = 1326 TDMA frame（6.12s）
CCCH
SACCH/TCH
SDCH
FACCH
1 multiplex frame = 26 TDMA frames（120ms）
1 multiplex frame = 51 TDMA frame 1 24 25 1 49 50
1 TDMA frame = 8 timeslot（120/26 = 4.615ms） 1 2 3 4 5 6 7 20

21. GSM Frame 21

22. Control Channel Frame 22

23. Time Slot Data Bursts 23

24. GSM Frame Structure 24

25. Physical Channel
The physical channel adopts FDMA and TDMA techs. On the time domain, a specified channel occupies the same timeslots in each TDMA frame, so it can be identified by the timeslot number and frame number. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 25

26. GSM Speech 26

27. GSM Speech 27

28. Channel Type-Summary 14.4Kbit/s FR TCH (TCH/F14.4)
Data CH
4.8Kbit/s FR TCH (TCH/F4.8)
TCH
4.8Kbit/s HR TCH (TCH/H4.8)
FR Voice Traffic Channel (TCH/FS)
Voice CH
Enhanced FR Traffic Channel (TCH/EFR)
HR Traffic Channel (TCH/HS)
channel
FCCH (down)
SCH (down)
BCH
BCCH (down)
RACH (up)
CCH
CCCH
AGCH (down)
PCH (down)
SDCCH
DCCH
FACCH
SACCH 28

29. Traffic Channel Signaling Channel Channel Type BCH :
Transmit voice and data
Signaling Channel
transmit the signaling and synchronous data between BTS and MS.
BCH :
Frequency Correction CHannel（FCCH）
-- for MS error correction
Synchronous Channel（SCH)
-- for MS frame synchronization and BTS recognization
Broadcasting Control CHannel（BCCH）
-- broadcasting information(cell selection information, etc..) 29

30. Channel Type
DCCH
Self-help Dedicated Control Channel（SDCCH）
for channel distribution information transmission
Slow Associated Control Channel （SACCH）
combined with one traffic channel or SDCCH, to transmit some specific information of user information
Fast Associated Control Channel （FACCH）
combined with one traffic channel, taking the same signal as SDCCH. It occupies the service channel to transmit signaling information. 30

31. Cell Mode Layout Omni-directional cell Adopt omni-directional antenna，
the overall directional propagation characteristic is the same.
Directional cell
In general, cell with multi-sector is in common use. Every directional cell adopts directional antenna. 31

32. BTS Mode Capacity Note: TRX-transceiver,each TRX handles 1 frequency.
When the traffic is very low, and no possibility for quick increment, Omni-directional cell is used in common. Otherwise, we suggest to adopt the sector cell.
Note: TRX-transceiver,each TRX handles 1 frequency.
Coverage Area
Sector cell is often used to enlarge the cell coverage radius because of the higher antenna gain.
For special coverage ,such as road coverage, two-sector cell is adopted firstly. 32

33. System capacity Erlang : GOS:
the traffic intensity of a totally occupied channel (i.e. the call hour of a unit hour or the call minute of a unit minute). For example, the traffic of a channel occupied for 30 minutes in an hour is 0.5 Erlang)
GOS:
defined as the probability of call blocking or the probability when the call delay time is longer than a given queuing time. 33

34. Reasons for Interference
The transmission path is very complex, ranging from the simple line-of-sight transmission to encountering such terrain as buildings, hills and trees. Wireless channels are extremely unpredictable.
Abrupt drop, or fading, of signal strength in the land mobile wireless channel is quite common. The fading feature of the mobile channel depends on the radio wave propagation environment.
Environmental factors:
Terrain (mountains, hills, plains, water bodies, etc.);
The quantity, heights, distribution and materials of buildings;
The vegetation of the region;
Weather conditions;
Natural and artificial electromagnetic noises;
Frequency;
How MS is moved. 34

35. Interference Co-Channel Interference Adjacent Channel Interference
Conception: the interference among the signals of co- channel cells is called co-channel interference.
Result from : Frequency reuse
Reduction method: co-channel cells must physically be spaced at a minimum interval to ensure adequate isolation of transmissions.
Adjacent Channel Interference
Conception: The signal interference from the frequency adjacent to that of the signal used is called adjacent channel interference.
Reduction method: accurate filtering and channel allocation (maximizing channel intervals of the cell). Interval of frequency reuse inter-cell interference, such as C/I, C/A 35

36. Solution -Anti-interference
FH technology
Dynamic power control (DPC)
Discontinuous Transceiving (DTX)
Diversity receiving technique 36

37. Frequency Hopping Technique
Reason:
counteract Rayleigh Fading
scatter interference among multiple calls
Types:
Base band frequency hopping
keeps the transmission and receiving frequency of each carrier unit unchanged, but merely sends FU transmission data to different carrier units at different FN moments.
radio frequency hopping
controls the frequency synthesizer of each transceiver, making it hop according to different schemes in different time slots. 37

38. Discontinuous Speech Transmission (DTX)
Two aims can be achieved by adopting DTX mode:
lower the total interference electric level in the air
save transmitter power.
TRAU BTS
BTS MS
Speech frame
480 ms
comfort noise frame 38

39. Diversity Reception Technique
The multi-path propagation of radio signals causes magnitude fading and delay time.
Space Diversity (antenna diversity)
Polarization Diversity
orthogonal polarization diversity.
horizontal polarization and vertical polarization.
Frequency Diversity
The working principle of this technology is that such fading won’t take place on the frequency outside the coherence bandwidth of the channel. 39

40. Frequency Reuse “4 ´ 3” reuse mode:
one group includes 3 sectors /site ,12 frequency which are distributed to 4 sites. Every site owns 3 frequency. 40

41. Frequency Reuse “3 ´ 3” reuse mode:
one group includes 3 sectors /site ,9 frequency which are distributed to 3 sites. Every site owns 3 frequency. 41

42. Numbering Arrangement
International Mobile Subscriber Identification number (IMSI)
It identifies a unique international universal number of a mobile subscriber, which consists of MCC+MNC+MSIN.
1) MCC: country code, 460
2）MNC: network code, 00 or 01
3）MSIN: subscriber identification, H1H2H3H4 9XXXXXX,
H1H2H3H4: subscriber registering place
H1H2: assigned by the P&T Administrative Bureau (operator )to different provinces, to each province
H3H4: assigned by each province/city
the IMSI of user will be written into the SIM card by specific device and software and be stored into the HLR with other user information. 42

43. Mobile Subscriber ISDN Number（MSISDN）
It is the subscriber number commonly used. China uses the TDMA independent numbering plan:
CC+NDC+ H1H2H3H4 +ABC
CC: country code, 86
NDC: network code, 135—139, 130
H1H2H3H4: HLR identification code
ABCD: mobile subscriber number inside each HLR 43

44. International Mobile Equipment Identification code (IMEI)
It will uniquely identify a mobile station. It is a decimal number of 15 digits. Its structure is:
TAC+FAC+SNR+SP
TAC=model ratification code, 6 digits
FAC=factory assembling code, 2 digits
SNR=sequence code, 6 digits
SP=reserved, 1 digit 44

45. Mobile Subscriber Roaming Number (MSRN)
The MSRN is temporarily distributed to the subscriber by the VLR according to the request by the HLR when this subscriber is called. The MSRN is released and can be assigned to other subscriber later.
　　 CC + NDC M1M2M3 + ABC
　 CC: country code, 86
　　 NDC: mobile network code, 135—139, 130
　　 M1M2: same as the H2H3 of MSISDN
　　 ABC:
Temporarily Mobile Subscriber Identification Number (TMSI)
To insure the IMSI security, the VLR will assign an unique TMSI number for the accessed subscriber. It is used locally only and is a 4-byte TMSI number BCD code. 45