GSM Fundamental

1
GSM Fundamental

• By
• Uke Kurniawan Usman

2
Agenda

• Network Architecture
• Functional Layer of GSM
• Air Interface
• System Capacity
• Anti Interference Technology
• Network Planning
• Numbering arrangement

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

5
GSM Network Entity
Base Transceiver Station ( BTS )

• 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

6
GSM Network Entity
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.

7
GSM Network Entity
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).

8
GSM Network Entity
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 VLR address

9
GSM Network Entity
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

10
GSM Network Entity
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
11
Agenda

• Network Architecture
• Functional Layer of GSM
• Air Interface
• System Capacity
• Anti Interference Technology
• Network Planning
• Numbering arrangement

12
Overview Function Layers of GSM-1
13
Protocol Stack Structure of GSM
14
Agenda

• Network Architecture
• Functional Layer of GSM
• Air Interface
• System Capacity
• Anti Interference Technology
• Network Planning
• Numbering arrangement

15
TDMA
time

• 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.

User 3
User 2
User 1
Frequency
GSM adopts TDMA/FDMA mode channel width 200KHz
each channel has 8 timeslots
16
GSM Timeslot and Frame structure
Frequency
200KHz
time
BP
15/26ms
interval
17
Frequency Resource
EGSM900 up 880890MHz down
925935MHz duplex interval 45MHz bandwidth
10MHz, frequency interval 200KHz

• GSM900
• up 890915MHz
• down 935960MHz
• duplex interval 45MHz
• bandwidth 25MHz,
• frequency interval 200KHz

GSM1800 up 1710-1785MHz
down 1805-1880MHz duplex interval 95MHz,
working bandwidth 75MHz, frequency interval
200KHz
GSM1900MHz up18501910MHz down19301990MHz dupl
ex interval 80MHz, working bandwidth
60MHz, frequency interval 200KHz
18
Frequency Resource
General Priority
Single Band Network
900MHz
High
1800MHz
Low
1900MHz
New Operator
Propagation Characteristic
For Operator
For Subscriber
19
Frequency Resource
Single Band Network
900MHz
Single Band
1800MHz
Dual Band
1900MHz
Triple Band
In a sense, the network determines the handsets
can be selected. But nowadays, most handsets
support dual band.
20
Frequency Resource
Single Band Network
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
21
Timeslot and Frame structure
1 super high frame 2048 super frame 2715648
TDMA frame
BCCH
CCCH
1 super frame 1326 TDMA frame(6.12s)
SACCH/TCH
SDCH
FACCH
1 multiplex frame 26 TDMA frames(120ms)
1 multiplex frame 51 TDMA frame
0
1
25
24
50
49
1
0
1 TDMA frame 8 timeslot(120/26 4.615ms)
0
1
7
6
5
4
3
2
22
Physical Channel
0
1
7
6
5
4
3
2
8
9
15
14
13
12
11
10
16
23
22
21
20
19
18
17
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.
23
Channel Type-Summary
14.4Kbit/s FR TCH (TCH/F14.4)
9.6Kbit/s FR TCH(TCH/F9.6)
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)
FCCH (down)
channel
SCH (down)
BCH
BCCH (down)
RACH (up)
CCH
CCCH
AGCH (down)
PCH (down)
SDCCH
DCCH
FACCH
SACCH
24
Channel Type

• Traffic Channel
• Transmit voice and data
• Signaling Channel
• transmit the signaling and synchronous data
  between BTS and MS.

25
Channel Type

• 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..)

26
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.

27
Structure of 51-frame Control CH
28
Channel Combination Type

• Several logic channels combine together in
  some way to form some specific types of channel
  to transmit user data or signaling information.
  They are called combined channels. One combined
  channel can be mapped to a physical channel.
• There are the following combined channels
• a TCH/F FACCH/F SACCH/TF
• b TCH/H(0,1) FACCH/H(0,1) SACCH/TH(0,1)
• c TCH/H(0,0) FACCH/H(0,1) SACCH/TH(0,1)
  TCH/H(1,1)
• d FCCH SCH BCCH CCCH
• e FCCH SCH BCCH CCCH SDCCH/4(0...3)
  SACCH/C4(0...3)
• f BCCH CCCH
• g SDCCH/8(0 ..7) SACCH/C8(0 .. 7)
• CCCH PCH RACH AGCH

29
Channel Assignment inside cells

• Small capacity cell with only 1 TRX
• TN0 FCCHSCHCCCHBCCHSDCCH/4(0,_,3)SACCH/C4(0
  ,_,3)
• TN1-7 TCH/FFACCH/FSACCH/TF
• The medium-size cell with 4 TRXs
• 1TN0 group FCCHSCHBCCHCCCH
• 2 SDCCH/8(0,_,7)SACCH/C8(0,_,7)
• 29 TCH/FFACCH/FSACCH/TF

30
Channel Assignment inside cells

• Large-size cell with 12 TRXs
• 1 TN0 group FCCHSCHBCCHCCCH
• 1 TN2 group, 1 TN4 group and 1 TN6 group
  BCCHCCCH
• 5 SDCCH/8(0,_,7)SACCH/C8(0,_,7)
• 87 TCH/FFACCH/FSACCH/TF

31
Agenda

• Network Architecture
• Functional Layer of GSM
• Air Interface
• System Capacity
• Anti Interference Technology
• Network Planning
• Numbering arrangement

32
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.
33
BTS Mode

• Capacity
• 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.

34
System capacity
Erlang 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.
35
Agenda

• Network Architecture
• Functional Layer of GSM
• Air Interface
• System Capacity
• Anti Interference Technology
• Network Planning
• Numbering arrangement

36
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.
37
Reasons for interference

• 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.

38
Interference

• Co-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. 

39
Interference

•  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

40
Solution -Anti-interference

• FH technology
• Dynamic power control (DPC)
• Discontinuous Transceiving (DTX)
• Diversity receiving technique

41
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.

42

• 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.

43
Diversity Reception Technology

• 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 wont take place on the frequency
  outside the coherence bandwidth of the channel.

44
Agenda

• Network Architecture
• Functional Layer of GSM
• Air Interface
• System Capacity
• Anti Interference Technology
• Network Planning
• Numbering arrangement

45
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.
46
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.
47
Agenda

• Network Architecture
• Functional Layer of GSM
• Air Interface
• System Capacity
• Anti Interference Technology
• Network Planning
• Numbering arrangement

48
Numbering Arrangement
International Mobile Subscriber Identification
number (IMSI)
It identifies a unique international universal
number of a mobile subscriber, which consists of
MCCMNCMSIN. 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 PT 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.
49
Numbering Arrangement
Mobile Subscriber ISDN Number(MSISDN)
It is the subscriber number commonly used. China
uses the TDMA independent numbering
plan CCNDC H1H2H3H4 ABC CC country code,
86 NDC network code, 135139, 130 H1H2H3H4 HLR
identification code ABCD
mobile subscriber number inside each HLR
50
Numbering Arrangement
International Mobile Equipment Identification
code (IMEI)
It will uniquely identify a mobile station. It is
a decimal number of 15 digits. Its structure
is TACFACSNRSP TACmodel ratification code,
6 digits FACfactory assembling code, 2
digits SNRsequence code, 6 digits SPreserved, 1
digit
51
Numbering Arrangement
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 00 M1M2M3
ABC CC country code, 86 NDC mobile
network code, 135139, 130 M1M2 same as the
H2H3 of MSISDN ABC 000 -- 999
52
Numbering Arrangement
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.