2. 2
TOPICS
• GSM CONCEPTS
• GSM SYSTEM ARCHITECTURE
• IDENTITIES USED IN GSM
• GSM CHANNELS
• GSM RADIO LINK
• MOBILITY MANAGEMENT
• CALL MANAGEMENT
• RADIO RESOURCE MANAGEMENT
3. 3
TOPICS
• GSM CONCEPTS
• GSM SYSTEM ARCHITECTURE
• IDENTITIES USED IN GSM
• GSM CHANNELS
• GSM RADIO LINK
• MOBILITY MANAGEMENT
• CALL MANAGEMENT
• RADIO RESOURCE MANAGEMENT
4. 4
Telecom Basics
• Communication
– Voice and Data
– Analog and Digital
– Circuit Switched and Packet Switched
– Media - Copper Wire, Co-axial cable, Air, Optical
Fibre
– Networks -PSTN, ISDN, PDN and Mobile
Networks
5. 5
Background to GSM
• 1G : Advanced Mobile Phone Service (AMPS)
• Analog, Circuit Switched, FDMA, FDD
• 2G : Digital Advanced Mobile Phone Service (D-AMPS)
• Digital, Circuit Switched, FDMA, FDD
• 2G : Global System for Mobile (GSM)
• Digital, Circuit Switched, FDMA and TDMA, FDD
• 2G : Code Division Multiple Access (CDMA)
• Digital, Circuit Switched, CDMA, FDD
7. 7
1982: Groupe Spécial Mobile (GSM)
created
1984: Description of GSM features
1985: List of recommendations settled
1987: Initial MoU (Memorandum of
Understanding) aside the drafting
of technical specifications was
signed by network operators of 13
countries:
1988: Validation and trials, of the radio
interface.
1991: First system trials are
demonstrated at the Telecom 91
exhibition.
1992: Official commercial launch of
GSM service in Europe. First
Launch in Finland
1993: The GSM-MoU has 62
signatories in 39 countries
worldwide.
1995: Specifications of GSM phase 2
are frozen.
1999: GSM MoU joins 3GPP (UMTS)
GPRS Trials begins
2000: 480M GSM Network operators
Worldwide
First GPRS Networks roll out
End 2002: 792M GSM Net work
Operators Worldwide
Development of the GSM Standard
8. ver2.2
12 SERIES
OPERATION AND
MAINTENANCE
01 SERIES
GENERAL 02 SERIES
SERVICE ASPECTS
03 SERIES
NETWORK ASPECTS
04 SERIES
MS-BSS INTERFACE AND
PROTOCOLS
05 SERIES
PHYSICAL LAYER ON THE
RADIO PATH.
06 SERIES
SPEECH CODING
SPECIFICATIONS
07 SERIES
TERMINAL ADAPTERS
FOR MOBILE STATIONS
11 SERIES
EQUIPMENT AND TYPE
APPROVAL SPECIFICATIONS
10 SERIES
SERVICE INTERWORKING
09 SERIES
NETWORK
INTERWORKING
08 SERIES
BSS TO MSC INTERFACES
GSM Specifications
9. ver2.2
Increasing GSM Data Rates
Transmission
Time
GPRS = General Packet Radio Service
HSCSD = High Speed Circuit Switched Data
EDGE = Enhanced Data rate for GSM Evolution
UMTS = Universal Mobile Telecommunication System
10 sec 1 min 10 min 1 hour0
UMTS
E/GPRS
ISDN
PSTN
GSM
webe-mail photo
web photoe-mail
web photo
video
clipreportphoto
web photoe-mail
video
clipreport
video
clipreport
video
clipreport
video
clipreport
10. 10
throughputkbps
10 k
100 k
64 k
1 M
2 M
1 k
1998 1999 2000 2001 2002
Time frame
UMTSUMTS
GPRSGPRS
HSCSDHSCSD
9.69.6
14.414.4
packet
GPRS = General Packet Radio Service
HSCSD = High Speed Circuit Switched Data
EDGE = Enhanced Data rate for GSM Evolution
UMTS = Universal Mobile Telecommunication System
EDGE
circuit
Wireless Data Technology Options
12. 12
Cellular
Networking technology
that breaks geographic
area into cells shaped
like honey comb
Cell
is the radio coverage
area of one base
transceiver station
1
2
3
4
5
6
7
6
7
2
1
5
GSM Concepts -
Cellular Structure
13. 13
What are the types in
GSM Network?
• GSM-900 (Channels 125 operating band 900Mhz
carrier spacing 200khz spacing 45Mhz)
• GSM -1800 (Channels 374 spacing 95Mhz)
• GSM -1900(Used in USA)
14. 14
Multiple Access Technique
• Multiple Access – Achieved by dividing the available
radio frequency spectrum, so that multiple users can
be given access at the same time.
• FDMA - Frequency Division Multiple Access
– ( eg: GSM each Frequency channel is 200KHz)
• TDMA - Time Division Multiple Access
– ( eg: GSM each frequency channel is divided into
8 timeslots)
• CDMA - Code Division Multiple Access
– (eg: IS95- Each User data is coded with a unique
code)
15. 15
Duplex Technique
• Duplex - How the up link and Down link of a user
is separated
• FDD - Frequency Division Duplex
– (eg:In GSM the up link and down link of a user is
separated by 45MHz )
• TDD - Time Division Duplex
– (the up link and down link of a user will be at the same
frequency but at different Time )
16. 16
Frequency band
Uplink 890 - 915 MHz
Downlink 935 - 960MHz
Duplex Frequency Spacing 45MHz
Carrier separation 200KHz
Frequency Channels 124
Time Slots /Frame(Full Rate) 8
Voice Coder Bit Rate 13Kbps
Modulation GMSK
Air transmission rate 270.833333 Kbps
Access method FDMA/TDMA
Speech Coder RPE-LTP-LPC
GSM System specifications
17. 17
Uplink 890 MHz to 915 MHz
Down Link 935 MHz to 960 MHz
25 MHz divided into 125 channels of 200 KHz
bandwidth
890.0 890.2 890.4 914.8 915.0
935.0 935.2 935.4 959.8 960.0
UP
DOWN
Access Techniques
18. 18
Time Division Multiple Access
Each carrier frequency subdivided in time domain
into 8 time slots
Each mobile transmits data in a frequency, in its
particular time slot - Burst period = 0.577 milli secs.
8 time slots called a TDMA frame. Period is .577 * 8
= 4.616 milli secs
0 1 2 3 4 5 6 7
4.616 ms
0.577 ms
Access Techniques ...
20. 20
GSM in comparison with other
Standards
• GSM gives mobility without any loss in Audio quality
• Encryption techniques used gives high security in the
air Interface and also use of SIM.
• Bit Interleaving for high efficiency in Transmission.
• Variable Power (Power budgeting- extend battery life)
• Minimum Interference.
• Features-CCS7 Signaling
– SMS (Short Message Services)
– Emergency Calls
– CELL Broadcast
21. 21
TOPICS
• GSM CONCEPTS
• GSM SYSTEM ARCHITECTURE
• IDENTITIES USED IN GSM
• GSM CHANNELS
• GSM RADIO LINK
• MOBILITY MANAGEMENT
• CALL MANAGEMENT
• RADIO RESOURCE MANAGEMENT
23. 23
GSM Network
OMC
AUC
HLR
MSC
EIRVLR
BSC
BTS
MS
External
PSTN &
PDN N/W
SS
BSS
Switching
System
Base Station
System
MS Mobile Station
BTS Base transceiver System
BSC Base Station Controller
MSC Mobile Switching Center
HLR Home Location Register
VLR Visitor Location Register
EIR Equipment Identity Register
AUC Authentication Center
OMC Operation And Maintenance Center
25. 25
GSM utilizes two bands of 25 MHz. 890-915
MHz band is used for uplink while the
935-960 MHz is used for downlink.
The frequency bands are divided into 200
KHz wide channels called ARFCNs (Absolute
Radio Frequency Channel Numbers) i.e.
there are 125 ARFCNs out of which only 124
are used.
Each ARFCN supports 8 users with each user
transmitting / receiving on a particular time
slot (TS).
Fundamentals
1
2
……
…….
123
124
1
2
……
…….
123
124
76543210
76543210
Data burst = 156.25 bit periods = 576.9µs
960 MHz
959.8MHz
200KHz
935 MHz
935.2 Mhz
915 MHz
200KHz
45 MHz
Downlink (TDMA frame) = 8 TS
Uplink (TDMA frame)
Delay
TS: Time slot
914.8 MHz
890.2 MHz
890 MHz
DOWNLINK
UPLINK
ThereforeTherefore 1 TDMA1 TDMA frame = 156.25 x 8 = 1250 bitsframe = 156.25 x 8 = 1250 bits
and has a duration of 576.92and has a duration of 576.92µµs x 8 = 4.615 mss x 8 = 4.615 msThe technology
26. 26
Mobile Station (MS)
• Hand portable unit
• Contains Mobile Equipment(ME) and
Subscriber Identity Module (SIM)
27. 27
Mobile Equipment(ME)
• Frequency and Time Synchronization
• Voice encoding and transmission
• Voice encryption/decryption functions
• Power measurements of adjacent cells
• Display of short messages
• International Mobile Equipment Identifier (IMEI)
28. 28
SIM
• Portable Smart Card with memory (ROM-6KB to
16KB-A3/A8 algorithm, RAM- 128KB TO 256KB,
EEPROM- 3KB to 8KB )
• Static Information
– International Mobile Subscriber Identity(IMSI)
– Personal Identification Number (PIN)
– Authentication Key (Ki)
• Dynamic Information
– Temporary Mobile Subscriber Identity(TMSI)
– Location Area Identity (LAI)
– Phone memories, billing information
– Ability to store Short Messages received
29. 29
Base Transceiver Station
(BTS)
• Handles the radio interface to the mobile station.
• Consists of one or more radio terminals for
transmission and reception
• Each Radio terminal represents an RF Channel
• TRX and MS communicates over Um interface
• Received data transcoding
• Voice encryption/decryption
• Signal processing functions of the radio interface
• Uplink Radio channel power measurements
30. 30
Base Station Controller (BSC)
• Provides all the control functions and physical links
between the MSC and BTS
• External Interfaces
– ‘Abis’ interface towards the BTS
– ‘A’ interface towards the MSC
• Monitors and controls several BTSs
• Management of channels on the radio interface
• Alarm Handling from the external interfaces
• Performs inter-cell Handover
• Switching from ‘Abis’ link to the ‘A’ link
• Interface to OMC for BSS Management
31. 31
Mobile Switching Center
(MSC)
• Performs call switching
• Interface of the cellular network to PSTN
• Routes calls between PLMN and PSTN
• Queries HLR when calls come from PSTN to mobile
user
• Inter-BSC Handover
• Paging
• Billing
32. 32
Home Location Register
(HLR)
• Stores user data of all Subscribers related to the
GMSC
– International Mobile Subscriber Identity(IMSI)
– Users telephone number (MS ISDN)
– Subscription information and services
– VLR address
– Reference to Authentication center for key (Ki)
• Referred when call comes from public land network
33. 33
Visitor Location Register
(VLR)
• Database that contains Subscriber
parameters and location information for all
mobile subscribers currently located in the
geographical area controlled by that VLR
• Identity of Mobile Subscriber
• Copy of subscriber data from HLR
• Generates and allocates a Temporary
Mobile Subscriber Identity(TMSI)
• Location Area Code
• Provides necessary data when mobile
originates call
34. 34
Authentication Center (AuC)
• Stores Subscriber authentication data called Ki, a
copy of which is also stored in in the SIM card
• Generates security related parameters to authorize a
subscriber (SRES-Signed RESponse)
• Generates unique data pattern called Cipher key (Kc)
for user data encryption
• Provides triplets - RAND, SRES & Kc, to the HLR on
request.
35. 35
EIR (Equipment Identity
Register)
• EIR is a database that contains a list of all valid
mobile station equipment within the network, where
each mobile station is identified by its International
Mobile Equipment Identity(IMEI).
• EIR has three databases.,
– White list - For all known,good IMEI’s
– Black list - For all bad or stolen handsets
– Grey list - For handsets/IMEI’s that are
on observation
38. 38
GSM Protocols
• CM - Connection Management
• MM - Mobility Management
• RR - Radio resource
• LAPDm - LAPD for mobile
• LAPD - Link Access Procedure for D channel
• BTSM - BTS Management Part
• BSSAP - BSS Application Part (BSC - MSC)
• DTAP - Direct Transfer Application Part (MS - MSC)
• MAP - Mobile Application Part
• MTP - Message Transfer part of SS7
• SCCP - Signalling Connection Control Part of SS7
• TCAP - Transaction Capabilities Application Part
• ISUP - ISDN User Part
39. 39
Functional Plane of GSM
MS BTS BSC MSC/ HLR GMSC
VLR
MS BTS BSC MSC/VLR HLR GMSC
CC
MM
RR
Trans
40. 40
TOPICS
• GSM CONCEPTS
• GSM SYSTEM ARCHITECTURE
• IDENTIFIERS USED IN GSM
• GSM CHANNELS
• GSM RADIO LINK
• MOBILITY MANAGEMENT
• CALL MANAGEMENT
• RADIO RESOURCE MANAGEMENT
41. 41
Subscriber Identity -MSISDN
• The MSISDN is a GSM directory number which
uniquely identifies a mobile subscription in the Public
Switched Telephone Network (PSTN).
• Calls will be routed from the PSTN and other
networks based on the Mobile Subscribers’ MSISDN
number.
• MSISDN= CC + NDC + SN
– CC= Country Code (91)
– NDC= National Destination Code(98370)
– SN= Subscriber Number (12345)
42. 42
International Mobile
Subscriber Identity [IMSI]
• Subscriber always identified within the GSM network
by the IMSI
• This is used for all signaling in the PLMN stored in
SIM and HLR/VLR
• The IMSI consists of three different parts
– MCC = Mobile Country Code(3 Digits)
– MNC = Mobile Network Code(2 Digits)
– MSIN = Mobile Station Identification Number(Upto 10 digits)
43. 43
Temporary Mobile Subscriber
Identity [TMSI]
• The TMSI is used for the subscriber’s confidentiality.
• It should be combined with the LAI to uniquely
identify a MS.
• Since the TMSI has only local significance (that is,
within the MSC/VLR area), the structure may be
chosen by each administration.
• The TMSI should not consist of more than four
octets.
44. 44
Mobile Station Roaming
Number[MSRN]
• HLR knows in what Service area the subscriber is
located.
• In order to provide a temporary number to be used
for routing, the HLR requests the current MSC/VLR to
allocate a Mobile Station Roaming Number(MSRN) to
the called subscriber and to return it.
• At reception of the MSRN, HLR sends it to the MSC,
which now can route the call to the VLR where the
called subscriber is currently registered.
45. 45
International Mobile
Equipment Identity [IMEI]
• The IMEI is used for equipment identification. An
IMEI
• uniquely identifies a mobile station as a piece or
assembly of equipment.
• IMEI = TAC + FAC + SNR + sp
– TAC= Type Approval Code (6 digits),determined by GSM
body
– FAC= Final Assembly Code (2 digits), identifies
themanufacturer
– SNR= Serial Number (6 digits), uniquely identifying all
equipment within each TAC and FAC
– sp = Spare for future use (1 digit)
46. 46
Location Area Identity
• LAI identifies a location area which is a group of
cells..
• It is transmitted in the BCCH.
• When the MS moves into another LA (detected by
monitoring LAI transmitted on the BCCH) it must
perform a LU.
• LAI = MCC + MNC + LAC
– MCC= Mobile Country Code(3 digits), identifies the country
– MNC= Mobile Network Code(1-2 digits), identifies the GSM-
PLMN
– LAC= Location Area Code, identifies a location area within a
GSM PLMN network. The maximum length of LAC is 16
bits,enabling 65536 different location areas to be defined in
one GSM PLMN.
47. 47
TOPICS
• GSM CONCEPTS
• GSM SYSTEM ARCHITECTURE
• IDENTITIES USED IN GSM
• GSM CHANNELS
• GSM RADIO LINK
• MOBILITY MANAGEMENT
• CALL MANAGEMENT
• RADIO RESOURCE MANAGEMENT
48. 48
Channels : differentiating between
Physical and Logical channels
Physical channels : The combination of an ARFCN
and a time slot defines a physical channel.
Logical channels : These are channels specified by
GSM which are mapped on physical channels.
49. 49
Physical channel:
One timeslot of a TDMA-frame on one carrier
is referred to as a physical channel.
There are 8 physical channels per carrier in
GSM,channel 0-7(timeslot 0-7)
Logical channel:
A great variety of information must be
transmitted between BTS and the MS,for e.g.
user data and control signaling.Depending
on the kind of information transmitted we
refer to different logical channels.These logical
channels are mapped on physical channel.
Channel concept
50. 50
Logical Channels on Air interface
LOGICAL
CHANNELS
COMMON
CHANNELS
DEDICATED
CHANNELS
BROADCAST
CHANNELS
COMMON
CONTROL
CHANNELS
DEDICATED
CONTROL
CHANNELS
TRAFFIC
CHANNELS
FCCH BCCHSCH SDCCH SACCH FACCH
PCH AGCHRACH TCH/F TCH/EFRTCH/H
51. 51
Frequency plan and importance of
BCCH
B3
B2
B9
B6 B4
B1
Sectored
antennas
MS ( monitoring the
broadcast radio B1 in ‘idle
mode’ )
…..…..SF I…..BBBBSF
F0 F50F2 F3 F4 F5 F10 F11F1
•F,S,B exist in time slot 0 of each frame
B7
B8
B5
B10
B11
B12
BPL frequency plan:
Broadcast frequencies :
15 Broadcast channels = 48-62
15 Hopping channels = 32-46
52. 52
Broadcast channels BCH
• Broadcast Channel-BCH
– Alloted one ARFCN & is ON all the time in every cell.
Present in TS0 and other 7 TS used by TCH.
• Frequency correction channel-FCCH
– To make sure this is the BCCH carrier.
– Allow the MS to synchronize to the frequency.
– Carries a 142 bit zero sequence and repeats once in every
10 frames on the BCH.
• Synchronization Channel-SCH
– This is used by the MS to synchronize to the TDMA frame
structure within the particular cell.
– Listening to the SCH the MS receives the TDMA frame
number and also the BSIC ( in the coded part- 39 bits).
– Repeats once in every 10 frames.
53. 53Back
1. The MS is monitoring the BCCH and has all the decoded
information stored on the SIM ( including the LAC)
2. As soon as the mobile is on a TCH it sends the signal
strength indication on the corresponding SACCH
3. The BSC monitors the signal strengths and on analysis
sends a ‘handoff request’ on FACCH. The handoff
process is completed on the FACCH.
4. After the completion of call, the MS starts monitoring the
BCCH again. On finding the LAC (stored on SIM) and that
decoded from the BCCH to be different , the MS requests
a ‘Location Update’ through SDCCH.
54. 54
Broadcast channels BCH ...
• BCH
– The last information the MS must receive in order to receive
calls or make calls is some information concerning the cell.
This is BCCH.
– This include the information of Max power allowed in the
cell.
– List of channels in use in the cell.
– BCCH carriers for the neighboring cells,Location Area
Identity etc.
– BCCH occupies 4 frames (normal bursts) on BCH and
repeats once every Multiframe.
– This is transmitted Downlink point to multipoint.
• Cell Broadcast Channel - CBCH
– Used for the Transmission of generally accessible
information like Short Message Services(SMS)
55. 55
What information does Broadcast Control channel
(BCCH) contain?
Serves as a Beacon for the Cell
Country Code (CC) and the Network Code (NC)
Location Area Identity (LAI)
List of neighboring cells which should be monitored by MS
List of frequencies used in the cell
Cell identity
Back
56. 56
Common Control Channels
CCCH
• CCCH-
– Shares TS-0 with BCH on a Multiframe.
• Random access channel-RACH:
– Used by Mobile Station for requesting for a channel. When
the mobile realizes it is paged it answers by requesting a
signaling channel (SDCCH) on RACH. RACH is also used
by the MS if it wants to originate a call.
– Initially MS doesn’t know the path delay (timing advance),
hence uses a short burst (with a large guard period = 68.25
bits).
– MS sends normal burst only after getting the timing advance
info on the SACCH.
– It is transmitted in Uplink point to point.
57. 57
Common Control Channels
CCCH ..
• Access Grant Channel-AGCH
– On request for a signaling channel by MS the network
assigns a signaling channel(SDCCH) through AGCH. AGCH
is transmitted on the downlink point to point.
• Paging Channel-PCH
– The information on this channel is a paging message
including the MS’s identity(IMSI/TMSI).This is transmitted on
Downlink, point-to-multipoint.
58. 58
Dedicated Control Channels-
DCCH
• Stand alone dedicated control channel(SDCCH)
• AGCH assigns SDCCH as signaling channel on
request by MS.The MS is informed about which
frequency(ARFCN) & timeslot to use for traffic.
• Used for location update, subscriber authentication,
ciphering information, equipment validation and
assignment of TCH.
• This is used both sides, up and Downlink point-point.
59. 59
Dedicated Control Channels-
DCCH
• Slow associated control channel-SACCH
– Transmission of radio link signal measurement, power
control etc.
– Average signal strengths(RXLev) and quality of service
(RXQual) of the serving base station and of the neighboring
cells is sent on SACCH (on uplink).
– Mobile receives information like what TX power it has to
transmit and the timing advance. It is associated with TCH
or SDCCH
• Fast associated control channel-FACCH
– Used for Hand over commands and during call setup and
release. FACCH data is sent over TCH with stealing flag set
60. 60
Traffic Channels-TCH
• TCH carries the voice data.
• Two blocks of 57 bits contain voice data in the normal
burst.
• One TCH is allocated for every active call.
• Full rate traffic channel occupies one physical
channel(one TS on a carrier) and carries voice data
at 13kbps
• Two half rate (6.5kbps) TCHs can share one physical
channel.
61. 61
TOPICS
• GSM CONCEPTS
• GSM SYSTEM ARCHITECTURE
• IDENTITIES USED IN GSM
• GSM CHANNELS
• GSM RADIO LINK
• MOBILITY MANAGEMENT
• CALL MANAGEMENT
• RADIO RESOURCE MANAGEMENT
62. 62
GSM Radio Link
• Speech Coding -Done at Transcoder of BSC and MS
– The Linear Predictive Coder uses RPE-LTP(Regular Pulse
Excitation- Long Term Prediction)
– Converts 64kbps voice to 13kbps(260 bits every 20ms)
• Channel Coding - Done at BTS and MS
– Uses Convolution Coding and CRC (Cyclic Redundancy
Check)
– Converts 13 kbps to 22.8 kbps (456 bits per 20ms)
63. 63
GSM Radio Link
• Bit Interleaving - Done at BTS and MS
• Encryption - Done at BTS and MS
– EX OR data with cipher block, which is generated by
applying A5 Algorithm to the Ciphering Key(Kc)
• Multiplexing - Done at BTS
• Modulation - Done at BTS and MS
– GMSK(Gaussian filtered Minimum Shift Keying)
– Phase change of +90 for 0 and -90 for 1
64. 64
Speech Coding
BP A/D SPEECH
ENCODER
CHANNEL
CODING
LP D/A SPEECH
DECODER
CHANNEL
DECODING
BAND
PASS
300 Hz -
3.4 kHZ
Every 125µ s value is
sampled from analog
signal and quantised by
13 bit word
Data rate = 13/125*10 -6
= 104 kbps
Every 20ms 160 samples
taken
Data rate = 160 * 13/20ms
= 104 kbps
Linear Predictive Coding & Regular
Pulse Excitation Analysis
1. Generates 160 filter coeff
2. These blocks sorted in 4 sequence
1,5,9,…37 / 2,6,10----38/
3,7,11…39/8,12,16…40
3. Selects the sequence with most
energy
So data rate = 104/4 = 26 kbps
Long term prediction analysis
1. Previous sequences stored in memory
2. Find out the correlation between the
present seq. And previous sequences
3. Select the highest correlation sequence
4. Find a value representing the difference
between the two sequences.
Reduces data rate = 26 kbps/2 = 13 kbps
ie 260 bits in 20ms
50 132 78
1A 1B 2
1A = Filter Coeff
block ampl, LTP
params
1B = RPE pointers &
pulses
2 = RPE pulse & filter
params
50 3 132 4
3 crc bits
Four 0 bits for codec
378 coded bits
Conv coding rate = 1/2 delay = 4
78
456 bits in 20 ms = 22.8 kbps
57 x 8 = 456
To modulator
66. 66
Burst
• The information format transmitted during one
timeslot in the TDMA frame is called a burst.
• Different Types of Bursts
– Normal Burst
– Random Access Burst
– Frequency Correction Burst
– Synchronization Burst
67. 67
Normal Burst
T
3
Coded Data
57
S
1
T. Seq.
26
S
1
Coded Data
57
T
3
GP
8.25
Tail Bit(T) :Used as Guard Time
Coded Data :It is the Data part associated with the burst
Stealing Flag :This indicates whether the burst is carrying
Signaling data (FACCH) or user info (TCH).
Training Seq. :This is a fixed bit sequence known both to
the BTS & the MS.This takes care of the
signal deterioration.
156.25 bits 0.577 ms
68. 68
T
3
Training Sequence
41
Coded Data
36
T
3
GP
68.25
Random Access Burst
T
3
Fixed Bit Sequence
142
T
3
GP
8.25
T
3
Coded Data
39
Training Sequence
64
Coded
Data 39
T
3
GP
8.25
Freq. Correc. Burst
Synchronization Burst
156.25 bits 0.577 ms
156.25 bits 0.577 ms
156.25 bits 0.577 ms
69. 69
Transmission on the
radio channels
• A timeslot has a duration of .577 m seconds (148 Bits)
• 8 timeslots(8 x 0.577 = 4.62 ms) form a TDMA frame
• If a mobile is assigned one TS it transmits only in this time
slot
• and stays idle for the other 7 with its transmitter off, called
bursting
• The start on the uplink is delayed from downlink by 3 TS
periods
• One TS = duration of 156.25 bits, and its physical contents is
• called a burst
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
Downlink
BTS > MS
Uplink
MS > BTS
Offset
75. 75
Network Attachment
• Cell Identification
• MS scans complete GSM frequency band for
highest power
• Tunes to highest powered frequency and looks
for FCCH. Synchronizes in frequency domain
• Get training sequence from SCH which follows
FCCH. Synchronizes in time domain.
• Accesses BCCH for network id, location area and
frequencies of the neighboring cells.
• Stores a list of 30 BCCH channels
76. 76
Network Attachment…..
• PLMN Selection
• Get the operator information from SIM.
• Cell Selection
• Selected cell should be a cell of the selected
PLMN
• Signal strength should be above the threshold.
• Cell should not be barred
• Location Update
• Register with the network by means of location
updation procedures.
77. 77
MS BTS BSC (G)MSC VLR HLR
Action
Channel Request (RACH)
Channel Assignment (AGCH)
Authentication Request (SDCCH)
Authentication Response (SDCCH)
Comparison of Authentication param
Accept LUP and allocTMSI (SDCCH)
Ack of LUP and TMSI (SDCCH)
Entry of new area and identity into
VLR and HLR
Channel Release (SDCCH)
MS Location Update
(registration)
Location Update Request (SDCCH)TMSI + old LAI
78. 78
Security - Authentication
Authentication center
provides RAND to Mobile
AuC generates SRES using
Ki of subscriber and RAND
Mobile generates SRES
using Ki and RAND
Mobile transmits SRES to
BTS
BTS compares received
SRES with one generated
by AuC
MS
Ki RAND
A3
SRES
RAND
SRES
SRES
Auth Result
AuCBTSMS
79. 79
Security - Ciphering
Data sent on air
interface ciphered
for security
A5 and A8
algorithms used to
cipher data
Ciphering Key is
never transmitted
on air
MS
Ki RAND
A8
Kc
MS Network
Um interface
A5 A5
Kc Kc
Data DataCiphered
Data
80. 80
TOPICS
• GSM CONCEPTS
• GSM SYSTEM ARCHITECTURE
• IDENTITIES USED IN GSM
• GSM CHANNELS
• GSM RADIO LINK
• MOBILITY MANAGEMENT
• CALL MANAGEMENT
• RADIO RESOURCE MANAGEMENT
81. 81
Communication Management
(CM)
• Setup of calls between users on request
• Routing function i.e. Choice of transmission
segments linking users
• Point to Point Short message services
82. 82
Mobile Originated Call
• Request for Service
• Authentication
• Ciphering
• Equipment Validation
• Call Setup
• Handovers
• Call Release
83. 83
MS
MS
BTS
BTS
BTS
BSC
BSC
MSC
VLR
GMSC
HLR
PSTN
EIR
AuC
Req for dedicated channel
for signaling (RACH)
Give SDCCH
Allocates SDCCH using the AGCH
Sends call set-up request including
dialled digits on SDCCH
Call set-up forwarded
to BSC
Call set-up forwarded
to MSC
Authentication request
(SDCCH)
Authentication response
(SDCCH)
Authentication response
(SDCCH)
Assigns TCH Req
Activate TCH
TCH assigned
Assn complete
Release SDCCH
SDCCH released
ACM
Ring tone over FACCH
Ring alert
Called Sub answers
Connect
message
Ring tone ceases over FACCH
Speech path enabled
Mobile Originated Call
85. 85
Mobile Terminated Call
MS
MS
BTS
BTS
BTS
BSC
BSC
MSC
VLR
GMSC
HLR
PSTN
EIR
AuC
Land to
Mobile call
(MSISDN)
Query for
VLR info
Reply
(MSRN)
Route
to MSC
Query VLR
for LAC and
TMSIPaging
the area
(+TMSI)
TMSI Paged
on PCH
Paging
Ch. REQ
over RACH
Allocate SDCCH
over AGCH
Page RESP on SDCCH
( TMSI + LAI)
Page RESPage RES
Authentication and Ciphering procedure done as seen in Location Updation
Assign. REQ
Assignment CMD
(=TCH) on SDCCH
* MS tunes
* Assgn CMP
* Phone rings
Connect traffic Ch.to trunk
frees SDCCH
Assgn CMP
Network Alerting
86. 86
TOPICS
• GSM CONCEPTS
• GSM SYSTEM ARCHITECTURE
• IDENTITIES USED IN GSM
• GSM CHANNELS
• GSM RADIO LINK
• MOBILITY MANAGEMENT
• CALL MANAGEMENT
• RADIO RESOURCE MANAGEMENT
87. 87
Radio Resource Management
• Establish maintain and release stable connections
between MS and MSC
• Manage Limited Radio and Terrestrial resources
• Handover process is the sole responsibility of the RR
Layer
• Functions of RR layer are performed by MS and BSC
and partly by MSC
89. 89
BTS commands MS at different
distances to use different power levels
so that the power arriving at the BTS’s Rx is
approximately the same for each TS
- Reduce interference
- Longer battery life
Power Control
90. 90
Handover
Means to continue a call even a mobile crosses
the border of one cell to another
Procedure which made the mobile station really
roam
Handover causes
RxLev (Signal strength , uplink or downlink)
RxQual (BER on data)
O & M intervention
Timing Advance
Traffic or Load balancing
91. 91
Handover Types
• Internal Handover (Intra-BSS)
– Within same base station - intra cell
– Between different base stations - inter cell
• External Handover (Inter-BSS)
– Within same MSC -intra MSC
– Between different MSCs - inter-MSC
93. 93
Periodic Measurement
Reports (SACCH)
Periodic Measurement
Reports
HO required
Activate TCH(facch)
with HoRef#
if
1. Check for HO passed
2. Channel avail in new BTS
Acknowledges and
alloctes TCH (facch)
HO cmd with HoRef#
Receives new BTS data(FACCH)
MS tunes into new frequency
and TS and sends HO message to
new BTS (facch)
Periodic Measurement
Reports (SACCH)
HO performed
Release TCH
Cell 1
Cell 2
BSC
BTS 1
BTS 2
Intra BSC handover
94. 94
Discontinuous
Transmission
• Discontinuous Transmission(DTX) allows the
radio transmitter to be switched off most of the
time during speech pauses.
• A Silence Indicator Block is transmitted at
500bps, which generates a comfort noise
• Down Link interference is decreased.
• Up link battery is saved
95. 95
Frequency Hopping
• Frequency Hopping permits the dynamic switching of
radio links from one carrier frequency to another.
• Base Band Hopping
– At the BTS each the timeslot is shifted to another
transceiver, which is transmitting at the hop
frequency. User will be connected to different
Transceivers depending on hop sequence.
• Synthesis Hopping
– At the BTS transceiver changes the frequencies used.
The user will be connected to only one transceiver.
• Decreases the probability of interference
• Suppresses the effect of Rayleigh fading
96. 96
Wireless Data
98 99 2000 2001
GSM
DATA
HSCSD
GPRS
EDGE
UMTS
SIM
Toolkit
WAP
Data Application
Time
Circuit Switched technology
Packet Switched technology
Technology for Applications
SMS Data: 160 α-numeric characters
User Data Rate : 9.6kbps
One time slot over the air interface
High Speed Circuit Switched Data
User Data Rate:14.5kbps
Use multiple timeslots (max=8),
hence max rate = 115.2kbps.
Needs a duplexor in MS for
simultaneous Tx and Rx
Add-on to GSM network :
PCU; Packet Segmentation/re-assembly and scheduling
• Radio channel access control and management
• Transmission error detection and retransmission.
• Power control
SGSN: GPRS mobility
• Encryption
• Charging
GGSN : Interface to the PDN, Internet
Max user data rate : 21.4 kbps
Dynamic rate adaptation to suit the radio conditions at
that time ( 9.05 kbps, 13.4 kbps, 15.6 kbps 21.4 kbps)
W@P Gateway W@P ServiceW
@
P
F
o
n
e
Internet
Mobile Network
Surf the Internet while on the move
W@P Gateway :
• Adaptation of the information to the mobile
• Compression of the data
• Buffering of the information
Enhanced Data rate for GSM Evolution
• EDGE is an enhancement of GPRS and CSD technologies.
• Based on the current GSM technology - same TDMA frame
structure, same bandwidth (200 kHz).
• Uses 8-PSK modulation instead of GMSK.
• Requires good propagation conditions.
• Allows upto 48 kbps (EGPRS) and upto 28.8 kbps (ECSD) on every
radio channel
• EDGE helps GSM-Only operators to compete with UMTS.
Universal Mobile Telecommunication Standards
• Innovative Service Architecture : VHE Concept - providing the us
the same look and feel of its personalized services independent of
network and terminal.
• Global Convergence : Fixed/Mobile, Telecom/Datacom, public/private
• Mobile Multimedia driven market.
• Wideband bearers - 2GHz band ( 5 MHz per carrier), -max. 2Mbps
97. 97
References
• Wireless and Personal Communication Systems.
Vijay.K.Garg and Wilkes
• Overview of the GSM System and Protocol
Architecture, IEEE Comm. Magazine, Moe Rahnema.
• The GSM System for Mobile Communications- Michel
Mouly & Marie-Bernadette Pautet
• Overview of the GSM Comm- John Scourias.
99. 99
Location Updates
Location Updates can be classified into
two:
Periodic Location Updates:
This occurs as per the timer set by the network operator.
If the MS does not perform this update the MSC marks
the MS as ‘Detached’ on the VLR.
Location Update on a handover:
This occurs if during a handover the MS is moved into a
new Location Area Code (LAC).
