gsm- lecture 2012 print
TRANSCRIPT
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HLR (Home Location Register)It is a permanent databaseabout Mobile subscribers genreally 1 per GSM
operator in a area.
For every incoming call the current location of the subscriber is foundfrom HLR which queries the serving VLR for routing information
It contains
1. List of all subscribers in the circle
2. IMSI
3. Service Subscription information
4. Billing Information
5. Information about current location6. Service restrictions
7. Supplementary services
8. Mobile terminal charceteristics
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VLR (Visiting Location Register)
It is a temprory database, one VLR per MSC. It contains information about
subcribers who are currently in the sevice are covered by MSC/VLR
It contains information about
1. Current location information about the MS(Location area ,cell identitities)
2. TMSI (Temporary mobile station identity)
3. Features currently activated
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Equipment Identity Register
Maintains information about authenticate terminals so that fraudulent stolen ,
non-type-approved terminals can be denied service
Maintains White gray and black lists that may be consulted by networl for
checking authenticity of terminal requesting service
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Logical Channels
1. Traffic Channel (TCH)
2. Control Channels (CCH)
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TCH
CCH
Speech ------ Full Rate(22.8 Kb/s)
Half Rate 11.4 KBp/s
Data-------------- 9 .8 Kb/s
4.6 Bb/s
2.4 Kb/s
BCCH FRREQUENCY CONTROL(FCCH)
(Broadcast) SYNCHRONISATION (SCH)
Speech
DCCH Fast Associated (FACCH)Slow assiciated (SACCH)
Stand Alone(SDCCH)
CCCH Paging (PCH)
(Common) Access Grant (AGCH)
Random Accee (RACH)
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GSM Traffic Channels
Full Rate : User data in one TS per
frame
Half Rate : User data in one TS per
alternate frame
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Full Rate Speech and Data Channels
1. Full Rate Speech channel TCH/FS : Raw data rate 13 kbps. Coded datarate 22.8 kbps
2. Full Rate data channel TCH/F9.6: Raw data rate 9.6 kbps. Coded data
rate 22.8 kbps
3. Full Rate Dta channel for 4.8 Kbps- carries raw user data at 4.8 Kbbps +Forward error correcting coding data is sent at 22.8 Kbps
4. Full Rate Dta channel for 2.4 Kbps- carries raw user data at 4.8 Kbbps
with additional forward error correction data is sent at 22.8 Kbps
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Half Rate Speech and DataChannels
1. Half Rate Speech Channel TCH/HS sampling rate half of the full rate:: Raw data
rate : 6.5 kbps :Channel coding is added to digitised speech Coded data rate : 11.
kbps.
Half Rate Data channel : TCH/H4.8. carries raw user with additional forward errorcorrection applied , The data rate 4.8 kbps is sent at 11.4 kbps
Half Rate data channel :TCH/H2.4- carriers raw user data at 2.4 Kbps, additional
forward error correction , the data is sent at 11.4 Kbps
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GSM Control Channels
Broadcast Channel : BCH
Common Control Channel:CCH
Dedicated Control Channel:DCCH
B d t C t l Ch l BCH
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Broadcast Control Channels:BCH
Operates in Forward link.
Transmits data in first Time slot of certain GSM frames
34 ARFCNS / Forward Link
Data transmission in To time slot(a) Broadcast control channel BCCH- Unidirectional BS to MS
(b) Frequency correction channel FCCH Accurate tuning to BS
(c) Synchronization channel - SCCH Frame Synchronisation
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Broadcast Control Channel(BCCH)
Forward control Channel.Brodcasts information such as
1. Cell and network identity
2. Operating charecteristics of cell(Current control channel,
channel avaliabilty,congestion)3. List of channels currently in use within the cell
4. Frame 2 to 5 in control multi frame contains BCCH data
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Frequency Correction Channel(FCCH)
Occupies TS0 of every First Frame Frame 0. Repated every 10
Frames in the Control chgannel multiframe.
Allows susbcriber unit to synchronize its internal frequency to
exact frequency of Base sation
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FCCH Data Burst
3Start
bits
142 bits of all
zeroes
3 stopbits
8.25 bitsguard
period
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Synchronization Channel(SCH)
Broadcast in TS0 of a Frame Immediately after every FCCH frame
1. Use to identify the serving Base station so that ech mobile unit can
synchronize with it
2. The frame number is sent with Base station identity code.
3. Since different users may be at different distances fro BS it is
necessary to adjust timing information so that received signal is
synchronized with BS clock.
4. BS issues coarse timing advancement commands to MS via SCH
5. SCH is transmitted once every 10 Frames
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SCH Burst
3start
bits
39 data bits64Training
bits
39 Data bits 3stop
bits
8.25 bitsGuard
period
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Control Multi-frame
0
F
1
S
2
B
3
B
4
B
5
B
6
C
10
F
11
S
20
F
21
S
49
C
50
I
F : FCCH burst(BCH) I : Idle
S : SCH burst (BCH)
B : BCCH burst(BCH)
C : PCH/AGCH burst(CCCH)
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Common Control Channels
(CCCHs)1. Paging Channels(PCH) (Forward Link/Down Link/)2. Random Access Channels(RACH) (Reverse Link/Uplink)
3. Access Grant Channel(AGCH) (Forward Link/Down Link/)
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Paging Channel(PCH)
Provides paging signals from BS to all mobiles in a cell
Notifies subcsriber regarding incoming call
Transmit IMSI of Target Subscriber on an incoming call
Broadcast ASCII text messages to all subscribers as a part of the SMS feature.
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Random Access Channel(RACH)
Reverse Link. Uses all the 51 control frames.
1. Used by subcriber to acknowledges page freom PCH
2. Used by Mobiles to originate a call
3. In establishing service BS responds to RACH by allocating channel andassigning a standalone dedicated channel (SDCCH) for signalling during call.
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Access Grant Channel(AGCH)
Used by BS to provide forward link communication to mobile
Assign Dedicated resources to mobile
Instructs the mobile to operate in a particular physical channel in response to a
RACH sent by a mobile station in a previous CCCH frame.
Used by BS to respond to RACH sent by mobile station
It is the final CCH sent by BS before user is moved off Control Channel
D di d C l Ch l
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Dedicated Control Channels(DCCHs)
There are 3 types of dedicated Control channels
1) Stand alone dedicated control channel
2) Slow associated control channel
3) Fast associated control channelThey are Bi-directional. DCCH can exist in any time slot and in any
frame except in TS0 of BCH ARFCN
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Stand alone dedicated control
channel(SDCCH)Carries signaling data between base station and mobile .
SDCCH ensures that MS and Base station remain connected while
the BS and MSC verify subscriber unit and allocate resources.
SDCCH is an intermediate channel which accepts newly connected
call from the BCHand hold the traffic while waiting for Base station
to allocate TCH
SDCCH is used to send authentication and alert messages.
Sl A i t d C t l
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Slow Associated ControlChannel(SACCH)
1 .. 12 S .13 24 I/S0
SACCH is always associated with TCH or SDCCH.
Each ARFCN carries SACCH data for all its cuurent users
On the Forward Link/Downlink: used to send slow but
continuously cahnging information such as transmit Power
level instructions, Timing Advance Instructions
On the Reverselink/Uplink Link : SACCH carries information
of RSSI(Received Signal Strength Info) , quality of TCH,BCH
measurement results of Neighboring cell.
SACCH is transmitted on 13th
Frame and 26th
Frame.
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Fast Associated ControlChannel(FACCH)
57 1 5713 26 8.253
Stealing Flags
Carries urgent messagescontains same type of inforamtion as
SDCCH.
FACCH is assigned whenever SDCCH has not been dedicated
for a user and there is urgent message such as handoff request
FACCH gains access to aTime slot by setting frames from the
traffic channel.This is done by stting Stealing bits.If stealing
bita are set the TS contains FACCH data
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Location Updating
1. MS sends location update request to
VLR new
BTS
BTS
BTS
BTS
BTS
BTS
BSC
BSC
MSC
Old
MSC
New
HLR
VLROld
VLR
New
11
1
2
34
4 41
BTS
i i
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BTS
BTS
BTS
BTS
BTS
BTS
BSC
BSC
MSC
Old
MSC
New
HLR
VLROld
VLR
New
11
1
2
34
4 41
BTS
Location Updating
2. VLR sends to HLR the address of
the VLR new and IMSI of MS.This
updating of HLR not required if the
new area is served by the same VLR
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BTS
BTS
BTS
BTS
BTS
BTS
BSC
BSC
MSC
Old
MSC
New
HLR
VLROld
VLR
New
11
1
2
34
4 41
BTS
3.Service and security related data for
the MS is downloaded to the new VLR
Location Updating
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BTS
BTS
BTS
BTS
BTS
BTS
BSC
BSC
MSC
Old
MSC
New
HLR
VLROld
VLR
New
11
1
2
34
4 41
BTS
4. The MS is sent an acknowledgement
of successful location update.
Location Updating
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BTS
BTS
BTS
BTS
BTS
BTS
BSC
BSC
MSC
Old
MSC
New
HLR
VLROld
VLR
New
11
1
2
34
4 41
BTS
5. The HLR requests the old VLR to
delete the data relating to the MS
Location Updating5
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Mobile Call Origination
MSC GMSC
VLRLE
PSTN
Telephone
BSC
BTS
1
1
1
1.The MS sends the dialed number
indicating service requested to the
MSC
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Mobile Call Origination
MSC GMSC
VLRLE
PSTN
Telephone
BSC
BTS
2 2
2. The MSC checks from the VLR if the MS
is allowed the requested service.
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Mobile Call Origination
MSC GMSC
VLRLE
PSTN
Telephone
BSC
BTS
3
3. If the call is allowed the MSC routes the call
to GMSC
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Mobile Call Origination
MSC GMSC
VLRLE
PSTN
Telephone
BSC
BTS
4
4. The GMSC routes the call to the local
exchange of called user
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Mobile Call Origination
MSC GMSC
VLRLE
PSTN
Telephone
BSC
BTS 5
5. The LE applies ringing to the called
terminal
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Mobile Call Origination
MSC GMSC
VLRLE
PSTN
Telephone
BSC
BTS
6
6. Answer back ring tone from the called
terminal to LE
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Mobile Call Origination
MSC GMSC
VLRLE
PSTN
Telephone
BSC
BTS
7777
7
7. Answer back signal is routed to MS through MSC
which also completes the speech path to the MS
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Mobile Call Termination
MSC GMSC
VLRLE
PSTN
Telephone
BSC
BTS
1.PSTN user dials the MSISDN of the called user
in GSM
1
2
3,
74
9
5
8
6
10
1111
11
12
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2. lE routes the call to the GMSC of the called GSM user3. The GMSC uses the dialled MSISDN number to determine the serving
HLRfor the GSM user and interrogates it to obtain the requiredrouting number
4. The HLR requests the current serving VLR for the called party MSNfor a MSRN(MS Roaming Number) so that call can be correctly routedthrough MSC
5.The VLR passes the MSRN to HLR
6 HLR passes the MSRN to the GMSC
7 Using MSRN the GMSC routes the call to the serving MSC
8 MSC interrogates the VLR for the current loaction area identity(LAI) forthe MS
9 VLR provides current LAI for MS to MSC
10 MSC pages the MS via appropriate BSS.The MS responds to the page
and sets up the necessary signalling links11. When BSS has established necessary radio links.MSC is informed
and call is delivered to MS
12. When MS answers the call connection is completed to aclling PSTNuser
A h i i d
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Authentication andEncryption Sequence
BSC MSC
VLRHLR
BTS
1
2
1. A terminal location update VLR sends IMSI to HLR.
2. HLR returns security triplets(RAND,SRES,Kc)
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Authentication Sequence
BSC MSC
VLRHLR
BTS
3
33
3
3. VLR sends RAND to MS
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Authentication Sequence
BSC MSC
VLRHLR
BTS
4
4 4
4
4. MS calculates SRES and returns to
VLR. It also calculates cipher key Kc
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Authentication Sequence
BSC MSC
VLRHLR
BTS
5
55
5. If the SRES returned by the MS matches with
the stored SRES, VLR sends the cipher key Kc
to BTS which uses Kc for ciphering the radio
path.
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BTS
B
BTSA
BSC
A
BSC
B
MSC A
MSC B
HLR
VLR A
VLR B
INTER MSC HANDOVER
1
234
5
6
7
1. BSC A informs MSC A tha t MS needs
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handover from BTS A to BTS B
2. MSCA informs MSC B that handover fromBTS A to BTS B is underway
3. MSC A commands BSC A/BTS A toproceed with handover to BTS B
4. BTS A commands MS to change to aspecified channel on BTS BB
5. MS informs BTS B that it is on the specifiedchannel on BTS B
6. BTS B informs BSC A/MSC A that handoveris complete
7. MSC B informs MSC A that handover toBTS B is complete
S h di i GSM
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Speech coding in GSM
Signal Processing
RPE/LT
E
Channel
Encoder
Interleav
er
A/D Modulat
or
DuplexerSegment
ation
RPE/LT
EDecoder
Channel
Decoder
D/A DeModul
ator
DuplexerDeSegme
ntation
DeInterleaver
Mobile Station
Base Station
8kHz sampling
13 bits/sample
160 sampless
13 bits/sample
260 bits/frame
13 bits/sample
22.8 Kb/s
450 bits/frame 33.85 Kb/s per user
270.8 Kb/s per burst
Speech coding in GSM
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Speech coding in GSM Digitised speech is passed at 64 Kbps though a speech coder which
compresses the 64 Kbps PCM speech to 13 Kbps data rate.
The transcoder models the vocal tract of the user and generates a set of Filterparameters that are used to represent a segment of speech (20 ms) and only
the Filter parameters and impulse input to the filter are transmitted on the radiointerface
GSM transcoder also permits detection of silent periods in speech sampleduring which the transmitter is turned off to save battery power
The Transcoded speech is error protected by passing it through a channelencoder, which utilizes both parity code and convolution code.
Channel encoding increases bit rate from 13 Kbps (260 Kb/20 ms speech) 22.8Kbps(456bits/20 ms) for GSM full rate coder and (11.4Kbps ,16 slots per frame)for GSM half rate coder.
The interleaved data is then modulated by means of Gaussian Minimum shiftkeying(GMSK) and passed through Duplexer which provides filtering to isolatetransmit and receive signals
GSM speech coding leads to better speech quality. It introduces additionaldelayed. Dealy introduced by speech coding(20 ms) , interleaving(37 ms) , A/Dconversion(8 ms) , and processing for transmission and switching (15 ms) addup to 80 ms
For connection to PSTN this 80 ms delay is in addition to existing PSTN delay.Therefore echo controlling devices become neccesssary for GSM calls that usePSTN