Post on 02-Jun-2018
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R.N.SHARMA
Sr.SDE(NOKIA)
SW-I FACULTY,ALTTC GZB
ALT CENTRE
ALTTC
An Over ViewOf
GSM Channel Concepts
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OBJECTIVES:
Upon completion of this Lecture the Trainees
will be Able to Describe the GSM Logical &Physical Channels.
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1. Introduction
2. Describe the Difference Between Physical & Logical
Channels
3. Describe Various Logical Channels
(I) Broad Cast Channels.
(II) Dedicated Channels
4. Describe mapping of channels in GSM Frame
5. Summery.
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GSM
Uplink & Downlink
Frequency Bands
GSM 900 Mhz
Uplink 890-915Mhz
Down Link 935-960Mhz
BT
S
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GSM Specifications
GSM 900
Mobile to BS (UP-LINK) - 890 to 915 MHz
BS to Mobile (DOWN -LINK) - 935 to 960
MHz
Bandwidth - 25 MHz
GSM 1800
Mobile to Cell (UP-LINK) - 1710 to 1785 MHz
Cell to Mobile (DOWN -LINK) - 1805 to 1880 MHz
Bandwidth - 75 MHz
RF Spectrum :
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GSM - MULTIPLE ACCESS GSM uses both FDMA & TDMA
Freq
Mhz.890.2
1
890.4
2
890.6
3
890.8
4
891.0
5 6
914.8
124
FDMA Access along Frequency axis
Each RF carrier 200khz apart
Total 124 RF Channels available.One or more carrier assigned to each base station
...
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GSM
FDMA
25 MHz 25 MHz
Mobile to Base
0 1 2
890.2 890.4 890.6(MHz)
Base to Mobile
0 1 2
935.2 935.4 935.6
200 kHz45MHz
Channel layout and frequency bands of operation
890 935 960915
200 kHz
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GSM
TDMA
87
65
43
21
87
65
43
21
45 MHz
Frequency
F2F1(Cell transmit)
F2F1(Cell Rx)
Amplitude
Typical TDMA/ FDMA frame structure
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TDMA Frame
Physical Channel
(0.577ms)
The TDMA frame time slot of 0.577ms is known
as physical channel while the contents of physicalchannel according to their roles are called as
logical channel
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Physical and Logical channel
Physical Channel
Each timeslot in TDMA frame is called a physical channel.
There are 8 physical channels per carrier in GSM.
Physical channels may be used to carry speech data or
signaling
information.
Logical Channel
The Information carried by physical channels is known as
logical
channel.
There are a several type of logical channels available in
GSM.
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GSM
LOGICAL CHANNELS
USER INFORMATION( TRAFFIC)
SIGNALLING INFORMATION (CONTROL)
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Logical Channels
Logical
Channels
Dedicated
ChannelsCommon
Channels
Full-Rate
Half-Rate
Common
Control
Channels
Dedicated
Control
Channels
Broadcast
Channels
SDCCH
SACCH
FACCH
RACH
PCH
AGCH
FCCH
SCH
BCCH
Traffic
Channels
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Common channelsare used to broadcast different
information to MS & for setting up signalingchannels between the MSC/VLR & the MS
Common
Channels
Common
Control
Channels
BroadcastChannels
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Broadcast Channels
FCCH (Frequency Correction Channel) Provides the
frequency correction information used by the mobile
station.
SCH (Synchronization Channel) Contains the BaseStation Identity Code (BSIC) and the TDMA frame
number used for synchronization of the mobile station to
the frame structure of a new BTS.
BCCH (Broadcast Control Channel)Used to broadcast
general information, related to network, to all mobile
stations.
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Broadcast Channels.
SCH(Synchronization Channel):- BTS sendsTDMA frame number on SCH by which MS
synchronize it self with GSM system.
SCH
TDMA Frame Number BSIC
BSIC:-N/W color cod & Base Station color cod
Down link
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Broadcast Channels.
Broadcast Control Channel(BCCH):-
1. System Type 900/1800
2. LAI
3. Neighbor Cell BCCH Information
4. Frequency hopping used or not?
5. Type of Training sequence used
6. Max power allowed in cell
Down link
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Broadcast Channels.
BCCH.
7. Paging Group
8. Max Timing advance allowed
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Common Control Channels (CCCH)
PCH (Paging Channel)Used to page the mobile station. PCH
information is transmitted over the downlink It contain IMSI or
TMSI.
RACH (Random Access Channel )Used by a mobile station to
Request access to the system. RACH information is transmitted
over the uplink.
AGCH (Access Grant Channel)Used to assign a SDCCH for
call setup. AGCH information is transmitted over the downlink.
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Dedicated Control Channels (DCCH)
SDCCH (Stand alone Dedicated Control Channel)Carries
signaling information during call setup
SACCH (Slow Associated Control Channel)Transmits callControl data and measurement reports during the call.
FACCH (Fast Associated Control Channel)Carries urgent
Signalling information for handover etc.
.
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GSM
THREE TYPES OF CONTROL CHANNELS
Dedicated control channel DCCH
P - P For Registration SDCCH
,authentication SACCH
& Handover FACCH
Broadcast control channel BCCH
P- MP For Freq Correction FCCH
For Syncronisation SCH
BCCH
Common control channel CCCH
For ACCESS Management PCH
RACH
AGCH
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OPERATIONALCONCEPTS
IDLE MODE
IDLE MODE
ACCESS PROCDURE DEDICATED MODE
MS O/G Call
MS I/C Call
----FCCH---- SCH
----BCCH
----RACH
----AGCH----SDCCH
----TCH
----PCH
----RACH----AGCH
----SDCCH
----TCH
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Common channelsare generally transmitted
on TS0of BCCH carrier frequency
F SB B B B C0 C0 C0 C0
F S C1 C1 C1 C1 C2 C2 C2 C2
F SC3 C3 C3 C3 C4 C4 C4 C4
F SC5 C5 C5 C5 C6 C6 C6 C6
F SC7 C7 C7 C7 C8 C8 C8 C8
I
Down Link
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01 2 3 4 5 6 7
Broadcast/Control Information
Traffic Information
Question
If MS is chandelling calls then how it
can receive SMS
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TCH Structure:-
TTTTTTTTTTTTATTTTTTTTTTTTI12 250
It get SMS on SACCH as it
comes after every 12 TCH
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Conclusion:-
Discussed Frequency Spectrum used in GSM.
Explain Channel Definition & difference b/w
Physical & Logical channel.
Discussed Various Logical Channels.
Discussed over all GSM frame structure
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THANKS !!