AIR interface info of GSM
Transcript of AIR interface info of GSM
-
7/29/2019 AIR interface info of GSM
1/45
An Introduction to
Air Interface of GSM
-
7/29/2019 AIR interface info of GSM
2/45
Evolution Of GSM
-
7/29/2019 AIR interface info of GSM
3/45
Milestones in GSM
-
7/29/2019 AIR interface info of GSM
4/45
GSM REFERENCE MODEL
-
7/29/2019 AIR interface info of GSM
5/45
CM
MM
RR
LAPDm
Layer 1 Layer1
LAPDm
RRBTSM
LAPD
Layer 1 Layer 1
LAPD
BTSM
RR BSSAP
SCCP
MTP MTP MTP
SCCP SCCP
BSSAP TCAP
CM
MMMAP
Um Abis AMSBTS BSC
MSC
V/HLR
Protocol Layer of GSM
-
7/29/2019 AIR interface info of GSM
6/45
Air Interface Salient Points:
Multiple Access Scheme: TDMA + FDMA
Frequency Bands 900 MHz
Uplink: 890-915 MHz
Downlink: 935-960 MHz
Total No. of Carriers : 124 1800 MHz
Uplink: 1710-1785 MHz
Downlink: 1805-1880 MHz
Total No. of Carriers :374
Channel Bandwidth : 200 KHz
Duplex Spacing: 45 MHz
Channels/Carrier: 8
-
7/29/2019 AIR interface info of GSM
7/45
Traffic Channel Multiframe
-
7/29/2019 AIR interface info of GSM
8/45
Control Channel Multiframe
-
7/29/2019 AIR interface info of GSM
9/45
Layers of Protocol Stack
Layer 1 Physical Layer
TDMA/FDMA radio interface on MS to BSS
E1 link on BTS to BSC
MTP Layer1 on BSC to MSC
Layer 2 Data Link Layer
LAPDm used on Air interface
LAPD on BTS to BSC
MTP Layer2 on BSC to MSC
-
7/29/2019 AIR interface info of GSM
10/45
Layer 3
RR Management Sublayer
Manages the Radio interface.
Terminates at BSS from MS.
MM Sub layer
Terminated at MSC.
Messages from or to MSC are relayed transparently fromBSS.
-
7/29/2019 AIR interface info of GSM
11/45
CM Sublayer
Terminates at MSC
Contains entities that consist of CC including call-related
supplementary services, SMS, and call independentsupplementary services support (SS).
BTSM
This layer looks after the management of all aspects of radiochannels including radio link layer, control channels andtransceiver management.
SCCP & MTP
SCCP & MTP protocols are used to implement the data linkand Layer 3 transport functions for carrying the call controland mobility management signaling messages on the BSS-MSC Link.
-
7/29/2019 AIR interface info of GSM
12/45
BSSAP
Used to implement all procedures between the MSC and the BSSthat require interpretation and processing of information related tosingle calls and resource management
TCAP & MAP
- These are the interfaces between the MSC and the HLR/VLR.
-
7/29/2019 AIR interface info of GSM
13/45
Air Interface
Multiple Access Scheme: TDMA + FDMA
Frequency Bands
Uplink: 890-915 MHz
Downlink: 935-960 MHz
Channel Bandwidth : 200 KHz
Duplex Spacing: 45 MHz
Total No. of Carriers : 124 Channels/Carrier: 8
Coding on the Air Interface
-
7/29/2019 AIR interface info of GSM
14/45
MSCA/D
33.85 kbps/user
270.8 kbps/frame
Channel
EncoderInterleaver
Deinter-
leaver
DemodulatorModulator
Error
Correction
Desegmen-
tation
RPE-LTP
decoder
RPE-LTP
encoder
Segmen-
tation
D D
13 kbps
(260 bits/frame)
Duplexers
22.8kbps
456 bits/frame
Coding on the Air Interface
-
7/29/2019 AIR interface info of GSM
15/45
Coding on the Radio Path
The analog signal is segmented in 20 ms. Segments
Speech coding (RPE-LTP) is used to model the Speechsegments at a data rate of 13 Kbps.
This data is error protected by channel encoding, thusincreasing bit rate to 22.8 Kbps
Interleaving performed to reduce burst errors. Depth of8 is used for interleaving.
This data is used for modulating the carrier. GMSK isused as modulation technique.
TDMA F d B t St t
-
7/29/2019 AIR interface info of GSM
16/45
TDMA Frame and Burst Structure
-
7/29/2019 AIR interface info of GSM
17/45
Frame Structure in Air Interface
-
7/29/2019 AIR interface info of GSM
18/45
Organization of Bursts, TDMA Frames, and
Multiframes for Speech and Data
-
7/29/2019 AIR interface info of GSM
19/45
Logical Channel Structure in GSMLogical Channels
Full Rate 22.8kbps
Half Rate 11.4kbps
Speech
9.6 kbps
4.8 kbps
2.4 kbps
Data
TCHtraffic
Duplex
FCCHfreq correction
Downlink
SCH
syncronizationDownlink
BCCHBroadcast Control
Downlink
BCHBroadcast
PCHpaging
Downlink
AGCH
access grantDownlink
RACHrandom access
Uplink
CCCHcommon
FACCHfast associated
Duplex
SACCH
slow associatedDuplex
SDCCHstand - alone
Duplex
DCCHdedicated
CCHcontrol
-
7/29/2019 AIR interface info of GSM
20/45
Logical Control Channels
-
7/29/2019 AIR interface info of GSM
21/45
Burst Types in GSM
-
7/29/2019 AIR interface info of GSM
22/45
Traffic Channels
Gross bit rate 22.8 kbps
Net bit rate at 13 kbps for Speech
Gross bit rate at 12, 6, or 3.6 kbps for Data
Transmission rates of the Data services
compatible to the existing 9.6, 4.8, and 2.4 kbpsPSTN & ISDN services
TCH/F
-
7/29/2019 AIR interface info of GSM
23/45
TCH/H
Gross bit rate of 11.4 kbps
Net bit rate at 5.6 kbps for Speech
Net bit rate at 6 or 3.6 kbps for Data
Generally TCH/H is not used.
-
7/29/2019 AIR interface info of GSM
24/45
FCCHThis downlink channel continuously transmits
unmodulated carrier frequency for frequency
correction of the MS.
SCHUsed for frame synchronization of MS
Contains information about TDMA frame
number and BSIC.
Broadcast Control Channels
-
7/29/2019 AIR interface info of GSM
25/45
BCCH
Broadcasts general information about the cell. viz
Neighbour Cell information
MS transmit power maximum on CCHs
Local Area Identification
-
7/29/2019 AIR interface info of GSM
26/45
Common Control Channels
PCH
Used to page the MS during mobile terminated
call setup.
Paging messages are sent to the area where the
recipient MS is located.
AGCH
-
7/29/2019 AIR interface info of GSM
27/45
AGCH
Used for sending access grant messages which
assign the MS to a SDCCH or directly to TCH in
response to a request placed on RACH by MS.
RACHUsed to transfer uplink messages in response to the
call initiation request placed by the MS or in
response to a paging request or automatically aspart of location update
-
7/29/2019 AIR interface info of GSM
28/45
Dedicated Control Channels
FACCHUsed as a main signaling link for the transmission of
data e.g. handover commands.Required for every call setup and release
FACCH is transmitted in the burst stealing mode bypre-empting a portion of the speech/user data
information bits during active call.
-
7/29/2019 AIR interface info of GSM
29/45
SACCH
Uplink SACCH is used by the MS to report the radio
strengths of the surrounding cells and receive quality of
the serving cell TCH.
Downlink SACCH is used to transmit some common
information also present on BCCH. Thus the MS,
while on TCH, can receive the relevant broadcast
information inspite of being unable to monitor theBCCH.
-
7/29/2019 AIR interface info of GSM
30/45
SDCCH
A duplex pt-to-pt channel which is used forsignaling.
Carries all signaling between the BTS and the
MS when no TCH is allocated.
Used for service requests (e.g SMS), locationupdates, subscriber authentication, ciphering
initiation, equipment validation and assignment toa TCH
-
7/29/2019 AIR interface info of GSM
31/45
Logical Channel to Physical
Channel Mapping
Logical channels FCCH,SCH,BCCH,CCCH are time
division multiplexed on carrier 0 (C0) in time slot 0
(T0).
C0 T0 is always a broadcast control channel and is
always transmitting.
Remaining 7 time slots of C0 can be used for traffic.
T ffi Ch l M ltif St t
-
7/29/2019 AIR interface info of GSM
32/45
Traffic Channel Multiframe Structure
24 slots used for traffic out of 26
Slot 12 used for SACCH
Slot 25 is empty
-
7/29/2019 AIR interface info of GSM
33/45
FCCH and SCH
One SCH slot follows each FCCH slot 8 BPs later
Each channel uses 5 slots in each 51 multiframe.
Common Channels Multiframe Structure
-
7/29/2019 AIR interface info of GSM
34/45
BCCH and PAGCH
BCCH is repeated 4 times every 51 multiframe
PAGCH ( PCH + AGCH) is repeated 36 times every 51 multiframe
Common Channels Combination
-
7/29/2019 AIR interface info of GSM
35/45
Common Channels Combination
-
7/29/2019 AIR interface info of GSM
36/45
Types of Bursts in GSM
Access Burst
Used by the RACH when no channel parameters are known.
41 synch bits, 36 data bits and 68.25 guard bits
8 TB 8 TB41 SYNCHRONIZATION BITS 36 DATA BITS 68.25 GP
Synchronization Burst
-
7/29/2019 AIR interface info of GSM
37/45
Synchronization Burst
Used by BTS for synchronization with MS.
Used by SCH.
Frequency Correction Burst
Used by the FCCH.
Contains all data bits as 0.
Generates a sine wave which is used for frequency correction.
8 TB
8 TB8 TB
8 TB64 SYNCHRONIZATION BITS39 DATA BITS 39 DATA BITS 8.25 GP
8.25 GP142 FIXED BITS (ALL ZEROS)
Normal Burst
-
7/29/2019 AIR interface info of GSM
38/45
Normal Burst
Has 114 bits of data.
Used by all other channels except those mentioned above.
Has training sequence which is used for identifying the correct signal
from all the multi path signals
Stealing bits are used by FACCH for using the TCH.
3 TB 57 DATA BITS 57 DATA BITS26 TRAINING
SEQUENCE
STEALING BITS
3 TB 8.25 GP
-
7/29/2019 AIR interface info of GSM
39/45
Dummy Burst
Transmitted when no other bursts are to be transmitted
Used for signal quality monitoring.
8.25 GP3 TB 3 TB26 TRAINING
SEQUENCE
-
7/29/2019 AIR interface info of GSM
40/45
Call Setup Scenarios
Mobile Originated Call
-
7/29/2019 AIR interface info of GSM
41/45
-
7/29/2019 AIR interface info of GSM
42/45
-
7/29/2019 AIR interface info of GSM
43/45
Mobile Terminated Calls
-
7/29/2019 AIR interface info of GSM
44/45
-
7/29/2019 AIR interface info of GSM
45/45