NTUEE Mobile Communications KC Chen 1 GSM, GPRS, and EDGE Prof. Kwang-Cheng Chen Institute of Communications Engineering National Taiwan University FAX: (02) 2368 3824 email: [email protected]
NTUEE Mobile Communications KC Chen 1
GSM, GPRS, and EDGE
Prof. Kwang-Cheng ChenInstitute of Communications Engineering
National Taiwan UniversityFAX: (02) 2368 3824
email: [email protected]
NTUEE Mobile Communications KC Chen 2
Outlinesq Introductory System Constructionq GSM Architecture and Principlesq Physical Layerq Data Link Layerq Network Layerq Testing
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GSM Phase 1 Services
TelephonyEmergency callsShort-message: point-to-
point and cell broadcastTelefaxAsynchronous dataSynchronous dataAsynchronous PAD
access (packet switched)Alternate speech/dataCall forwardingCall barring
Teleservices
Bearerservices
Supplement-ary services
Full-rate 13 kbps
Alphanumericalinformation
Group 3300-9.6 kbps
Category Services Comments
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GSM Phase 2 Services
TelephonyShort-message servicesSynchronous dedicated
packet data accessCalling/connected line
identity presentationCalling/connection line
identity restrictionCall waitingCall holdMultiparty comm.Closed user groupAdvice of chargeOperator barring
Teleservices
Bearerservices
Supplement-ary services
Half-rate 6.5 kbps
2.4-9.6 kbps
Conference call
On-line information
Category Services Comments
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GSMp GSM stands for Global System for Mobile.p GSM (group special mobile) was first
developed by the CEPT.p GSM services follow ISDN and are classified
as teleservices and data services.p Subscriber Identity Module (SIM) is a memory
device storing ID, networks or countries for services, privacy keys, etc.
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Further Standardization (I)p New bearer services and data-related
improvementsüHSCSD (high-speed circuit-switched data)ü14.4 kbps (single-slot) dataüGPRS (general packet radio service)üEDGE (enhanced data rates for global evolution)
p Speech-relatedüEFR (enhanced full-rate) speech codecüAMR (adaptive multi-rate) codecüTFO (tandem free operation)
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Further Standardization (II)p Mobile station (MS) positioning relatedüCell identityüUplink time of arrival (TOA) and enhanced
observed time difference (E-OTD)üGPS and A-GPS
p Frequency band-relatedüGSM-400/700/850
p Supplementary, billing, relatedp Service platformsüSIM application toolkitüCustomized applications for mobile network
enhanced logic (CAMEL)
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GSM System Architecture
BTS
BTSBSC
BTS
BTSBSC
HLR VLR AUC
MSC
OMC
PSTNISDNDatanet.
Base StationSubsystem Network Switching Subsystem
SS7A
Abis
Air
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Registrationp When a mobile station is on, a scanning
algorithm scans the whole GSM frequency band.
p If a network is detected, mobile station reads system information from (forward) base channel.
p If current location is not the same as it was when the mobile station off, registration procedure starts.
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MS BTS BSC (G)MSC VLR HLR Actionchannel requestchannel activationactivation knowledgechannel assignmentlocation updateauthetication requestauthetication responsecomparison of authet.assignment of new
area and TMSIack. of area and TMSIentry area & ID into
VLR & HLRchannel release
Registration in Network
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MS BTS Actionchannel requestchannel assignmentcall establishment requestauthentication requestauthentication responseciphering commandciphering complete and in functionsetup messagecall proceedingassignment of a traffic channelassignment complete & all messages on channelalerting (ringing)connect (call party accepted the call)connect ack. (two-way call)speech data
MobileOriginatedCall Establishment
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MS BTS Actionpaging mobile stationchannel requestchannel assignmentanswer to paging & on the assigned channelauthentication requestauthentication responserequest to transmit in the ciphered modeack. of ciphered modesetup msg. for the incoming callconfirmationassignment of a traffic channelack. of traffic channelalerting (caller getting ringing sound)connect when mobile off-hookacceptance of connected msg.exchange of speech data
MobileTerminated CallEstablishment
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Handoff in Analog Systemsp Base station monitors the quality of link
between a mobile station and itself. If the quality degraded, it requests adjancent cells to report power level for the mobile. Network decides the frequency to use in the new cell and eventually command change.
p Mobile station is passive and cell sites are equipped with measuring receiver.
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Handover in GSM
p The mobile station monitors the perceived power levels of neighboring cells that are provided by the base station. Measurement report is periodically sent back to the base station that might conduct measurements too. In case necessity of a handover, it can be performed without delay.
p GSM distinguished different types of handovers.
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Types of GSM Handover
p In case a handover is performed within the area of a BSC, BSC handles this simple handover and MSC is just informed.
p In case a mobile crossing boundary of a BSC, MSC has to control the handover.
p For a handover between 2 MSCs, the first MSC still has to maintain control of call managment, though 2nd MSC will handle evantually.
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GSM Authentication
authenticationalgorithm
Mobile StationUm
Interface Network
= ?SRES
KEY (in SIM) RAND (generatedrandom number)
(SRES)
A set of (RAND,SRES) are stored in the HLR & VLR for theuse of authentication center.
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Cipheringp The ciphering algorithms are usually based
on certain one-way function.p If a ciphering algorithm A5 is used to encipher
a data stream in GSM system, the same algorithm is used to decipher.
p In current system, only A5/1 algorithm is used. But for non-COCOM countries, a simpler A5/2 is used. Both algorithms can coexist in western European countries.
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Dynamic CipheringMS Um Network
Kc
Ki RAND
A8
A5 A5
CipheringCommand
DATA DATACipheredData
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Temporary Mobile Subscriber Identity (TMSI)
p To prevent an intruder from identifying a GSM user IMSI, TMSI is assigned to each subscriber using the network during the location updating and is used for reporting, calling, paging as long as remaining activities.
p The assignment, administration, updating of TMSI is performed by the VLR. When MS off, it is stored on the SIM card.
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Handset HW
BasebandProcessor
RF PA
Antenna
MultimediaCo-Processor
Memory
Power/Battery ManagementIrDA
BluetoothWLANWiMAXUWBFM
DVB/DAB-TDVB-HDSC
SD/MSMP3
MPEG, H.264LCD Driver
LCD Controller
SIM
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Handset SW
BasebandProcessor
RF PA
Antenna
MultimediaCo-Processor
Memory
Power/Battery Management IrDABluetooth
WLANWiMAXUWBFM
DVB/DAB-TDVB-HDSC
SD/MSMP3
LCD DriverLCD Controller
SIMLayer 1/2/3
MMI, drivers,Middleware,
Appl. SW
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Physical Layer- Layer 1
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GSM Frame Structure...Superframe
6.12 sec51 Multiframe
... 26 Frames120 msec
8 Time Slots4.615 msec 0 7
0.57692 msec156.25 bits
Tail Bit
3 57 1 1 326 57 8.25
Stealing Flag Guard Period
Coded Data Midamble
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GSM Radio Subsystem
p GSM uses a combination of TDMA and FHMA, and FDD.
p 200 kHz wide channels called ARFCNs (absolute radio frequency channel numbers)
p Each ARFCN pair is separated by exactly 45 MHz with 3 time slots spacing.
p channel data rate 270.833 kbps using BT=0.3 GMSK.
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GSM Traffic CHannels (TCH)
p full rate speech at 13 kbps with channel coding added to 22.8 kbps
p full rate data for 9600/4800/2400 bps. With FEC, data is sent at 22.8 kbps.
p half-rate speech at 6.5 kbps and can carry up to 11.4 kbps
p half-rate data at 4800/2400 bps.
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GSM Control Channels (CCH)
p Broadcast Channels (BCH): broadcast control channel (BCCH), frequency correction channel (FCCH), synchronization channel (SCH).
p Common Control Channels (CCCH): paging channel (PCH), random access channel (RACH), access grant channel (AGCH).
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CCHp Dedicated Control Channel (DCCH):
stand-alone dedicated control channel (SDCCH), slow associated control channel (SACCH),
p fast associated control channel (FACCH).
p bidirectional with the same format and function on both forward and reverse links.
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Frequencies: Primary GSM
p Mobile station transmits in 890-915 MHz. Base station transmits in 935-960 MHz. 125 channels are numbered from 0 to 124.
p Within the system, only the absolute radio frequency channel number (ARFCN) is used (from 1 to 124).
p Channel 0 is used as the guard band for GSM and other applications.
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Frequencies: E-GSM
p Additional 10 MHz bandwidth has been added to the bottom end of the duplex bands.
p It results in 50 more channels with numbers from 974 to 1023.
p Channel number 0 is returned for use in extended GSM and channel 974 serves as the guard band.
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DCS-1800 or PCNp Same signaling and messaging
techniques as GSM.üAlso known as GSM-1800
p 1710-1785 MHz for uplink and 1805-1880 MHz for downlink. Duplex spacing is 95 MHz with 374 channels.
p Channel numbers are 512 to 885.
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PCS-1900/DCS-1900p Same DCS-1800 system for North
America PCS.üAlso known as GSM-1900
p Lower frequency starts from 1850 MHz with 80 MHz duplex spacing.
p Channel numbers range from 512 to 810.
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Power Levels in GSMPowerClass
Max. Power of aMobile Station (dBm)
Max. Power of aBase Station (dBm)
1 20W(43) 320W(55)2 8W(39) 160W(52)3 5W(37) 80W(49)4 2W(33) 40W(46)5 0.8W(29) 20W(43)6 10W(40)7 5W(37)8 2.5W(34)
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Power Levels in DCS-1800 and Phase II GSM
PowerClass
Max. Power of DCS-1800MS (dBm)
Max. Powerof DCS-1900MS (dBm)
Max. Powerof DCS-1800BTS (dBm)
Max. Powerof DCS-1900BTS (dBm)
1 1W(30) 1W(30) 20W(43) 20-40W2 0.25W(24) 0.25W(24) 10W(40) 10-20W3 2W(33) 5W(37) 5-10W4 2.5W(34) 2.5-5W
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Macro-cell and Micro-cellbad coverage
hot spot
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Macro-cell and Micro-cellbad coverage
hot spot
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Power Levels for Micro-BTS
PowerClass
Max. Powerof GSMMicro-BTS
Max. Powerof DCS-1800Micro-BTS
Max. Powerof PCS-1900Micro-BTS
M1 0.25W 1.6W 0.5-1.6WM2 0.08W 0.5W 0.16-0.5WM3 0.03W 0.16W 0.05-0.16W
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Pulse Power Profile
147 bits0.5428 msec
dB+4+1-1-6
-30
-70
10us10us8us
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Time Division Duplex (TDD)in GSM
0 1 2 3 4 5 6 7 0 1 2 3
5 6 7 0 1 2 3 4 5 6 7 0
BTS transmits
MS transmtsTDMA Frame 4.615msaround 216.6 Hz effect
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TDDp no need for a dedicated duplex stage
(duplexer); only requiring fast-switching synthesizer, RF filter paths, fast antenna switching
p increased battery life or lighter batteryp better quality and lower cost
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Normal Burst
T3
Coded Data57
S1
TrainingSequence 26
S1
Coded Data57
T3
GP8.25
148 bits = 0.54612 msec
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Tail Bits (T)p used as guard time to cover the
uncertainty during power ramping up and ramping down.
p The tail bits are always set to be zero, while the demodulation process requires initial zero bits.
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Stealing Flag (S)p These two bits are an indication to the
receiver whether the incoming burst is carrying signaling data (to maintain the link) or user data (traffic).
p Indicating flag is needed since signaling data are very important and go to different places.
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Training Sequencep Let radios synchronize their receivers
with burst, e.g. equalizer for multipath fading.
p 8 sequences are defined in GSM. All radios in a particular cell share the same training sequence.
p An equalizer in GSM can compensate up to 16 micro-sec path delay.
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Guard Period (GP)p No data is transmitted and is just
considered as guard time, to avoid possible overlap of radiation power of two bursts.
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Random Access Burst
T8
T3
SynchronizationSequence 41
Coded Data36
Guard Period68.25
88 bits = 0.32472 msec
68.25 bits = 0.252 msec which is equivalent to 75.5 kmpropagation delay.
That is, the max. allowed distance between mobile stationand BTS is 37.75 km. Based on other system parameters,the max. cell size is 35 km in GSM.
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Frequency-Correction Burst
T3
T3
GP8.25
fixed bit sequence142
148 bits = 0.54612 ms
An all zeros sequence can meet the purpose of frequencycorrection due to the nature of GMSK.
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Synchroniation BurstT3
T3
Coded Data39
Coded Data39
SynchronizationSeq. 64
GP8.25
148 bitsAt beginning of mobile communicating to network, it only detectsthe frequency of base channel and needs to know the training seq.and system parameters. This is done by the synchronization burst.In this kind of burst, in addition to a longer synchronization seq.,coded data contains the BSIC (base station information code)including BCC (BS color code) and NCC (national color code),and shortened TDMA frame number.
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Logical Channelsp A logical channel carries signaling data or
user data. It can be mapped into any physical channel (frequency and time slot).
p Once a physical channel is assigned to carry the content of a logical channel, the assignment shall not change.
p 7 combinations of logical channels.p GSM distinguishes between traffic channels
and control channels.
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Traffic Channels
p TCH/FS (traffic channel/full-rate speech): 13 kbps net speech rate.
p TCH/HS (traffic channel/half-rate speech): future application without speech quality degradation.
p TCH/F9.6/4.8/2.4: data transmission at rates of 9.6/4.8/2.4 kbps.
p TCH/H4.8/2.4:
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Control Channelsp braodcast channelsp common control channelsp dedicated control channelsp associated control channels
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Broadcast Channels (BCH)
BCHs are only transmitted by the base station and provide information for MSs to synchronize with the network. Three types of BCH:
p broadcast control channel (BCCH)p frequency-correction channel (FCCH)p synchronization channel (SCH)
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Common Control Channels (CCCH)
p CCCH support the establishment of a dedicated link between a mobile and a BTS. CCCH provides tools for call setups and can originate from the network or mobiles.
p Three types of CCCH.
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Common Control Channels (CCCH): continued
p random access channel (RACH): to request a dedicated channel and only used by mobiles.
p paging channel (PCH): BTS calls individual MSs within its cell.
p access grant channel (AGCH): where MS gets information from BTS on which dedicated channel for its immediate needs.
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Dedicated Control Channels (DCCH)
used for message transfers between network and MS, not for traffic, and also used for low-level signaling messages among radios.
p standalone dedicated control channel (SDCCH)
p slow associated control channel (SACCH): carrying control and measurement parameters/routine data to maintain a link.
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Fast Associated Control Channel (FACCH)
p In downlink, a BTS transmits a reduced set of system parameters to keep mobile up to date on the latest changes in the system. In uplink, MS reports the measurement results.
p FACCH can carry the same information as SDCCH but FACCH replaces all/part of a traffic channel.
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Logical Channels and Directions
Logical Channel MS BTSTCH <----->FACCH <----->BCCH <-----FCCH <-----SCH <-----RACH ----->PCH <-----AGCH <-----SDCCH <----->SACCH <----->
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Channel Combinations1. TCH/FS+FACCH/FS+SACCH/FS2. TCH/HS(0,1)+FACCH/HS(0,1)
+SACCH/HS(0,1)3. TCH/HS(0)+FACCH/HS(0)+SACCH/HS(0)
+TCH/HS(1)+FACCH/HS(1)+SACCH/HS(1)4. FCCH+SCH+CCCH+BCCH5. FCCH+SCH+CCCH+BCCH+SDCCH/4
+SACCH/46. CCCH+BCCH7. SDCCH/8+SACCH/8
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Multiframe Structurep Each channel combination requires one
single physical channel. Multiframe structure made of a fied number of TDMA fames allows logial channels to be ordered into time slots.
p 26-multiframe structure is used for the traffic channel combinations and 51-multiframe structure is used for signaling combinations.
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Traffic Channel Frame Structure (26-Multiframe)
p For combination I (TCH/FS), the first 12 fames for traffic data (speech & data), 13rd frame for SACCH, another 12 frames for traffic, and the last frame idle for MS to measure etc.
p 120 ms totally.
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Traffic Channel Frame Structure
(26-Multiframe): continuedp For combination II or III (TCH/HS), 2 half-rate
speech channels are packed onto one 26-multiframe structure. One logical channel uses every other TDMA frame. Frame 13 for SACCH1 and 26 for SACCH2.
p Combination II for one half-rate channel and III for two half-rate channels.
p FACCH may take a position of traffic channel if necessary.
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Signaling Frame Structure(51 Multiframe)
p NOT carrying any user data.p more complex as incorporating 4
different channel combinations and structures.
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Combination IV (downlink):FCCH+SCH+CCCH+BCCCH
F0
S1
BCCH2-5
CCCH6-9
CCCH12-19
CCCH22-29
CCCH32-39
CCCH42-49
I50
FCCH
SCH
idle
CCCH includes PCH and AGCH
235.38 ms
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Combination IV (uplink):
R0
R1
BCCH2-5
CCCH6-9
CCCH12-19
CCCH22-29
CCCH32-39
CCCH42-49
R50RACH
• This combination is normally used for cells with severalcarriers and a large amount of traffic on CCCH.
• It can be transmitted on any frequency available in timeslot 0. The frequency here is a reference for neighboringcells.
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Combinations V VI VIIp Combination V is the minimum for smaller
cells with only one or two transceivers. It may assign up to 4 DCCHs.
p Combination VI is similar to IV but without FCCHs and SCHs for cases with a huge number of transceivers.
p Combination VII is to provide routine signaling. 8 DCCHs may be used to servce 8 parallel signaling links on one physical channel.
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Cell Broadcast Channel (CBCH)
p CBCH supports a part of the group of short message services (point-to-omnipoint). An operator is thus able to transmit messages to its subscribers.
p CBCH is always mapped on the 2nd subslot of SDCCH independently for channel combination V and VII.
p CBCH only in downlink and no ack.
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Block and Convolutional Coding of Full-Rate Speech
Class Ia50 bits
Class Ib132 bits
Class II78 bits
block codingof clas Ia bits
with3 CRC bits adding 4 bits
of zeros toreset codec
378 coded bits 78 bits
convolutional code r=1/2 K=5
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Coding for 9.6 kbps Data Transmission
p 9.6 kbps coding in terminal equipment => 240 bits a frame (at 12 kbps)
p By adding 0000, 244 bits.p By r=1/2 K=5 convolutional code, 488
coded bits.p Puncturing 32 coded bits, 456 coded
bits.
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Coding for 2.4 kbps Datap 2.4 kbps at terminal equipment => 72
bits (at 3.6 kbps)p By adding 0000, 76 bitsp By r=1/6 K=5 convolutional code, 456
coded bits.
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Coding for Signaling Channel
signaling information184 bits
parity40 bits
0000
Fire Code
convolutional code r=1/2 K=5
456 coded bits
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Speech Coding for Mobile Communications
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Speech Coders
Waveform Coders Source Coders
Time Domain Frequency Domain
Nondifferential Differential
LPC
VocodersSBC
ATCPCMDELTA
CVSDM
ADPCM
APC
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ADPCM for CT-2
+4-bit adaptivequantizer
adaptive scalingfactor generator
inverse adaptivequantizer
adaptivepredictor
+
-
inputanalogwaveform
output
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Channel Vocoder: Speech Generation Model
Anaylzer Transmission
NoiseSource
PulseSource
VocalTractFilter
secondary source
speechoutput
speech
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Linear Predictive Coders (LPC)
The LPC system models the vocal tract as an all-pole linearfilter with transfer function
H z G b zkk
Mk( ) / ( )= +
=
−∑11
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LPC Coding System
Buffer
LPCFilter
Voiced/UnvoicedDecision
PitchAnalysis
Encoder
Encoder
Encoder
CHANNEL
Decoder
Decoder
Decoder
SYNTHESIZER
Excitation
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Code-Excited LPC (CELP)p Coder and decoder have a predetermined
code book of stochastic (zero-meam white Gaussian) excitation signals.
p Transmitter searches its codebook for best perceptual match and the corresponding index is transmitted.
p The receiver uses the index for synthesizer.p CELP coders are extremely complicated.
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GSM cellular RPE-LTP 13CD-900 cellular SBC 16IS-54 cellular VSELP 8IS-95 cellular CELP 8IS-95 PCS PCS CELP 14.4PDC cellular VSELP 4.5/6.7/11.2CT-2 cordless ADPCM 32DECT cordless ADPCM 32PHS cordless/PCSADPCM 32DCS-1800 PCS RPE-LTP 13PACS PCS ADPCM 32
Standards Service Speech Coder Bit Rate (kbps)
Speech Coders Used in Various Mobile Radio Systems
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GSM Codecp regular pulse excited long term
prediction (RPE-LTP)p combination of RELP (France) and
MPE-LTP (Germany)p 13 kbpsp complicated and power hungry
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GSM Speech EncoderHammingWindow
Segmentation
Pre-emphasis
LPCInverseFilter
STPAnalysisFilter
+ LPFGridSelection M
UX
LTPAnalysisFilter
Pre-processing STP LTP RPE
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GSM Speech Decoder
DEMUX
GridPosition/RPEDecoding
LTPSynthesisFilter
STPSynthesisFilter
Post-Processing
output
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Transmissionp Speech coder issues 260 bits every 20 msec.p 50 bits out of 260 bits describe filter coef.,
block amplitude, LTP parameters and are class Ia under channel coding protection.
p 132 bits describe RPE pointers, RPE pulses, some LTP parameters and are class Ib.
p 78 bits contain RPE pulse and filter parameters and are class II.
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Discontinuous Transmission (DTX)
p When a pause is detected by speech transcoder, we discontinue/suspend radio tx. for the duration of pause, 50% duty cycle.
p Voice activitiy detection (VAD) determines the presence/absence of speech, even under strong background noise.
p Every 480 ms, a silence descriptor (SID) frame is transmitted to yield presence.
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Adaptive Multi-rate Codec (AMR)p 1999, ETSI approved AMR codec by
Ericsson, Nokia, Siemens.ü3GPP adopted AMR laterüAMR contains a set of fixed-rate speech, channel
codecs, fast in-band signaling, link adaptation.• Operating at full-rate (22.8K bps) and half-rate (11.4K
bps)• Ability to adapt to radio channel and traffic load
conditions, to select optimal channel mode (HR/FR) and codec mode
• Tradeoff between speech and channel coding to deliver best possible combination of speech quality and system capacity
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AMR Speech & Channel Codingp AMR (and EFR) utilizes algebraic code
excitation linear prediction (ACELP)p A combination of 8 speech codecsü12.2, 10.2, 7.95, 7.4, 6.7, 5.9, 5.15, 4.75 kbps
• All for full-rate codec• Lower 6 rates for half-rate codec
üAMR NB (narrow band) with GMSK in rel’98üError correction is based on recursive systematic
convolutional (RSC) coding with puncturingü6-bit CRC is used for detecting bad frames
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AMR In-band Signaling & Link Adaptationp Both MS and BS perform channel quality
measurementüCodec mode command (up link) or codec mode
request (down link) is sent over radio interface in in-band messages
p The receiving end uses information to select the best codec mode for prevailing channel conditionüCodec mode indicator is sent over radioüCodec mode might be different in up/down links
but the channel mode (FR/HR) must be the sameüNetwork controls codec/channel mode, and MS
followsüAMR contains voice activity detection (VAD) and
DTX
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Link adaptation
Speechin
Speechout
Multi-rate
SpeechEncoder
Multi-rate
ChannelEncoder
Multi-rate
SpeechDecoder
Multi-rate
ChannelDecoder
MIu
SMIu
SMRd
ModeRequest
Generator
DownlinkQualityMeas.
MCu
SMIu
MCu
Link
ada
ptat
ion
QIu
MRd
Mobile station (MS)
Radio Channel(uplink)
Radio Channel
(downlink)
MIu
SMRd
Multi-rate
ChannelDecoder
MIu
S
MRd
Downlinkmode
control
Uplinkmode
control
Multi-rate
ChannelEncoder
MCu
SMId
SMId
MCu
QIu
UplinkQualityMeas.
MCd
Abis/ter
Abis/ter
MIu
S
Multi-rate
speechdecoder
Multi-rate
speechencoder
SMId
MCd
Speechout
Speechin
Base transceiver station (MS) Transcoder (TC)
S- Speech QI- quality indicator MC- codec mode command (inband signaling)MR- codec mode request (inband signaling)MI- codec mode indicator (inband signaling)
U=UplinkD=Downlink
AMR Codec System
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Bit Allocation of AMR Codec(Kbps) LPC LTP FCB Gains Total12.2 38 30 140 36 24410.2 26 26 124 28 2047.95 27 28 68 36 1597.4 26 26 68 28 1486.7 26 24 56 28 1345.9 26 24 44 24 1185.15 23 20 36 24 1034.75 23 20 36 16 951.75 29 0 0 6 35
FCB: fixed codebook ACB: adaptive codebook
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Data Link Layer - Layer 2
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Layer 2 GSM Signalingp Protocol used for signaling transfer
between a MS and a BTS is link access procedure for the Dm-channel (LAPDm).
p It is adapted from link access protocol data (LAPD) in ISDN networks.
p LAPD is used in GSM on Abis interface between BTS and BSC.
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Principle of Link Controlp Similar to ARQüStop-and-wait
• Transmitter waits until acknowledgement• Low efficiency
üSelective• Resend only those with errors• Memory size
üGo-back-N• Transmitting N packets then waiting for
acknowledgement• Widely used in link control protocols
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Tasks of Data Link LayerThe data link layer is responsible for the correct and completetransfer of information blocks between layer 3 entities over GSMair interface. The protocol have the following functions:
• organization of layer 3 information into frames• peer-to-peer transmission of signaling data in defined formats• recognition of frame formats• establishment, maintainance/supervision, termination of one or
parallel data links on signaling channels• acknowledgement of transmission and reception of numbered
information frames (I-frames)• unacknowledged transmission and reception of unnumbered
infromation frames (UI-frames)
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Frame Format A
addressfield
controlfield
length indicatorfield
fill bits
1 octet
variable length
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Frame Format B
addressfield
controlfield
length indicatorfield
information field& fill bits
1 octet
variable length
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Frame Formats A & Bp Frame format A is used when no signaling but
wanting to keep the signaling channel.p When signaling is ready for transmission,
frame format B is used, which contains an information field. Such a frame is called an I-frame.
p When numbered I-frames are transmitted, it is referred as the acknowledged mode and the procedure called multi-frame operation.
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Frame Formats Abis and Bbis
Abis Length IndicatorField
Fill Bits
Length IndicatorField
Information Field& Fill Bits
Bbis
Formats Abis and Bbis are equivalent to formats A and Bbut they are only used in the unacknowledged mode ofsignaling data transfer.
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Address Fieldp In GSM control channels, the address field is
fixed at one octet.p It is primarily used to addressed the service
access point (SAP), a defined interaface which provides services to a layer 3 entity.
p GSM provides two SAPs on radio interface: for signaling and for short message.
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Address Field: continued
8 7 6 5 4 3 2 1
X LPD SAPI C/RE/A
LPD=00 for link protocol discriminatorSAPI=000 for layer 3 signaling
011 for short messagesC/R=0 for mobile sending a command
1 for mobile sending a responseE/A=0 for next octet is a part of address E/A=1 for GSM control channels
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Control FieldIt consists of only one octet and is only in frame formats A & B. 3 types:
p I-frame: numbered and carrying numbered layer 3 information
p S-frame: control functions like I-frame ack., requests for repartitions, intermittent suspension of numbered information transfers.
p U-frame: unnumbered type frames offering additional data link functions.
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Control Field: continued8 7 6 5 4 3 2 1
8 7 6 5 4 3 2 1
8 7 6 5 4 3 2 1
N(R) P N(S) 0
N(R) P/F
P/FU U U U U 1 1
1S S 0
I-frame
S-frame
U-frame
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I-frame: This type of frames are numbered and carrynumbered Layer 3 information.
S-frame: Supervisor frames are control function like(a) I-frame ack. with fill frame (Format A)(b) request for repetitors(c) intermittent suspension of numbered informationtransfers
U-frame: The unnumbered frames offer additional datalink functions for Layer 2 and allow for the transfer of unnumbered and unack. information frames on controlchannels.
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Control Field Parametersp N(S) Transmitter Send Sequence
Number: modulo-8 counterp N(R) Transmitter Receive Sequence
Number: also a modulo-8 counterp Poll/Final Bit: Poll bit is set when a
response is requested; final bit is set when a response to a command is sent back.
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Control Field Parameters: Supervisor and Unnumbered
Bitsp Receive Ready RR frame, SS=00, has 3
functions: a data link entity is ready to receive an I frame; ack. reception up to N(R)-1 frames; reset Layer 2 in case not ready
p Receive Not Ready, RNR frame, SS=01: can not receive I-frame
p Reject, REJ frame, SS=10: reception of one or more frames is required.
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Control Field: U Framep SABM Command, UUUUU=00111: Set
asynchronous balanced mode starts the modulo-8-counted I-frame transmissions.
p DISC Command, UUUUU=01000: Disconnect ends a multi-frame operation session.
p UA Response, UUUUU=01100: Unnumbered ack. is set to ack. an SABM or DISC.
p UI Command, UUUUU=00000: transmission of unnumbered information within the frame.
p DM Response, UUUUU=00011: sent from a data link layer entity when multiframe operation is not allowed.
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Length Indicator Field
8 7 6 5 4 3 2 1L M EL
One octet is sufficient for GSM signaling.
L stands for the length of Information Fieldin the remainder of the frame.M=0 either an entire layer 3 message included
or the last part of segmented messageM=1 another part of message followingEL=1 the last octet in the length indicator fieldEL=0 not the last octet
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Network Layer - Layer 3
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Layer 3p The network layer of GSM, also referred
as signaling layer, uses a protocol to establish, maintain, terminate mobile connections.
p Three sublayer defined for Layer 3 (network layer): radio resource management (RR), mobility management (MM), connection management (CM).
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RR Sublayerp responsible for management of
frequency spectrum, system reaction to radio environment changes, maintaining of a clear channel between PLMN and MS.
p including channel assignment, power control, time alignment, handover, etc.
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RR Sublayer Proceduresp channel assignment procedurep channel releasep channel change and handover proceduresp change of frequencies, hopping sequences or
algorithms, frequency tablesp measurement report from mobilesp power control and timing advancep modification of channel modesp cipher mode setting
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MM Sublayerp support of user mobility, registration,
management of mobile datap checking user & equipment identityp checking allowed services for usersp support of confidentiality (e.g. TMSI)p user securityp provision of MM connection, based on
RR, to CM
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MM Sublayer Procedures
p location updatep periodic updatingp authenticationp IMSI attachp IMSI detachp TMSI reallocationp indentification
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CM Sublayerp managing all functions necessary for
circuit switching call control in GSM PLMN
p call control responsibilities, which are amost identical to a fixed ISDN network,
p call control entity in GSM establishing, maintaining,and releasing call connection for communication links.
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CM Sublayer Proceduresp mobile-originated call establishmentp mobile-terminated call establishmentp changes of transmission mode during
an ongoing callp call re-establishment after interruption of
an MM connectionp dual-tone multi-frequency (DTMF)
control for DTMF transmissions
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Structure of Layer 3 Message
8 7 6 5 4 3 2 1
TI ProtocolDiscriminator
TIflag
0 Message Type
Information Elementsmandatory
Information Elementsoptional
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Transaction Identifierp TI is a pointer to distinguish multiple
parallel CM connections and various simultaneous transactions.
p For RR & MM, TI is not relevant, TI=0000.
p TI flag indicates originator of a CM connection. It is set 0 by the originator and 1 when sent back.
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Protocol Discriminatorp PD links Layer 3 protocol to the
addressed entity and identifies 6 protocols: radio resource management (0110), mobility management (0101), call control (0011), short message services (1001), supplementary service (1011), test procedure (1111).
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Information Elementsp Mandatory IEs have a reserved place in
structure of message; optional IEs carry information element identifier (IEI) telling receiver the purpose of information contained.
p 4 possible IE types: mandatory fixed length (MF), mandatory variable length (MV), optional fixed length (OF), optional variable length (OV).
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Testing GSM
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First Generation GSM Radio Test
SC
ENC
HWC
DEC
BDM
RF/SYNTH
MOD
O-att
I-att
DEMOD
PersonalComputer
RF-out
RF-in
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Transmitter Measurementsp RF powerp frequency error and phase errorp special transmitter power measurements:
peak power, power-time template, burst timing
p measurements in spectrum: due to modulation, due to switching transients, spurious emissions, intermodulation attenuation
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Measurements on Digital Receivers
p BER, residual BER, frame erasure ratep sensitivity p cochannel rejectionp adjacent channel rejectionp intermodulation rejectionp blocking & spurious response rejection
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Test of Layer 1p synchronization and timingp power controlp radio channel management
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Fading Environmentsp rural area (RA)p hilly terrain (HT)p typical urban (TU)p equalizer (EQ)
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Test of Layer 2p establishment of an acknowledged data linkp error control during data link establishmentp seq. counting during ack. block transferp segmentation and concatenationp loss of I-framep reaction to erroneous C/R in address fieldp reaction to erroneous values in control fieldp reaction to invalid frames
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Block Diagram of Mobile Station
antennacombiner
VCO &synthesizer
controlsignaling
unit
channelcodec
speechcodec
A/DD/A
receivingcircuits
transmittingcircuits
A/D
D/A
equalizerdemodulatordemultiplexer
burst building unitmultiplexermodulator telephone
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Additional RF Tests on a MSp bad-frame indication performancep intermodulation rejectionp transceiver test for spurious emission
measurement in active & idle states.
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Signaling Test of Layer 1p downlink power controlp correction of burst timingp report of actual timing advance & power
levels (uplink SACCH)p measurement report
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Block Diagram of Base Station
VCO &synthesizer
controlsignaling
unit
channelcodec
speechcodec
receivingcircuits
transmittingcircuits
A/D
D/A
equalizerdemodulatordemultiplexer
burst building unitmultiplexermodulator
speechcodec
signaling
Abis
64 kbps
64 kbps
A-law
64 kbps
13 kbps
16 kbps
3 kbps in-bandsignaling
BTS BSC
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Iridium:Satellite Mobile Using GSM
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Briefingp 66 LEO (low-earth-orbit) satellites in 6 polar
orbital planes which 780 km above sea-surface. Each has 48 L band beams for subscriber coverage.
p Constellation of satellites is controlled by the system control segment (SCS). SCS also decides frequency planning and routing information.
p It is a packet switching network.
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Gateway
Internationalswitching
center
PSTN
SystemControl
Segment
K-band
L-band K-bandL-band
Iridium System Overview
ISU
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Iridium Gateway
InternationalSwitch &PSTN
MOC GMS
MSC
HLRVLREIR
ETC
MOC: message origination controllerGMS: gateway management systemETC: earth station controllerEIR: equipment identity register
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INMARSATp The only commercial satellite mobile
communication systemü3 geo-stationary satellites over Pacific,
Indian, Atlantic oceansüSupporting speech, data, video trafficüSmall VSAT and portable terminalsüOriginally for marine-time applications
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General Packet Radio Services: GPRS
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What Is GPRS?Conventional Way: Circuit Switched Data
A
HLR
PSTN
Data overVoiceC
IRC
UIT
SW
ITC
HE
D MSC/VLR
GSMBTS
BSC
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What Is GPRS?Packet Switched Technology on GSM
Internet
GbA
PSDN
HLR
PSTN
MSC/VLR
PAC
KE
TSW
ITC
HE
D
GGSN
SGSNBSC
GSMBTS
Packet Data
GGSN: Gateway GPRS Support Node
SGSN: Serving GPRSSupport Node
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What Is GPRS?GPRS VS Circuit Switched Data
TS1TS1TS2TS2TS3TS3
Circuit Switched DataCircuit Switched Data
TS1TS1GPRSGPRS
TimeTime
Stochastic Multiplexing
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0 1 2 3 4 5 6 7 0 1
5 6 7 0 1 2 3 4 5 6
0 1 2 3 4 5 6 7 0 1
0 1 2 3 4 5 6 7 0 1
5 6 7 0 1 2 3 4 5 6
5 6 7 0 1 2 3 4 5 6
3 slots: 4th slot: 5th slot:
Downlink
Uplink
Monitor
Downlink
Uplink
Monitor
Downlink
Uplink
Monitor
1-slot
2-slot
3-8-slot
GPRS Multi-slot Capabilities
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What Is GPRS?GPRS Network Seen by IP Network
Subnetwork191.200.44.xxx
Host155.222.33.55
Source: Nokia
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Why GPRS?Operator’s Viewp First attractive data service for GSM.p Optimal support for packet switched traffic.p First step to the 3rd generation.p The possibility to offer new services.p Better network efficiency.p Higher revenue.
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Why GPRS?User’s View
p A global and wireless access to the Internet !p All existing TCP/IP applications can be used.p New and attractive services.p Users stay on the line long but only pay for the
capacity used.p Data rate from 9.05 kbps up to 171.2 kbps.ü 9.05 kbps per channel by CS-1 (Channel Coding Scheme 1).ü 13.4 kbps by CS-2, 15.6 kbps by CS-3, and 21.4 kbps by CS-
4.
ü Maximum date rate: 21.4 x 8 = 171.2 kbps.
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Services on GPRSGPRS is only a bearer!p E-mailp File transferp Shopping and ticket salesp Banking and finance managementp Newsp Webp Traffic informationp Stock pricesp And many others...
GPRS Logical Architecture
New Interface ( IP/X.25 )New Interface ( FR )
SGSN: Serving GPRS Support NodeGGSN: Gateway GPRS Support Node
New Interface ( IP )
New Interface ( SS7 )
SGSN GGSN
SGSN
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pp SGSNSGSNüSame level as the MSC/VLR.üConnected to the BSS with Frame Relay.üDetects new GPRS MSs in its service area.üRecords location of MSs in its service area.üSends/Receives data packets to/from the MSs.
pp GGSNGGSNüProvides interworking with the PDN (e.g., the
Internet).üLooks like a router, when seen by the Internet.üConnected to the SGSN via an IP-based backbone.
New Elements for GPRS
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Enhanced Elements for GPRSpp HLRHLRüEnhanced with GPRS subscriber data and
routing information.pp MSC/VLRMSC/VLRüEnhanced for co-ordination of GPRS and Circuit
Switched services (e.g., combined location update, paging for circuit-switched calls via the SGSN ).
pp BSSBSSüSupports flexible radio channel allocation, and
supports a new interface to the SGSN.pp SMSSMS--GMSC and SMSGMSC and SMS--IWMSCIWMSCüSupports SMS transmission via the SGSN.
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Internet
IP based backbone
Illustration - GPRS Attach
GGSN
SGSN
BSS
HLR
GGSN
SGSN
BSSAttach
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Internet
IP based backbone
Illustration - Activate an IP Address
GGSN
SGSN
BSS
HLR
GGSN
SGSN
BSSActivate
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Internet
IP based backbone
Illustration - Intra SGSN Routing Area (RA)
Update
GGSN
SGSN
BSS
HLR
GGSN
SGSN
BSSRA Update
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Internet
IP based backbone
Illustration - Inter SGSN RA Update
GGSN
SGSN
BSS
HLR
GGSN
SGSN
BSSRA Update
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Internet
IP based backbone
Illustration - Data Routing from the Internet to
the MS
GGSN
SGSN
BSS
HLR
GGSN
SGSN
BSS
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Internet
IP based backbone
Illustration - Data Routing from the MS to the
Internet
GGSN
SGSN
BSS
HLR
GGSN
SGSN
BSS
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Internet
IP based backbone
Illustration - MS to MS Routing via the same
GGSN
GGSN
SGSN
BSS
HLR
GGSN
SGSN
BSS
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Internet
IP based backbone
Illustration - MS to MS Routing via the same
GGSN
GGSN
SGSN
BSS
HLR
GGSN
SGSN
BSS
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Internet
IP based backbone
Illustration - MS to MS Routing via Different
GGSNs
GGSN
SGSN
BSS
HLR
GGSN
SGSN
BSS
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Illustration - Data Routing for Roaming MS
HLR
Operator 2backbone
Internet
Operator 1 backbone
GGSN
SGSN
BSS
SGSNBG
Inter-operatorbackbone
BG
GGSN
Transmission plane
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Transmission plane ( continued )
üGTP: GPRS Tunneling Protocolü IP: Internet ProtocolüUDP: User Data ProtocolüTCP: Transmission Control ProtocolüSNDCP: Subnetwork Dependent Convergence
ProtocolüLLC: Logical Link ControlüBSSGP: BSS GPRS ProtocolüNS: Network ServiceüRLC: Radio Link Control functionüMAC: Medium Access Protocol
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Transmission plane ( continued )
p GPRS Tunneling ProtocolüBy GTP, many packet data protocol ( e.g., IP, X.25
) can be supported, even if the protocol is not supported by all SGSNs.üGTP header contains an IMSI (International Mobile
Subscriber Identifier) and an NSAPI (Network Service Access Point Identifier) .üBelow GTP, IP ( V4 or V6 ) is used as a backbone
network protocol. Ethernet, ISDN, or ATM may be used below IP.üTCP carries GTP protocol data unit for X.25, UDP
carries GTP protocol data unit for IP.
NTUEE Mobile Communications KC Chen 158
Transmission plane ( continued )
p Subnetwork Dependent Convergence ProtocolüMultilplexing, segmentation, and compression.
TLLI: Temporary Logical Link Identifier
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Transmission plane ( continued )
p RLC/MAC
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Transmission plane ( continued )
p RLC/MAC (uplink)üThe access to the uplink uses a Slotted-Aloha
based reservation protocol.
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Transmission plane ( continued )
p RLC/MAC (uplink)üA selective ARQ protocol that provides
retransmission of erroneous RLC data blocks.
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Transmission plane ( continued )
p RLC/MAC (downlink)üThe network initiates packet to an MS that is in
Standby state by sending a Packet Paging Request.
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Transmission plane ( continued )
p RLC/MAC (downlink)
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Transmission plane ( continued )
p LLCüProvides a reliable logical link between the MS
and its SGSN.üAcknowledged mode for Packet Data Unit.üUnacknowledged mode for signaling and SMS.
p BSS GPRS ProtocolüConveys routing information between SGSN and
BSS.p Network ServiceüFrame Relay.
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Signaling plane: MS-SGSN
p GMM: GPRS Mobility Managementp SM: Session Management
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Signaling plane: SGSN-HLR
p MAP: with enhancement for GPRS
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Signaling plane: SGSN-MSC/VLR
p BSSAP+: A subset of Base Station System Application Part ( BSSAP ) . It supports signaling for “Mobility Management Functionality” ( e.g. combined RA/LA update )
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Signaling plane: GSN-GSN
p GTP: GPRS Tunneling Protocolp UDP: User Datagram Protocol
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Signaling plane: GGSN-HLR-based on MAP
p MAP: Supports signaling for “Network-Requested PDP ( Packet Data Protocol ) Context Activation Procedure”
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Signaling plane: GGSN-HLR-based on GTP and MAP
p Interworking: between GTP and MAP
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Referencesp CHT Labs. Presentationp GSM 03.60 Version 6.3.2 ( 1999-07 )p GSM 03.64 Version 6.2.0 ( 1999-05 )p Nokia’s White Paper on GPRSp http://www.nokia.comp http://www.ericsson.comp http://www.motorola.comp http://www.alcatel.comp http://www.nortelnetworks.com
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EDGE
EDGE: Enhanced data rate for GSM evolutionECSD: Enhancement of HSCSDEGPRS: Enhancement of GPRS for through per time slot
NTUEE Mobile Communications KC Chen 173
Logical architecture
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Transmission Plane
Note: Data flow is not simple at all.
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Network architecture for supporting HSCSD (High Speed
Circuit-Switched Data)
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Multiplexing of network protocols
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EGPRSp EGPRS is built on top of GPRS with major
impacts onüRFüPHYüRLC/MAC with inclusion of type II hybrid ARQ
• Information is first sent with an initial code rate (i.e. rate 1/3 punctured with PS 1 of selected MCS). If RLC data block is received in error, additional coded bits (i.e. output of rate 1/3 encoded data that is punctured with PS 2 of prevailing MCS) are sent and decoded together with already received code words until successful decoding.
• If is possible to use incremental redundancy mode called MSC-5-7 or MCS-6-9.
• With higher coding schemes, RLC window size is increased from 64 to 128.
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Modulation & Coding Scheme (MCS)
p MCS-1 to MCS-9üRLC/MAC header is strongly coded.
p 8-PSKü270.833 ksps (as GMSK)ü3 bits/symbolüPayload per burst: 342 bits (vs 114 bits)üGross rate per time slot: 68.4 kbps (vs 22.8
kbps)
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EGPRS MCSMCS Code Rate Modulation Data Rate / time
slot (kbps)Family
9 1.0 8-PSK 59.2 A
8 0.92 54.4 A
7 0.76 44.8 B
6 0.49 29. A
5 0.37 22.4 B
4 1.0 GMSK 17.6 C
3 0.8 14.8 A
2 0.66 11.2 B
1 0.53 8.8 C
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EGPRS coding and puncturing example
USF RLC/MACHdr. HCS E FBI Data=592 bits BCS TB E FBI Data=592 bits BCS TB
36 bits 135 bits 1836 bits 1836 bits
Rate 1/3 convolutional coding Rate 1/3 convolutional coding
36 bits 124 bits 612 bits
Puncturing
SB=8 612 bits 612 bits 612 bits 612 bits 612 bits
PuncturingPuncturing
P1 P2 P3 P1 P2 P3
1392 bits
3 bits 45 bits 612 bits 612 bits
(MCS-9: uncoded 8-PSK, two RLC blocks per 20ms)
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Network architecture
(a) 57.6 kbps non-transparent service
(b) 56.0 / 64.0 kbps transparent service