mobilink_trainnig workshop for optimization gsm basic

OPTIMIZATION TRAINNING WORKSHOP

Day 1GSM BASIC

MOBILINKDEC2005

By:Michael LingAIRCOM ConsultantsRF Optimization North

GSM BASIC

GSM Architecture

Interface

GSM Architecture-BTS• The BTS performs the following functions:1) Manages the radio channels.

2) Transfers signaling information to and from Mobile Stations.

• Each BTS network component provides radio channels (RF carriers) for a specific RF coverage area.

• The RF channel is the communications link between the MS within an RF coverage area and the BSC.

• All BTS network components that provide RF channels for the same geographic area are located at a single BTS.

GSM Architecture-BSC• The BSC performs the following functions:

1) Controls the BTS and RXCDR components

2) Performs call processing, operations, and maintenance.

3) Provides the interface between the RXCDR and the BTSs.

• The BSC receives signaling and traffic data from the MSC via theRXCDR.

• Control channels are always under the control of the BSC. However, many types of call handling messages do not directly affect the BSC and for these the BSC serves simply as a relay point between the MSC and the MS.

• BSC to perform handovers between the BTSs under its control without involving the MSC (inter-BTS, inter-cell and intra-cell).

GSM Architecture-RXCDR• The RXCDR routes the O&M data packets between the BSS and

the OMC-R, and traffic channels (voice) between the BSS and MSC.

• Each link between the BSSs and the RXCDR typically consists of two 64 kbit/s O&M links plus traffic channels.

• The RXCDR is located between the MSC and the BSS, usually located in the same area as the MSC. The primary feature of the RXCDR is that it converts the 64 kbit/s PCM output of the MSC to a 16 kbit/s rate required for transmission over the air interface (between the BSS and the MS).

• Thus, four 16 kbit/s traffic channel can be fitted on each 64 kbit/s terrestrial circuit.

Exercise

• 30 PCM channel can carry how many 16kbits traffic channel?

GSM Architecture-MSC• The MSC handles the call set up procedures

and controls the location registration and handover procedures for all except inter-BTS, inter-cell and intra-cell handovers.

• Location registration (and location update) allows MSs to report changes in their locations enabling automatic completion of MS-terminated calls.

• GMSC-When the MSC provides the interface between the fixed and mobile networks, it is known as the Gateway MSC (GMSC).

GSM Architecture-Location Register• The Visitor Location Register (VLR) • The Home Location Register (HLR) • The Equipment Identity Register (EIR)

GSM Architecture-VLR• The Visitor Location Register (VLR) is a database containing

information about all MS that currently are located in the MSC service area.

• The VLR contains temporary subscriber information needed by the MSC to provide service for visiting subscribers.

• The VLR can be seen as a distributed HLR.

• When a Mobile Station (MS) roams into a new MSC service area, the VLR connected to that MSC requests data about the MS from the HLR and stores it. When the MS makes a call, the VLR alreadyhas the information needed for call set-up.

• The VLR also controls allocation of new Temporary Mobile Subscriber Identity (TMSI) numbers. A subscribers TMSI can be periodically changed to secure the subscribers identity.

GSM Architecture-EIR• The Equipment Identity Register (EIR), is a centralized

database for validating the International Mobile station Equipment Identity (IMEI).

• The database contains three lists:• 1) The white list contains the IMEIs of valid MSs.

• 2) The grey list contains IMEIs of equipment to be monitored and observed for location and correct function.

• 3) The black list contains IMEIs of MSs which have been reported stolen or are to be denied service.

SIM Module• By making a distinction between the subscriber identity and the mobile equipment

identity, a GSM PLMN can route calls and perform billing based on the identity of the subscriber rather than the mobile equipment being used. This can be done using a removable Subscriber Information Module (SIM). A smart card is one possible implementation of a SIM module.

• The following information is stored in the SIM:• 1) IMSI. This is transmitted at initialization of the mobile equipment.

• 2) TMSI. This is updated periodically by the PLMN.

• 3) MSISDN. This is made up of a country code, a national code and a subscriber number.

• 4) Local Area Identity (LAI). This identifies the current location of the subscriber.

• 5) Subscriber Authentication Key (Ki). This is used to authenticate the SIM.

• When the SIM is inserted in the mobile equipment, a location update procedure registers the subscribers new location, allowing the correct routing of incoming calls.

IMSI & TMSI

• What is IMSI?• What is TMSI?

International Mobile Subscriber Identifier (IMSI)

• Globally unique subscriber identity (15 digits max)• Comprises:

– Mobile Country Code (MCC)– Mobile Network Code (MNC) (operator)– Mobile Subscriber Identification Number (MSIN)

3 digits

MCC

9-10 digits

MSINMNC

2-3 digits

Example: 410 – Pakistan 01 – MOBILINK 123456789

Temporary Mobile Subscriber Identity (TMSI)

• Replaces IMSI• Unique only within a LA• Issued on IMSI attach and LA change• Comprises 32-bits:

8 bits

Octet

8 bits

Octet

8 bits

Octet

8 bits

Octet

International Mobile Equipment Identifier (IMEI)

• Globally unique MS equipment identity• Comprises:

– Type Approval Code (TAC) • (2-digit (49 = Germany) country code + 4-digit approval code )

– Final Assembly Code (FAC) • (Manufacturer: e.g. 10 & 20 = Nokia)

– Serial Number (SNR)• (unique 6-digit code)

– Spare digit• (default to 0)

6 digits

TAC

6 digits

SNRFAC

2 digits

Example: 495020 10 123456 7

X

1 digit

Location Area Identifier (LAI)

• Globally unique Identity• Comprises:

– Mobile Country Code (MCC)– Mobile Network Code (MNC) (operator)– Location Area Code (LAC)

3 digits

MCC

2 octets

LACMNC

2-3 digits

Example: 410 – Pakistan 01 54

Cell Identifier (CI) and Global CI (GCI)

• CI:– Identity unique to a cell within a location area (LA)– Fixed Length of 2 octets:

8 bits

Octet

8 bits

Octet

• GCI:– Globally unique cell identity– Comprises LAI +CI

Cell Identity(CI)

Location Area Identity (LAI)

Interfaces

• A, B, C, E, F, G, H………..

GSM Interface• Air Interface: MS-to-BTS (also referred to as the

UM Interface).• Abis Interface: Remote BTS-to-BSC.• A Interface: BSC-to-MSC.• B Interface: MSC-to-VLR.• C Interface: MSC-to-HLR/AUC.• E Interface: MSC-to-MSC.• F Interface: MSC-to-EIR.• G Interface: VLR-to-VLR.• H Interface: HLR-to-AUC.

System Specification Of GSM900• 890 MHz – 915 MHz on uplink• 935 MHz – 960 MHz on downlink

• EGSM Including • 880 - 890 MHz on uplink • 925 - 935 MHz on downlink.• Channel Number (ARFCN): 1 --- 125

• Duplex distance 45 MHz

• Carrier separation 200 kHz, (the first carrier at 890.2 MHz)

• Modulation GMSK

• Air transmission rate 270 kbit/s

• Access method TDMA

1800• 1710–1785 MHz on uplink• 1805–1880 MHz on downlink

• The duplex distance is 95 MHz.• Channel Number (ARFCN): 512 --- 885

Time Slot & TDMA Frames

• A TS has duration of 3/5200 seconds (0.577 ms).

• Eight TSs form a TDMA frame, with approximately 4.62 ms duration.

• At the BTS the TDMA frames on all of the radio frequency channels in the downlink direction are aligned. The same applies to the uplink. The start of a TDMA frame on uplink is, however, delayed by a fixed time corresponding to three TS periods as shown in.

• The reason for this delay is to allow the same TS number to be used in both uplink and downlink directions without requiring the MS to receive and transmit simultaneously.

TDMA Frames

26 frames-TCH multi frame

• Multiframe 26-frames traffic channel multiframe

• From 26 TDMA frames.

• One multiframe 26-frame = 120ms.

• The frame number 12 (13th frame) used by SACCHwhich carry link control info to and from MS and BTS.

• Last frame, frame number 25 ( 26th frame) is idle frame. UL and DL transmission is temporary stop at this frame. The MS will go to “search mode” in a effort to interrogate (decode) a neighboring BSIC.

26 frames-TCH multi frame

26 frames-TCH multi frame• It completes this process every 480ms, or four

26-TCH multi frames.

• The message that it sends to the BSS (on SACCH, uplink) contains the Receive Signal Strength Indication (RSSI) of the adjacent cells, plus that of the link from the BSS itself and also an indication of the quality of the current connection.

51-frame control channel multi frame

• One multiframe 51-frame = 235.4ms• How to get this value?

51-frame control channel multi frame

CHANNEL CONFIGURATIONSConfiguration of Signaling Channels

Combined Configuration

0 7

ts0=bcch/sdcch/4/pch/agch

Separated Configuration

0 7

ts0=bcch/pch/agch ts1=sdcch/8

CHANNEL CONFIGURATIONSCombined CCCH/SDCCH/4 Multiframe

f s bb b b c fc fc sc c c c cc c c fc fs t t t t tt t t f ft t t t tt t t fs fs s s s ss s ss

t t tt r r s fs ss s s s r r rr r r rs fr r r r r rr r r r fr r r r tr t t tr ft t t r tr t tt

Downlink

Uplink

51 TDMA frames = 235 ms

t

0

1. 2. 3. 4.

CHANNELS f = FCCH b = BCCH r = RACH i=idle s = SCH/SACCH c = CCCH t = SDCCH/4

Channel Concept-Logical Channel

Physical Channel

• We have so far looked at the different logical channels existing in the system. These logical channels are mapped onto the physical channels in a certain way. Before we examine how, we shall define the term burst.

• The information format transmitted during one time slot in the TDMA frame.

• Question: How many types?What are the usages?

5 types of Burst

• Normal burst• Frequency correction burst• Synchronization burst• Access burst• Dummy burst

Frequency Hopping

• Every burst transmitted over the Air Interface can be sent on a different RF carrier frequency. This is called frequency hopping.

• This capability provides a high degree of immunity to interference and fading.

Interference

F1

F2 F3

MS_1 MS_2 MS_3

No hopping Interference

F1

F2 F3

MS_1 MS_2 MS_3

With hopping

F1

F2

F3 F1

F2 F3

average

Frequency Hopping

• SFH• BBH

• SFH-The transceiver re–tunes to a different frequency set (Tx & Rx) on each TDMA burst (approx 577ms).

• In theory, there is no restriction on the number of frequencies the transceiver unit can hop on. However, GSM specifications limit the total number to 64 frequencies for a SFH transceiver unit.

• BBH-In this method, the transceiver unit will always transmit at an assigned frequency.

• Frequency hopping is done by switching the information frame of one call from one radio to another radio within a cell,

Frequency Hopping

• MA• HSN• MAIO

Frequency Hopping ExerciseGiven:• MAIO Offset : 6• MAIO Step : 2• HSN : 5• 3 cells with 1 TRX(BCCH) & 3 TRX(TCH)

Fill In The Blank:

Sector HSN MAIO Offset MAIO step TRX MAIO value for all RTF1 ? 0 ? trx1 ?

trx2trx3trx4

2 ? 6 ? ? ?3 ? 12 ? ? ?

Downlink Power Budget

BTS Tx Output Power

CombinerLoss

Duplex FilterLoss

Gab Antenna Gain

Path Loss

Lp

MS Antenna Gain

Feeder Loss

Gam

Lfm

Ld

Lfb

Feeder Loss

Lc

Input to mobile

PinMS

PoBSPinMS = PoBS - Lc - Ld - Lfb + Gab - Lp + Gam - Lfm

Downlink Power Budget Analysis

• Power input to the mobile (dBm):

PinMS = PoBS - Lc - Ld - Lfb + Gab - Lp + Gam - Lfm

PoBS = Power output from BTS TRX dBmLc = BTS combiner loss dBLd = BTS duplex filter loss dBLfb = BTS Feeder loss dBGab = BTS antenna gain dBiLp = Path loss dBGam = Mobile antenna gain dBiLfm = Mobile station feeder loss dB

Downlink Power Budget -Example

• A class 4 mobile has a sensitivity of -102 dBm. Allowing a margin for fading, we take the minimum signal strength at the cell boundary as - 90 dBm. This is to be 10 km from the base station.

• Find the BTS output power, PoBS , required given the following data:BTS combiner loss Lc = 6 dBBTS duplex filter loss Ld = 1 dBBTS feeder loss Lfb = 7 dB

Omni antenna gain Gab = 12 dBHata path loss for 10 km Lp = 132 dB

Mobile antenna gain Gam = 0 dBiMobile station feeder loss Lfm = 0 dBi

Uplink Power Budget

BTS Rx

Duplex FilterLoss

Antenna Gain GabGdBS

Diversity GainMS Antenna Gain

Feeder Loss

Gam

Lfm

Ld

Feeder Loss

Path Loss

LpLfb

Input to BTS Rx

Output from mobile

PoMS

PinBSPinBS = PoMS - Lfm + Gam - Lp + GdBS + Gab - Lfb - Ld

Uplink Power Budget - Example• Using the data given earlier for downlink, find the input power to the base station if:

• Output power of mobile PoMS= 33 dBm (2 W class 4 mobile)• Diversity reception gain at base station GdBS= 5 dB

Other Power Budget Factors

• Building/Vehicle Penetration Loss

• Body Loss

• Additional Fast Fade Loss

• Interference Degradation Loss

Propagation ModelOkumura-Hata

COST 231

Which is use and why?????

Propagation Model-Exercise

Exercise: Calculate free space loss in 1800MHz frequency at 5km with antenna height is 40m?

Base Station Identity code (BSIC)

NCC: 0-7BCC: 0-7

DecOct

637762766175607459735872577156707

556754665365526451635062496148606

475746564555445443534252415140505

394738463745364435433442334132404

313730362935283427332632253124303

232722262125202419231822172116202

1517141613151214111310129118101

77665544332211000

76543210

BCCNCC

DecOct

637762766175607459735872577156707

556754665365526451635062496148606

475746564555445443534252415140505

394738463745364435433442334132404

313730362935283427332632253124303

232722262125202419231822172116202

1517141613151214111310129118101

77665544332211000

76543210

BCCNCC

Paging

• How many types?• What is the different?• Why need paging?

System Information• Sys_info 1 1) Cell channel description2) RACH control information

• Sys_info 21) Neighbor cell BCCH frequency list2) Indication of which NCC allowed to monitor

• Sys_info 2ter1) Neighbor cell BCCH frequency in different band2) RACH control information

System Information• Sys_info 3Cell Option1) Cell identity2) LAI3) Power central information4) DTX information5) RLTCell selection parameters6) Cell reselect for LA reselection7) Maximum transmit power allowed8) Minimum access RXlev of cell9) RACH control information

System Information

• Sys_info 41) LAI2) Cell selection parameters (same as in sys_info 3)3) RACH control information4) CCCH channel description

• Sys_info 51) Neighbor cell BCCH frequency list

• Sys_info 5ter1) Neighbor cell BCCH frequency list in different band

System Information

• Sys_info 61)Cell Identity2)LAI3)Cell options:• Power control information• DTX• RLT• NCC

System Information

• Sys_info 131)SI 13 Rest Octets2)GPRS MA3)GPRS cell Allocation4)GPRS Power Control parameters

Sys Information Type 1

Sys Information type 2

Sys Information Type 3

System Information Type 4

Call Flow• Call Events1) Idle Mode

2) Call Attempt

3) Dedicated/Signaling Mode

4) Call Setup

5) Call Established

6) Call End

Call Processing-MOCMobile Originating Call

Authentication

Ciphering Mode Setting

Service Request

Immediate assignmentCHAN REQIMM ASSIGN

CM SERV REQ

AUTH REQAUTH RES

CIPH MOD CMDCIPH MOD COM

MS NETWORK

MOC

Call Confirmation

Call Accepted

Assignment of Traffic Channel

Call InitiationSETUP

CALL PROC

ASSIGN CMD

ALERT

CONNECTCONNECT ACK

ASSIGN COM

Call Processing-MTCMobile Terminating Call

Authentication


Service Request

Immediate assignmentPAG REQ

CHAN REQ

PAG RES

AUTH REQAUTH RES


MS NETWORK

IMM ASSIGN

Call Processing-MTC

Call Confirmation

Call Accepted

Assignment of Traffic Channel

Call InitiationSETUP

CALL CONF

ASSIGN CMD

ALERT

CONNECTCONNECT ACK

ASSIGN COM

MS Trigger Disconnect

Disconnect, MS Initiated

Release

Call Clearing

DISCONNECTREL

CHAN REL

MS NETWORK

REL COM

LULocation Update

Authentication


Service Request

Immediate assignmentCHAN REQIMM ASSIGN

LOC UPD REQ

AUTH REQAUTH RES


LOC UPD ACCTMSI REAL COM

CHAN RELChannel Release

MS NETWORK

LU

3 different type of Location Update• Normal

• Periodic

• IMSI attach

Normal LU• Normal location updating is initiated by the MS

when it detects that it has entered a new location area.

• compare the broadcast Location Area Identity (LAI) with the one stored in the MS

• location updating type normal will be initiated and the new LAI will be stored in the MS.

Periodic LU• To reduce unnecessary paging of a mobile that

has left the coverage area, has run out of battery power or for any other reason has the wrong status in the MSC/VLR, there is a type of location updating called periodic registration.

• The periodic registration timer is implemented in the MS. It will be reinitiated every time the MS returns to idle mode after being in dedicated mode.

IMSI attach

• IMSI attach/detach operation is an action taken by an MS to indicate to the network that it has entered into idle mode/inactive state.

• MS is powered on, an IMSI attach message is sent to the MSC/VLR.

• MS is powered off, an IMSI detach message is sent

• This prevents unnecessary pagings of powered off mobiles.

SMS• Short Message Service (SMS) provides a means

of sending text messages consisting of up to 160 alpha numeric characters.

SME = Short Message Entity, SC = Service Center

In the case of a MT SMS, the MSC interfacing with the SC is called SMS-GMSC. In case of a MO SMS, it is called SMSIWMSC (Inter working MSC)

Handover

HO-SynHandover, Synchronized

New Channel, New Cell

HANDO CMDHANDO ACC

ACTIVE CALL

MS NETWORK

HANDO ACCHANDO ACC

HANDO ACCHANDO COM

ACTIVE CALL

Old Channel, Old Cell

HO Non-SynHandover, Non-Synchronized


HANDO CMDHANDO ACC

ACTIVE CALL

MS NETWORK

.HANDO ACC

PHYS INFOHANDO COM

ACTIVE CALL


Handover Failure

MS NETWORK

ACTIVE CALL



HANDOVER CMD

RLT or Interference

HANDOVER FAIL Old Channel, Old Cell

ACTIVE CALL

FULL – SUB Measurements• RXQUAL_FULL

– measurements are taken over a full 104 TDMA Multiframe cycle i.e. the time taken to transmit one full SACCH message on the uplink as ameasurement report

• RXQUAL_SUB

– measurements are used when DTX is implemented.

– With DTX, only certain TDMA frames contain speech information, the remainder are filled with SID frames, providing comfort noise only.

– RXQUAL_SUB measurements are taken over 12 TDMA frame periods only.

– However, RXQUAL_SUB should be used when comparing power measurements with neighbouring cells that also have DTX implemented

Discontinuous Transmission (DTX)

• In a conversation, a person generally only speaks for about 30% to 40% of the time

• DTX makes use of this by reducing transmission when no voice signal is detected

• Uses a Voice Activity Detection (VAD) unit • Advantages:

– Reduces interference– Prolongs battery life of mobile

Silence Descriptor (SID)

• Silence Description Frames (SID) are sent at the end of a speechframe - prevents sudden cut off of sound

• SID frames also sent periodically during periods of silence

• Receiver produces ‘comfort noise’ for the listener

• If speech frames are lost, they can be extrapolated from previous frame to fill the gap

Voice activity SID frames Signal transmitted by mobile

Discontinuous Reception (DRX)• Allows MS to power down parts of its circuitry in idle mode• MSs within a Location Area divided into paging groups • MS only listens paging requests within its own group• Increases battery life of MS

TA

• TA=32=?km• Why?

Timing Advance Concept

• Signal from MS1 takes longer to arrive at BTS than that from MS2• Timeslots overlap - collision

1 2 3

MS1 - Timeslot 1

1 2 3

MS2 - Timeslot 2

time

time

1 2 3

1 2 3

time

• Timing Advance signal causes mobiles further from base station to transmit earlier -compensates for extra propagation delay

1 2 3

MS1 - Timeslot 11 2 3

MS2 - Timeslot 2

1 2 3

1 2 3

time

time

time

Timing Advance

Timing Advance – Tx / Rx Delay• Timing Advance value reduces the 3 timeslot offset between

downlink and uplink

0 1 2 3 4 5 6 7

Delay 3 timeslots

Downlink

Uplink

TimingAdvance

Actual delay

Uplink

• The Timing Advance technique is known as adaptive frame alignment

0 1 2 3 4 5 6 7

0 1 2 3 4 5 6 7

Thank you

mobilink_trainnig workshop for optimization gsm basic

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