2G Drive Test Analysis with TEMSWorkshop

Gaurab Dipta Barua

Manager

Radio Network Solution

20 April 2023

Slide 2

BRIEF GSM OVERVIEW

TEMS MAIN SCREENS

EXAMPLES OF INVESTIGATIONS drop call along M11 towards Cambridge Handover: influence of layer priority

AGENDA

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Slide 3

INTRO: TEMS SNAPSHOT

Timeslot, TA, RXLEV, RXQUAL, … WHAT ARE THEY !?!

WHAT DO THEY DO !?!

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Slide 4

BRIEF GSM OVERVIEW

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Slide 5

GSM voice : 1 Time Slot <=> 1 user

1 TDMA frame = 8 Time Slots = 8 x 577 us = 4.615 ms time

0 3 4 6 76 7 0

GSM BASIS: THE TDMA FRAME (Time Division Multiple Access)

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Slide 6

FR: Full Rate 13 kbits/s

HR: Half-Rate 5.6 kbits/s => doubles network capacity

EFR : Enhanced Full Rate 12.2 kbits/s AMR: Adaptive Multi-Rate ranges from 4.75 to 12.2 kbits/s

SPEECH CODEC’s (COmpression and DECompression)

time

Full Rate

Half Rate

Illustration: Full Rate versus Half Rate

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Slide 7

I am talking I am listeningTRANSMISSION

I am talking

NO TRANSMISSION

I am listening

DISCONTINUOUS TRANSMISSION (DTX)

Discontinuous transmission takes advantage of silence periods in normal speech,

which for a typical conversation represents roughly 50% of the conversation.

Advantage of DTX :

- Battery saving

- Does help combating interference by inhibiting the transmission of the radio signal when not required.

The interference generated is thus statistically more than halved.

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Slide 8

P-GSM (Primary-GSM): 1-23, 62-99

E-GSM (Extended-GSM): 975-995

GSM-1800 (also known as DCS): 541-568

Notes:

Vodafone allocate odd channels 63,65,67…99 for BCCH for GSM cells

(same rule applies for GSM-1800)

Example of cell configuration with 4 PGSM and 2 EGSM channels

GSM FREQUENCY CHANNELS ON VODAFONE NETWORK

ARFCN

Absolute Radio Frequency

Channel Number

GSM range [0 to 1023]

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Slide 9

FREQUENCY HOPPING

HSN is the Hopping Sequence Number. HSN=0: cyclic sequence otherwise pseudo random sequence

Frequency hopping does average interference in the network.

MAIO is the Mobile Allocation Index Offset (Not used in Baseband hopping) Frequency offset that prevents adjacent channel interference within a cell as well as co- and adjacent

channel interference in co-sited cells when using synthesised frequency hopping.

Baseband hopping (used on Vodafone network)

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Slide 10

LETTER CELL TYPEB UMTS Pico CellC UMTS Micro CellD DCS1800 Macro CellE Training CellG GSM900 Macro CellS GSM 900 Micro CellP DCS 1800 Indoor CellI GSM 900 Indoor CellT Test CellU DCS1800 Micro CellW UMTS Macro Cell

Vodafone Cell Site Prefix Information

20 April 2023

Slide 11

PAGING and LOCATION AREA

LA1

LA2

TRYING TO REACH

THIS MOBILE THIS MOBILE IS CURRENTLY REGISTEREDON OUR NETWORK IN LOCATION AREA 1

=> WAKING UP ALL MOBILES IN LA1 !!

NETWORK

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Slide 12

CELL GLOBAL IDENTITY

MCC : Mobile Country CodeMNC : Mobile Network CodeLAC : Location Area Code

Location Area Identification

(LAI) Cell Global Identity

(CGI)CI : Cell Identity

Example of MCC and MNC

Country Operator MCC MNC

United Kingdom o2 234 10

United Kingdom Vodafone 234 15

United Kingdom T-Mobile 234 30

United Kingdom Orange 234 33

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Slide 13

RXLEV = Received Signal LevelRXQUAL = Received Signal Quality (dedicated mode)

BER = Bit Error Rate

FER = Frame Erasure Rate

SIGNAL LEVEL MEASUREMENTS (1/2)

Relation between RXQUAL and BER

RXQUAL BER0 BER < 0.2%1 0.2% < BER < 0.4%2 0.4% < BER < 0.8%3 0.8% < BER < 1.6%4 1.6% < BER < 3.2%5 3.2% < BER < 6.4%6 6.4% < BER < 12.8%7 12.8% < BER

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Slide 14

C/I = Carrier over Interference ratio

SQI: Speech Quality Index

NOTE:

Use RxLev Sub, RxQual Sub measurements when DTX is activated

(RxLev, RxQual are measured over 104 TDMA frames

whilst Rx Sub measurements are reported over 12 TDMA frames only)

SIGNAL LEVEL MEASUREMENTS (2/2)

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Slide 15

TA=1 means BTS-MS distance = 550 meters

GSM network computes TA parameter and asks mobile to send frames earlier

to compensate flying time differences between signals.

30 km

Without TA compensation => Overlap With TA compensation

0 1 2 3 5 6 7 0 1 2 5 6 7

TIMING ADVANCE (Adaptive Frame Alignment)

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Slide 16

Power control level Nominal Output power (dBm)0-2 393 374 355 336 317 298 279 25

10 2311 2112 1913 1714 1515 1316 1117 918 7

19-31 5

MS POWER

MS power control level :

Mobile station transmit power mapped to a number between 0 and 31

according to the transform in GSM 05.05, ch. 4. Valid only in dedicated mode.

GSM 400 and GSM 900 and GSM 850

33 dBm = 2 W

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Slide 17

If SACCH frame : not successfully decoded=> counter = counter - 1 successfully decoded => counter = counter + 2

RADIO LINK TIMEOUT

Counter=0 DISCONNECTION !!

54

32

1

RL Tim

eout

coun

ter

20 April 2023

Slide 18

Selection criteria : C1>0 otherwise NO SERVICE !! with C1 = RXLEV - RXLEV_ACCESS_MIN (simplified formula)

RXLEV_ACCESS_MIN Minimum received signal level in dBm at the MS for permission to access the network

Reselection criteria : C2 candidate cell > C2 current cell with C2 = C1 - CELL_RESELECT_OFFSET (simplified formula)

IDLE MODE

CELL SELECTION / RESELECTION

TEMS snapshot

cells sorted by C1, C2

20 April 2023

Slide 19

Handover :The switching of a call in progress from one radio channel to another to secure the continuity of an established call

distance

Received Signal Level

DEDICATED MODE

HANDOVER

-80 dBm

-60 dBm

-100 dBm

I AM JUST ABOUT TO DO A HAND ...

… OVER !!CLICK

20 April 2023

Slide 20

BROADCAST CONTROL CHANNEL (BCCH)

B C C HB C C H

The BCCH is transmitted FULL POWER by a Base Transceiver Station (BTS)to provide the signalling information requiredby the MS (Mobile Station) to access and identify the network.

20 April 2023

Slide 21

BCCH = 73

BSIC = 54BSIC = 54

BCCH = 73

BSIC = 46BSIC = 46

Base Station Identity Code (BSIC) is a 6 bit 'colour code' broadcaston the SCH (Synchronisation Channel) in GSM systems,which uniquely identifies the beacon frequency.

BASE STATION IDENTITY CODE (BSIC)

20 April 2023

Slide 22

RACHRACH : : RRandom andom AAccess ccess CHCHannelannel

Uplink channel used by mobiles to request a service to the network

AGCHAGCH : : AAccess ccess GGrant rant CHCHannelannel

Downlink channel used by network to allocate mobile a dedicated channel

SDCCH : Stand Alone Dedicated Control CHannel

carries signalling information for authentication, call establishment, and for sending SMSs

TCH : Traffic CHannel

to carry voice traffic (e.g. TCH/F for Full rate, TCH/H for Half rate)

SACCH : Slow Associated Control CHannel

Associated with dedicated channel, carries signal measurement, power control, Timing Advance

FACCH : Fast Associated Control CHannel used at handover command

LOGICAL CHANNELS AND SIGNALLING

TCH TCH TCH TCHFACCH

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Slide 23

Mobile Network

RACH CHANNEL REQUEST Mobile requests Network for allocation of radio resourceAGCH IMMEDIATE ASSIGNMENT Network transmitting radio resource (channel, frequency, Timeslot, etc)

CM SERVICE REQUEST Mobile initiating connection with Network

AUTHENTICATION REQUEST Network checks if the subscriber has been authenticatedAUTHENTICATION RESPONSE

CIPHER MODE COMMAND Network initiates ciphering of the data being sent on the channel.CIPHER MODE COMPLETE The channel is ciphered so as to protect the call from eavesdropping.

SETUP Setup message contains the dialed digits and other information needed for call establishment.CALL PROCEEDING The mobile is informed that the call setup is in progress.

ASSIGNMENT COMMAND Network assigns a Traffic CHannel to mobileASSIGNMENT COMPLETE

ALERTING Network informs the mobile that the called subscriber is being alerted via a ring

…

CONNECT Network informs the mobile that the call has been answered.CONNECT ACKNOWLEDGE

T C

HS

D C

C H

IDLEMODE

DEDICATED

MODE

GSM CALL FLOW : Mobile Originating Call

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Slide 24

TEMS SNAPSHOTS

20 April 2023

Slide 25

MAP PRESENTATION

55435543

Legend :

SITE

SERVER

NEIGHBOUR

LINK toNeighbour

20 April 2023

Slide 26

BAR CHARTS

IDLE MODE

DEDICATED MODE (Plain colour=Serving cell)

R X Q U A LR X Q U A L

Speech Quality IndexSpeech Quality Index

Frame Erasure RateFrame Erasure Rate

Carrier / InterferenceCarrier / Interference

NeighboursNeighbours receivedreceived signal signal levellevel

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Slide 27

EVENT SYMBOLS AND THEIR MEANING

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Slide 28

IDLE MODE REPORTS

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Slide 29

DEDICATED MODE REPORTS

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Slide 30

LAYER 3 SIGNALLING

RXLEV 0 less than -110 dBmRXLEV 1 -110 dBm to -109 dBmRXLEV 2 -109 dBm to -108 dBm

::

RXLEV 62 -49 dBm to -48 dBmRXLEV 63 greater than -48 dBm

RXLEV Mapping(3GPP TS 05.08)

20 April 2023

Slide 31

EXAMPLESOF

INVESTIGATIONS

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Slide 32

EXAMPLE 1 :

HIGH DROPPER ALONG M11 TOWARDS CAMBRIDGE

Cell G1011.1 %TCH DROP

0

0.5

1

1.5

2

2.5

5090

1

5090

2

5090

3

5090

4

5090

5

5090

6

5090

7

5090

8

5090

9

5091

0

5091

1

5091

2

TARGET

=> CELL G1011.1 DOES NOT MEET THE 1% DROP TARGET !!=> CELL G1011.1 DOES NOT MEET THE 1% DROP TARGET !!

20 April 2023

Slide 33

G5543.1 good !!

G5543.2 weak !!

G1011.1 weak !!

DIFFICULTDIFFICULT

AREA !!AREA !!

EXAMPLE 1 : ANALYSIS

55435543

10111011

20 April 2023

Slide 34

Cell G1011.1 %TCH DROP

0

0.5

1

1.5

2

2.5

5090

1

5090

3

5090

5

5090

7

5090

9

5091

1

5091

3

5091

5

5091

7

5091

9

5092

1

5092

3

TARGET

EXAMPLE 1 : SOLUTION

AFTER 6 dB offsetAFTER 6 dB offset

between G5543.1 and G1011.1 !!between G5543.1 and G1011.1 !!

=> Try to make cell G5543.1 more attractive, especially more than cell G1011.1

20 April 2023

Slide 35

EXAMPLE 2 :

LAYER PRIORITY AND HANDOVER

-79 dBm much stronger than -93 dBmWHY DO NOT WE HANDOVER FROM D5779.1 TO G1194.2 !!!?

20 April 2023

Slide 36

EXAMPLE 2 : EXPLANATION

To improve capacity of the network, Vodafone use Hierarchical Cell Structure (HCS)

feature that helps efficiently distributing traffic between cells. Layer 1 : Sxxxx Street Level Micro cell (SLM) Layer 2 : Dxxxx 1800 macro cell Layer 3 : Gxxxx 900 macro cell

mobile won’t handover from D5779.1 to G1194.2

even though -79 dBm is better than -93 dBm

As long as signal does not go below LayerThr - LayerHyst (-87 dBm)

20 April 2023

Slide 37

REFERENCES

ERICSSON Active Library Explorer http://alex.vfl.vodafone/cgi-bin/alex

BSS R11

TEMS Investigation User’s Manual (HELP)

3GPP Specifications http://www.3gpp.org/specs/numbering.htm

20 April 2023

Slide 38

THANK YOU