Drive Test Analysis

System Optimisation GroupChina GSM Core Engineering

August 11, 2000

Jim Luan, Lin Mubao

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Drive Test Procedure

Drive Test

Netplan

FICS

Statistics Analysis

Problem Finding

VOT/GEP

Preparation

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Preparation (1)• Definition File

– Without it, it is impossible to observe overshooing neighbors– GenDef7.exe can convert FP to definition file

Neighbor list with definition

file

Neighbor list without definition

file

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Preparation (2)

• Frequency Plan & Configuration map

• Software:TEMS, FICS, GEP, VOT

• Hardware: TEMS, GPS, Portable PC

• Test Problem Sheet

• Route

• Map

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Drive Test• For Benchmark

– 2 minutes per call– 10 – 15 minutes a log files– Force to appropriate band (GSM only, DCS

only or Dual)

• For Special Problem– Planning route– No limitation

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TEMS Introduction

• Interface

• Functions

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Log File Process TEMS Log File

NetPlan

FICS

VOT/GEP

.CSV.FMT

Route Map

.STA

Excel VB

.NP/.TXT Much shorter cycle time by VOT and GEP.

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TEMS .log file Analysis

• Undecoded BCCH

• BSIC Undecode in Other Site

• No Handover

• Delay Handover

• Ping Pong Handover

• Negative Handover

• Overshooting

• High Overlapping

• No Dominant Server

• Poor Coverage

• Unreasonable Serving Area

• Interference

• Handover Failure

• Handover Loss

• UL Drop

• Drop Call

• Sudden Power Drop

• MS Power Rapid Increase

Below lists common problems which can be observed from Drive Test Log.

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Undecoded BCCH (1)Description:

– BSICs can’t be decoded in 5s– Usually consider 3 strongest neighbors

Reason:– GCLK shift, only decode same site BSICs– Channel interference– Non-BCCH carrier, no dedicated spectrum for

BCCH

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Undecoded BCCH (2)

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BSIC Undecode in Other Site

Description:– BSIC in same site can be decoded but not for

other sites– Handover can only happen in intra-site basis– It is similar to former Undecoded BCCH case

Reason:– GCLK shift

• GCLK recalibration is required• No one monitors OMC-R alarms

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No Handover (1)Description:

– Neighbor BSIC is decoded and COMMON handover requirement is fulfilled but there is never a handover

Reason:– Missing neighbor

• No such neighbor in CM database

– Incorrect external neighbor• Target cell’s LAC/BCCH/BSIC in add_neighbor is different from those in equip_rtf• Engineer modifies external neighbor at MMI, not through GUI• Never use OMC-R Proxy Cell to propagate external neighbor information

– N < hreqt. Great HO_MARGIN. Improper algorithm 1-7 setting– Missing_rpt =1– Serving cell overshoots/covers too far away– Refer to GSM BSS Statistics Analysis Handbook

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No Handover (2)

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Delay Handover (1)Description:

– Neighbor BSIC is decoded but handover occurs in much later time

Reason:– All possible neighbors suffer blocking– Large hreqt * hreqave– qual_power_flag is enabled, full BTS/MS power must

be reached before handover– Large handover_recognized_period and bssmap_t7

setting– Refer to GSM BSS Statistics Analysis Handbook

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Delay Handover (2)

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Ping Pong Handover (1)Description:

– Lot of handovers between cells– “Time between Handover” is around hreqt*hreqave of

such HO cause

Reason:– Improper hardware calibration– Hardware fault– UL/DL interference– Negative handover– Different coverage footprint for antennas of a cell

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Ping Pong Handover (2)

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Negative Handover (1)

Description:– Serving cell hands over to a weaker neighbor

Reason:– ho_only_max_power is enabled

– qual_margin_flag is disabled

– ho_margin_usage_flag is enabled with negative ho_margin_rxqual/rxlev

– Negative HO_MARGIN

– Micro-cellular algorithms are enabled, especially type 5

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Negative Handover (2)

-59dBm before

HO

-66dBm after HO

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OverShooting (1)Description:

– Cell shoots at far distance but that location has closer cells around

Reason:– Overshooting cell has small downtilt, 0 degree!– Overshooting cell has too high altitude– Closer cells have overshooting as well– BSIC of closer cells can’t be decoded

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OverShooting (2)

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High Overlapping (1)

Description:– Cells have major rxlevel difference within

±5dB

Reason:– Overshooting– Too many cells in that area– Poor antenna downtilt

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High Overlapping (2)

Over Lapping Area

-65dBm

-65dBm

-65dBm

-65dBm

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No Dominant Server (1)

Description:– Rxlevel of best neighbors are close to that of

serving cell

Reason:– Poor antenna downtilt– Lack of near-by site

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No Dominant Server (2)

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Poor Coverage (1)

Description:– Low rxlevel with rxquality– In rural area, rxlevel is less than 15 (-95dBm)– In city center, rxlevel is less than 35 (-85dBm)– Different location has different threshold, noise level is the key

point

Reason:– Lack of cell site– BSIC of dominant server can’t be decoded– Dominant server has blocking or cell-bar– Handover problem. E.g. missing & incorrect neighbor, negative

handover, no & delay handover

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Poor Coverage (2)

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Unreasonable Serving Area (1)

Description:– Coverage area of the cell is incoherent to the

antenna direction

Reason:– Wrong cable connection to antennas– Incorrect record of antenna orientation– Incorrect ANTENNA_SELECT

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Unreasonable Serving Area (2)Cell ID:101

BCCH: 35

Cell ID:102

BCCH: 40

Cell ID:103

BCCH: 45

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Interference (1)

Description:– High rxlevel with rxquality

Reason:– Channel interference– Not using dominant server– No handover– Turn the corner with delay handover

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Interference (2)

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Handover Failure (1)

Description:– MS fails to reach target cell, so return to source cell

– MS sends HO FAILURE and UL-SABM to source cell and there is response

Reason:– Channel interference

– Poor coverage

– External interference at UL, like wideband repeator

– Refer to GSM BSS Statistics Analysis Handbook

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Handover Failure (2)

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Handover Loss (1)Description:

– MS fails to reach target cell, but can’t return to source cell

– MS sends HO FAILURE and UL-SABM to source cell but no response

Reason:– Channel interference– Poor coverage– External interference at UL, like wideband repeator– Refer to GSM BSS Statistics Analysis Handbook

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Handover Loss (2)

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Description:– BSS doesn’t receive UL SACCH for link_fail times

– BSS stops transmitting DL power

Reason:– External interference

– Channel interference

– Faulty ancillary. UL path loss >>> DL path loss

– Refer to GSM BSS Statistics Analysis Handbook

UL Drop (1)

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UL Drop (2)

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Drop Call (1)Description:

– DL case: Radio_link_timeout counter decreases to 0

– UL case: link_fail counter decreases to 0

– Layer 2: BSS/MS send SABM/DISC in every T200 for N200+1 times, and no response from recipient

Reason:– All cases in this presentation

– Refer to GSM BSS Statistics Analysis Handbook

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Drop Call (2)

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Sudden Power Drop (1)

Description:– Dedicated ARFCN has significant non-power control

rxlevel difference from rxlevel of BCCH

Reason:– No/improper TX power calibration

– Faulty ancillary. E.g. combiner, filter..

– Different cable lengths from BTS to antennas

– Due to air combing, so antennas have different coverage footprints

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Sudden Power Drop (2)

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Description:– MS rapidly increases its TX power due to

• Optimised Power Control or

• UL SACCH multiframes aren’t received for link_fail - link_about_to_fail times

Reason:– Sudden UL interference, e.g. wideband repeator,

channel interference

– Too much rapid power down

– l_rxlev_ul_p is too small

MS Power Rapid Increase (1)

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MS Power Rapid Increase (2)

UL power rapid increase from 19 to

5 suddenly

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How GEP Help?Help to identify below problem in VISUAL basis• Co-channel interference• Adjacent-Channel interference• Mutual neighbor• Missing neighbor• Unreasonable neighbor• Incorrect external neighbor

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How VOT Help?Help to identify below problem in VISUAL basis• Ping pong HO• Overshooting• No dominant server• Poor coverage• Unreasonable serving area• Interference• HO failure• HO loss• Drop call

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How CM Extractor Help?Extract most BSS parameter for reference• Cell – e.g. hreqave,hreqt,N,P…• BTS – e.g. antenna_select…• RTF – check any incorrect external neighbor• Neighbor – e.g. ho_margin, delay_timer…

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How NPM Help?• Provide cell statistics for VOT display• Provide BSS and system level 23 key statistics• Provide detail troubleshooting statistics