Driving Test & Analysis

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DRIVING TEST

ANALYSIS

RNP-RNO

10rd Dec 2008

Dao Anh Phuong - RF Engineer



Drive Test Procedure

Drive Test

Netplan

FICS

Statistics Analysis

Problem Finding

VOT/GEP

Preparation




Preparation

Parameter BTS table, Cell name file

Software:TEMS, NEMO

Hardware: TEMS, GPS, Portable PC

Test Problem Sheet

Route

Digital Map




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




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.




Undecoded BCCH

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




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




No Handover

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 inequip_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




Delay Handover

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/MSpower must be reached before handover

• Large handover_recognized_period andbssmap_t7 setting




Ping Pong Handover

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




Negative Handover

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




Handover Failure

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




OverShooting

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




OverShooting




High Overlapping

Description:

• Cells have major rxlevel difference within

±5dBReason:

• Overshooting

• Too many cells in that area• Poor antenna downtilt




High Overlapping

Over Lapping Area

-65dBm

-65dBm

-65dBm

-65dBm




Poor Coverage

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 levelis 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 & incorrectneighbor, negative handover, no & delay handover




Unreasonable Serving Area

Description:

• Coverage area of the cell is incoherent to the

antenna directionReason:

• Wrong cable connection to antennas

• Incorrect record of antenna orientation• Incorrect ANTENNA_SELECT




Unreasonable Serving Area

Cell ID:101

BCCH: 35

Cell ID:102

BCCH: 40

Cell ID:103

BCCH: 45




THANK YOU !


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