Post on 28-Apr-2015
description
System Optimisation GroupChina GSM Core Engineering
August 11, 2000
Jim Luan, Lin Mubao
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System Optimisation GroupChina GSM Core Engineering
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