call path trace
TRANSCRIPT
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What is CPT orCall Path Trace
by Dr. Hatem MOKHTARI• These are BSS statistics showing the performance of a cell in terms of :
• Link Balance : DL Path Loss – UL Path Loss
• Distribution of DL RXQUAL/RXLEV samples
• Distribution of Timing Advance
• Drive Tests alone cannot help assess all the problems especially UL performance
• It is important to compare DL AND UL :
• RF Losses in view of detecting HW Problems such as TRX, TMA, cables, etc
• Quality and Level to assess accurately which link is defficient and correct it
• Timing Advance stats will help understand Ping-Pong HO and the extent of a cell and compare it according to marketing
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Signal strength (SS) and quality measurements principles
UL SSUL Qual
DL SSDL Qual
DL SS(1)DL SS(2)..DL SS(6)
neighbours
BSC
Σ
��
Number of defined neighbours
32 20 16 10
Number of measurements per neighbour
3 5 6 10
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M inimum signal stregthcriterion fu lfilled?
Ranking according toPower Budget?
Stronger than serving cell+ hoM arginLev/Qual?
NoDiscard n
For all reported neighbour cells n
Yes
Yes
Power budget evaluation >hoM arginPBGT?
Yes
No
NoD iscard n
Load < Load threshold?
Yes
No
Reduce ranking accordingto hoLoadFactor
Keep ranking according tohoPriorityLevel
R ank according to signal strengthwith in own priority level
R ank according to signal strengthwith in reduced priority level
H andover candidate list
Yes
No
D iscard n
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Definition of Link Balance• Link Balance equation is given by :
Where DLPL is :
• EIRP(BTS) :
• Sensitivity(MS) = Sstatic(MS) + Lccc(=0) – Gant(MS) – DiversityGain(=0)
• And the DLPL :
• EIRP(MS) :
• Sensitivity(BTS) = Sstatic(BTS) + Lccc – Gant(BTS) – DiversityGain
ULPLDLPLdB −=∆ )(
)()( MSySensitivitBTSEIRPDLPL −=CCCLBTSGantBTSPoutBTSEIRP −+= )()()(
)()( BTSySensitivitMSEIRPULPL −=)0()()()( =−+= CCCLMSGantMSPoutMSEIRP
ainDiversityGMSSBTSSMSPoutBTSPoutdB staticstatic −−+−=∆ )()()()()(
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Link Balance (self-test)• Compute the Link Balance ∆(dB) using the following assumptions :
• BTS : Sstatic = -110 dBm
• Pout = 20 W
• Cable losses = 2.5 dB
• Antenna Gain = 18 dBi
• XPOL Diversity Gain = 3 dB
• MS : Sstatic = -100 dBm
• Pout = 1 W
• Antenna Gain = 0 dBi
• In case where no diversity is involved, what solution do you propose to keepthe path balanced?
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Uplink and Downlink Quality SamplesAre balanced => no Quality problem seemingly !
Most of the calls are Completed at about1.5 km !
High amount of Low level samples :Coverage problem in a high traffic area
Few calls made at the vicinity of the cellWith high DL Level because UL is Power-controlled
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Mean Link BalanceCentered around 2.5 dB
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Call Path Trace(Self-Test)
• Given the Histograms in the figure belowwhat problems do we have and how can wesolve them? Do we need additional data to solve the problem?
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Worst Cell List• This is the list of the cells for which have two major concerns :
– Substantial Amount of Traffic
– Bad Quality Performance
• The Worst cells are ranked based upon :– Carried Traffic
– Percentage of HO causes due to :• DL/UL Quality
• DL/UL Level
• Power Budget
• Good cell statistical performance would lie within the following :– % of HO due Power Budget : > 80 %
– % of HO due to DL/UL Quality and/or DL/UL Level : within 20 %
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HO Causes• High % of HO Causes due to Quality :
– DL => Generally CCI and/or ACI
– UL => Generally a Hardware Problem :• TMA (if any) alarms
• BTS RX problem (check TRX)
• Double check with CPT the Link balance
• High % of HO causes due to Level– DL =>
• Due to terrain and lack of best servers
• Hardware problem : check the connectors, PA, Antenna connections, etc.
– UL => • Due to TMA (if any) Problem
• Due to Hardware Problem
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Worst Cell List (an example)
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WCL Self-Test• Given the WCL Chart in the figure below, analyse the 10 Worst
Cells and especially for which reason this ranking is done?
– What kind of action do you propose for each cell given the commentssupplied ?
– Cell with CI = 46623 has a coverage problem, what indication explains this ?
– What do you propose to remove the cell with CI = 46623 from this list ?
– Cell with CI = 46462 has a PBGT HO cause about 60% and about 40% combination of DL Qual and DL Level
• Why this cell is ranked 10 instead of 2 or 3 for example?• Does this cell need a frequency retune ?
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WCL Self-Test
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