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

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

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

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 −−+−=∆ )()()()()(

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?

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

Mean Link BalanceCentered around 2.5 dB

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?

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 %

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

Worst Cell List (an example)

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 ?

WCL Self-Test