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What is CPT or Call 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 BSC DL SS DL Qual
DL SS(1) DL SS(2) . . DL SS(6)
UL SS UL Qual
Σ
neighbours
Number of defined neighbours
Number of measurements per neighbour
32
20
16
10
3
5
6
10
Fo r all rep orted n eigh b our cells n
No D iscard n
M in im u m sign al stregth criterio n fu lfilled ? D iscard n Y es No
R an kin g acco rd in g to P o w er B u d get?
No
S tro n ger th an servin g cell + h o M argin L ev/Q u al?
Y es
No D iscard n
Y es
P o w er b u d get evalu ation > h oM argin PB G T ?
Y es
No
L oad < Load th resh old?
Y es R ed uce rank in g accordin g to h oLoad Factor
K eep ran kin g accord ing to h oP riorityLev el
R an k accordin g to signal stren gth w ith in ow n p riority level R an k accordin g to signal stren gth w ith in red uced p riority level
H andover can did ate list
Definition of Link Balance • Link Balance equation is given by :
∆(dB) = DLPL − ULPL
Where DLPL is : DLPL = EIRP( BTS ) − Sensitivity ( MS ) • EIRP(BTS) : EIRP( BTS ) = Pout ( BTS ) + Gant ( BTS ) − LCCC • Sensitivity(MS) = Sstatic(MS) + Lccc(=0) – Gant(MS) – DiversityGain(=0) • And the DLPL : ULPL = EIRP( MS ) − Sensitivity ( BTS ) • EIRP(MS) : EIRP( MS ) = Pout ( MS ) + Gant ( MS ) − LCCC (= 0) • Sensitivity(BTS) = Sstatic(BTS) + Lccc – Gant(BTS) – DiversityGain
∆ (dB) = Pout ( BTS ) − Pout ( MS ) + S static ( BTS ) − S static ( MS ) − DiversityGain
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 keep the path balanced?
Uplink and Downlink Quality Samples Are balanced => no Quality problem seemingly !
Most of the calls are Completed at about 1.5 km !
High amount of Low level samples : Coverage problem in a high traffic area Few calls made at the vicinity of the cell With high DL Level because UL is Power-controlled
Mean Link Balance Centered around 2.5 dB
Call Path Trace (Self-Test) • Given the Histograms in the figure below what problems do we have and how can we solve 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 comments supplied ? – 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 ?