gsm ul-dl unbalance solutions-special subject training v2 1
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GSM UL-DL Unbalance & Solutions
---- Special Subject Training V2.1
Suitable for staff with junior P&O skill certificates (lower than certificate III)
Issued by GSM Network Planning & Optimization Dept.
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Internal Use Only
Version introduction
Version Date Writer Assessor Amendment records
V1.0 2009-01-24 Chen Chun Zheng Hao
Fei Aiping
None
V2.0 2009-03-27 Fei Aiping Yang Jiazhi 1. Simplified judgment criteria,
making them only relevant
to product and frequency
band;2. Added V2 counter;3. Added 8PSK modulation
method and decision
conditions;
4. Added explanations of
influence from TA and
coverage enhancementtechnique.
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Training goals
To know definition of link balance
To master calculation process of link
balanceTo understand the factors influencing
link balance and the checking process
of link balance
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Contents
Definition of link balance
Theoretical calculation of link balance
Test method of link balance
Analysis and elimination of link unbalance
Practical cases
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Internal Use Only
Definition of link balance
What is link balance?
In radio communications, ULand DL, they each have theirown transmitting power,equipment loss, pathloss andreceiving sensitivity. Strictlyspeaking, link balance means
that the UL-DL radio pathlossdifference is 0.
For each network, link balanceis one of the key factors tosetting up network andensuring network performance.
UL-DL unbalance may result innetwork problems, such asfailure in starting a call,handover failure and silent call,etc..
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Deviation range of link balance
link balance judgment actually refers to judging thedeviation range. In UL-DL calculation, a deviation
within 10dB is allowed.
If this range is exceeded, we can say that the link is
in unbalanced status, hence some network
optimizations or engineering checking procedures
should be considered so as to solve the problem.
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Explanations on engineering margin
Origin of the engineering margin10dB: UL/DL power control
Since we set it according to the more conservative
threshold, the cell marginal power control wont take
effect. So we dont need to consider it here.
BTS UL measurement calibration deviation --3dB
Difference in carrier output power --1dB
Measurement difference value under DTX --0.5dB
Difference in combiner loss --0.5dB
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Explanations on engineering margin
The difference between MS actual power and the reported
power class--2dB;
As for power control process, the difference between MS actual
power and power control class can reach to 5db.;
Take these factors into consideration, we set the MS actual
power deviation range to be 3dB .
normal extreme
1
1 W (30 dBm) 2 2.52 8 W (39 dBm) 0.25 W (24 dBm) 2 2.5
3 5 W (37 dBm) 4 W (36 dBm) 2 2.5
4 2 W (33 dBm) 2 2.5
5 0.8 W (29 dBm) 2 2.5
Tolerance (dB) for
conditionsPower class
GSM900 Nominal
Maximum output
power
DCS1800 Nominal
Maximum output
power
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Explanations on engineering margin
Influence from radio environment--
2 dB
In practice, call quality is
affected by environment and
many other factors, such as
fluctuation in signal level, which
can be very big sometimes, so
we accept a deviation of 2dB
in engineering.
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Contents
Definition of link balance
Theoretical calculation of link balance
Test method of link balance
Analysis and elimination of link unbalance
Practical cases
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Internal Use Only
Calculation formula of link balance
PB link balance value)
RxLevDL-RxLevUL=BtsTxPwrMax-MsTxPwrMax
RxLevDLDL level of MS receiving BTS signal
RxLevDL=BtsTxPwrMax-RadioPathLossDL
RxLevULUL level of BTS receiving MS signal
RxLevUL=MsTxPwrMax-RadioPathLossUL
BtsTxPwrMaxrack-top output power
RadioPathLossradio pathloss, UL and
DL are the same
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Equipment parameters Transmitting power
Product
transmitting power
Terminal
transmittingpower
Power
class
GSM 900 Nominal
Maximum output
power
DCS 1800 Nominal
Maximum output
power
PCS 1900 Nominal
Maximum output
power
1 - - - - - - 1 W (30 dBm) 1 W (30 dBm)
2 8 W (39 dBm) 0.25 W (24 dBm) 0.25 W (24 dBm)
3 5 W (37 dBm) 4 W (36 dBm) 2 W (33 dBm)
4 2 W (33 dBm)
5 0.8 W (29 dBm)
Product seriesMax transmitting power
GMSK modulation 8PSK modulation
BTS V3_DTRU
BTS V2_ETRM60W 47.8 dBm 40W 46 dBm
BTS V2_TRM 40W 46 dBm -- --
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Internal Use OnlyEquipment parameters
typical values for combiner
loss
Combiner lossModule Condition Combining loss (dB)(typical value)
CDUG Jump combiner 0.8
2 in 1 4.2
CEUG 2 in 1 3.4
3 in 1 5.5
CENG 6 in 1 5.3
CDUD Jump combiner 0.8
2 in 1 4.4
CEUD 2 in 1 3.6
3 in 1 5.5
CEND 6 in 1 5.5
CDUP Jump combiner 0.8
2 in 1 4.4
CEUP 2 in 1 3.6
3 in 1 5.5
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Standard value for link balance
Adopt BTS V3 product series
8PSK modulation method
BTS static power class=0
common BTS type (PA output port is directly connected with CDUcombiner input port)
common antenna system (excl. TA, repeater and indoor distribution
system) Exclude various kinds of coverage enhancement techniques
Frequency band PBstandard
900M 46-4.4-339dB
1800M 46-4.2-3012dB
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Normal deviation range of link balance
Taking into consideration the engineer margin of 10dB, thenormal deviation range of link balance should be:
Frequency band Normal PB deviation range
900M -1~19dB
1800M 2~22dB
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Contents
Definition of link balance
Theoretical calculation of link balance
Test method of link balance
Analysis and elimination of link unbalance
Practical cases
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Internal Use OnlyMeasurement method of link balance
measurement
task at OMCR
UL/DL power control is counted into the statistics at
OMCR; the statistics gathered are about cells but not
carriers.
Counter nameBTS_V2 BTS_V3
Total value of uplink signal
strength of wireless channels
C10710 C901120010
Number of received uplink
signal strength samples of
wireless channels
C10707 C901120007
Total value of downlink signalstrength of wireless channels
C10714 C901120014
Number of received downlink
signal strength samples of
wireless channels
C10711 C901120011
UL level statistical average C10710/ C10707 C901120010/ C901120007
DL level statistical average C10714/ C10711 C901120014/ C901120011
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PB calculation formula
Influence from dynamic power control
10dB shall be deducted in the PB calculation formula for
900M cells
Influence from UL channel grain
BTS V2_TRM shall deduct UL channel gain of 14dB
Frequency
band
Product series
BTS V3(dB)/ BTS V2_ETRM(dB) BTS V2_TRM(dB)
900MDL level statistical average(UL level
statistical average -10 )
DL level statistical average(UL level statistical
average -10 -14)
1800M
DL level statistical averageUL level
statistical average
DL level statistical average(UL level statistical
average -14)
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Influencing factors in link-balance calculation
In order to obtain precise PB value, the following factors shallbe taken into consideration in calculation:
Influencing factors Explanations
Frequency band of existing
network
There is a difference of 3dB in judgment criteria due
to different frequency bands;
Model of BTS products used
& modulation method
adopted
Judgment criteria for different BTS products are
different for the BtsTxPwrMax is different.
Combining method adopted Combiner level 1 is adopted in the judgment criteria.
CduLoss difference caused by other combining
methods shall be eliminated.
If external TA installed? In the judgment criteria, default is NO TA; if external
TA is installed, its influence on UL-DL shall be
eliminated.
If coverage enhancement
technique adopted?
The gain produced by coverage enhancement
technique shall also be eliminated.
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Internal Use OnlyMeasurement method of link balance
RMA
signaling analysis
Record Abis signaling for th problem cells,
choose measurement report; import signaling data to RMS, then use TRX
equation to automatically generate the
scattergram of link balance vs TA ;
The benefits of using TRX equation are as
follows:
When RMA calculates UL-DL difference,
it considers influence from UL-DL powercontrol;
investigate carriers, which is good for
locating problem carriers in the cell.
Note: When RMA signaling analysis tool is
adopted, we need to choose the cells
frequency band according to actual situations.
Definition (China Unicom) :
(sample points with |DL-UL leveldifference|>=15dB)*100%/(total samplepoints)
Cells with this indicator>= 30% are
confirmed to have UL-DL unbalance.
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Contents
Definition of link balance
Theoretical calculation of link balance
Test method of link balance
Analysis and elimination of link unbalance
Practical cases
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Internal Use Only
Performance analysis-link balance analysis
Static
power
control
Filter out cells with link
unbalance
No
Investigate system
equipment
Adjust parameters
Yes
Indoor distribution
System &repeater
No
Investigate
repeater system
Yes
No
improvement
No
improvement
No improvement
Antenna
system
problem
Abnormal
installation of
antenna
CDU
problem
Abnormal
carrier
output
Abnormal
carrier UL
calibration
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Analysis of link-unbalance causes
Link unbalance caused by external TA connecting to antenna, repeater or
indoor distribution system The UL-DL of these external devices can be unbalanced, which can cause
the whole BTS system link to be unbalanced.
Cable connection problem
If the cable connection between feeder, jumper or antenna and RFequipment is not tight, increase UL-DL level loss and UL-DL level
difference can be caused, thus resulting in link unbalance. Carrier hardware problem
Carrier output power deviates from normal value;
If the gain of carrier UL receive channel is small, it causes UL-DL leveldifference to increase.
CDU problem
The increased insertion loss in DL channel will cause DL level to decreaseand reduce UL-DL level difference, thus coverage will be smaller;
Problem with UL receive channel will cause DL level to decrease, andreduce UL-DL level difference, thus silent call or call drop will be resulted.
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Contents
Definition of link balance
Theoretical calculation of link balance
Test method of link balance
Analysis and elimination of link unbalance
Practical cases
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Internal Use Only
Case 1: Link unbalance caused by repeaterSubscribers complained about frequent call drops.
The problem cell was located after call tests were made; traffic statistics
analysis showed in this 900M cell, (DL-UL) level difference was 25dB,
which was far beyond the normal link balance range .
while the daily average of DL-UL level difference in Cell 2 (under
the same BTS) was 2dB.
checked CDU and carrier, but no fault was found.
connected the problem cells antenna (its antenna is connected with
repeater) to the normal Cell2.
PB value in cell2 increased due to change on antenna .
The receive tributary with repeater has caused UL-DL level difference.
Problemdescription
Handling
process
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Case 2: Cable connection problemCustomers complained that MS displayed signal available, but calls couldnt be
established.
After call tests were made, problem cell was located. We discovered from trafficanalysis that the UL-DL level difference in the cell was 30dB, which exceeded the
normal range.
On-site checking was needed.
Changed carrier first.
During changing the carrier, we found the cable connector was not tightened.
Checked statistical result the next day, UL-DL level difference dropped to 6dB,
which was within the normal range.
After test, we found that UL-DL level difference of carrier was improved by about
1dB, which could not be the main cause for the improvement. Considering the
loose connector, we could confirm that poor cable connection was the main causefor link unbalance.
Loose cable connection could result in PB unbalance.
Problemdescription
Handling
process
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Equipment maintenance
Bad PB statistical result may be caused by broken
connector or cable, bad antenna VSWR or drop of
equipment.
Regular maintenance schedule is recommended, in order
to locate the parts with problem before the situation grows
worse.
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Case 3: Carrier problem
Problem description:
Subscribers complained thathandover happened frequently
when they made calls around a
cell. Test was made at the site
being complained about.
Sectional drawing of the test is
shown bellow: Test phenomena
Handover from 1800M to 900M
cells happened after MS
occupied a 1800M cell;
Handover from 900M to 1800Mcells happened after MS
occupied a 900M cell;
Handover between 900M and
1800M cells happened
frequently.
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Case 3: Carrier problem
Problem analysis Handover cause analysis
1800M900M handover cause: UL level handover
900M1800M handover cause: PBGT handover
Number of UL level handover in 1800M cells takes 90%
of total.
PB unbalancemay exist;
After traffic statistics analayis, we found UL-DL level
difference of the 1800M cells was all above 25dB.
Its confirmed to be UL-DL unbalance.
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Case 3: Carrier problem
Handling process
After KPI analysis, voice service in 1800M cells wasconfirmed normal.
Checked power control settings, no errors found.
Checked cable connections, no loose connectors, nodamaged heads.
Changed carrier, PB value decreased to 10dB.
Result of retest displayed frequent handover problem wassloved.
Carrier problem resulted in PB unbalance.
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Questions for thinking
When we calculate link balance, what factors need tobe taken into consideration? Why?
As for link unbalance caused by too low UL level, what
methods can be employed to make adjustment?
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