go_na15_e1_1 gsm coverage problem & solution 19
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7/28/2019 GO_NA15_E1_1 GSM Coverage Problem & Solution 19
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GSM Coverage problem & Solution
ZTE university
7/28/2019 GO_NA15_E1_1 GSM Coverage Problem & Solution 19
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Objectives
To know different kinds of coverage problem, their causes and solutions.
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Contents
Overview o f Coverage Prob lem
Main Causes of Coverage Problem & Solutions
Procedures of Handling Coverage Problem
Typical Cases
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Contents
Overview of Coverage Problem
Main Causes o f Coverage Problem & Solut ions
Procedures of Handling Coverage Problem
Typical Cases
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Main causes of weak coverage
Weak coverage
too small BTS power
too low antenna height
too small down-tilt
hardware problem
Obstruction of buildings
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Main causes of over coverage
too high antenna height
inappropriate down-tilt
poor antenna performance
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Causes of no-serving cell coverage
unreasonable planning
of antenna parameters
inappropriate type of antenna
too large or too small
carrier transmission power
shrunk coverage caused
by equipment problem
influence of changes
in radio environment
unreasonable settingof handover parameters
unreasonable setting of
cell reselection parameters
no-serving cell coverage
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Contents
Overview of Coverage Problem
Main Causes of Coverage Problem & Solutions
Procedures o f Hand l ing Coverage Problem
Typical Cases
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Procedures of Handling Coverage Problem
Check setting of problem BTS’ radio parameters
Check if strong interference source exists
Check hardware
Check antenna system
Analyze the local geographical environment to
see if site location and type of site are appropriate
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Contents
Overview of Coverage Problem
Main Causes of Coverage Problem & Solutions
Procedures of Handling Coverage Problem
Typ ical Cases
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Poor coverage at cold storage warehouse
【Problem description】
Subscribers complained about the poor coverage around a cold storagewarehouse of animal foodstuff; it was difficult to detect signal even whenthey were not far from the warehouse.
【Problem analysis】
According to subscriber’s complaint, we confirmed there was problem with
coverage around the warehouse. We found all radio parameters of the sitewere set correct at OMCR. Statistical report showed that idle data of interference band and UL/DL quality data distribution were normal.Hardware operated normally, as shown in OMCR warning report.
Hardware engineers went to the site and checked the system of the BTS,tested power amplifier's power and VSWR, they were all shown normal.Connection between equipment was correct. Antenna azimuth and down-tilt were all set reasonable.
Through DT on site, network engineers found that the signal strength of the antenna main lobe was weak, while that of the side lobes wasstronger, so they tentatively confirmed the problem was due to antennafault.
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Poor coverage at cold storage warehouse
【Problem handling】 After the antenna was replaced with a new one, the coverage improved
greatly, so did the speech quality.
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Poor coverage of a BTS
【Problem description】 Subscribers complained about weak signal strength around a Food
Bureau (near a BTS).
【Problem analysis】 According to subscriber’s complaint, we confirmed there was
problem with the BTS' coverage. We found all radio parameters of
the site were set correct at OMCR. Statistical report showed thatidle data of interference band and UL/DL quality distribution werenormal. Hardware operated normally, as shown in OMCR warningreport.
Hardware engineers went to the site and checked the system of theBTS, tested amplifier's power and VSWR, they were all shownnormal. Connection between equipment was correct. Antennaazimuth and down-tilt were all set reasonable.
Through DT on site, network optimization engineers found that theBTS’ coverage was in normal condition. While the Food Bureau,where subscribers complained about the signal, was 4km awayfrom the BTS, and only indoor signal was weak (covered by Cell2).
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Coverage shrinking after BTS starts operation
【Problem description】 After Cell3 of a BTS started to operate, its coverage range was
found shrunk. On highway 3km away from the BTS, where the BTS
tower was visible, MS could not detect Cell3’s signal. MS could
receive signal when it’s around the BTS, and the signal level was
about -60dB. 【Problem analysis】
We checked in radio resource management centre and found
Cell3’s static power class was set 2, which meant its static power
was reduced by 4dB, so we reset it to be 0. The next day, MS on
highway 3km away from the BTS could receive Cell3’s signal, andits level was -60—70; and the signal level around the BTS was
strong, which was about -40dB.
we concluded that the cell’s coverage shrinking was caused by
wrong setting of static power control at OMCR.
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High handover failure rate due to skip-zone
coverage 【Problem description】
Configuration of a mountain site was S11, and the local network wassingle band GSM900. From indicator statistics of the past week, we foundhandover success rate of Cell2 under the BTS kept very low, which wasaround 80%, while TCH allocation failure rate was completely normal.
【Problem analysis】 First, we could exclude the possibility of hardware problem and
interference, because there were no TCH assignment failures, whichexplained that MS could successfully occupy TCHs assigned to it by BSC;from DT analysis, we could see when signal level was above -90dbm, nocall drops happened to MS, and speech quality was good, which couldprove that no serious interference existed. Through further analysis, wefound the target cell for handover was a bit far from Cell2; and probablyadjacent cell relations were not set right during assignment planning,which resulted in isolated-island effect.
we could make area A and area B become adjacent cells to Cell2; whileCell2 coverage at A and B was already very weak, so Cell2 should not beadjacent cell to A and B .
After adjustment, handover success rate of Cell2 increased greatly, from80% to 96%.
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High handover failure rate due to skip-zone
coverage
Cell2
Cell1
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Questions for thinking
Which parameters can be adjusted to improvecoverage?
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