gsm rno training-coverage problems and solutions_r2.0

Internal Use Only▲

Coverage Problems and SolutionsR2.0

Suitable for staff with junior P&O skill certificates (lower than certificate III)Issued by Network Optimization System Dept.

GSM Training Materials forGSM Training Materials for Skill Certificates Skill Certificates


Version Introduction

Version Date Author Reviewed by Amendment Records

R1.0 2007-6-21 Ji Jun Gan Wenjun First edition

R2.0 2009-3-13 Ji Jun Gan Wenjun The document template was renewed.


Training Goals

To know different kinds of coverage problems, their causes and solutions.


Contents

Overview of Coverage ProblemsMain Causes of Coverage Problems and SolutionsProcedure of Handling Coverage Problems

Typical Cases


Overview of Coverage Problems

Weak coverage

Over coverage

No-serving cell coverage

Too small coverage range will cause high call drop rate and a large number of customer complaints.

Too large coverage will result in frequent handovers, and mutual interference as well, if it’s rather serious, and network indicators will also be affected.

When cell reselection parameters and handover scenarios are similar, or there are two or more cells with similar signal strength, pingpong handover is easy to be caused during calls.


Contents


Typical Cases


Main Causes of Weak Coverage

Weak coverage

too small BTS power

too low antenna height

too small down-tilt

hardware problem

Obstruction of buildings


Main Causes of Over Coverage

too high antenna height

inappropriate down-tilt

poor antenna performance

Internal Use Only▲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 caused by changes of radio environment

unreasonable setting of handover parameters

unreasonable setting of cell reselection parameters

no coverage of serving cell


Contents


Typical Cases


Procedure of Handling Coverage Problems Check settings of problem BTS’ radio parameters

Check whether strong interference source exists

Check hardware

Check antenna system

Analyze the local geographical environment to see whether site location and type of site are appropriate


Contents


Typical Cases


Poor Coverage at Cold Storage Warehouse Problem description

Subscribers complained about the poor coverage around a cold storage warehouse of animal foodstuff; it was difficult to detect signal even when they were not far from the warehouse.

Problem analysis According to subscriber’s feedback, we confirmed there was

problem about coverage around the warehouse. We found all radio parameters of the site were set correct at OMCR. Statistical report showed that data of idle interference band and of UL/DL quality 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 reasonably.

Through DT on site, network engineers found that the signal strength of the antenna main lobe was weak, while that of the side lobes was stronger, so they tentatively confirmed the problem was due to antenna fault.


Poor Coverage at Cold Storage Warehouse

Problem handling After the antenna was replaced with a new one, the coverage

improved greatly, so did the voice quality.


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 that idle data of interference band and UL/DL quality 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 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 optimization engineers found that the BTS’ coverage was in normal condition. While the Food Bureau, where subscribers complained about the signal, was 4km away from the BTS, and only indoor signal was weak (covered by Cell2).


Poor Coverage of a BTS

Problem handling After we confirmed there

was nothing wrong with parameters and equipment, we suggested to adjust the equipment of Cell2 (which had only 1 TRX) (to bypass CDU combiner and reduce pathloss).

Tested cell Before power adjustment

After power adjustment

Cell2 16W （ power after CDU ） 32W （ power

after CDU ）

Test place Before adjustment After adjustment Food warehouseCell 2

Outdoor level:－ 87dbm-- － 97dbmPoor speech quality;

Impossible to establish

call indoors

Cell 2Outdoor level:－ 76dbm-- － 86dbmGood speech qualityIndoor level:－ 86dbm-- － 96dbmNormal speech with a little noise


Handle Shrunk Coverage

Problem description After the BTS has been operating for a period of time, some of the areas,

which were covered before, became blind coverage or weak coverage area.

Problem analysis The BTS was an isotropic site with a height of 50m and power of 40W.

Normally, this kind of BTS can cover a distance of 4km. The coverage of this BTS (ARFCN 124) became smaller by DT. At place 1km away from the BTS, the MS receive level dropped to bellow -85dBm.

The BTS has been operating for 2 years, but the rack dust shelter has never been cleaned ever since the beginning. After we took out the dust gauze, we saw plenty of dust, which greatly abated the rack fan’s ability to ventilate and chill equipment and hindered TRX, PA and combiner to radiate heat, thus their normal operation was affected.

We took down and cleaned the dust gauze, then reinstalled it. From analysis of a new round DT of the same area, we found the coverage improved greatly than before. MS receive level at the former place increased by 5 ～ 10dB.


Coverage Shrinking After BTS Commissioning

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, and its 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.


High Handover Failure Rate Due to Skip-Zone Coverage Problem description

Configuration of a mountain site was S11, and the local network was single band GSM900. From indicator statistics of the last week, we found handover success rate of Cell2 under the BTS kept very low, which was around 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, which explained that MS could successfully occupy TCHs assigned to it by BSC; from DT analysis, we could see when signal level was above -90dbm, no call drops happened to MS, and speech quality was good, which could prove that no serious interference existed. Through further analysis, we found the target cell for handover was a bit far from Cell2; and probably adjacent 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; while Cell2 coverage at A and B was already very weak, so Cell2 should not be adjacent cell to A and B .

After adjustment, handover success rate of Cell2 increased greatly, from 80% to 96%.


High Handover Failure Rate Due to Skip-Zone Coverage


Question

Which parameters can be adjusted to improve coverage?

gsm rno training-coverage problems and solutions_r2.0

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