GSM UL-DL Unbalance Solutions-Special Subject Training V2 1

8/10/2019 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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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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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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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





Practical cases


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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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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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Practical cases


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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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Practical cases


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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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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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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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GSM UL-DL Unbalance Solutions-Special Subject Training V2 1

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