OMF005002 Coverage Fault Analysis ISSUE1.0

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OMF005002 Coverage Fault Analysis ISSUE1.0 Table of Contents

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Table of Contents

Course Description ...........................................................................................................................1Course Introduction......................................................................................................................1Course Objectives........................................................................................................................1References...................................................................................................................................1

Chapter 1 Overview...........................................................................................................................2Chapter 2 Network Optimization Handling Flow of Coverage Faults ..........................................3

2.1 Coverage Reduction a Period after BTS Cutover..................................................................32.1.1 Check Whether There is Interference or Bad Electromagnetic Environment Whichis Causing Higher Environmental Noise in the Entire Area..................................................32.1.2 Check Whether There is VSWR Alarm or Main and Diversity Reception Alarm of

Antenna Feeder in the Operation &Maintenance Console ..................................................42.1.3 Check Whether Parameters Affecting Coverage are Set Reasonably .......................42.1.4 Check Engineering Parameters such as Down Tilt Angle and Azimuth of BaseStation Antenna ....................................................................................................................42.1.5 Check the Output Power at the Top of TRX ...............................................................42.1.6 Check Whether the Receiving Sensitivity of the BTS Is Normal.................................42.1.7 Use a SITEMASTER to Further Check Whether the VSWR Is Less Than 1.5 ..........52.1.8 Check Whether the Tower Top Amplifier (TTA) Is Working Normally ........................52.1.9 Check Buildings in the Faulty Cell ..............................................................................52.1.10 Check Surroundings of BTS Antenna.......................................................................52.1.11 Check the Change of Propagation Environment ......................................................5

2.2 Coverage Fault Caused by BTS Expansion ..........................................................................52.2.1 Check Combiner Difference before and after Expansion ...........................................52.2.2 Check Whether there is Interference or Bad Electromagnetic Environment Which isCausing High Environmental Noise in the Entire Area ........................................................62.2.3 Check Whether There is VSWR Alarm or Main and Diversity Reception Alarm of

Antenna Feeder in the Operation & Maintenance Console .................................................62.2.4 Check Whether the Antenna Feeder Is Connected Inversely.....................................62.2.5 Check Whether New Antenna Type Selection Is Reasonable....................................82.2.6 Check Whether Antenna Installation Meets the Requirements ..................................82.2.7 Check the Location of BCCH TRX Tx Antenna of Omnidirectional Dual Tx Antenna 82.2.8 Check Whether the Elevation and Azimuth to the Two Directional Antennas AreConsistent When Directional Dual Tx Antennas Are Used..................................................92.2.9 Check the Output Power at the Top of the TRX .........................................................92.2.10 Check Whether the Receiving Sensitivity of the BTS Is Normal...............................92.2.11 Check Whether the TTA is Working Normally ..........................................................92.2.12 Check the Output Power at the Top of Different TRXs When the MaximumCoverage Configuration Solution Is Used............................................................................9

2.3 Coverage Fault Caused by BTS Relocation or New BTS .....................................................92.3.1 Check Whether the Azimuth and Installation Height of a Antenna after and beforeBTS Relocation Are Consistent............................................................................................92.3.2 Down Tilt Angle of Directional Antenna for Relocation Network...............................10 2.3.3 Check Whether the Power at the Top of a Relocated BTS Is Consistent with That ofthe Original One .................................................................................................................102.3.4 Check Whether the Receiving Sensitivity of the BTS Is Normal...............................102.3.5 Check Whether There is Interference or Bad Electromagnetic Environment Whichis Causing High Environmental Noise in the Entire Area...................................................102.3.6 Check Whether There is VSWR Alarm or Main and Diversity Reception Alarm of

Antenna Feeder in the Operation & Maintenance Console ...............................................102.3.7 Check Whether Parameters Affecting Coverage Are Set Reasonably.....................102.3.8 Check Whether the installation of the New Antenna Meets the Requirements after

the BTS Is Cut over or Relocated ......................................................................................10


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2.3.9 Check Whether the new Antenna Type Selection Is Reasonable ............................102.3.10 Check the Location of the BCCH TRX Tx Antenna of the Dual Tx Antenna ..........102.3.11 Check Whether the Elevation and Azimuth of the Two Directional Antennas AreConsistent if Directional Dual Tx Antenna Is Used ............................................................102.3.12 Check Whether the Antenna Feeder in a Cell Is Connected Inversely ..................102.3.13 Check Whether the TTA is Working Normally or Not .............................................112.3.14 Check the Output Power at the Top of Different TRXs When the MaximumCoverage Configuration Solution Is Used..........................................................................11

Chapter 3 Typical Solutions to Coverage Faults of an Existing Network .................................123.1 BTS Version Upgrading .......................................................................................................123.2 Ominidirectional BTS ...........................................................................................................12

3.2.1 Reducing the Influence of Tower Shadow upon Coverage ......................................123.2.2 Check Whether the Fault Can Be Removed by Increasing the Top Power of theBTS ....................................................................................................................................123.2.3 Using Zero Filling Antenna or Builtin Down Tilting Antenna to Solve the Problem ofDark under Tower an Ominidirectional BTS in a Mountain .............................................143.2.4 Replacing an Omnidirectional Antenna with a Directional Antenna to Solve theCoverage Problem .............................................................................................................14

3.3 Coverage of a Directional BTS ............................................................................................153.3.1 Removing Coverage Faults by Adjusting the Down Tilt Angle of the Antenna.........153.3.2 Solution by Increasing the Top Power of the BTS ....................................................163.3.3 Coverage Solution by Using Antenna with High Gain and Wider Horizontal Lobe...17

Chapter 4 Common Coverage Faults and Solutions ...................................................................184.1 Water Penetration into Antenna...........................................................................................184.2 Passive Intermodulation of Antenna....................................................................................184.3 Improper Antenna Selection ................................................................................................184.4 Influence of Iron Tower upon Radiation of Ominidirectional Antennas ...............................194.5 Antenna Feeder Installation.................................................................................................20

4.5.1 Installation of Directional Antennas...........................................................................204.5.2 Installation of Omnidirectional Antennas...................................................................214.5.3 Connection Faults of Anntenna Feeder, Combiner (Divider) and CDU....................224.6 Tower Top Amplifier (TTA) ..................................................................................................23

4.7 Common Faults Affecting Coverage in Engineering Applications of the Front-end Moduleof a BTS .....................................................................................................................................23

4.7.1 Isolator Damage........................................................................................................234.7.2 Damage of Duplexer or Other Filters ........................................................................244.7.3 False VSWR Alarm ...................................................................................................244.7.4 LNA Damage.............................................................................................................244.7.5 Low Output Power of TRX and HPA.........................................................................24

4.8 Parameter Settings Affecting Coverage ..............................................................................24Chapter 5 Introduction to Coverage Cases ..................................................................................27

5.1 Case I An Omnidirectional Antenna Preset with a Down tilt Angle Is Used .......................275.2 The Antenna Shaping Technology Is Used .........................................................................28

5.3 Installation Fault of an Omnidirectional Antenna.................................................................285.4 Uplink Loss Increase Caused by Combiner ........................................................................295.5 Poor Uplink Coverage Caused by TRX...............................................................................31

Chapter 6 Appendix A Signal Strength Indication of MSs.........................................................32


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OMF005002 Coverage Fault Analysis ISSUE1.0 Course Description

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Chapter 1 Course Description

Course Introduction

This course gives a detailed analysis of coverage faults: First the course describescoverage faults caused by BTS cutover, expansion and relocation, then introducesthe common factors affecting coverage and finally presents case analysis.

Course Objectives

After learning this course, you should be able to:

" Master the common factors affecting coverage" Master coverage fault analysis flow.

References


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OMF005002 Coverage Fault Analysis ISSUE1.0 Chapter 2 Overview

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Chapter 2 Overview

Various factors will cause wireless coverage faults, which can generally divided intofour types: Faults caused by incomplete network planning or imperfect wirelessnetwork architecture, equipment faults, engineering faults and faults resulted fromnew coverage requirements of clients. Different methods should be used to handledifferent coverage faults.

This document will give detailed description of coverage faults caused by imperfectwireless network architecture or new coverage requirements of clients, since suchfaults are normally removed by new network planning. This document mainlydescribes common coverage fault handling flow and typical coverage fault handlingmethods, summarizes various causes of coverage faults from the aspect ofengineering and presents the corresponding measures.


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OMF005002 Coverage Fault Analysis ISSUE1.0 Chapter 3 Network Optimization Handling Flow of Coverage Faults

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3.1.2 Check Whether There is VSWR Alarm or Main and Diversity ReceptionAlarm of Antenna Feeder in the Operation &Maintenance Console

The user can conduct troubleshooting with the combination of VSWR alarm

information and main & diversity reception alarm information in the Alarm Console.The diversity reception alarm refers to the alarm message reported when the diversity(main) reception signal is continuously less than the main (diversity) reception signalby a certain value in a certain period of time. This alarm facilitates the timely detectionof (main) diversity tributary faults. If such alarms are found, please check the antennafeeder.

3.1.3 Check Whether Parameters Affecting Coverage are Set Reasonably

For the check of parameters, refer to the detailed description of the followingparameter setting.

3.1.4 Check Engineering Parameters such as Down Tilt Angle and Azimuthof Base Station Antenna

The increase of the down tilt angle or the deviation of the azimuth of an antenna willreduce the coverage of the BTS. During engineering implementation, notice thatwhether fasteners are tightened and whether the strength of supports on the towermeets the requirements. Only in this way can the capability of wind resistance beimproved so as to reduce the possibility of such faults.

3.1.5 Check the Output Power at the Top of TRX

Firstly, check whether the connection lines of the TRX are in perfect connection;secondly, test whether the power at the top of the TRX is normal. If the power is not

normal, use a power meter to check powers of TRX and combiner equipment (EDU,CDU and SCU) segment by segment, so as to determine whether the output power ofthe TRX and the power loss after passing the combiner equipment (EDU, CDU andSCU) are normal. If the test indicates that the output power of the TRX has decreasedand the power loss of the combiner equipment is excessively large, replace the faultyhardware.

Note: Please use a digital power meter to test the peak power of the TRX and theCombiner. When using a pointer-type power meter to test, since the tested power isthe mean power, please notice that whether non-BCCH is in the full-timeslot and fullpower transmission mode, so as to convert and obtain the accurate power or tomaintain and operate the TRX (send idle BURST) so that the TRX can transmitsignals in the full-timeslot and full power mode.

3.1.6 Check Whether the Receiving Sensitivity of the BTS Is Normal

Use test instruments such as CMD57 to check whether the coverage reduction of aBTS is caused by the decrease of the receiving sensitivity of the BTS.

Furthermore, we can trace messages of the ABIS interface and use statistic methodto obtain the relationship between level and bit error rate (obtaining the correspondinglevel value according to a bit error rate of 2%). This method can only be used to make

judgment when the sensitivity decreases severely.


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3.1.7 Use a SITEMASTER to Further Check Whether the VSWR Is Less Than1.5

Since the tolerance of the VSWR alarm threshold of CDU or EDU is very great, if the

power at the top of the TRX is normal after check, use a SITEMASTER to furthercheck whether the VSWR is less than 1.5 so as to remove the fault cause that thetolerance leads to greater VSWR but there is no alarm. If the VSWR is abnormal,check whether water penetrates into the antenna or feeder or whether there is

arrester fault, etc.

3.1.8 Check Whether the Tower Top Amplifier (TTA) Is Working Normally

Check whether the Operation & Maintenance Console has any TTA alarm. Normally,such a fault is caused by LNA (Low Noise Amplifier) damage or water penetration intothe TTA. The LNA damage is normally accompanied by a TTA alarm (abnormal TTAcurrent). Normally no alarm is generated if water penetrates into the TTA. However,the RF loss is greater, which will decrease the receiving sensitivity of the system

severely.

3.1.9 Check Buildings in the Faulty Cell

New buildings may block the propagation of electromagnetic waves, which will lead tosignal attenuation so that the remote regions cannot be covered and subscriberscannot use mobile stations normally. In particular, tall buildings near base stationsaffect the propagation of electromagnetic waves greatly.

3.1.10 Check Surroundings of BTS Antenna

Check whether there are any other antennas (such as microwave antennas),

decorations, billboards, trees or glass curtain walls (they may block the antenna)around an antenna. These factors may affect the receiving and transmission of theantenna and hence the coverage of the BTS. If such a phenomenon occurs, adjustthe azimuth of the corresponding antenna or change the antenna height to reduce the

influence.

3.1.11 Check the Change of Propagation Environment

Change of electromagnetic wave propagation environment will lead to reduction ofsignals received at the radio terminal, especially, in mountain regions, the propagationof electromagnetic waves depends upon reflections of many hillsides. If thevegetation of a mountain changes, the coverage of a BTS will be reduced. Naturalfactors such as climate and vegetation have some influence upon electromagnetic

waves. With the variation of tree area (thickness), season, species and forest beltorientation, the propagation loss is also different. The maximum recorded value is30dB.

3.2 Coverage Fault Caused by BTS Expansion

If the coverage is reduced to some degree after expansion, please check thefollowing items:

3.2.1 Check Combiner Difference before and after Expansion

The loss differs greatly in different combiner modes (including EDU, CDU and SCU).

When conducting expansion, make configuration strictly according to the


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configuration recommendations of Huawei to try to prevent any loss increase fromexpansion.

Check whether parameters affecting coverage are set reasonably.For the check of parameters, refer to the following details of parameter settings.

3.2.2 Check Whether there is Interference or Bad ElectromagneticEnvironment Which is Causing High Environmental Noise in the Entire Area

For the specific interference location, refer to the related interference troubleshootingguide.

3.2.3 Check Whether There is VSWR Alarm or Main and Diversity ReceptionAlarm of Antenna Feeder in the Operation & Maintenance Console

3.2.4 Check Whether the Antenna Feeder Is Connected Inversely

The inverse antenna feeder connection is a common fault in construction of a newBTS or in BTS expansion or relocation. Several common faults and solutions aredescribed as follows.

1. Wrong connection of Tx antennaPossible fault phenomena for fault location:a. A Mobile Station (MS) seizes a cell, but the MS cannot make outgoing calls (the Rx

antenna is in another direction and the uplink is not so well)}.b. One-way conversationc. Call drop always occurs at a certain distance from the cell (such a phenomenonnormally does not occur easily near the BTS).

d. Call drop after frequent handover (in most cases, the handover is triggered byuplink signal strength or uplink quality factor)e. It is found in the drive test that the field strength level distribution diagram of theBCCH frequency between neighboring cells is in disorder.

f. Severe accidental co-channel or neighboring channel interferenceConduct drive test or perform test around the BTS antenna to check the change oflevel strength of the BCCH frequency in the cell. Thus, such faults can be easilydetected.

1) Judgment method when a test MS is usedNear a BTS to be checked, first determine a cell to be tested according to theindication of a compass and lock the test MS to the BCCH frequency of the cell to betested (or directly observe and compare the receiving level of each cell). For a

SAGEM test MS, directly use the level ordering function to view. In principle, thereceiving level of the current cell should be higher than the levels of the other twocells of the same BTS. Perform test around the BTS. If the test result conforms to theabove rule, it indicates that the Tx antenna in the cell of the BTS has been installedcorrectly. Furthermore, we should exclude the reason of strong reflection around theBTS antenna and meanwhile consider the influence of sidelobes. According toexperiences, the surrounding test can judge such faults easily. If fault occurs in anindividual cell, conduct multi-point tests in the cell direction to verify fault location.


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Tr

aveldirection

Note:

Due to the influence of antenna back lobes and reflection signals, the tested signalsof the three cells near the BTS will be very close to each other. Therefore, try toperform frequency lock test at a distance at least 50 meters away from the main lobe

direction of the antenna.

2) Judgment in drive testAs shown in Figure 3-1, it is indicated that frequencies of Cells 2 and 3 in TianjinVillage is in the opposite direction of the BTS cell. The service frequency displayed inthe service area of frequency 99 in cell 2 is 105, while that of frequency 105 in cell 3is 99. Thus, it can be judged that the antennas in cells 2 and 3 are connected

inversely.

Dali WaikuanBu i ld ing

Dali ICBC Center

Tianjinvillage

Shiriliang

Figure 3-1 Case of wrong connection of Tx antennas

2. When dual Tx antenna and dual Rx antenna are usedIf the judgment method of wrong connection of the TRX antenna where the mainBCCH is located is the same as the above-mentioned, when the TRX antenna wherethe non-main BCCH is located is connected wrongly, the traffic statistics will obviouslyshow a higher congestion rate. By registering the frequency scanning function in thecells, it can be seen that greater difference exists in diversity scanning levels. In thiscase, exchange the two Tx antennas and use the above method, and the fault can beeasily found.

3. In the BTS2X combiner mode (no sharing of transmitting and Rx antennas), the Tx

antennas are installed correctly, while both Rx antennas are installed wrongly


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In this case, both the uplink/downlink balance statistics and traffic statistics indicescan indicate such a fault. If both Rx antennas are connected wrongly, since severeuplink and downlink unbalance occurs, the main traffic statistics indices are normallyunsatisfactory. Please use the uplink/downlink balance performance indices to make

judgment. However, since the current version of BTS (Version 05.0529, inclusive)

does not report Received Signal Strength Indicator (RSSI) accurately, theuplink/downlink balance performance measurement indices have greater errors,please make proper correction (4-5dB should be subtracted in the uplink).

4. In the BTS2X combiner mode (no sharing of transmitting and Rx antennas), if theTx antennas are connected correctly, while one Rx antenna is correct and the otherRx antenna is connected wrongly, or when the main Rx antenna and the Tx antennas

share the same antenna and the diversity is connected inverselySuch a fault is difficult to detect, please conduct hardware check, exchange thetransmitting and Rx antennas (notice whether there is TTA and TTA type so as toprevent TTA damage) or disconnect one Rx antenna without service interruption tomake judgment (this method can locate fault easily, but it needs cooperation ofrelated personnel). In addition, we can use the cell frequency scanning performance

measurement to make judgment: If the main and diversity antennas are not installedconsistently or one of them is connected inversely, greater inconsistency will appearin the main/diversity scanning level statistics. In this way, we can judge wrongconnection of Rx antennas.

3.2.5 Check Whether New Antenna Type Selection Is Reasonable

For antenna use principles, refer to antenna selection. Unreasonable antennaselection can hardly meet the coverage requirements. In engineering installation andnetwork planning, select appropriate antennas according to the antenna selectionprinciples so as to attain the best coverage. Special caution should be taken thatwhen the antenna installation height is relatively greater, please select shapedantennas or electrical down-tilt antennas so as to prevent the occurrence of Darkunder the tower. In the meantime, try to reduce the number of omnidirectionalantennas in wide coverage areas. Some coverage faults can be removed by the useof directional antennas. (Furthermore, if the antenna installation height is greater inwide coverage areas, try to avoid the problem that signals are stronger beyond 35KMbut MSs cannot access the network. In this case, consider the dual timeslot solutionto attain the purpose of wide coverage.)

3.2.6 Check Whether Antenna Installation Meets the Requirements

Firstly, check whether the installation height, azimuth and down tilt angle of anantenna meet the design requirements. Normally, an important coverage area shouldbe free from the shadowing area of the iron tower. In the meantime, try to make an

important coverage area perpendicular to the diversity direction of the antenna so asto achieve the best diversity effect in the area. Try to make the distance from anantenna to the tower be 1.5 meters. Try to reduce the coverage shadow of the towerand meanwhile the installation pole of an omnidirectional antenna should not beoverlapped with the effective radiation part of the antenna.

3.2.7 Check the Location of BCCH TRX Tx Antenna of Omnidirectional DualTx Antenna

Considering the influence of the tower, the BCCH TRX Tx antenna should be locatedon the side of the important area so as to prevent the location of the important area inthe coverage shadow area formed due to blocking of the iron tower. To preventassignment failure due to coverage inconsistency of BCCH TRX and TCH TRX, usethe Intelligent Underlay/Overlay (IUO) channel allocation algorithm. Furthermore, try


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to make the important coverage area perpendicular to the diversity direction of theantenna so as to achieve the best diversity effect in the cell.

3.2.8 Check Whether the Elevation and Azimuth to the Two Directional

Antennas Are Consistent When Directional Dual Tx Antennas Are Used

If the elevation and azimuth of the two directional antennas are inconsistent, call drop,assignment failure and handover failure easily occur. Hence, the coverage of the BTSwill be reduced for subscribers. In the meantime, considering the influence of thetower, the BCCH TRX Tx antenna should be located on the side of the important areaso as to prevent the location of the important area in the coverage shadow areaformed due to blocking of the iron tower. Furthermore, try to make the importantcoverage area perpendicular to the diversity direction of the antenna so as to achievethe best diversity effect in the cell.

3.2.9 Check the Output Power at the Top of the TRX

Please refer to Section 2.13.2.10 Check Whether the Receiving Sensitivity of the BTS Is Normal

Please refer to Section 2.13.2.11 Check Whether the TTA is Working Normally

Please refer to Section 2.13.2.12 Check the Output Power at the Top of Different TRXs When theMaximum Coverage Configuration Solution Is Used

To obtain the maximum coverage, different TRXs often use different combinationmodes, which will cause the coverage of the BCCH TRX to be greater than that of theTCH TRX. Thus, it will lead to assignment failure of the TCH TRX. Therefore, it isnecessary to use the Intelligent Underlay/Overlay (IUO) technology. Set the TA valuesof the underlay and overlay reasonably and determine the allocation order of theunderlay and overlay according to the receiving level conditions upon assignment, soas to prevent assignment failure due to low transmitting level of the underlay and alsoto avoid channel congestion of the overlay.

3.3 Coverage Fault Caused by BTS Relocation or New BTS

3.3.1 Check Whether the Azimuth and Installation Height of a Antenna afterand before BTS Relocation Are Consistent

Due to the limitation of installation space on the tower, for new antenna and feeders,the old equipment can be relocated only after the new equipment is established.Therefore, the azimuth of the antenna of the new BTS is always not as reasonable asthat of the original BTS and even the antenna installation height is different. Thedirect sequence of the change of main lobe direction of an antenna is the signalreduction in the original coverage area. Please pay special attention to the prevention

of azimuth inconsistency upon BTS relocation in wide coverage occasions.


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3.3.2 Down Tilt Angle of Directional Antenna for Relocation Network

Normally, the down tilt angle should remain unchanged. To control the coverage indowntown area due to new BTSs, enlarge the tilt angle properly. However, we shouldmake detailed record.

3.3.3 Check Whether the Power at the Top of a Relocated BTS Is Consistentwith That of the Original One

Please refer to Section 2.13.3.4 Check Whether the Receiving Sensitivity of the BTS Is Normal

Please refer to Section 2.13.3.5 Check Whether There is Interference or Bad Electromagnetic

Environment Which is Causing High Environmental Noise in the Entire Area

Please refer to Section 2.13.3.6 Check Whether There is VSWR Alarm or Main and Diversity ReceptionAlarm of Antenna Feeder in the Operation & Maintenance Console

Please refer to Section 2.13.3.7 Check Whether Parameters Affecting Coverage Are Set Reasonably

Please refer to Section 2.13.3.8 Check Whether the installation of the New Antenna Meets theRequirements after the BTS Is Cut over or Relocated

Please refer to Section 2.13.3.9 Check Whether the new Antenna Type Selection Is Reasonable

Please refer to Section 2.13.3.10 Check the Location of the BCCH TRX Tx Antenna of the Dual TxAntenna

Please refer to Section 2.13.3.11 Check Whether the Elevation and Azimuth of the Two DirectionalAntennas Are Consistent if Directional Dual Tx Antenna Is Used

Please refer to Section 2.13.3.12 Check Whether the Antenna Feeder in a Cell Is Connected Inversely

Please refer to Section 2.1


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3.3.13 Check Whether the TTA is Working Normally or Not


3.3.14 Check the Output Power at the Top of Different TRXs When theMaximum Coverage Configuration Solution Is Used



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OMF005002 Coverage Fault Analysis ISSUE1.0 Chapter 4 Typical Solutions to Coverage Faults of an Existing Network

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Chapter 4 Typical Solutions to Coverage

Faults of an Existing NetworkThe concept of an entire network should be used in coverage consideration (forexample, with combined consideration of interference and expansion). Try to analyzeand solve problems with the point of view of development so as to prevent the blindpursuit for Super BTS coverage in current network conditions. Take expansionpressure into consideration. For coverage requirements exceeding the normalcoverage possibility, actively guide our clients to solve the coverage problem byadding new BTSs or site type alteration. On the other hand, we should place anemphasis on reasonable coverage requirements put forward by the clients and try ourbest to solve the problem in an optimized way. To improve the satisfaction of ourclients, this chapter also presents the unusual solutions for reference in solving theproblem of coverage in some wide coverage areas and of BTSs without expansion

possibility.

4.1 BTS Version Upgrading

The sensitivity will be improved after BTS version upgrading. Furthermore, theNumber of SACCH multiframes of BTS3X (later than Version 05.0529) also can beset to 31. Thus, the Minimum receiving signal level of MS can be reduced (forexample, changed to 10 or lower) so as to enlarge the available range of the cell.Notice that the Minimum access threshold of RACH (BTS3X) should also bedecreased sot that an MS can access normally on cell edges, so as to prevent thefault that the MS has signals but cannot make any calls.

4.2 Ominidirectional BTS

4.2.1 Reducing the Influence of Tower Shadow upon Coverage

Normally, an important area should be free from the shadow of the iron tower. Try tomake the direction of an important area be perpendicular to the main/diversitydirection of the antenna so as to achieve the best diversity effect in the area.

Try to make the distance from an antenna to the tower be 1.5 meters. Try to reducethe coverage shadow of the tower and meanwhile the installation pole of anomnidirectional antenna should not be overlapped with the effective radiation part ofthe antenna. For example, no antenna support is used when an omnidirectionalantenna is installed in a certain site. The antenna is directly installed on the frame of

the external platform of the iron tower. The antenna is only about 1 meter to the mainbody of the tower. Thus, the coverage of the antenna in the back of the tower isrelatively narrower. It is necessary to make alteration. Add an antenna support so thatthe distance between the antenna and the iron tower is greater than 1.5 meters, so asto improve the coverage. Furthermore, we can exchange the diversity antenna andthe Tx antenna so that the Tx antenna and the important area are free from theshadow of the iron tower.

4.2.2 Check Whether the Fault Can Be Removed by Increasing the TopPower of the BTS

The top power (the power at the top of the BTS) increase should follow the principle

of uplink/downlink balance. Do not increase the top power at will in a blind manner so


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as to prevent severe limitation on uplink signals; otherwise, the actual coverage is notimproved at all. To the contrary, the interference upon the multiplexing cell in thesystem is increased. The list of calculated results based on the uplink/downlinkbalance principle is as follows:In a system without TTA, the output power of the BTS should be balanced in theuplink and downlink.

Combining mode Lcb (dB) Output power of900M (dBm) Output power of1800M (dBm)

Dual duplexer 1.5 44 42EDU 1 43.5 41.5CDU 4.5 47 45

SCU+CDU mode 8 50.5 48.5In a system with TTA, the output power of the BTS should be balanced in the uplinkand downlink.

Combining mode Lcb Towerheight Lfd of 900M Lfd o f 1800M Outputpower of

900M (dBm)Output power of

1800M (dBm)Dual duplexer 1.5 25 meters 1(7/8') 1.5 (7/8') 47 45.5

50 meters 2 (7/8') 2.2 (5/4') 48 46.260 meters 2.4 (7/8') 2.6 (5/4') 48.4 46.680 meters 2.4 (5/4') 3.5 (5/4') 48.4 47.5100meters

3 (5/4') 4.3 (5/4') 49 48.3EDU 1 25 meters 1(7/8') 1.5 (7/8') 46.5 45

50 meters 2 (7/8') 2.2 (5/4') 47.5 45.760 meters 2.4 (7/8') 2.6 (5/4') 47.9 46.180 meters 2.4 (5/4') 3.5 (5/4') 47.9 47100meters

3 (5/4') 4.3 (5/4') 48.5 47.8CDU 4.5 25 meters 1(7/8') 1.5 (7/8') 50 48.5

50 meters 2 (7/8') 2.2 (5/4') 51 49.260 meters 2.4 (7/8') 2.6 (5/4') 51.4 49.680 meters 2.4 (5/4') 3.5 (5/4') 51.4 50.5100meters

3 (5/4') 4.3 (5/4') 52 51.3SCU+CDU 8 25 meters 1(7/8') 1.5 (7/8') 53.5 52

50 meters 2 (7/8') 2.2 (5/4') 54.5 52.760 meters 2.4 (7/8') 2.6 (5/4') 54.9 53.180 meters 2.4 (5/4') 3.5 (5/4') 54.9 54100meters

3 (5/4') 4.3 (5/4') 55.5 54.8For an O1 BTS, the EDU or TRX can be used (without the connection of a CDU) todirectly implement transmission via the duplexer interface so as to prevent thedecrease of the top power due to transmission CDU loss (3.5dB).

For an O2 BTS, replace the CDU with an EDU to increase the power at the top of the

BTS (hereinafter called top power) by 3.5dB.

For an O3 BTS, replace the SCU with a CDU so that the CDU+CDU mode is used toimprove the top power by 3.5dB. Even more, the BCCH TRX can be used to directly


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implement output via the duplexer interface without passing the CDU, so as toimprove the BCCH TRX by 7dB and improve the TCH TRX by 3.5dB.

For an O4 BTS, replace the SCU with a CDU so that the CDU+CDU mode is used to

improve the top power by 3.5dB.If the CDU + CDU configuration mode is used with an O4 BTS, the use of 40W TRXwill lead to slight downlink limitation. If the coverage is very important, use a PBU(80W) to improve the top power. After the PBU (80W) is used, the uplink will be

limited to some degree. To achieve the maximum coverage, add a TTA.

Where, when BCCH and TCH have different TRX powers, inconsistent coverage maylead to TCH TRX assignment failure. To remove this fault, use the IUO solution andassign the overlay or underlay in precedence according to receiving level.

To improve the top power, first consider modifying the combining mode. If thecoverage requirements cannot be satisfied yet after the combining mode is used, usea PBU (80W). According to uplink/downlink balance principle, a TTA should be addedto improve the coverage efficiently.

4.2.3 Using Zero Filling Antenna or Builtin Down Tilting Antenna to Solvethe Problem of Dark under Tower an Ominidirectional BTS in a Mountain

The Dark under tower always occurs to a BTS at the top of a mountain. Themaximum gain of a high-gain shaped omnidirectional antenna is 12dBi. Huawei setsthe zero filling percentage of such an antenna to 25% (i.e., the depth of the first zerois -12dB) and sets the electrical down tilt to 3 in a fixed manner. Since there is adown tilt of three degrees, the gain in the 0 direction is the same as that of anordinary high-gain omnidirectional antenna (10.5-11dBi). This kind of antenna isrelatively an ideal one applicable to mountain and hill coverage, which can solve theproblem of Dark under tower due to great antenna installation height. Since a

shaped antenna only fills the first zero under the antenna, if the antenna installationheight is too greater, the antenna also cannot solve this problem. Therefore, it isrecommended that the radial distance R (from a building needing effective coverageto the antenna) and the antenna installation height H should meet the followingrelationship:

H


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15

requirements is hard to meet the coverage requirements, alter it to a directional BTS.The half power angle of the horizontal lobe of a directional antenna is 65 or 90 andthat of an omnidirectional antenna is 360, so after alteration, the edge coverage ofcells in a directional BTS possibly is poorer than that of the original omnidirectionalBTS. In network planning, we should not only make sure that the main lobe of a

directional antenna should point to the important coverage area, but also shouldclarify the coverage difference between the directional antenna and theomnidirectional antenna.

4.3 Coverage of a Directional BTS

4.3.1 Removing Coverage Faults by Adjusting the Down Tilt Angle of theAntenna

Many coverage faults of a directional BTS can be removed by adjusting the down tiltangle of the antenna properly so as to achieve perfect coverage in the area.Therefore, to optimize a directional BTS, first understand the features of the antennadirectivity pattern, including horizontal directivity pattern and vertical directivity pattern.Master the features of the main lobe and adjust the azimuth and down tilt anglereasonably. The calculation of the down tilt angle of an antenna is given as follows:Suppose the coverage radius is D(m), the antenna height is H(m), the down tilt angleis and the vertical half power angle is , the relationship between the main lobebeam of the antenna and the ground level is shown in as shown in Figure 4-1:

Figure 4-1 Calculation of down tilt angle of an antenna

It can be seen from the above figure that when the down tilt angle of the antenna is 0,the main lobe of the antenna beam (i.e., the main energy) radiates along thehorizontal direction; when the down tilt angle of the antenna is not 0, the extendedline in the main lobe direction will finally intersect with a point on the ground (Point A).The antenna has a certain beamwidth in the vertical direction, so from Point A toPoint B, there will still be stronger energy radiation. According to the technical

performances of the antenna, within the half power angle, the antenna gaindecreases slowly; beyond the half power angle, the antenna gain (especially theupper lobe) will decrease rapidly. Therefore, when considering the size of the down tiltangle of the antenna, it can be thought that the actual coverage of the antenna iswithin the point of intersection (Point B) between the extended line of the half powerangle and the ground level.

If the technical parameters of the antenna are known, adjust the down tilt angleaccording to the method described in Guide to Adjustment of Down Tilt Angle of

Antennas. If the accurate antenna data cannot be obtained on site or there is noefficient method to adjust the antenna parameters accurately, the simplest and mostpractical onsite adjustment method is as follows: Use a test MS to observe changesof the coverage level in important coverage areas at the same time when the towerengineers are adjusting the antenna, so as to guide the tower engineers to make

further adjustment. The final adjustment principle is adjustment to the best coverage.


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This method also can prevent parameter calculation offset due to inaccurate antennapattern provided by the antenna manufacturer.

4.3.2 Solution by Increasing the Top Power of the BTS

The top power (the power at the top of the BTS) increase should follow the principleof uplink/downlink balance. Do not increase the top power at will in a blind manner soas to prevent severe limitation on uplink signals; otherwise, the actual coverage is notimproved at all. To the contrary, the interference upon the multiplexing cell in thesystem is increased. The list of calculated results based on the uplink/downlinkbalance principle is as follows:

In a system without TTA, the output power of the BTS should be balanced in theuplink and downlink.

Combining mode Lcb (dB) Output power o f 900M Output power of 1800MDual duplexer 1.5 44 42EDU

1 43.5 41.5

CDU 4.5 47 45

SCU + CDU mode 8 50.5 48.5In a system with TTA, the output power of the BTS should be balanced in the uplinkand downlink.

Combiningmode Lcb Towerheight Lfd of 900M Lfd o f 1800M Output powerof 900M Output powerof 1800M

Dualduplexer 1.5 25meters 1(7/8') 1.5 (7/8') 47 45.5

50meters

2 (7/8') 2.2 (5/4') 48 46.260meters

2.4 (7/8') 2.6 (5/4') 48.4 46.680meters

2.4 (5/4') 3.5 (5/4') 48.4 47.5100meters

3 (5/4') 4.3 (5/4') 49 48.3EDU 1 25

meters1(7/8') 1.5 (7/8') 46.5 45

50meters

2 (7/8') 2.2 (5/4') 47.5 45.760meters

2.4 (7/8') 2.6 (5/4') 47.9 46.180meters

2.4 (5/4') 3.5 (5/4') 47.9 47100meters

3 (5/4') 4.3 (5/4') 48.5 47.8CDU 4.5

25meters

1(7/8') 1.5 (7/8') 50 48.550meters

2 (7/8') 2.2 (5/4') 51 49.260meters

2.4 (7/8') 2.6 (5/4') 51.4 49.680meters

2.4 (5/4') 3.5 (5/4') 51.4 50.5100meters 3 (5/4') 4.3 (5/4') 52 51.3


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Combiningmode Lcb Towerheight Lfd of 900M Lfd o f 1800M Output powerof 900M Output powerof 1800M

SCU+CDU 825meters

1(7/8') 1.5 (7/8') 53.5 5250meters

2 (7/8') 2.2 (5/4') 54.5 52.760meters

2.4 (7/8') 2.6 (5/4') 54.9 53.180meters

2.4 (5/4') 3.5 (5/4') 54.9 54100meters

3 (5/4') 4.3 (5/4') 55.5 54.8For an S1 BTS, the EDU or TRX can be used (without the connection of a CDU) todirectly implement transmission via the duplexer interface so as to prevent thedecrease of the top power due to transmission CDU loss (3dB).

For an S2 BTS, replace the CDU with an EDU to increase the power at the top of theBTS (hereinafter called top power) by 3dB.

For an S3 BTS, replace the SCU with a CDU so that the dual CDU mode is used toimprove the top power by more than 3dB. Even more, the BCCH TRX can be used todirectly implement output via the duplexer interface without passing the CDU, so as toimprove the BCCH TRX by 6-7dB and. improve the TCH TRX by more than 3dB.

For an S4 BTS, replace the SCU with a CDU so that the dual CDU mode is used toimprove the top power by more than 3dB.

If the CDU + CDU configuration mode is used with an S4 BTS, the use of 40W TRX(900MHz) will lead to slight downlink limitation. If the coverage is very important, usea PBU (80W) to improve the top power. After the PBU (80W) is used, the uplink willbe limited to some degree. To achieve the maximum coverage, add a TTA.

Where, when BCCH and TCH have different TRX powers, inconsistent coverage maylead to TCH TRX assignment failure. To remove this fault, use the IUO solution andassign the overlay or underlay in precedence according to receiving level.

4.3.3 Coverage Solution by Using Antenna with High Gain and WiderHorizontal Lobe

In a wide coverage area, if the a directional antenna has narrower horizontal lobe, toimprove the coverage on the boundary of two sectors, use a directional antenna withwider horizontal lobe. For example, replace the original 65 antenna with a 90antenna to improve the coverage. Caution should be taken when making suchmodifications in areas with great expansion potentials such as downtown areas, so asto prevent the problem that the interference cannot be reduced efficiently and theantenna has to be replaced repeatedly in the future due to wider horizontal lobe of theantenna.


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OMF005002 Coverage Fault Analysis ISSUE1.0 Chapter 5 Common Coverage Faults and Solutions

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Chapter 5 Common Coverage Faults andSolutions

5.1 Water Penetration into Antenna

Water penetration into an antenna is a very accidental quality accident. The so-calledwater penetration hereinafter refers to water penetration into the internal RFconnection channel inside an antenna (possibly the water enters the antenna fromoutside or the water is the condensed water generated due to internal temperaturechange). The sequences of water penetration include: the increase of the VSWR ofthe antenna, obvious increase of loss, coverage reduction and even switch-off of the

power amplifier. There are two water penetration causes:

Design or production defects of the manufacturer: If such defects do exist, many

water penetration accidents may happen in rainy season. Feed back such defectsimmediately.

On-site installation errors: The antenna is not installed according to the instructionalmanual. For example, an antenna that should not be installed upside down is installedupside down, and the two drain holes of an antenna supporting the installation upsidedown are not handled correctly according to the instructional manual.

5.2 Passive Intermodulation of Antenna

Interferences caused by passive intermodulation of antenna and various connectors:The check method is as follows: Exclusive method, i.e., connect the antenna feederwithout interference in the neighboring sector to the local sector. And then use the

same method to exclude the feeder. If any fault is found, replace the antenna.

5.3 Improper Antenna Selection

Dark under tower phenomenon: When the antenna installation height exceeds 50meters, if the first zero of the main beam of the antenna is not filled in, the Darkunder tower phenomenon easily occurs. Dark under tower is also called Shadowunder tower, means that subscribers needing coverage are located in the first zerodepth or the second zero depth and neighboring areas under the antenna directivitypattern. Therefore, please select antennas with zero filling.

When a directional 3-sector antenna is used to achieve a wide coverage, select anantenna with higher gain and with a half power angle greater than 90. A too low half

power angle will lead to too low a gain in the direction in two neighboring sectors,which will cause two low a coverage radius.

If the down tilt angle of an antenna is too great, do not select a full mechanical downtilt antenna. Select the mode of fixed electrical down tilt + mechanical down tilt orcontinuously adjustable electrical down tilt (0-10) + mechanical down tilt. Themechanical down tilt angle should not exceed the half power beamwidth on thevertical plane of the antenna.

The Front-to-Back (F/B) ratio of the antenna cannot meet the requirements ofindividual or some BTSs. Since dense multiplexing has found wider and widerapplications in UNICOM, some BTSs have higher requirements for the front-to-backratio of antennas. Therefore, please select BTS antennas with high front-to-back ratio.

If an antenna needs to be replaced due to faults, try to use an antenna of the same

type from the original manufacturer; otherwise, coverage difference may occur.


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5.4 Influence of Iron Tower upon Radiation ofOminidirectional Antennas

Please attach great importance to the influence of an iron tower upon the coverage of

an omnidirectional antenna. The estimation of the damage to the directivity pattern ofan ominidirectional antenna caused by an iron tower is very complicated, andfurthermore, difference distances between subscribers and the iron tower will lead togreat different influences. Figure 5-1 shows the directivity pattern of anominidirectional antenna without any shadow. Figure 5-2 shows the influence of aniron tower upon the remote field directivity pattern of an omnidirectional antenna.

Figure 5-1 Directivity pattern of an ominidirectional antenna without any shadow

Figure 5-2 Square iron tower with a side length of 1 meter; the antenna is installed in thediagonal direction of the iron tower with a distance of 1.5 meters from the tower.

Therefore, when an antenna is installed on an iron tower or metal tube, please followthe following rules:


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" Do not overlap the metal pipe with the effective radiator of the

omnidirectional antenna (the effective radiator of an antenna refers to

the radome of the omnidirectional antenna).

" Try not to install the integrated omnidirectional antenna onto the metal

pipe (pole).

" When an omnidirectional antenna is installed on an iron tower, make

sure that the distance between the antenna and the nearest end face

of the tower should be greater than 6 wavelengths.

" The omnidirectional Dual Tx (i.e., two Tx antennas) coverage

technology is not recommended. Since the omnidirectional antennas

are installed on both sides of the tower, affected by the tower, the two

antennas have greater coverage differences (a maximum of 10dB) in

some directions. It is still a technical challenge to tackle as for how to

compensate such differences.

" The installation perpendicularity of an omnidirectional antenna should

at least be less than 1/8 of the half power angle beamwidth on the

vertical plane.

For the solution to the influence of an iron tower upon an antenna, first consider thecorrect engineering installation.

Note:

To meet the requirements for wide coverage and reduce combining loss,omnidirectional dual Tx antennas are used on some networks. According to theabove calculation and analysis, since the omnidirectional antenna are installed onboth sides of the tower, affected by the tower, the two antennas have greatercoverage differences (a maximum of 10dB) in some directions. Therefore, the

omnidirectional dual Tx coverage technology is not recommended.

5.5 Antenna Feeder Installation

5.5.1 Installation of Directional Antennas

1. Inverse installation of Tx antenna

Wrong connection of the Tx feeder and the corresponding cell antenna leads towrong spatial connection of the Tx antenna and Rx antenna in the same cell, whichaffects the coverage due to inconsistent coverage of Tx and Rx antennas.

Solution: Such an error relatively easily occurs on network. Besides that the Project

Supervisor should check the installation quality according to the Project QualityCheck Standards, network planners can also find such fault by analyzing the fieldstrength distribution map of BCCH frequencies or analyzing the uplink/downlinkbalance measurement in BSC traffic statistics during drive test.

2. Inverse connection of Rx antenna

Wrong connection between the Rx feeder and the corresponding cell antenna

Solution: After excluding faults such as antenna fault, water penetration into the Rxantenna and excessive VSWR, the on-site engineer should check whether the Rxantenna is connected inversely. At the earlier stage of the project, the ProjectSupervisor should strictly check whether the engineering team has made correctidentification on feeders according to the specifications.

3. Inconsistent azimuth and elevation or greater azimuth and elevation errorsbetween the Tx and Rx antennas


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This fault is generated because the engineering team does not construct according toHuawei installation specifications. In fact, certain requirements for errors of theazimuth and elevation are specified in the installation specifications: The azimutherror should not be greater than 5 and the elevation error should not exceed 0.5.Excessive azimuth and elevation errors will lead to coverage inconsistency between

the Tx and Rx antennas. Thus, it is difficult to make calls on the coverage edges orcall drop easily occurs.

Solution: The engineering team and the on-site supervisor should performconstruction strictly according to the installation specifications.

4. Diversity distance between Tx and Rx antennas or isolation of the iron towerInsufficient spatial diversity distance between Tx and Rx antennas or isolation of theiron tower will also affect the coverage. The requirements for the two items are alsospecified in the installation specifications. For an M900 system, the valid spatialdiversity distance between the Tx and Rx antennas should be greater than 4 meters;for an M1800 system, the valid spatial diversity distance between Tx and Rxantennas should be greater than 2 meters. The distance between the mount supportfor an antenna and the iron tower should be greater than 1.5 meters, and meanwhile,

the mount support should be in the 45 protection range of the arrester, so as toguarantee that there is sufficient isolation distance between the antenna and the

tower and to prevent lightning attack.

Solution: Normally, the diversity distance between Tx and Rx antennas and theisolation distance of the iron tower depend upon the installation position of theantenna support, and meanwhile low height of the arrester will also affect the isolationdistance between the antenna and the tower. All these items belong to theengineering preparations of the equipment buyer at the earlier stage and are hard tocontrol on site. Therefore, we should make sufficient communications with theequipment buyer and the stage of engineering survey and design, put forwardHuaweis requirements in this respect and sign a memorandum of survey and design.

5. An omnidirectional cell has shadow in the neighboring coverage areaWhen installing a directional antenna, notice whether the coverage area will has anygreater shadow. Normally, such a shadow is caused by a larger blocking object nearthe BTS such as a tall building or high mountain. Try to avoid any blocking objectsduring installation. When installing a directional antenna on the top of a building,prevent the edge of the building from blocking beam radiation. Try to install theantenna as close to the edge as possible, so as to reduce or eliminate the generationof any shadow. Due to the complexity of the topside of the building, if the antennashould be installed far away from the edge of the building, try to mount the antenna ina place higher above the topside. In this case, consider the factors such as floorbearing and wind resistance of the antenna.

5.5.2 Installation of Omnidirectional Antennas

1. The radiator of an omnidirectional antenna is blocked by the pole

The phenomenon that the coverage is affected due to the blocking of the radiator ofan omnidirectional antenna by the pole often occurs on networks. Normally, there isan installation sheath at the bottom of an omnidirectional antenna, which is used forthe installation connection between the omnidirectional antenna and the antenna pole.When an antenna is installed, the top of the installation sheath should be flush with ora bit higher than the top of the pole, so as to prevent any influence upon the validtransmission of the antenna.

Solution: During engineering implementation, strictly follow Huawei construction flowand specifications.

2. Diversity distance of an ominidirectional antenna and the isolation between the

antenna and the iron tower


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The phenomenon that insufficient spatial diversity between antennas and insufficientisolation from the iron tower leads to poor coverage often occurs on networks.Insufficient spatial diversity will reduce the diversity gain so that the receivingsensitivity will be reduced. Although the influence of the iron tower upon thetransmission of an omnidirectional antenna is unavoidable, the increase of the

isolation distance between the antenna and the iron tower will reduce such influence.Solution: During installation, the distance between an omnidirectional antenna andthe tower should be greater than 2 meters. For a 900M system, the effectivehorizontal diversity distance of the omnidirectional antenna should be greater than 4meters, while for a 1800M system, the effective horizontal diversity distance of theomnidirectional antenna should be greater than 2 meters.

3. The installation plane of an omnidirection antenna is not vertical to the horizontalplaneIf the installation plane of an omnidirectional antenna is not vertical to the horizontalplane, the antenna directivity patter will distort in the coverage area such that theantenna coverage will be affected. There are two possible causes: The antennasupport is not vertical to the horizontal plane; the antenna support is not installed

firmly or has low bearing and wind resistance performance.

Solution: To prevent occurrence of the above phenomena, perform constructionaccording to the following specifications. For unstandardized installation caused bythe equipment buyer, sign a memorandum with the equipment buyer.

1) The installation plane of the antenna support should be vertical to the horizontal

plane.

2) If the antenna support protrudes out the iron tower platform, make sure that theantenna is within the protection area of the arrester. The protection area of thearrester is in the range from the top of the arrester to a down tilt angle of 45, asshown in Figure 5-3:

Figure 5-3 Installation of arreseter

During engineering implementation, strictly follow Huawei construction flow andspecifications.

5.5.3 Connection Faults of Anntenna Feeder, Combiner (Divider) and CDU

Unstandardized connections and bindings of various connectors of the antennafeeder system lead to water penetration into various connectors, inform connection ofvarious RF cables of the combiner/divider and CDU cause the reduction of the Tx andRx performances and inconsistent jumper connections (at the top of the BTS) anddata configurations result in inverse connection of Tx and Rx antennas in each cell.

All these factors will affect the effective coverage of a BTS.


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5.7.2 Damage of Duplexer or Other Filters

Filters are metal parts. For some BTSs, the transportation conditions are very severe,so possibly the internal structure of individual CDU filters or duplexers may bedamaged. If such a fault occurs, the VSWR on the antenna port is very great. The

solution is to replace the faulty parts.

5.7.3 False VSWR Alarm

If a Level 2 false alarm occurs since the VSWR alarm inside the CDU is not stableitself, the power amplifier will be turned off and the whole BTS will stop working.Therefore, replace the CDU in time.

5.7.4 LNA Damage

If the LNA is damaged, the CDU will report the alarm information. The consequenceis the decrease of the receiving sensitivity. The following phenomenon seldom occurs:

Both the main and diversity LNAs are damaged. In this case, if both tubes balancingamplification are damaged, the uplink channel will be interrupted. Therefore, LNAdamage will affect the uplink coverage severely. On the site, we can use aSITEMASTER to check the channel gain of the LNAs.

5.7.5 Low Output Power of TRX and HPA

Low output power of the TRX and HPA will affect the downlink coverage. ExchangeTRX and HPA with other normal cells to make judgment or directly measure the

output power. Replace the any faulty card in time.

5.8 Parameter Settings Affecting Coverage

[TRX configuration table]TRX power level:

BTS30 Version 0407 supports the setting of power levels 0 through 6, BTS Version0529 supports the setting of power levels 0 through 10, all versions of BTS20 runningon networks support static power settings of levels 0 through 10. Microcell BTSssupport static power settings of levels 0 through 13. Here, power level 0 indicatesthe maximum power. If it is set to too low a value, the downlink coverage will beaffected directly. Furthermore, if different combining modes are used, notice whetherthe output power of each TRX at the top is consistent. To improve the maximumcoverage of the equipment, in principle, the combining mode with the maximumBCCH TRX power is used. In addition, the IUO solution is used to prevent

assignment failure due to assignment to TRX with lower power.[Antenna Feeder Configuration Table]TTA available/not availableValue range: TTA available/not available

Power attenuation factor:

If no TTA is used, set the Power attenuation factor to 0; if a TTA is used, set thepower attenuation factor according to the loss conditions of the feeder. In principle,

the power attenuation factor = TTA gain Feeder loss.

Where, the gain of a simplex TTA is 14, the gain of a duplexer TTA is 14 and that of atriplex is 12.

For a BTS using the CDU system, set the power attenuation factor according to the

TTA gain and feeder loss and adjust the CDU gain.


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In an early BTS2Xcombiner/divider mode (a TTA is mandatory) system, the power

attenuation factor is set to 10 in a fixed manner.

If the power attenuation factor is still set to zero when a TTA is used, small signals willbe easily blocked and the coverage will be affected.

[System Message Data Table]Invalid radio link counter

This parameter is used for an MS to determine when to disconnect a call if SACCHdecoding fails. Once an MS is assigned with a dedicated channel, it will turn on thetimer (S). After than, whenever a SACCH message cannot be decoded, the readingof S will be subtracted by 1; whenever a SACCH message is decoded correctly, thereading of S will be added by 2. If the reading of S is decreased to zero, eitherreestablishment or release should be performed. If this parameter is set to too low avalue, temporary radio link fault easily occurs, which will lead to call drop. Thereforeto reduce the call drop rate in edge areas, try to improve the available range in theprecondition of guaranteeing the performance index. (This parameter acts on

downlink).

Value range of the maximum power control level of an MS:

Recommended value: 5 (900M), 0 (1800M), wrong setting will lead to lower Tx powerof the MS upon access so as to affect the coverage.

Minimum Rx signal level of an MSIt indicates the minimum Rx signal level necessary for residence of the MS in thelocal cell. This parameter directly affects the value of C1. If the value of C1 is lessthan zero, the MS will be disconnected from the network. Set this parameteraccording to the principle of uplink/downlink balance so as to prevent the

phenomenon that the MS has signal but cannot make any calls.Recommended value: 8

Power offset indication

It is used to judge whether to calculate the power used by a Class 3 MS of DCS1800.Combine power offset to determine its function together.

Power offsetThis parameter means that after random access, if the initial power command is notreceived, the power used by a Class 3 MS of DCS1800 is equal to Maximum Tx

power level of an MS + Power offset.

[Cell Attribute Table]Number of SACCH multiframesIt is used when a BTS informs the BSC of radio link connection failure. The BSS

judges radio link failure according to bit error rate on the uplink SACCH. If the bit errorrate of the uplink within the time set by this parameter is greater than the setthreshold, the BTS will send a connection failure indication message to the BSC. Thenumber of SACCH multiframes and radio link failure counter in the system messagerespectively define the radio link connection failure time of uplink and downlink, so as

to reduce call drop rate.


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Related parameters of BTS2X RACH:

RACH busy threshold

It is the random access level threshold. If this parameter is set to too high a value, itwill lead to access failure upon higher downlink signals. This parameter does not

affect the uplink access of BTS3X.

Random access error threshold

This parameter can be simply thought of as random access signal error threshold.The higher the threshold, the higher the requirement for access signal quality, hencemore difficult the coverage edge access.

Related parameters of TS3X RACH:

Minimum RACH access level:

This parameter refers to the random access level threshold. If it is set to too high avalue, it will lead to access failure upon higher downlink signals (the same as RACHbusy threshold of BTS2X).

Whether handover and power control parameters are set reasonably:In a wide coverage area, please check whether the Uplink/downlink Edge HandoverThreshold, Edge Handover Hysteresis and the Minimum Rx Power Level of thecandidate cell are set reasonably. Improper setting will lead to call drop due tohandover delay and cause the wrong impression that a certain segment cannotimplement continuous coverage.

If the Expected Uplink/downlink Power Control Threshold or Upper Power ControlThreshold/Lower Power Control Threshold is set to too low a value, call drop alsoeasily occurs.


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OMF005002 Coverage Fault Analysis ISSUE1.0 Chapter 6 Introduction to Coverage Cases

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Chapter 6 Introduction to Coverage Cases

6.1 Case I An Omnidirectional Antenna Preset with a Downtilt Angle Is Used

Fault descriptionA suburb omnidirectional BTS uses a Katherin/11dBi (gain) omnidirectional antennawith longer coverage distance: The limit distance toward flat terrain can reach 9km.However, the coverage is not so wider in areas nearer to the BTS: In a small town800 to 1400m away from the BTS, it was measured that the Rx level is about -90dBm.

Fault analysis and disposalAfter on-site survey, it was found that the antenna installation height of the BTS wastoo greater, the iron tower for installing the antenna was 50m high and the tower is

built on a small hill, so the height difference between the antenna and the town wasclose to 120m. Therefore, we judged that this was the Dark under towerphenomenon of an omnidirectional antenna. After further analysis based on the datacollected, the antenna for this BTS was a Katherin omnidirectional antenna, theantenna gain was 11dBi and the vertical half power angle was 7. Calculatedaccording to the effective antenna installation height 120m, the place where the halfpower angle of the main lobe of the antenna fell to ground was about 2000m from theBTS. Therefore, we judged that the town was beyond the coverage of the main lobeof the antenna. Then, we observed the fluctuation of the Rx levels according to thedrive test map, and estimated that the town just fell to the radiation range of a zeropower point of the antenna. Furthermore, due to the greater distance from thesurrounding mountains, the BTS could not rely on the compensation of reflectionsignals, so the Rx level in the town was very low.

We replaced the original antenna with an omnidirectional antenna with a preset downtilt angel of 5 and tested again. It was found that within 3km, the measured Rx levelwas increased by 15~20dB. The Rx level was even increased by 30dB in some areas.The improvement was very obvious.

Before modification

After modi ficati on

Driv e test diagram for BT S coverage lvel

AncienttownH

Distance

Total

Figure 6-1 Effective pattern of level test before and after antenna replacement


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6.2 The Antenna Shaping Technology Is Used

Fault descriptionAfter a BTS was cut over, the town government complained that the signals were too

weak, they could not make calls indoors, although the BTS was not far away from thetown government.

Fault analysis and disposalAfter test, it was found that signals in other areas of the town were distributednormally. However, signals in the town government near the BTS were notsatisfactory. The outdoor signal was about -85dBm, but the indoor signal drops to -95~100dBm. It was observed that the antenna height of the BTS was 80m and theantenna installation was normal. We doubt that possibly the town government wasexactly in the zero point coverage position of the antenna. The BTS antenna was an

ANDREW 11DBi omnidirectional antenna. We replaced it with a zero filling antennaand tested again, and it was found that the field strength had increased by about20dBm. Thus, the fault was removed.

6.3 Installation Fault of an Omnidirectional Antenna

Fault descriptionA user complained that after a new BTS for a local network was cut over, thecoverage distance was shorter and the 2KM signal was less than -90dBm in flatterrains.

Fault analysis and disposalAccording to the complaint of the user, we went to the new BTS. In a place about2KM from the BTS, the test MS showed that the field strength was about -95dBm,and the surrounding terrains were relatively flat. The BTS really did not meet thecoverage requirements.

After arriving at the BTS, it was found that the planes of the main Tx antenna anddiversity Rx antenna the BTS were in parallel with the highway and furthermore, themain Tx antenna was installed in the opposite direction to the direction in which wecame. Obviously, such installation did not meet the engineering installationspecifications.

The correct installation is shown in the right half part of Figure 6-2.


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Highway

Highway

Figure 6-2 Installation position of an omnidirectional antenna

6.4 Uplink Loss Increase Caused by Combiner

Fault descriptionA user complained that a village facing cell 2 of a 312 BTS could not make phonecalls, but the MS could receive signals near the highway at the end of the village andcould make calls barely enough. The highway was about 50M from the village. Theuser required that the coverage of the BTS should reach the village. On the site, weunderstood that this village was on the edge of the coverage of cell 2. When an MS

was connected, the TA value was generally above 10. The terrains were verycomplicated, the village was in a cove and the received signals were signals reflectedby the mountains. The configuration of cell 2 was as follows: 2 TRXs, 1 CDU, a triplexTTA (main) and a simplex TTA (diversity) for the antenna feeder, single polarizationantenna, the antenna gain is 17dBi and the antenna installation height is 34M.

Fault solution:

1. After on-site survey, it was found that there was not much space for adjusting thedown tilt angle of the antenna.

2. Considering the actual situations, we determined to change the configuration of cell2 to improve the coverage. First, we used 1 TRX (60W) and 1 CDU. The TRX wasconnected to the TX_DUP port of the CDU. Thus, the uplink signal was increased byabout 4 dB. After test, it was found that the signals could cover the village, but were

not so good. There were signals in the village 20M from the highway, but it wasdifficult to make conversation. Then, we used the configuration of 1 EDU + 1 PBU +1 TRX (40W). Since power of the RF signal from the PBU was 80W without anycombining loss, the downlink signal was improved by about 6dB, compared to theoriginal configuration of 2 TRX + 1CDU. We also upgraded the BTS version from03.0529 to 05.0529 to improve the uplink sensitivity and performed test. The testresult showed that the BTS could meet the call conditions and subscribers in thevillage could make calls normally.

3. However, on the next day, the user complained that MSs had signal indication of 2to three bars in the village, but when a subscriber made a call, the subscriber couldonly hear two toot tones and then call drop occurred. On-site test indicated that therewere -85dB to -95dB signals in the village, but subscribers could not make outgoingcalls and even more, the subscribers could not make outgoing calls normally on theside of the highway at the end of the village where they could make call originally.


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After remote wireless interface tracing, it was found that severe uplink/downlinkunbalance occurred to the cell, with a difference about 20 dBm. However, the tests inrecent several days had indicated that the existing equipment could meet thecoverage requirements. Based on the analysis according to the present situations,we judged that the uplink could not meet the requirements and some fault had

occurred to the uplink Rx channel. Where, the uplink Rx channel mainly includedwireless channel, antenna, TTA, feeders, jumper and connectors, CDU, RF cablesand connectors, TRXs, etc. Therefore, we should use the exclusive method toremove the fault points.

(1) Wireless channel and antenna: Uplink and downlink are consistent, so the faultpossibility is lower.

(2) TTA: Check whether the data configuration is complete. Possibly the TTA wasburned.

(3) Others: On-site test is necessary.

4. Check the Antenna Feeder Configuration Table, it was found that the option of

TTA available/not available in the table was set to TTA available and the powerattenuation factor was set to0. According to the requirements, after a TTA is used,the power attenuation factor should be set according to the feeder loss. In principle,the power attenuation factor = TTA gain Feeder loss. Where, the gain of a simplexTTA should be 14, the gain of a duplexer TTA should be 14 and that of a triplexshould be 12. For a BTS using the CDU system, set the power attenuation factoraccording to the above-mentioned TTA gain and feeder loss and adjust the CDU gain.If the power attenuation factor is still set to zero when a TTA is used, small signals willbe easily blocked and the coverage will be affected. The loss for a 34m feeder and aconnector jumper is about 3dB. Set the power attenuation factor to 9. The dynamicsetting of the antenna feeder configuration table does not need fill-in of command lineparameters. After modifying the antenna feeder configuration table, set the entire

table to BSC and then just reset the related site.

5. We modified the Antenna Feeder Configuration Table and then performed test, andit was found that relatively severe uplink/downlink unbalance still existed in cell 2.Considering that at the beginning when the card was replaced, the TTA current wasset to too great a value, which led to the generation of a TTA current alarm. Andfurthermore, the RF connection cable from the EDU to the top of the cabinet might betwisted due to multiple tests. Therefore, we tested the antenna feeder part of the EDUegress. Since the uplink of the village facing the current cell 2 was worse than that ofthe original 1 CDU + 1TRX (60W), the original CDU and 1 TRX (60W) could bereplaced to test whether the antenna feeder part of the CDU egress had failed. Theoriginal CDU and 1 TRX (60W) were used for cell 2 and meanwhile the TRX wasdirectly connected to the TX_DUP port of the CDU (such that the combining loss ofthe Tx channel could be reduced by 3dB). On-site test showed that Outgoing callscould be made on the side of the highway at the end of the village, so we judged thatthere was a low possibility that the antenna feeder Rx channel had failed after the

CDU egress.

6. Thus, we located the fault to fall into the part between the EDU and the TRX, so itwas necessary to test the EDU, TRX and the RF Rx cable between them. On the site,we first replaced the TRX and the RF Rx cable and then performed test. The testresult showed that the uplink performance was not improved at all. Then, we used 1TRX (40W) + 1 PBU + 1 CDU (100W) (since no EDU was available, so we used a100W CDU to replace the EDU) and tested the EDU. The test result showed that thedownlink coverage was the same as that when the original EDU was used, i.e.,subscribers in the village now could make outgoing calls smoothly and the coverage

also met the requirements.

7. Finally, the test result showed that the Rx channel of the EDU had failed, which led

to greater uplink signal loss and severe uplink/downlink unbalance in this cell.


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6.5 Poor Uplink Coverage Caused by TRX

Fault descriptionA BTS had been cut over and put into operation for about one or two years in an area.

Suddenly the user complained that sometimes it was difficult for subscribers to makecalls near the BTS. Subscribers often could not make outgoing calls or call drop oftenoccurred. The probability of such fault was relatively high. This BTS was a BTS20.

Analysis based on the traffic statistics showed that in the two or three days when theuser complained, the TCH congestion rate in the cell suddenly increased (as high as41%), the call drop rate was 28% and the TA value is about 1 when call drop occurred.In this case, we emphasized on the check of TRX uplink/downlink balancemeasurement. It was found that the TRX statistics of non-main BCCH frequencies inthis cell was abnormal. In uplink/downlink statistics, the normal TRX statistic ruleshould be sequential decrease from level 1 to level 11. However, the uplink/downlinkstatistics of this TRX card showed that the statistic times of level 11 was far greaterthan that of level 1. According to the definition of traffic statistics, the cause was thatthe uplink signal strength was far less than the downlink signal strength. Thus, it could

be judged that the performance of this TRX card had been deteriorated after runningfor a period of time.

Fault solution:

1. We conducted remote traffic statistics analysis and judged the fault cause. It wasjudged that the TRX card had failed.

2. We blocked the so-called faulty card at the far end and observed the trafficstatistics for three or four hours, and it was found that the traffic statistics of the cellwas normal: the congestion rate was less than 3% and the call drop rate was lessthan 1%.

3. The local maintenance personnel carried a TRX card and replaced the faulty one

at the near end. After the TRX card replacement, calls were normal in drive test.

4. Continuous traffic statistics observation did not show any fault again.


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OMF005002 Coverage Fault Analysis ISSUE1.0 Chapter 7 Appendix A Signal Strength Indication of MSs

Chapter 7 Appendix A Signal StrengthIndication of MSs

In idle state, an MS displays the Rx level of the BCCH in the service cell; in busy state,it displays the Rx level of the TCH channel. There are not unified standards for theindication of signal strength (number of bars). Each manufacturer has its ownspecifications. According to large numbers of tests of mainstream MSs in the marketby Huawei, the corresponding relationship between the level strength of MSs and thenumber of bars displayed is as follows:Relationship between the level strength of MSs and the number of bars displayed

MS type Level strength (dBm)5 bars 4 bars 3 bars 2 bars 1 bar

NOKIA 8210 and 3210 None >-85 -85~-90 -90~-95 -95~-100Samsung Anycall-600 >-85 -85~-90 -90~-95 -95~-100 -100~-

105

Motorola-L2000 >-80 -80~-90 -90~-95 -95~-100 -100~-105

Motorola-7689 >-80 -80~-90 -90~-95 -95~-100 -100~-105

Motorola-CD928 >-85 -85~-90 -90~-100 -100~-105

-100~-105

Siemens 3518i None >-70 -70~-80 -80~-90 -90~-100PHILIPS-Xenium969 None >-80 -80~-90 -90~-100 -100~-

110

Ericsson T28SC >-75 -75~-85 -85~-90 -90~-95 -95~-105Ericsson T18SC6 bars>-70dBm -70~-75 -75~-85 -85~-95 -95~-100 -100~-105SAGEM >-80 -80~-90 -90~-95 -95~-105 -110~-

105

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OMF005002 Coverage Fault Analysis ISSUE1.0