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  • 8/2/2019 Chapter9 Network Optimization


    Wireless Network Planning Table of Contents

    Table of Contents

    Chapter 9 Network Optimization ............................................................................................ 1

    1.1 Process of Network Optimization .............................................................................. 1

    1.2 Common Tools Used in Network Optimization ......................................................... 3

    1.2.1 ANT Drive Test Equipment.............................................................................. 3

    1.2.2 Signaling Analyzer ......................................................................................... 4

    1.2.3 Spectrum Analyzer ......................................................................................... 4

    1.2.4 Network Optimization Software ....................................................................... 4

    1.3 Wireless Network Problems Positioning and Solving .................................................. 6

    1.3.1 Obtaining Basic Information ........................................................................... 61.3.2 Coverage ....................................................................................................... 7

    1.3.3 Capacity ........................................................................................................... 8

    1.3.4 Interference .................................................................................................... 9

    1.3.5 Handover .................................................................................................... 10

    1.3.6 Call Drop .................................................................................................... 10

    1.4 Problem Positioning according to Network Indices .................................................. 12

    1.4.1 TCH Call Drop Rate ..................................................................................... 12

    1.4.2 TCH Congestion Rate .................................................................................. 16

    1.4.3 SDCCH Call Drop Rate .............................................................................. 17

    1.4.4 SDCCH Congestion Rate ........................................................................... 17

    1.4.5 Rate of Handover Completion ....................................................................... 18

    1.4.6 Traffic Analysis ............................................................................................ 20


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    Wireless Network Planning Chapter 9 Network Optimization

    Chapter 9 Network Optimization

    Network optimization serves for the pursuit of a maximum application of networkresource and a maximum improvement of QoS. Meanwhile, it also contributes tofoundations and principles for future network expansion. Optimization here refers tooptimization based on a sound implementation of network planning. In this sense,optimization is a supplement to the aspects failing to be taken into adequateconsideration or resource adjustment for burst situations as suggested in a largetraffic burst. Generally, drive test, traffic statistics and subjective perception on the partof human are taken as the basis for optimization, moreover signaling tracking andanalyzing almost plays a crucial role in solving difficult problems.

    1.1 Process of Network Optimization

    The mobile communication network of GSM generally falls into Mobile Switching-Transporting Part and Radio Part. Due to the mobility of subscribers and thecomplexity of radio waves in propagation, the Radio Part always becomes thedecisive factor affecting the QoS of the GSM network. Wireless network optimizationrefers to reasonable modification to planning and designing of communicationnetworks according to certain principles so that a more reliable, more economicnetwork operation, a higher QoS, and a higher utilization ratio for network resourcecan be achieved. Undoubtedly, this is of great significance for network operators andsubscribers. Procedures for network optimization are as follows:

    Preparatory Work

    Obtaining Basic Information

    of Network on Site

    Does it meet the

    performance indices?

    Network Optimization Report



    Drive Test and Traffic Statistics


    Data Analysis

    Network Parameter Modification

    Preparatory work at early stage include obtaining knowledge of progressive status innetwork construction, analyzing the operation status of network, preparing for

    optimization test equipment and software, network planning report, collection ofengineering and designing documents, etc. Obtaining of basic network information at


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    site include further inspections on local radio environment, hot spots of traffic,confirmation of engineering parameters and network indices for practical installation,communication with customers to understand specific demand of customers. Datacollection covers subjective reflection of mobile subscribers, data collection in drivetest, OMC data collection, etc. Data analysis include background analysis of

    optimization software, OMC traffic statistical analysis, tools for network optimizationanalysis, etc. Network Parameter modification includes network engineeringparameter modification and network function parameter modification. Networkperformance indices are in conformity with the General Indices of State Standard.Network Optimization Report covers measures used in this optimization, networkperformance indices expected, and positive suggestions for network development.


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    1.2 Common Tools Used in Network Optimization

    1.2.1 ANT Drive Test Equipment

    ANT software can be used in re-selection test with mobile station in idle state,frequency scanning test, timed call-up test, continuous connection test, etc. Throughsimulating the actual state of subscribers in practical application, field intensitydistribution, Carrier-To-Interference Ratio, voice quality and other on site data can beobtained. Meanwhile, the actual installation status of antenna and feeders can also beverified. Various test measures can be applied in combination with others according todemand. According to test result, modification to system parameters, antenna statusshall be implemented accordingly. Among them, modification to system parametersmainly covers modification to transmission power, frequency configuration, handover

    level, parameters of adjacent cells, traffic load, the numbers of SDCCH and TCHchannels for configuration, etc. Modification to antenna state has an important effecton coverage improvement and interference reduction. It mainly covers adjustment toantenna height hanging on masts, azimuth, down tilt, etc. Functions of ANT testsoftware are mainly as follows:

    I. Supports Multimode Test

    ANT optimization software supports frequency scanning and call connection test in fullfrequency band. In two-handset-test mode, the software supports dual network testand interference test.

    II. Real-time Graphic Description Window

    In idle state, the ANT Optimization software can display real time BCCH field intensityand main information of the host cell and six neighboring cells. In connection mode, ANT optimization software can also display real time handover behavior and allindices of connection quality.

    III. Geological Positioning Function

    ANT Optimization Software applies high precision GPS in geographical positioning.Path of drive test and all performances of a handset (as Call Drop, handover failure,assignment failure, etc) can be displayed in real time icons. In background analyzing,data playing-back, problem positioning and geographical representation of all indices

    can be implemented.

    IV. Data Analysis and Statistical Function

    Background analysis of ANT optimization software cover Blind Zone of networkcoverage, lonely island positioning, co-channel interference and adjacent channelinterference, frequency scanning analysis, etc. According to users demand, ANToptimization software can automatically create wireless measurement and statisticalreport including interference statistics, wireless indices statistics, system performanceevaluation, and engineering parameter inspection.


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    1.2.2 Signaling Analyzer

    Signaling Analyzer MA-10 can be used in on-line test of the ABIS interface signalinginformation, A-G interface signaling information, SS7 interface signaling information

    of ISUP, TUP, and INAP. It can also be applied in testing of error code covering PCMBERT and GSM BERT in transmission routes and analyzing in background offlinestate by opening the signaling information files. There are five sub applicationprograms in MA-10 Test Software. Respectively they are MA-10 Control (on-line testof interface signaling for ABIS interface, A-G interface, and error code), MONITORABIS offline (ABIS interface signaling analysis offline), MONITOR MSC offline (A-Ginterface signaling analysis offline), GSM-BERT offline (error code inspection andanalysis offline), PCM-BERT offline(error code inspection and analysis offline).

    With Signaling Analyzer MA-10, a network optimization engineer can collect andanalyze data of Abis interface and A interface, survey the complete process ofsignaling connection, extract survey report, and carry out contrastive study of thesedata against downlink signal collected from drive test (This ingenuous use of timepoints as indices and a combined application of latitude and longitude stored in

    equipment for downlink drive test can generate a uplink coverage graph and qualitygraph), so that the operation state of the entire network can be obtained. In this way,major causes and locations of Call Drop, handover failure, traffic congestion and otherproblems in a cell can be spotted.

    1.2.3 Spectrum Analyzer

    A spectrum analyzer is mainly used in test of attributes of a frequency domainincluding spectrum, power of adjacent channels, quick scanning of time domain,spurious radiation, inter-modulation attenuation, etc. A spectrum analyzer is frequentlyused in network optimization to carry out electromagnetic background test. Thefollowing example presents the HP E4402 in application.

    In electromagnetic background test, a small omni-directional antenna can beconnected to the spectrum analyzer to implement broadband omni-directional test. AsHP E4402 is equipped with a built-in pre-amplifier, no external amplifier is needed. Atthis time, scanning frequency of the spectrum analyzer is generally set in 880 960MHz900MHzor 17001890MHz1800MHz. Reference level can be setas 0dBm and amplitude of each line as 10dBm. Shall a signal be detected, scanningbandwidth will be narrowed down according to frequency band of the signal, andreference level, amplitude of each line, and resolution bandwidth will also be properlymodified to carry out a detailed analysis of the signal.

    Signal positioning is similar to this operation. The only difference between the two liesin that the omni-directional antenna is changed into a directional antenna. By swingingthe directional angle and watching the magnitude of the signal, location of the signal

    can be spotted.

    1.2.4 Network Optimization Software

    Network Optimization Software is a kind of application software. It can, in a properway to indicate statistical data of calls, to assist commission and maintenancepersonnel and network optimization personnel in spotting network problems. SoftwareInput includes configuration data of Data Management Terminal, traffic statisticalresults and commissioning engineering data recorded in BSC Traffic StatisticalTerminal. Data output of the software is in diagrams and tables along with failurespotting and suggestions for solutions. In addition, the output also supports flexiblereport forms.


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    Functions of general network optimization software shall be as follows:

    Introduction of Traffic Statistical data, configuration data, and networkplanning data

    Display of digital map in geographical representation

    Trend representation with flexible customization

    View Traffic Statistical result: Multi-functions and View with self-defining configuration

    Data Filter: automatic detection of unusual points and indicate ingeographical representation

    Index analysis and failure diagnose.

    Free report function covers self-defined report, template management,report preview, lead into and out of report, report in any format, creationof report across BSCs.

    Parameter Analysis includes, but is not limited to co-channel searching,neighboring channel searching, BSIC searching, CGI agreementinspection, neighboring cell searching and geographical representation

    Function of Experience Lab

    Engineering Management

    Good optimization software can adequately act as everyday work platform for radioengineers and maintainers (supervisors and optimizers). HUAWEI possesses a self-developed Optimization software SNA.


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    1.3 Wireless Network Problems Positioning and Solving

    1.3.1 Obtaining Basic Information

    The purpose of obtaining basic information of a network lies in finding out possibleaspects with problems and making out a test plan and an optimization plan accordingto actual situations so as to avoid blind operation.

    Firstly, a familiarity with planning state of earlier stages is prerequisite. To this end,document for earlier stage network planning is needed. The documents may includeplanning report, table of engineering parameters, network topology, report forfrequency planning, report of cell parameter design, etc. This may offer a general ideaof the network. Distinctive problems can also be detected from it.

    Secondly, progressive status of the present project is also needed. For example,status of base station installation completion, modifications to planning, especiallythose to engineering parameters, state of commissioning and simple drive test.Special attention shall be paid to network loophole caused by engineering erectionquality or progressive status. The example suggested in handover failure andinterference in large areas caused by uncompleted construction of base stations orerection errors is a good case in point.

    The following cases of optimization all refer to optimization after a sound earlier stageplanning and a good implementation of the planning. In optimization practice,however, there are always installation problems and hardware problems as suggestedin installation of antenna in opposite directions, problems with some carriers of basestation, etc. This optimization is a continuous effort of error correction. No more

    details will be accounted here.

    I. Traffic Statistical Data

    From major indices including TCH Call Drop rate, TCH congestion rate, SDCCH CallDrop rate, SDCCH congestion rate, handover completion rate, network operationstatus can be understood.

    With traffic volume on the network, traffic statistical data is an important method tounderstand network performance.

    II. Drive Test Data

    For a network in commissioning, an extensive drive test shall be carried out tounderstand the network status when traffic volume becomes very low or nil. Ifnecessary, transmission function of idle BURST in the base station can be started tostudy the downlink interference status under high traffic simulation. Necessaryadjustment shall be furnished for practical problems.

    Shall failure be proved within a specific area according to traffic statistics, a practicaldrive test in this area can be used to confirm the failure a step further so that propersolution may be adopted.


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    III. An Overall Knowledge of Network Coverage, Interference State, Traffic


    IV. Subjective Sense

    Possible problems of the network can be judged from complaints of customers,suggestions of telecom companies, subjective senses of engineers on site, etc.

    1.3.2 Coverage

    Range of cell coverage is one of the important indices in QoS evaluation for GSMnetworks. Major factors affecting coverage are as follows:

    I. Blind Zone for Signals

    A Blind Zone results from no overlapping between coverage areas of two basestations or no overlapping caused by obstructions.

    Should there are more subscribers in the non-overlapping area of two base stations,or dimension of the area is relatively bigger, construction of a new base station isexpected. Increasing the coverage range of these two base stations (as the casesuggested by increasing transmission power, height of antenna) so that theoverlapping depth of coverage may reach a level of 0.27R (R here refers to radius ofthe cell). Meanwhile, care should be taken to possible co-channel interference andadjacent channel interference caused by coverage expansion.

    (2) A Blind Zone caused by valley and back hillside can be recovered by constructingnew base stations and repeaters in those areas. Repeaters can effectively recoverBlind Zones in coverage area and expand the scope of coverage. On the other hand,

    repeaters can also bring about inter-modulation interference, co-channel interferenceand adjacent channel interference to other cells. Therefore, interference should betaken into consideration in introduction of repeaters in application.

    (3) Blind Zones within tunnels, underground garages, and tall buildings can berecovered by introduction of repeaters, leak cables, or micro station technologies.

    II. Cross Cell Coverage

    In actual networks, signals emitted from high base stations can be transmitted on hillylandforms or along roads to places far way. Hence the island problem was created.When a call is connected into the island of a base station, which is far from the basestation, configuration handover in this cell may immediately result in Call Drop once

    the mobile station leaves this island area. To solve this problem, down tilt or gain ofthe antenna should be modified. Transmission directly along road should be largelyavoided so as to eliminate island effect by reducing the coverage of base stations.

    In coverage optimization, modification to azimuth and down tilt is often used tochange service range of the cell. Problem of Blind Zone caused by co-channelinference, adjacent channel interference and inter-modulation interference betweenTACS and GSM can be solved by eliminating interference.


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    1.3.3 Capacity

    I. Traffic Congestion

    With OMC traffic statistics data, TCH congestion rate can be obtained (withoccupation at all busy). It is also possible to judge the traffic congestion status bycomparing the busy hour traffic volume against calculation capacity of each basestation cell. For congestion cells, it is recommended that more carriers be added, orcell split, or construction of new base stations in common sites be adopted. It is alsoadvisable to adopt new dual frequency networks, micro cells, etc.

    II. Traffic Balance

    For some base stations with congestions, measures to ease the congestion are asfollows:

    (1) Modify the antenna height, down-tilt, transmission power of base stations andhandset.

    (2) Modify the configuration for part of parameters

    In overloaded areas, the minimum access level may be suitably increased andhandover threshold may be appropriately decreased to reduce traffic. Accordingly, theminimum access level may be properly reduced and handover threshold may beappropriately increased to increase traffic.

    Moreover, by setting CBQ and CBA of low traffic cells, these cells may be assignedwith higher selection PRI. A suitable increase in CRO can make it more easily for thecell to be re-selected.

    (3) Start-up Load Handover and Directional Retry


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    1.3.4 Interference

    PLMN cellular system makes use of frequency multiplexing to improve application

    efficiency of spectrum and to increase system capacity. Meanwhile, it also brings forthco-channel interference and adjacent channel interference (This is called internalinterference of the system.) In addition, there are also interferences caused by Multi-path Effect and external factors of the network as the interferences of TACS andrepeaters.

    I. Interference Positioning

    GSM is a dual system with a difference of 45MHz between uplink frequency anddownlink frequency. There might be interferences in both uplinks and downlinks.Downlink interference can be measured with instrument for drive test by maintainingthe conversation status. Level of voice quality can be used in positioning. Voicequality are of 7 levels. Corresponding bit error rates are listed in Table 3-1. General

    requirement of voice quality shall not be lower than 3, i.e. the code error rate shall beless than 1.6%.

    Table 3-1 Relational Correspondence between Signal Quality Level and Error Rate

    RxQual class Mean Ber (%) Ber range

    0 0.14 12.8%

    Uplink interference can be positioned with the numbers of interference bands and CallDrop rates in HUAWEI OMC traffic statistics terminal. Interference band is anindication of idle TCH levels of 5 grades in all. Level ranges can be set through DataConfigurationTerminal. Look at the following example:

    Table 3-2 Level Range of Interference Band

    Interference Band 1 -110 -105dBmInterference Band 2 -105 -98dBm

    Interference Band 3 -98 -90dBm

    Interference Band 4 -90 -87dBm

    Interference Band 5 -87 -47dBm

    Generally, shall idle channel fall into Interference Band 4 and Interference Band 5continuously, it can be determined that there exists interference.

    Beside, measurement report for uplink and downlink can be viewed from SignalingAnalyzer MA-10 connected to ABIS interface. In this way, uplink interference and

    downlink interference can also be positioned.


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    II. Ways to reduce interference

    (1) Increase the distance between two adjacent cells of the same or neighboringfrequencies;

    (2) Decrease transmission power of base stations;

    (3) Modify antenna height;

    (4) Modify azimuth of the antenna;

    (5) Modify down tilt of the antenna;

    (6) Optimization of frequency configuration;

    (7) Start-up of anti-interference techniques used in GSM as Power Control,Discontinuous Transmission, Frequency Hopping, etc.

    (8) Due to non-linearity feature of TACS-TX amplifier, inter-modulation interferencemay be generated (as tertiary interference). Shall the signal be in the bandwidth of

    GSM receiver, it may have interference on the GSM receiver. Shall the TACS andGSM share a common site, inter-modulation interference may also be created. Inter-modulation reduction may be accomplished by increasing the transmission power ofGSM downlink and optimizing the frequency configuration.

    1.3.5 Handover

    When a mobile subscriber moves from one cell into another, handover mustbeimplemented. Otherwise, voice quality may be greatly reduced. In some cases,even Call Drop may occur. Frequent handover problems include voice qualitydeclination or Call Drop caused by handover failure and handover delay, voice qualitydeclination and system load increase caused by frequent handovers, unbalance

    traffic caused by unreasonable ratios of outgoing and incoming handovers.

    Drive test equipment can be used in testing of continuousconnection, tracking ofhandover failures, handover delays or frequent handovers, etc. With OMC trafficstatistical data, handover completion ratio, incoming and outgoing handover ratio ofthe cell can be analyzed.

    Causes and resolvent of abnormal handover are as follows:

    (1) Handover threshold configrated too low

    (2) Congestion in adjacent cells, no idle channel available

    (3) Configuration of relation with neighboring cells missing

    (4) Handover hysteresis and handover priority configuration inappropriate

    (5) Configuration for the best statistical time N, P inappropriate

    (6) Networking in combination with other cells consisting of products by othermanufactures, parameters of these external cells must be secured correct. Theseparameters cover LAC, CI, BCCH, etc.

    1.3.6 Call Drop

    In GSM network operation, Call Drop has been the hot spot of complaint fromcustomers. Call Drop here refers to Call Drop after distribution of traffic channels.There are various causes of Call Drop with the direct ones as field intensity,interference, and inappropriate configuration for parameters.


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    For our products, there are two critical parameters affecting Call Drop. One is radiolink timer failure for downlinks, the other is the number of SACCH multi-frames foruplinks. These two parameters shall be suitably configured according to traffic volumeand coverage.

    Causes of Radio Link Failure are as follows:(1) When the mobile station enters into a Blind Zone for field intensity coverage, CallDrop may result from RF factors.

    (2) Internal or external interference of the network may result in SACCH framedecoding failure. This further leads to CallDrop.

    (3) When a mobile station approaches cell boundary in driving, the mobile stationrequests for handover. As the definition for neighboring cells was lost, or there arecongestions in neighboring cells, there would be no cells available for handover. Thisfinally leads to a CallDrop.

    (4) With imbalance between uplinks and downlinks, a handover may result inCallDrop. For example, take the mobile station is in CELL 1. There exists imbalance

    between uplink and downlink in the neighboring cells, CELL 2 (suppose that there aregood downlinks but very weak uplinks.). According to downlink level, the mobilestation then makes out the sequence of cells to for incoming handover. The mobilestation may be directed into CELL 2. After the handset is directed into CELL 2, CallDrop may occur due to bad uplink.

    There are also Call Drops caused by non-radio link reasons as Abis interface failure, Ainterface failure, etc.


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    1.4 Problem Positioning according to Network Indices

    An important method to testify the effectiveness of optimization effort is to inspectmajor network indices covering TCH Call Drop rate, TCH Congestion rate, SDCCHCall Drop rate, SDCCH congestion rate, handover completion rate, traffic volume, etc.These indices can be expertly used in the analysis of network operation status.

    In analyzing traffic statistical indices, the first thing to be made clear is whether thereare cells with abnormal indices. Should there be, the abnormal cells must be analyzedone by one. In view of the seriousness caused by abnormal indices, major indices canbe basically arranged in the order importance as follows: TCH Call Drop rate, TCHcongestion rate, SDCCH Call Drop rate, handover completion rate, etc. Interferenceand coverage, however can affect many other indices at the same time, as manyindices are inter- related. Shall the problem of low handover completion rate beproperly solved, Call Drop may be improved to a certain extent. Therefore, in practical

    analysis and solution of a certain problem, effort may be focused on a certain indexwith combination of others.

    1.4.1 TCH Call Drop Rate

    Causes of high rate of call drop are as follows:

    (1) Interference (network internal interference, external interference, interference fromthe equipment itself.)

    (2) Bad coverage (Blind Zones, Lonely Islands)

    (3) Inappropriate handover (planning of adjacent cells, handover parameters.)

    (4) Imbalance between uplinks and downlinks (Tower Amplifier, Power Amplifier,Antenna Direction)

    (5) Inappropriate Parameter configuration (Counter for radio link failure, number ofSACCH multi-frames

    (6) Equipment problem (Carrier board, Power Amplifier, Tower Amplifier)

    Each factor will be analyzed as a subject as follows

    I. Interference (network internal interference, external interference)

    Judgment :

    (1) Analyze the regular patterns of interference band in traffic statistics

    With more than one idle channel presented in interference band three, four, and five,a judgment can be passed that there is interference in a general sense. Shall theinterference be an internal one, it generally increases with the increase of traffic.Usually, an external interference bears no relations with traffic volume. It shall also benoted here that interference band is reported uplink to BSC via RF resource indicationmessage by carrier channels of base stations in idle state. With busy channels atpresent, resource indication message becomes difficult to be reported uplink. Theinterference band statistics shall be considered in a comprehensive approach.

    (2) Measurement of receiving level performance (A matrix indicating relationshipbetween level and quality is expected.)

    This is a statistical task specifically for carriers. If there are too many high levels of low


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    quality, it suggests that there are co-channel interference, adjacent channelinterference, or external interference for the frequency band of this carrier board.

    (3) Proportion of bad Quality Handovers

    In the measurement of cell performance / the measurement of inter-cell handover

    performance , or in the measurement of outgoing cell handover performance, numberof attempts for outgoing cell handover caused by all sorts of reasons was recorded intraffic statistics. Shall there be too many handovers caused by bad quality, it suggeststhat there is interference. More handovers caused by bad uplink quality suggestsuplink interference. More handovers caused by bad downlink quality suggestsdownlink interference.

    (4) Measurement of receiving quality performance

    Specifically for carriers, the statistical data of average receiving quality will be madefor reference.

    (5) Measurement of Call Drop performance

    The average level and quality of Call Drop is recorded for reference.

    (6) Too many handover failures together with too many recovery failures.

    It is very possible that there is interference within the cell. This is for reference.


    (1) In actual drive test, check the road section with interference and inspectiondistribution of signal quality. Origins of overlapping signals causing interferenceshould be made clear in cells. According to actual status, interference can be avoidedby modifying the transmission power, down tilt of antenna, relations between adjacentcells, handover parameters, or frequency band planning of a cell concerned.

    (2) With a spectrum analyzer, interference frequency band can be detected. Source of

    interference can be spotted.

    (3) Adopt frequency hopping, DTX and power control.

    (4) Solve the equipment problems (as TRX self-excitation).

    II. Coverage (Blind Zones, and lonely islands)


    (1) Measurement of power control performance, the average uplink signal intensityand down link signal intensity are too low.

    (2) Measurement of receiving level performance, the ratio of low receiving level is

    detected too high.

    (3) In measurement of cell performance and performance of handover between cells,threshold level for handover prompt and average receiving level are detected too low.

    (4) In Call Drop Performance measurement, level at Call Drop too low and TAabnormal before Call Drop are detected.

    (5) Performance measurement of defined adjacent cells. Adjacent cell with too low anaverage level can be spotted.

    (6) The average level of a undefined adjacent cells is too high. There are too manysuch cells(lonely islands).

    (7) Performance measurement of defined adjacent cells. Average receiving level ofdefined adjacent cells is detected too high (excessive coverage).


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    (8) Measurement of power control performance, see if the average distance betweenMS and BTS is in conformity with design ideology.

    (9) Measurement of power control performance, see if the maximum distancebetween MS and BTS are overdue in several consecutive periods.

    (10) Performance test of outgoing handover from a cell, low handover completion rateinto a certain adjacent cell.


    (1) A drive test is recommended to be carried out in areas with estimated badcoverage.

    (2) Modify network parameter according to drive test. (transmission power of a basestation, down tilt and height of the antenna, minimum access level of handset,relations of adjacent cells, the minimum access threshold of handover candidate cells.

    (3) Increase base stations.

    III. Inappropriate handover (planning for adjacent cells and parameters for



    (1) Check the handover parameter. See if there is inappropriate parameterconfiguration.

    (2) Performance measurement of handovers between cells. More handover failurestogether with more recovery failures are detected.

    (3) Performance measurement of handover between cells. Too many handoverstogether with too many recovery completions are detected.

    (4) Performance measurement of undefined adjacent cells. Levels of undefinedadjacent cells are too high and the number of report for undefined cells goes beyondstandard.

    (5) Performance measurement for outgoing handovers: low rate of outgoing handovercompletion out of a cell (for a specific cell). Find out an adjacent cell with low incominghandover completion rate so that causes can be further detected from target cells.

    (6) Low rate of incoming handover completion. Inappropriate parameter configurationfor counterpart cells is detected.

    (7) TCH Performance measurement: Times of handover is not in proportion to timesof TCH call occupation completion. (handover/call>3)


    (1) Add appropriately adjacent cells.

    (2) Modify handover parameters.

    IV. Imbalance between uplinks and downlinks (Tower Amplifier, Power

    Amplifier, antenna direction.)


    (1) Register measurement for balance performance between uplinks and downlinksin traffic statistics. Analyze if there really exists imbalance between uplinks and



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    (2) Register Call Drop Performance Measurement in traffic statistics. Analyze thelevel and quality of uplinks and downlinks at Call Loss.

    (3) Register Power Control Performance Measurement in traffic statistics. Analyzethe average receiving level of uplinks and downlinks.


    (1) Check Tower Amplifiers and Power Amplifiers. Specifically for Tower Amplifierswith alarm, the test may be focused on the Tower Amplifiers with alarm. Currentvalues should be the main concern.

    (2) Check to see if the antenna direction is in accordance with design direction.

    (3) Check to see if it was caused by combiner alarm.

    (4) Check the MA-10 measurement report.

    (5) Check the BSC data configuration (Handset, transmission power of base stations,minimum access level of the handset.)

    V. Inappropriate configuration of radio parameters (counter for radio link

    failure, number of SACCH multi-frames.)

    Positioning of Problems:

    Check configuration for parameters concerned:

    System information data sheet: counter for radio link failure.

    Sheet of cell attributes: number of SACCH multi-frames, timer for radiolink connection.


    Modify inappropriate configuration for parameters mentioned above.

    VI. Equipment problems (carrier board, Power Amplifier, Tower Amplifier)


    (1) TCH Performance measurement: times of A interface failure abnormal with TCHoccupation.

    (2) TCH Performance measurement: TCH application ratio abnormal.

    (3) TCH Performance measurement: too many times of Call Drop and interruption onground link failure.

    (4) Shall Call Drop rate and congestion rate of this cell remain high, there might beproblems with part of the equipment.


    (1) Watch over transmission and board alarm (TC board failure, Alarm for PCMsynchronization loss at A interface, LAPD broken link, Power Amplifier board, HPA,TRX board alarm, CUI/FPU alarm). According to alarm data, analyze to see if there istransmission break or board failure (as suggested by carrier board failure or poorcontact.)


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    1.4.2 TCH Congestion Rate

    Main reasons of high TCH congestion rate are as follows:

    (1) Inadequate system capacity

    (2) Too much interference

    (3) Coverage

    (4) Handover reason

    (5) Inappropriate parameter configuration (system information)

    Every factor will be analyzed as a topic:

    I. Inadequate System Capacity or Traffic Imbalance


    (1) Too high a traffic for each line (DGT specifies that a cell with a traffic load greaterthan 0.8 per line is taken as a super busy cell. A cell with traffic load smaller than 0.1is taken as a super idle cell.)

    (2) With an applicable rate of 100% for channels, when there are too many times ofoccupation at all busy, there will be a long term all busy.

    (3) Traffic imbalance (inspect traffic imbalance between three sectors of a basestation or between several stations)

    (4) In performance statistics of incoming handover into a cell, there are too manyhandover failures because of congestion.


    (1) Capacity expansion or modification to carrier configuration between busy cells andidle cells.

    (2) Modify the cell coverage (modify transmission power of base stations, modifyazimuth, down tilt, and height of antenna.)

    (3) Modify major indices of cell (modify CRO, modify the minimum access level forhandsets, start-up load handover, modify cell priority, modify cell handoverparameters).

    II. Interference (network internal interference and external interference)

    TCH congestion rate falls into two parts. One is TCH occupation at all busy. Thisresults in real channel allocation failure and further leads to channel request failure.The other one is channel assignment failure caused by various reasons after theassignment command being sent out.

    Times of TCH occupation failure (including handover)--times of TCH occupation at allbusy, i.e. channel assignment failure caused by non-assignment availability factors.With too many occupation failures, there is possible interference within the network.

    Judgment and solutions:

    Refer to judgment and solution to interference in TCH Call Drop.


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    III. Causes of Handover (imbalance between incoming handovers and

    outgoing handovers)


    (1) Times of handover is not in proportion to that of TCH call occupation completion (3handover/call specifically for the cell)

    (2) Times of incoming handover is far greater than that of outgoing handover (thisresults in traffic imbalance).


    Modify handover parameters.

    IV. Parameter Configuration Inappropriate


    Check the handset configuration for the minimum access level.


    Modify the inappropriate parameter configuration

    V. Coverage (Blind Zones, lonely island)

    Judgment and solution:

    Refer to judgment and solution to coverage in TCH Call Drop rate.

    1.4.3 SDCCH Call Drop Rate

    For SDCCH Call Drop Rate, refer to analysis for TCH Call Drop Rate.

    1.4.4 SDCCH Congestion Rate

    Main factors causing high SDCCH congestion rate are as follows:

    (1) Inappropriate parameter configuration (system information)

    (2) Inadequate system capacity

    Each factor will be analyzed as a special topic as follows:

    I. Inappropriate parameter configuration


    Measurement of random access performance:

    Times of immidiate assignment completion (the sum of location update + the sum ofcalls and other reasons)/Times of immidiate assignment< 85%

    The above formula presents the ratio of handset report uplink est_ind againstimmidiate assignment command downlink. The ratio generally should be in the rangeof 8090%. With this ratio in abnormal, it suggests that there might be inappropriate

    configuration for relevant parameters.


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    (1) The ratio of immidiate assignment success is too low.

    (2) Ratio of location update times against times of all assignment instructions (toomany location update).


    (1) Parameter modification (threshold of random access error, RACH accessthreshold),maximum times for retransmission, the number of TS in transmissionexpansion.

    (2) Pay attention to parameter configuration for partition of location area and locationupdate (configuration for 1800MHz dual band network, CRO, cell reselectionhysteresis parameters, time for periodic location update, etc.)

    (3) In dual band networks, excessive location update may be caused by excessivehandover between mobile switch centers. Modification shall be made to handoverparameters of the 1800MHz dual network, CRO, etc.

    II. Inadequate system capacity

    Apart from factors mentioned above, there might be capacity problems. SDCCHconfiguration number shall be increased or dynamic SDCCH assignment function andTCH carrier shall be engaged.

    1.4.5 Rate of Handover Completion

    Subject for analysis: Adjacent cells with low rates for outgoing handover completionand service cell with low rates for incoming handover completion.

    First, judgment shall be passed onto the following issues according to inter cellPerformance measurement: Is the rate for incoming handover completion low? Is therate for outgoing handover completion low? Low rate of outgoing handover completionshall be further studied via cell Performance measurement to detect which is theadjacent cell with the lowest outgoing handover completion rate.

    Main reasons of low handover completion rate:

    (1) Inappropriate handover

    (2) Equipment failure (damage in certain carrier boards, etc.)

    (3) Congestion

    (4) Interference

    (5) Coverage

    (6) Imbalance between uplinks and downlinks

    (7) Clock problem (The base station changes into an internal clock, the upper clockbecomes unstable or the upper clock is overly floating.)

    In analysis, configuration of handover parameters, relations of adjacent cells, BTSsynchronization loss with BSC, and other problems can be eliminated in the firstplace. Further analysis may be carried out over other factors affecting low rate ofhandover completion.

    I. Inappropriate handover (planning for adjacent cells, handover arameters.)

    Position and Solution:


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    (1) Check to see if the configuration for handover thresholds of TA and BQ andhandover switch is appropriate.

    (2) Performance measurement of undefined adjacent cells: level and the number ofmeasurement reports of undefined adjacent cells exceed standard.Adjacent cells

    shall be suitably added.(3) In defining the Performance measurement of adjacent cells, defined adjacent cellswith few handovers can be spotted. These cells can be recommended to be deleted.

    (4) Times of handover is not in proportion to that of TCH call occupation completion.With handover/call>3, there might be ping-pong handovers. In this case, handoverparameters shall be inspected and modified. (Handover parameters includeconfiguration of layers, inter layer handover hysteresis, inter cell handover hysteresis,PBGT threshold, etc).

    (5)Inter cell handover Performance measurement: the average level for handoverprompt is detected too low. This may result from too low a handover thresholdincluding edge threshold in configuration.

    II. Equipment problem

    Subject for Analysis:

    A service cell with low rate of incoming handover completion and adjacent cells withlow rate of outgoing handover completion.

    Positioning of Problems:

    (1) There are channels being activated in target cells but NACK, TIMEOUT.

    (2) TCH availability abnormal.

    (3) Too many times of Call Drop and call interruption resulted from terrestrial linkproblem.

    (4) Shall Call Drop rate and congestion rate remain high in a cell, there might beproblems with part of the equipment.

    (5) Survey the transmission and board alarm (TC failure, A interface PCMsynchronization loss alarm, LAPD broken link, Power Amplification board, HPA, TRXalarm, CUI/FPU alarm) According to alarm data, see if there is a transmission failureor a malfunctioning board (as a carrier board failure or bad contact).

    (6) Check the provision of clock alarm.

    (7) Due to the fact that handover between base stations is limited by access level andquality, care shall be taken to configuration for relevant parameters (RACH access

    threshold, Random Access Error Threshold.)

    III. Congestion

    Subject for Analysis:

    A service cell with low rate of incoming handover completion and adjacent cells withlow rate of outgoing handover completion.

    Positioning of Problems:

    After the problem of inappropriate parameter configuration and equipment failurebeing solved, if there are

    (1) Too many incoming handover failures (caused by congestion) in measurement of


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    incoming handover performance;

    (2) Times of outgoing handover attempts - times of outgoing handover is too great inmeasurement of handover performance between cells. It suggests that there is nochannel available to be applied. There might be congestion in the target cell.

    With phenomenon mentioned above, the maximum number of TCH in all busy, thetime of all busy shall be studied to confirm the existence of congestion. Congestionshall be solved as follows.


    (1) Modify cell coverage (modify transmission power of base stations, modify theminimum access level, modify RACH access threshold, modify random access errorthreshold, modify down tilt of antenna.)

    (2) Modify major parameters of the cell (modify CRO, start-up load handover, modifycell priority and handover parameter of the cell.)

    (3) Capacity expansion or modification to configuration of carriers of the cell.

    IV. Others

    After the problems of parameter configuration, equipment failure, and congestionbeing solved, with reference to TCH Call Drop analysis, the problem of cells with lowrate for incoming handover completion and adjacent cells with low rate incominghandover completion can be solved by interference, coverage, balance for uplink anddownlink analysis and solution.

    1.4.6 Traffic Analysis

    Calculate traffic volume of the specific area (mean traffic per line) to see if it isnecessary to implement capacity expansion.

    Make out a list of super busy cells and super idle cells.

    Traffic trend. Based on historic traffic data, estimate the future trend of traffic.

    Analyze if there are cells with abnormal traffic volume.