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........................................................................... 6 1.3.2 Coverage....................................................................................................... 7 1.3.3 Capacity........................................................................................................... 8 1.3.4 Interference.................................................................................................... 9 1.3.5 Handover....................................................................................................

10

1.3.6 Call Loss (Drop)Drop..................................................................................

11

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

12

1.4.1 TCH Call Loss Drop Rate...........................................................................

12

1.4.2 TCH Congestion Rate.................................................................................. 16 1.4.3 SDCCH Call Loss rateSDCCH 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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Chapter 9

Chapter 9 Network Optimization

Network Optimization

Network optimization serves for the pursuit of a maximum application of network resource and a maximum improvement of QoS. Meanwhile, it also contributes to foundations and principles for future network expansion. Optimization here refers to optimization based on a sound implementation of network planning. In this sense, optimization is a supplement to the aspects failing to be taken into adequate consideration or resource adjustment for burst situations as suggested in a large traffic burst. Generally, drive test, call traffic statistics and subjective perception on the part of human are taken as the basis for optimization, but moreover signaling tracking and analyzing 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 SwitchingTransporting Part and Radio Part. Due to the mobility of subscribers and the complexity of radio waves in propagation, the Radio Part always becomes the decisive factor affecting the QoS of the GSM network. Wireless network optimization refers to reasonable modification to planning and designing of communication networks according to certain principles so that a more reliable, more economic network operation, a higher QoS, and a higher utilization ratio for network resource can be achieved. Undoubtedly, this is of great significance for network operators and subscribers. Procedures for network optimization are as follows: Preparatory Work ObtainingBasic Information of Network on Site Drive Test and Traffic Statistics Collection

Data Analysis

Network Parameter Modification

N

Does it meet the performance indices?

Y Network Optimization Report

Preparatory work at early stage include obtaining knowledge of progressive status in network construction, analyzing the operation status of network, preparing for optimization test equipment and software, network planning report, collection of engineering and designing documents, etc. Obtaining of basic network information 1



at 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. Data collection covers subjective reflection of mobile subscribers, data collection in drive test, OMC data collection, etc. Data analysis include background analysis of optimization software, OMC call traffic statistical analysis, tools for network optimization analysis, etc. Network Parameter modification includes network engineering parameter modification and network function parameter modification. Network performance indices are in conformity with the General Indices of State Standard. Network Optimization Report covers measures used in this optimization, network performance 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 handset mobile station in idle state, sweep checkfrequency scanning test, timed call-up test, continuous conversation connection test, etc. Through simulating the actual state of subscribers in practical application, field intensity distribution, Carrier-To-Interference Ratio, voice quality and other on site data can be obtained. Meanwhile, the actual installation status of antenna and feeders can also be verified. Various test measures can be applied in combination with others according to demand. According to test result, modification to system parameters, antenna status shall be implemented accordingly. Among them, modification to system parameters mainly covers modification to transmission power, frequency configuration, handover level, parameters of adjacent cells, traffic load, the numbers of SDCCH and TCH channels for configuration, etc. Modification to antenna state has an important effect on coverage improvement and interference reduction. It mainly covers adjustment to antenna height hanging on racks masts(mast), directional angle azimuth(azimuth), rake angle down tilt(title), etc. Functions of ANT test software are mainly as follows:

I. Supports Multimode Test ANT optimization software supports sweep and conversation frequency scanning and call connection test in full frequency band. In two-handset-test mode, the software supports dual network test and interference test.

II.

Real-time Graphic Description Window

In idle state, the ANT Optimization software can display real time BCCH field intensity and main information of the host cell and six neighboring cells. In conversation connection mode, ANT optimization software can also display real time switching operation handover behavior and all indices of conversation performanceconnection 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 Loss Drop, handover failure, allocation 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 network coverage, lonely island positioning, co-channel interference and neighboring adjacent channel interference, sweep frequency scanning analysis, etc. According to user’s demand, ANT optimization software can automatically create radio wireless test measurement and statistical report including interference statistics, radio wireless indices statistics, system performance evaluation, 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 signaling information, A-G interface signaling information, SS ＃ 7 interface signaling information of ISUP, TUP, and INAP. It can also be applied in testing of error code covering PCM BERT and GSM BERT in transmission lines routes and opening of signaling information files offline to be processed in background analysis analyzing in background offline state by opening the signaling information files. There are five sub application programs in MA-10 Test Software. Respectively they are “MA-10 Control (on-line test of interface signaling for ABIS interface, A-G interface, and error code), “MONITOR ABIS offline” (ABIS interface signaling analysis offline), “MONITOR MSC offline” (A-G interface signaling analysis offline), “GSM-BERT offline” (error code inspection and analysis offline), “PCM-BERT offline”(error code inspection and analysis offline). With Signaling Analyzer MA-10, a network optimization engineer can collect and analyze data of Abis interface and A interface, survey the complete process of signaling connection, extract survey report, and carry out contrastive study of these data against downlink signal collected from drive test (This ingenuous use of time points as indices and a combined application of latitude and longitude stored in equipment for downlink drive test can generate a uplink coverage graph and quality graph), so that the operation state of the entire network can be obtained. In this way, major causes and locations of Call Loss Drop, handover failure, traffic congestion and other problems in a cell can be spotted.

1.2.3

Spectrum Analyzer A spectrum analyzer is mainly used in test of attributes of a frequency domain including spectrum, power of adjacent channels, quick scanning of time domain, spurious radiation, inter-modulation attenuation, etc. A spectrum analyzer is frequently used in network optimization to carry out electromagnetic background test. The following example presents the HP E4402 in application. In electromagnetic background test, a small omni-directional antenna can be connected to the spectrum analyzer to implement broadband omni-directional test. As HP E4402 is equipped with a built-in pre-amplifier, no external amplifier is needed. At this time, scanning frequency of the spectrum analyzer is generally set in 880～960MHz（900MHz）or 1700～1890MHz（1800MHz）. Reference level can be set as 0dBm and amplitude of each line as 10dBm. Shall a signal be detected, scanning bandwidth will be narrowed down according to frequency band of the signal, and reference level, amplitude of each line, and resolution bandwidth will also be properly modified to carry out a detailed analysis of the signal. Signal positioning is similar to this operation. The only difference between the two lies in that the omni-directional antenna is changed into a directional antenna. By swinging the 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 proper way to indicate statistical data of calls, to assist commission and maintenance personnel and network optimization personnel in spotting network problems. Software Input includes configuration data of Data Control Platform Data Management Terminal, statistics and engineering data for commissioningtraffic statistical results and commissioning engineering data recorded in BSC Call Statistical Platform Traffic Statistical Terminal. Software output of data Data output of 4



the software is in diagrams and tables along with failure spotting and suggestions for solutions. In addition, the output also supports flexible charts report forms. Functions of general network optimization software shall be as follows: 

Introduction of Call Traffic Statistical data, configuration data, and network planning data



Display of digital map in geographical representation



Trend representation with flexible customization



View Call Traffic Statistical result: Multi-functions and View with selfdefining configuration



Data Filter: automatic detection of unusual points and indicate in geographical 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, creation of report across BSCs.



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



Function of Experience Lab



Engineering Management

Good optimization software can adequately act as everyday work platform for radio engineers and maintainers (supervisors and optimizers). HUAWEI possesses a selfdeveloped 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 possible aspects with problems and making out a test plan and an optimization plan according to 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 include planning report, table of engineering parameters, network topology, report for frequency planning, report of cell parameter design, etc. This may offer a general idea of 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, especially those to engineering parameters, state of commissioning and simple drive test. Special attention shall be paid to network loophole caused by engineering erection quality or progressive status. The example suggested in handover failure and interference in large areas caused by uncompleted construction of base stations or erection errors is a good case in point. The following cases of optimization all refer to optimization after a sound earlier stage planning and a good implementation of the planning. In optimization practice, however, there are always installation problems and hardware problems as suggested in installation of antenna in opposite directions, problems with some carriers of base station, etc. This optimization is a continuous effort of error correction. No more details will be accounted here.

I. Call Traffic Statistical Data From major indices including TCH Call Loss Drop rate, TCH congestion rate, SDCCH Call Loss Drop rate, SDCCH congestion rate, handover completion rate, network operation status can be understood. With voice traffic volume on the network, call traffic statistical data is a an critical measure important method to understand network performance.

II.

Drive Test Data

For a network in debugging commissioning, an extensive drive test shall be carried out to understand the network status when voice traffic volume becomes very low or nil. If necessary, transmission function of idle BURST in the base station can be started to study the downlink interference status under high traffic simulation. Necessary adjustment shall be furnished for practical problems. Shall failure be proved within a specific area according to call traffic statistics, a practical drive test in this area can be used to confirm the failure a step further so that proper solution may be adopted.

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III. An Overall Knowledge of Network Coverage, Interference State, Traffic Distribution 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 GSM networks. Major factors affecting coverage are as follows:

I. Blind Zone for Signals A Blind Zone results from no overlapping between coverage areas of two base stations 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 is expected. Increasing the coverage range of these two base stations (as the case suggested by increasing transmission power, height of antenna) so that the overlapping depth of coverage may reach a level of 0.27R ( R here refers to radius of the cell). Meanwhile, care should be taken to possible co-channel interference and adjacent channel interference caused by coverage expansion. (2) A Blind Zone caused by hollow ground valley and back hillside can be recovered by constructing new base stations and repeaters in those areas. Repeaters can effectively recover Blind Zones in coverage area and expand the scope of coverage. On the other hand, repeaters can also bring about inter-modulation interference, cochannel interference and adjacent channel interference to other cells. Therefore, interference should be taken into consideration in introduction of repeaters in application. (3) Blind Zones within tunnels, underground garages, and tall buildings can be recovered 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 hilly landforms 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 base station, configuration handover in this cell may immediately result in Call Loss Drop once the mobile station leaves this “island” area. To solve this problem, rake angle down tilt or power gain of the antenna should be modified. Transmission directly along road should be largely avoided so as to eliminate island effect by reducing the coverage of base stations. In coverage optimization, modification to directional angle azimuth and rake angle down tilt is often used to change service range of the cell. Problem of Blind Zone caused by co-channel inference, adjacent channel interference, and intermodulation interference between TACS and GSM can be solved by eliminating interference.

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1.3.3


Capacity I. Traffic Congestion With OMC call traffic statistics data, TCH congestion rate can be obtained (with occupation at all busy). It is also possible to judge the traffic congestion status by comparing the busy hour call traffic volume against calculation capacity of each base station cell. For congestion cells, it is recommended that more carriers be added, or cell split, or construction of new base stations in common sites be adopted. It is also advisable to adopt new dual frequency networks, micro cells, etc.

II.

Traffic Balance

For some base stations with congestions, measures to ease the congestion are as follows: (1) Modify the antenna height, down-dip tiltangle, transmission power of base stations and handset. (2) Modify the configuration for part of parameters In overloaded areas, the minimum access level may be suitably increased and handover threshold may be appropriately decreased to reduce traffic. Accordingly, the minimum access level may be properly reduced and handover threshold may be appropriately increased to increase traffic. Moreover, by setting CBQ and CBA of low traffic cells, these cells may be assigned with higher selection PRI. A suitable increase in CRO can make it more easily for the cell 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 forth co-channel interference and adjacent channel interference (This is called internal interference 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 and repeaters.

I. Interference Positioning GSM is a dual system with a difference of 45MHz between uplink frequency and downlink frequency. There might be interferences in both uplinks and downlinks. Downlink interference can be measured with instrument for drive test by maintaining the conversation status. Level of voice quality can be used in positioning. Voice quality 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 be less than 1.6%. Table 3-1 Relational Correspondence between Signal Quality Level and Error Rate RxQual class

Mean Ber (%)

Ber range

0

0.14

<0.2%

1

0.28

0.2 ... 0.4%

2

0.57

0.4 ... 0.8%

3

1.13

0.8 ... 1.6%

4

2.26

1.6 ... 3.2%

5

4.53

3.2 ... 6.4%

6

9.05

6.4 ... 12.8%

7

18.1

>12.8%

Uplink interference can be positioned with the numbers of interference bands and Call Loss Drop rates in HUAWEI OMC call traffic statistics terminal. Interference band is an indication of free idle TCH levels of 5 categories grades in all. Level ranges can be set through Data Configuration PlatformTerminal. Look at the following example: Table 3-2 Level Range of Interference Band Interference Band 1

-110 ～ -105dBm

Interference Band 2

-105 ～ -98dBm

Interference Band 3

-98 ～ -90dBm

Interference Band 4

-90 ～ -87dBm

Interference Band 5

-87 ～ -47dBm

Generally speaking, shall idle channel fall into Interference Band 4 and Interference Band 5 continuously, it can be determined that there exists interference. Beside, measurement report for uplink and downlink can be viewed from Signaling Analyzer MA-10 connected to ABIS interface. In this way, uplink interference and

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downlink interference can also be positioned.

II.

Ways to reduce interference

(1) Increase the distance between two adjacent cells of the same or neighboring frequencies; (2) Decrease transmission power of base stations; (3) Modify antenna height; (4) Modify directional angle azimuth of the antenna; (5) Modify down-dip angle 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, high level inter-modulation result interference may be generated (as tertiary interference). Shall the result signal be in channel the bandwidth of GSM receiver, it may have interference on the GSM receiver. Shall the TACS and GSM share a commensal common site, intermodulation interference may also be created. Inter-modulation reduction may be accomplished by increasing the transmission power of GSM downlink and optimizing the frequency configuration.

1.3.5

Handover When a mobile subscriber moves from one cell into another, handover must be completedimplemented. Otherwise, voice quality may be greatly reduced. In some cases, even Call Loss Drop may occur. Frequent handover problems include voice quality declination or Call Loss Drop caused by handover failure and handover delay, voice quality declination and system load increase caused by frequent handovers, voice traffic unbalance traffic caused by unreasonable ratios of outgoing againstand incoming callshandovers. Drive test equipment can be used in testing of continuous conversationconnection, tracking of handover failures, handover delays or frequent handovers, etc. With OMC call traffic statistical data, handover completion ratio, incoming and outgoing handover ratio of the cell can be analyzed. Causes and resolvent of handover abnormal handover and methods for trouble shooting are as follows: (1) Handover threshold configuration configrated too low (2) Congestion in adjacent cells, no free idle channels 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 other manufactures, parameters of these external cells must be secured correct. These parameters cover LAC, CI, BCCH, etc.

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1.3.6


Call Loss (Drop)Drop In GSM network operation, Call Loss Drop has been the hot spot of complaint from customers. Call Loss Drop here refers to Call Loss Drop after distribution of voice traffic channels. There are various causes of Call Loss Drop with the direct ones as field intensity, interference, and inappropriate configuration for parameters. For our products, there are two critical parameters affecting Call LossDrop. One is radio link timer failure for downlinks, the other is the number of SACCH multi-frames for uplinks. These two parameters shall be suitably configured according to traffic volume and coverage. Causes of Radio Link Failure are as follows: (1) When the mobile station enters into a Blind Zone for field intensity coverage, Call Loss Drop may result from RF factors. (2) Internal or external interference of the network may result in SACCH frame decoding failure. This further leads to Call LossDrop. (3) When a mobile station approaches cell boundary in driving, the mobile station requests for handover. As the definition for neighboring cells was lost, or there are congestions in neighboring cells, there would be no cells available for handover. This finally leads to a Call LossDrop. (4) With imbalance between uplinks and downlinks, a handover may result in Call LossDrop. 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 are good downlinks but very weak uplinks.). According to downlink level, the mobile station then makes out the sequence of cells to for incoming handover. The mobile station may be directed into CELL 2. After the handset is directed into CELL 2, Call Loss Drop may occur due to bad uplink. There are also Call Losses Drops caused by non-radio link reasons as Abis interface failure, A interface 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 inspect major network indices covering TCH Call Loss Drop rate, TCH Congestion rate, SDCCH Call Loss 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 call traffic statistical indices, the first thing to be made clear is whether there are cells with abnormal indices. Should there be, the abnormal cells must be analyzed one by one. In view of the seriousness caused by abnormal indices, major indices can be basically arranged in the order importance as follows: TCH Call Loss Drop rate, TCH congestion rate, SDCCH Call Loss Drop rate, handover completion rate, etc. Interference and coverage, however can affect many other indices at the same time, as many indices are inter- related. Shall the problem of low handover completion rate be properly solved, Call Loss 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 index with combination of others.

1.4.1

TCH Call Loss Drop Rate Causes of high rate of call loss drop are as follows: (1) Interference (network internal interference, external interference, interference from the 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 of SACCH 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 call traffic statistics With more than one free idle channels presented in interference band three, four, and five, a judgment can be passed that there is interference in a general sense. Shall the interference 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 be noted here that interference band is reported uplink to BSC via RF resource indication message by carrier channels of base stations in idle state. With busy channels at present, resource indication message becomes difficult to be reported uplink. The interference band statistics shall be considered in a comprehensive approach. (2) Measurement of receiving level performance (A matrix indicating relationship

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between level and quality is expected.) This is a statistical task specifically for carriers. If there are too many high levels of low quality, it suggests that there are co-channel interference, adjacent channel interference, or external interference for the frequency band of this carrier board. (3) Ratio of LowProportion of bad Quality Handovers In test the measurement of cell performance / test the measurement of inter-cell handover performance between cells, or in test the measurement of outgoing cell handover from cellsperformance, number of attempts for outgoing cell handover caused by all sorts of reasons was recorded in traffic statistics. Shall there be too many handovers caused by bad quality, it suggests that there is interference. More handovers caused by bad uplink quality suggests uplink interference. More handovers caused by bad downlink quality suggests downlink interference. (4) Measurement of receiving quality performance Specifically for carriers, the statistical data of average receiving quality will be made for reference. (5) Measurement of Call Loss Drop performance The average level and quality of Call Loss 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. Solution: (1) In actual drive test, check the road section with interference and inspection distribution of signal quality. Origins of overlapping signals causing interference should be made clear in cells. According to actual status, interference can be avoided by modifying the transmission power, pitch angledown tilt of antenna, relations between adjacent cells, handover parameters, or frequency band planning of a cell concerned. (2) With a frequency spectrometerspectrum analyzer, interference frequency band can be detected. Source of interference can be spotted. (3) Start up ofAdopt frequency hopping, DTX, and power control. (4) Solve the equipment problems (as TRX self-excitation).

II.

Coverage (Blind Zones, and lonely islands)

Judgment: (1) Measurement of power control performance, the average uplink signal intensity and 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 Loss Drop Performance measurement, level at Call Loss Drop too low and TA abnormal before Call Loss Drop are detected. (5) Performance measurement of defined adjacent cells. Adjacent cell with too low an average level can be spotted.

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(6) The average level of a undefined adjacent cells is too high. There are too many such cells(lonely islands). (7) Performance measurement of defined adjacent cells. Average receiving level of defined adjacent cells is detected too high (over excessive coverage). (8) Measurement of power control performance, see if the average distance between MS and BTS is in conformity with design ideology. (9) Measurement of power control performance, see if the maximum distance between MS and BTS are overdue in several consecutive periods. (10) Performance test of outgoing handover from a cell, low handover completion rate into a certain adjacent cell. Solution: (1) A drive test is recommended to be carried out in areas with estimated bad coverage. (2) Modify network parameter according to drive test. (transmission power of a base station, rake angledown tilt and height of the antenna, minimum access level of handset, relations of adjacent cells, the minimum access threshold of handover candidate cells for incoming handovers. (3) Add Increase base stations.

III.

Inappropriate handover (planning for adjacent cells and parameters for handover)

Judgment: (1) Check the handover parameter. See if there is inappropriate parameter configuration. (2) Performance measurement of handovers between cells. More handover failures together with more recovery failures are detected. (3) Performance measurement of handover between cells. Too many handovers together with too many recovery completions are detected. (4) Performance measurement of undefined adjacent cells. Levels of undefined adjacent cells are too high and the number of report for undefined cells goes beyond standard. (5) Performance measurement for outgoing handovers: low rate of outgoing handover completion out of a cell (for a specific cell). Find out an adjacent cell with low incoming handover completion rate so that causes can be further detected from target cells. (6) Low rate of incoming handover completion. configuration for counterpart cells is detected.

Inappropriate

parameter

(7) TCH Performance measurement: Times of handover is not in proportion to times of TCH call occupation completion. (handover/call>3) Solution: (1) Add appropriately adjacent cells. (2) Modify handover parameters.

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IV. Imbalance between uplinks and downlinks (Tower Amplifier, Power Amplifier, antenna direction.) Judgment (1) Register “measurement for balance performance between uplinks and downlinks” in call traffic statistics. Analyze if there really exists imbalance between uplinks and downlinks. (2) Register “Call Loss Drop Performance Measurement” in call traffic statistics. Analyze the level and quality of uplinks and downlinks at Call Loss.； (3) Register “Power Control Performance Measurement” in call traffic statistics. Analyze the average receiving level of uplinks and downlinks. Solution: (1) Check Tower Amplifiers and Power Amplifiers. Specifically for Tower Amplifiers with alarm, the test may be focused on the Tower Amplifiers with alarm. Current values 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 radio link connection.

Solution: Modify inappropriate configuration for parameters mentioned above.

VI.

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

Judgment: (1) TCH Performance measurement: times of A interface failure abnormal with TCH occupation. (2) TCH Performance measurement: TCH application ratio abnormal. (3) TCH Performance measurement: too many times of Call Loss Drop and interruption on ground link failure. (4) Shall Call Loss Drop rate and congestion rate of this cell remain high, there might be problems with part of the equipment. Solution:

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(1) Watch over transmission and board alarm (TC board failure, Alarm for PCM synchronization 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 is transmission break or board failure (as suggested by carrier board failure or poor contact.)

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 Judgment: (1) Too high a traffic for each line (DGT specifies that a cell with a traffic load greater than 0.8 per line is taken as a super busy cell. A cell with traffic load smaller than 0.1 is taken as a super idle cell.) (2) With an applicable rate of 100% for channels, when there are too many times of occupation at all busy, there will be a long term all busy. (3) Traffic imbalance (inspect traffic imbalance between three sectors of a base station or between several stations) (4) In performance statistics of incoming handover into a cell, there are too many handover failures because of congestion. Solution: (1) Capacity expansion or modification to carrier configuration between busy cells and idle cells. (2) Modify the cell coverage (modify transmission power of base stations, modify directional angelazimuth, rake angledown tilt, and height of antenna.) (3) Modify major indices of cell (modify CRO, modify the minimum access level for handsets, start-up load handover, modify cell priority, modify cell handover parameters).

II.

Interference (network internal interference and external interference)

TCH congestion rate falls into two parts. One is TCH occupation at all busy. This results in real channel allocation failure and further leads to channel request failure. The other one is channel assignment failure caused by various reasons after the assignment command being sent out. Times of TCH occupation failure (including handover)--times of TCH occupation at all busy, i.e. channel assignment failure caused by non-assignment availability factors. With too many occupation failures, there is possible interference within the network. 16



Judgment and solutions: Refer to judgment and solution to interference in TCH Call LossDrop.

III.

Causes of Handover (imbalance between incoming handovers and outgoing handovers)

Judgment: (1) Times of handover is not in proportion to that of TCH call occupation completion (3 handover/call specifically for the cell) (2) Times of incoming handover is far greater than that of outgoing handover (this results in traffic imbalance). Solution Modify handover parameters.

IV.

Parameter Configuration Inappropriate

Judgment: Check the handset configuration for the minimum access level. Solution: Modify the inappropriate parameter configuration

V.

Coverage (Blind Zones, lonely island)

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

1.4.3

SDCCH Call Loss rateSDCCH Call Drop Rate For ADCCH SDCCH Call Loss Drop rateRate, refer to analysis for TCH Call LossDrop 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 Judgment: Measurement of random access performance: Times of instant immidiate assignment completion (the sum of location renewal update + the sum of calls and other reasons)/Times of instant immidiate

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assignment< 85% The above formula presents the ratio of handset report uplink est_ind against instant immidiate assignment command downlink. The ratio generally should be in the range of 80 ～ 90%. With this ratio in abnormal, it suggests that there might be inappropriate configuration for relevant parameters. (1) The ratio of instant immidiate assignment success is too low. (2) Ratio of location renewal update times against times of all assignment instructions (too many location renewalsupdate). Solutions: (1) Parameter modification (threshold of random access error, RACH access threshold),maximum times for retransmission, the number of TS in transmission expansion. (2) Pay attention to parameter configuration for partition of location area and location renewal update (configuration for 1800MHz dual band network, CRO, cell reselection hysteresis parameters, time for periodic location renewalupdate, etc.) (3) In dual band networks, an exceedingly high rate ofexcessive location renewal update may be caused by an exceedingly high rate ofexcessive handover between mobile switch officescenters. Modification shall be made to handover parameters of the 1800MHz dual network, CRO, etc.

II.

Inadequate system capacity

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

1.4.5

Rate of Handover Completion Subject for analysis: Adjacent cells with low rates for outgoing handover completion and service cell with low rates for incoming handover completion. First, judgment shall be passed onto the following issues according to inter cell Performance measurement: Is the rate for incoming handover completion low? Is the rate for outgoing handover completion low? Low rate of outgoing handover completion shall be further studied via cell Performance measurement to detect which is the adjacent 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, and the upper level clock becomes unstable or the upper level clock has much deviationis overly floating.) In analysis, configuration of handover parameters, relations of adjacent cells, BTS 18



synchronization loss with BSC, and other problems can be eliminated in the first place. Further analysis may be carried out over other factors affecting low rate of handover completion.

I. Inappropriate handover (planning for adjacent cells, handover arameters.) Position and Solution: (1) Check to see if the configuration for handover thresholds of TA and BQ and handover switch is appropriate. (2) Performance measurement of undefined adjacent cells: level and the number of measurement reports of undefined adjacent cells exceed standard.（Adjacent cells shall be suitably added.） (3) In defining the Performance measurement of adjacent cells, defined adjacent cells with 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, handover parameters shall be inspected and modified. (Handover parameters include configuration of layers, inter layer handover hysteresis, inter cell handover hysteresis, PBGT threshold, etc). (5)Inter cell handover Performance measurement: the average level for handover prompt is detected too low. This may result from too low a handover threshold including edge threshold in configuration.

II.

Equipment problem

Subject for Analysis: A service cell with low rate of incoming handover completion and adjacent cells with low 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 Loss Drop and call interruption resulted from terrestrial link problem. (4) Shall Call Loss Drop rate and congestion rate remain high in a cell, there might be problems with part of the equipment. (5) Survey the transmission and board alarm (TC failure, A interface PCM synchronization loss alarm, LAPD broken link, Power Amplification board, HPA, TRX alarm, CUI/FPU alarm) According to alarm data, see if there is a transmission failure or 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 and quality, care shall be taken to configuration for relevant parameters (RACH access threshold, Random Access Error Threshold.)

III. Congestion Subject for Analysis: 19



A service cell with low rate of incoming handover completion and adjacent cells with low rate of outgoing handover completion. Positioning of Problems: After the problem of inappropriate parameter configuration and equipment failure being solved, if there are (1) Too many incoming handover failures (caused by congestion) in measurement of incoming handover performance; (2) Times of outgoing handover attempts - times of outgoing handover is too great in measurement of handover performance between cells. It suggests that there is no channel available to be applied. There might be congestion in the target cell. With phenomenon mentioned above, the maximum number of TCH in all busy, the time of all busy shall be studied to confirm the existence of congestion. Congestion shall be solved as follows. Solution: (1) Modify cell coverage (modify transmission power of base stations, modify the minimum access level, modify RACH access threshold, modify random access error threshold, modify rake angledown tilt of antenna.) (2) Modify major parameters of the cell (modify CRO, start-up load handover, modify cell 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 congestion being solved, with reference to TCH Call Loss Drop analysis, the problem of cells with low rate for incoming handover completion and adjacent cells with low rate incoming handover completion can be solved by interference, coverage, balance for uplink and downlink analysis and solution.

1.4.6

Traffic Analysis Calculate traffic volume of the specific area (mean traffic per line) to see if it is necessary 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.

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Network Optimization

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