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Wireless Network Planning Table of Contents
Table of Contents
Chapter 9 Network Optimization
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1 1.1 Process of Network Optimization
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1 1.2 Common Tools Used in Network Optimization
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1.2.1 ANT Drive Test Equipment
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3 1.2.2 Signaling Analyzer
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4 1.2.3 Spectrum Analyzer
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4 1.2.4 Network Optimization Software
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1.3 Wireless Network Problems Positioning and Solving
.............................................. 6 1.3.1 Obtaining
Basic Information
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6 1.3.2 Coverage
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7 1.3.3 Capacity
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8 1.3.4 Interference
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9 1.3.5 Handover
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10 1.3.6 Call Loss (Drop)Drop
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1.4 Problem Positioning according to Network Indices
.............................................. 12 1.4.1 TCH Call
Loss Drop Rate
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12 1.4.2 TCH Congestion Rate
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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
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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 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 Switching-Transporting 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
Obtaining Basic Information of Network on Site
Does it meet the
performance indices?
Network Optimization Report
Y
N
Drive Test and Traffic Statistics Collection
Data Analysis
Network Parameter Modification
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
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Wireless Network Planning Chapter 9 Network Optimization
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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Wireless Network Planning Chapter 9 Network Optimization
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 users 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 880960MHz900MHzor 17001890MHz1800MHz. 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
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Wireless Network Planning Chapter 9 Network Optimization
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 self-defining 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 self-developed Optimization
software SNA.
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Wireless Network Planning Chapter 9 Network Optimization
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, co-channel 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 inter-modulation
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 range0 0.14 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 -105dBmInterference Band 2 -105
-98dBmInterference Band 3 -98 -90dBmInterference Band 4 -90
-87dBmInterference 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,
inter-modulation 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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Wireless Network Planning Chapter 9 Network Optimization
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. Inappropriate
parameter configuration for counterpart cells is detected.
(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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Wireless Network Planning Chapter 9 Network Optimization
(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.
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Wireless Network Planning Chapter 9 Network Optimization
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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Wireless Network Planning Chapter 9 Network Optimization
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
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Wireless Network Planning Chapter 9 Network Optimization
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:
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Wireless Network Planning Chapter 9 Network Optimization
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.
20
Chapter 9 Network Optimization1.1 Process of Network
Optimization1.2 Common Tools Used in Network Optimization1.2.1 ANT
Drive Test EquipmentI. Supports Multimode TestII. Real-time Graphic
Description WindowIII. Geological Positioning FunctionIV. Data
Analysis and Statistical Function
1.2.2 Signaling Analyzer1.2.3 Spectrum Analyzer1.2.4 Network
Optimization Software
1.3 Wireless Network Problems Positioning and Solving 1.3.1
Obtaining Basic InformationI. Call Traffic Statistical DataII.
Drive Test DataIII. An Overall Knowledge of Network Coverage,
Interference State, Traffic DistributionIV. Subjective Sense
1.3.2 CoverageI. Blind Zone for SignalsII. Cross Cell
Coverage
1.3.3 CapacityI. Traffic CongestionII. Traffic Balance
1.3.4 InterferenceI. Interference Positioning II. Ways to reduce
interference
1.3.5 Handover1.3.6 Call Loss (Drop)Drop
1.4 Problem Positioning according to Network Indices1.4.1 TCH
Call Loss Drop RateI. Interference (network internal interference,
external interference)II. Coverage (Blind Zones, and lonely
islands)III. Inappropriate handover (planning for adjacent cells
and parameters for handover)IV. Imbalance between uplinks and
downlinks (Tower Amplifier, Power Amplifier, antenna direction.)V.
Inappropriate configuration of radio parameters (counter for radio
link failure, number of SACCH multi-frames.)VI. Equipment problems
(carrier board, Power Amplifier, Tower Amplifier)
1.4.2 TCH Congestion RateI. Inadequate System Capacity or
Traffic ImbalanceII. Interference (network internal interference
and external interference)III. Causes of Handover (imbalance
between incoming handovers and outgoing handovers)IV. Parameter
Configuration InappropriateV. Coverage (Blind Zones, lonely
island)
1.4.3 SDCCH Call Loss rateSDCCH Call Drop Rate1.4.4 SDCCH
Congestion RateI. Inappropriate parameter configurationII.
Inadequate system capacity
1.4.5 Rate of Handover CompletionI. Inappropriate handover
(planning for adjacent cells, handover arameters.)II. Equipment
problemIII. CongestionIV. Others
1.4.6 Traffic Analysis