The major steps used in RF
optimization are preparation, data collection, data analysis, and modification and realization.
1.Preparation of RF
Optimization
First of all make the objective of
the optimization KPI , divide the sites in clusters, make the test route, and collect tools and prepare documents for the RF optimization ready to ensure the smooth
operation of RF optimization.
Ø Prepare the optimization objective
Make the optimization
objective of the RF-related KPI indexes,including the coverage ratio, soft
handoff ratio, and pilot pollution ratio,which compose the network optimization
acceptance indexes.
Ø Divide site in clusters
Divide the sites into different cluster. Generally the sites located in same locality are grouped in a same cluster.Perform the concurrent RF
optimization for a group of sites instead of a single site. The concurrent RF
optimization for a group of sites ensures that co-frequency interference
between adjacent cells is considered in the network optimization.
Ø
Determine the DT route
Before starting a Drive Test, the DT route is made for verifying whether the Network meets acceptance KPIs
requirements. If the DT route for network acceptance is already scheduled,
ensure that the scheduled route contains the route for verifying whether the
network meets acceptance KPIs requirements.
2. Data Collection
Collect the MS/AT data by
the Drive Test, indoor test, and signaling tracing, and verify that the KPI
requirements are met based on the call tracing data and configuration data of
the BSC or access network (AN). This data is also used for data analysis.
Ø
Drive Test
During network deployment,
network optimization is always performed under the unloaded condition of the
network. Perform voice service or data service tests for the network in the according
to the service types in the network planning area. Use DT tools to collect the
radio signals for analyzing the outdoor signal coverage, handoff, and pilot
pollution problems.
After the communication
network is put into operation, the network load may be heavy. Hence, network
tests in the loaded condition are required. After completing the network
optimization in the unloaded condition, perform a test to verify that the
quality of the network in the loaded condition meets the requirements. The data
collection for the network in the loaded condition is similar to that for the
network in the unloaded condition.
Ø
Indoor Test
The services to be tested
by the indoor test must be provided in the seamless coverage network according
to the contract (for the commercial office) or planning report (for the trial
office). The method of indoor test is the same as that of the DT. An indoor
test is performed to test the signal coverage in the indoor coverage areas
(such as in building, supermarket, and underground train), critical places
(such as gymnasium and governmental offices), and some special test areas (such
as VIP areas) to discover, analyze, and solve RF problems.
Ø
BSC Configuration Data Collection
Before and during RF optimization,
collect the configuration data about the adjacent cells for network optimization
and collect additional configuration data from BSC. Then, check whether the
existing configuration data is consistent with the previous data record and the
planning data.
3.Data Analysis
Find out the problems of
the network, focus on the coverage, pilot pollution, and Handoff problems, and
take corresponding modification measures.
Ø
Coverage Analysis
Focusing
on signal distribution, the coverage analysis is a key task of RF optimization.
The coverage analysis includes the dominant cell analysis, downlink coverage
analysis, and uplink coverage analysis.
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No signal or poor signal coverage
If no signal is detected in
a cell according to the DT, the BTS may have no transmit power or the antennas
may be blocked during the test.
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Cross-cell coverage
If the signals from a cell
can be received in the surrounding cells, the Coverage of this cell is too
wide.The cross-cell coverage may be caused by improper site height or improper
settings of antenna tilt angles. The cross-cell coverage cells interfere with
adjacent cells. And the interference causes the decrease of system capacity.
You can increase the antenna tilt angle or lower the antenna height to solve
the cross-cell coverage problem. While solving the cross-cell coverage problem,
avoid the existence of no signal coverage area.
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No-dominant cell area
The no-dominant-cell area
refers to the area that has no dominant cell or the dominant cell changes
frequently. No dominant cell leads to frequent handoffs, reduces the system
efficiency, and increases the call drop ratio.You can modify the antenna tilt
angle and azimuth, enhance the coverage of a strong signal cell (or the nearby
cell), and reduce the coverage of other weak signal cells (or the remote cells)
to solve the no dominant cell problem.
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Downlink coverage analysis
Analyze pilot signal
strength and Rx power collected by the DT. If the pilot signal Rx power is
smaller than the thresholds, downlink coverage problems may exist. Mark the
area without signal coverage in the downlink and analyze the distance between
the area and adjacent BTSs. Analyze the ambient environment of the area and
check whether the distribution of Rxs in adjacent sites is normal. After the
analysis, you can judge whether the downlink coverage can be improved by
modifying antenna tilt angle and azimuth. Check whether a new area without
signal coverage exists after the coverage problem of a no signal coverage area
is solved by modifying the antenna. If the antenna modification cannot solve
the problems about no signal coverage areas, add more sites.
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Uplink coverage analysis
Analyze Tx power collected
by the DT.If the Tx is higher than the threshold, uplink coverage problems may
exist. Mark the areaswithout uplink coverage and check whether downlink
coverage is also unavailable in thoseareas. When both uplink and downlink
coverage is poor, the downlink coverage problemstake precedence over the uplink
coverage problems. If only uplink coverage is poor, youcan solve the problem by
eliminating the impact of uplink interference, modifying theantenna azimuth and
tilt angle, or adding the tower mounted amplifier (TMA).
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Interference Analysis
The interference analysis includes the uplink
interference analysis and downlink interference analysis. The interference
affects the cell capacity and even leads to the call drops and access failures.
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Downlink interference analysis
Analyze the pilot strength
Ec/Io collected by the DT.If the Ec/Io is lower than the threshold, uplink
interference may exist. Mark the areas withpoor Ec/Io and check whether
downlink Rx coverage is unavailable in these areas. If downlink Rx coverage is
poor, the coverage problem exits. Analyze the causes and then solve the
problem. If Rx coverage is good but the Ec/Io value is smaller than the
threshold, downlink interference exists. Analyze the interference causes and
then solve the problem.
ü
Uplink interference analysis
Check the forward load of each cell. If the
forward load of a cell is excessively high, and no high traffic volume exists,
the uplink interference exists. Analyze the causes of the uplink interference,
and then solve the problem.
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Pilot Pollution Analysis
The
pilot pollution means that an area has many strong pilots but does not have a
dominant pilot that is strong enough. If pilot pollution exists, the Ec/Io
deteriorates, call drop during handoff happens frequently, and the system
capacity drops.
The possible reasons for
the pilot pollution are:
The cell layout is
inappropriate; BTSs or antennas are installed in an excessively height; The settings
of antenna azimuth or tilt angle are improper;The pilot power settings are
improper; The ambient environments impact on the coverage area.
Perform the following steps
to analyze pilot pollution:
1. Confirm the pilot
pollution areas.
2. Analyze which cells
cause the pilot pollution in the emphasis area.
3. Analyze the Rx and the
Ec/Io distribution in the cells related to pilot pollution. Confirm
the cells where the coverage needs to be
reduced or improved, and provide solutions to the
pilot pollution.
Ø
Handoff Analysis
In RF optimization,
adjacency optimization and soft handoff ratio control involve handoffs. By modifying
RF parameters, you can control the size and the position of the handoff area to
reduce call drops due to dramatic signal change. This improves the handoff
success ratio.
The optimization of the
adjacent cell list concentrates on the missing configuration of adjacent cells. Use Nastar
to check the neighbor cell information and give suggestions about adding,
removing, or keeping neighbor cells for each cell.
Optimization of soft
handoff ratio Excessively high soft handoff ratio wastes system resources and decreases
system capacity. During RF optimization, ensure the cover rage,and control the
soft handoff ratio within an acceptable range. You can reduce or changethe soft
handoff region by increasing the tilt angle, modifying the azimuth, lowering
the antenna, or reducing pilot power.
4. Implementation and
Modification /Realization
Modify the engineering
parameters and cell parameters. After parameter Modification, conduct a test.
If the test results do not meet the target KPI Requirement, perform the problem
analysis and modification again until the all the KPI requirements are met.
You can modify engineering
parameters by modifying the antenna tilt angle or the antenna azimuth,
modifying antenna location, modifying antenna height, replacing antennas,
changing site location, and adding new sites.
The engineering parameter
modification helps to solve the coverage and interference problems,
and solve the hidden
problems about engineering installation, hardware, and antenna and feeder.
Modifications of
engineering parameters are associated with cell adjacency modification.
