01-04 RF Optimization.pdf

cBSS Network Optimization Guideline

4 RF Optimization

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RF Optimization

About This Chapter Chap ter RF optimization optimization is implemented by modifying the engineering parameters parameters and network parameters to achieve to achieve optimum RF signals. RF optimization aims to optimize radio signal coverage, decrease dec rease noise interference, and prevent pilot pollution. RF optimization also ensures that radio signal signal distribution and coverage are optimized before you start service optimization. Usually, RF optimization is performed for site clusters. That is, an optimization team is responsible for the data collection, problem analysis, and parameter modification for a site cluster. If problems lie in cluster edges or t hat parameter modification of a cluster may affect other clusters, negotiations among optimization teams are required to solve these problems. After completing site installations and single site verification for all the sites in the cluster, you can start RF optimization. Sometimes, in order to complete the network optimization project on schedule, you can start RF optimization after the site installations for a portion of sites are complete. Usually, when 80% or above of the total sites are constructed, RF optimization can be started. 4.1 Input and Output of RF Optimization Before starting RF optimization, make related engineering parameter table, cell parameter table, site survey report, network planning report, and single site verification checking table ready. After accomplishing RF optimization, write out corresponding engineering parameter table, cell parameter table, and and their change records. records. 4.2 Tools for RF Optimization Before performing RF optimization, make optimization tools, including software and hardware tools, ready. 4.3 Process of RF Optimization This describes the process of RF optimization. RF optimization process involves preparations, data collection, data analysis, and modification. 4.4 Preparations for RF Optimization Before RF optimization, determine the optimization objective, divide site clusters, and determine the test route. 4.5 Collecting Data for RF Optimization Issue 2.0 (2008-03-10)

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The data for RF optimization is collected by DTs and indoor tests. DTs are dominant. Whether indoor tests are required depends on the contract or the planning. 4.6 Analyzing Data for RF Optimization The focus of data analysis during RF optimization is the distribution of radio network signals. The data analysis involves coverage analysis, interference analysis, pilot pollution analysis, and handoff analysis. 4.7 Modifying and Implementing RF Optimization The modification measures taken in the RF optimization involve modifications of the adjacent cell list and engineering parameters. And the modification of engineering parameters is the main measure taken.

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4.1 Input and Output of RF Optimization Before starting RF optimization, make related engineering parameter table, cell parameter table, site survey report, network planning report, and single site verification checking table ready. After accomplishing RF optimization, write out corresponding engineering parameter table, cell parameter table, and their change records. Before starting the RF optimization, make the following documents ready: l

Engineering parameter table

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Cell par ameter table

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Site survey report

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Radio network planning report

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Single site verification checking table

In the RF optimization phase, the following documents are to be put out: l

Updated engineering parameter table and updated engineering parameter change record

l

Updated cell parameter table and updated cell parameter modification record

After the parameter modification, if the indexes collected by the DT meet the requirement for RF KPI indexes, the RF optimization completes. The next phase is service optimization.

4.2 Tools for RF Optimization Before perfor ming RF o ptimization, make optimization tools, including software and hardware tools, ready. Table 4-1 shows the software tools used in optimization. Table 4-1 Software tools used in optimization

Tools

Description

CAIT and Pilot Panorama

Used for collecting DT data

ACTIX

Used for analyzing DT data

Nastar

Used for checking parameter configurations and analyzing traffic statistics

Mapinfo

Used for displaying maps and creating route data

Table 4-2 shows the hardware tools used in optimization.

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Table 4-2 Hardware tools used in optimization

Tools

Description

A spectrum analyzer required and an YBT250 optional.

Used for locating the interference source in an interference test

Test terminal and data cables

Used for testing the CDMA services

Entire GPS


Laptop computers


Vehicle mounted converter

DC to AC, higher than 300 W

4.3 Process of RF Optimization This describes the process of RF optimization. RF optimization process involves preparations, data collection, data analysis, and modification. Figure 4-1 shows the process of RF optimization. Figure 4-1 RF optimization process

Table 4-3 describes the process of RF optimization. Table 4-3 RF optimization process

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Process

Task

Preparing for RF optimizati on

Determine the objective of the KPI optimization, divide site clusters, determine the test route, and make tools and documents for the RF optimization ready to ensure the smooth operation of RF optimization.


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Process

Task

Collecting data

Collect the MS/AT data by the DT, 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.

Analyzing data

Find out the problems of the network, focus on the coverage, pilot pollution, and handoff problems, and take corresponding modification measures.

Implemen ting modificati on

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.

4.4 Preparations for RF Optimization Before RF optimization, determine the optimization objective, divide site clusters, and determine the test route. Table 4-4 describes how to prepare for a test. Table 4-4 How to prepare for an RF optimization test

Task

Description

Determining the optimization objective

Determine 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.

Divide site clusters

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.

Determine the DT route

Before performing a DT, determine the DT route 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.

4.5 Collecting Data for RF Optimization The data for RF optimization is collected by DTs and indoor tests. DTs are dominant. Whether indoor tests are required depends on the contract or the planning.

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 Issue 2.0 (2008-03-10)


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unloaded condition 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.

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.

BSC Configuration Data Collection During RF optimization, collect the configuration data about the adjacent cells for network optimization and collect additional configuration data on the BAM server. Then, check whether the existing configuration data is consistent with the previous data record and the planning data.

4.6 Analyzing Data for RF Optimization The focus of data analysis during RF optimization is the distribution of radio network signals. The data analysis involves coverage analysis, interference analysis, pilot pollution analysis, and handoff analysis.

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. l

Dominant cell analysis Analyze the PN codes and the pilot strength collected by the DT. Table 4-5 describes the possible problems about the dominant cell.

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Table 4-5 Problems about the dominant cell

Problems About the Dominant Cell

Description

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.

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.

No-dominantcell 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.

l

Downlink coverage analysis Analyze pilot signal strength and Rx power collected by the DT. If the pilot signal and Rx power are 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.

l

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 areas without uplink coverage and check whether downlink coverage is also unavailable in those areas. When both uplink and downlink coverage is poor, the downlink coverage problems take precedence over the uplink coverage problems. If only uplink coverage is poor, you can solve the problem by eliminating the impact of uplink interference, modifying the antenna 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. Downlink interference analysis

l

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 with poor 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. Uplink interference analysis

l

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.

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.

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.

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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.

l

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 change the soft handoff region by increasing the tilt angle, modifying the azimuth, lowering the antenna, or reducing pilot power.


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4.7 Modifying and Implementing RF Optimization The modification measures taken in the RF optimization involve modifications of the adjacent cell list and engineering parameters. And the modification of engineering parameters is the main measure taken. 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.

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01-04 RF Optimization.pdf

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