What are the steps of RF Optimization? 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 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. 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. 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 interference between adjacent cells is considered in the network optimization. Determine the DT route
Before starting starting a Drive Test, Test, the DT route is made for verifying whether whether the Network meets 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.
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.
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 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.
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. 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-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. 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. 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).
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
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. 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.
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. 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.
