TD coverage optimization weapon-ZTE NES reverse coverage test system
The optimization of wireless network coverage is very important for improving the perception of existing network users. Good wireless network coverage is the prerequisite for ensuring the quality and indicators of mobile communication networks. And how to do coverage optimization faces the following challenges: How can we grasp the true coverage of the network and lay the foundation for optimization? How to avoid the limitations of traditional drive test tools (testing mobile phones and scanners) and discover network coverage problems in a comprehensive manner?
ZTE innovatively proposed the NES reverse coverage test system, which is much better than traditional drive test tools in terms of test data completeness, can truly reflect the coverage of the network, and provides strong support for network coverage optimization.
Limitations of traditional drive testing tools
At present, the commonly used coverage drive test tools in daily network optimization are test mobile phones and frequency sweepers. Both are used as the traditional multi-transmission single-receiving mode measurement system. The biggest limitation is that the receiver is used to measure multiple signals on the same frequency. There are problems with limited dynamic range and sensitivity. The test results cannot accurately reflect the true coverage of all cell signals in the network at each test point.
In addition, the measurement of the signal by the test mobile phone is also affected by the neighbor relationship, and only the cells in the neighbor list are measured. Due to leakage and addition of neighboring cells, the mobile phone cannot be reselected to a cell with a stronger signal than the current serving cell, and the signal measured by the test mobile phone cannot faithfully reflect the current network coverage.
Although the frequency scanner does not have the influence of neighbor relationship, reselection and handover, it is better than the test mobile phone in terms of reflecting the true coverage angle of the current network. However, the frequency sweeper stores the measured signal with the frequency point and the scrambling code as an index. When the network scale is large, it is inevitable that there is the same frequency co-scrambling code in the network, which is not conducive to post-processing software for data analysis.
The NES reverse coverage test system, as a measurement system in single-transmission and multi-reception mode, fundamentally avoids the problem of inaccurate measurement of co-frequency signals in multi-transmission and single-reception mode, and its test data is summarized and stored according to the cell ID as an index. Facilitate post-processing software analysis.
NES reverse coverage test system collects network coverage efficiently and accurately
System principle
The NES reverse coverage test system uses the TDD characteristics of the TD-SCDMA system to cooperate with the mobile transmitter station independently developed by ZTE at the specified frequency point and uplink time slot to realize the reverse coverage measurement function for TD base stations. When the network is idle, the mobile transmitting station is used to transmit the uplink signal at a fixed power along the test route. All base stations measure the signal and obtain measurement data such as signal reception level. The RNC side indexes the measurement data reported by all base stations according to the cell ID. Summarize and store. Figure 1 is a schematic diagram of the system.
Figure 1 Schematic diagram of NES reverse coverage test system
When the mobile launcher moves along the test route with the test vehicle, it can synchronize time and obtain latitude and longitude information through the GPS receiver. The system side records the cell transmission power configuration, uplink time slot measurement data and timestamp information combined with the GPS latitude and longitude, timestamp information and transmission power uploaded by the mobile transmission station through the air interface. Through the data processing of the post-processing software, all base stations in the test area can be obtained The single cell downlink coverage level distribution map (based on the test route) for coverage analysis; at the same time, the test data can also be applied to planning software for propagation model correction and other processing.
System advantages
Taking the TD live network test as an example, the reverse coverage test and the scanner antenna are placed outside the test vehicle, and the test route is the same. The coverage level of the cell is collected. Through comparative analysis of various aspects of the test data, it is reflected The advantages of the reverse coverage test system in terms of completeness of data collection.
â— Comparison of cell signal coverage
Taking a certain cell as an example, the analysis software is used to present the cell coverage of the cell obtained by the reverse coverage test system and the frequency scanner.
As can be seen from Figure 2, the reverse coverage test system is a single-transmission multi-reception mode test system, and there is no problem of limited dynamic range and sensitivity when the frequency sweeper measures multi-channel signals at the same frequency. The true coverage of a cell signal. However, due to its limitations, the frequency scanner can measure the coverage of the cell signal is very limited, especially some of the strong signals can not be demodulated, can not faithfully reflect the network coverage.
Figure 2 1110 cell signal coverage measured by two drive test tools
â— Comparison of pilot pollution prediction
Under the same conditions, conduct pilot pollution analysis on the reverse coverage test data and the frequency scanner test data. The red dot in Figure 3 is the predicted pilot pollution point. The connection indicates that the pilot pollution is caused by the signal of the connected cell. Table 1 is a list of pilot polluted cells.
Figure 3 Two types of drive test tools analyze the situation of cells in the same pilot pollution area
Table 1 List of pilot polluted communities
From the above analysis, it can be seen that at the same pilot pollution area, the reverse coverage test system can analyze that the pilot pollution is caused by the signals of 7 cells; while the scanner can only analyze the 4 cells. signal source. The reverse coverage test system can more comprehensively present the coverage problems in the network, enabling network optimization engineers to output the final solution "one-time" for the coverage problems and improve the optimization efficiency.
Combined with ACP to realize intelligent network optimization
ACP (automatic cell planning tool) mainly evaluates various aspects of network performance through different data sources (drive test data, traffic information, base station data and electronic maps, etc.), locates problem cells and problem areas, and automatically uses genetic algorithms Search for the best solution to improve network performance. In practical applications, the data source of ACP can use the complete network coverage data collected by the reverse coverage test system, and the ACP tool can be used to locate all network coverage problems at once and output coverage optimization solutions.
Taking an optimization area in the existing network as an example, the ACP optimization adjustment based on the reverse coverage test data is conducted for the pilot pollution problem in the area. Figure 4 shows the comparison before and after the optimization adjustment.
Figure 4 Comparison of pilot pollution before and after optimization area adjustment (red is the pilot pollution area)
Comparing the drive test data before and after the adjustment, it can be seen that the proportion of pilot pollution is reduced from 0.99% before the adjustment to 0.53% after the adjustment, and the network index is increased by 46%. At the same time, the PCCPCH RSCP and C / I of the adjustment area have also been greatly improved.
The advantages of the reverse coverage test system in terms of completeness of data collection can help network optimization engineers to find coverage problems that cannot be found with traditional drive test tools. On this basis, by combining with the ACP tool for antenna feed parameter optimization application, the output optimization adjustment scheme can be used as the final solution, avoiding the drawbacks of multiple testing and multiple adjustments in the traditional optimization method, and greatly improving the network optimization efficiency. After statistics, the ACP optimization adjustment based on the reverse coverage test data has improved the overall coverage optimization efficiency by at least 50%. As the size of the site increases, the efficiency improvement trend will become more obvious. Table 2 is the efficiency improvement statistics of 30 sites.
Table 2 Efficiency statistics
ZTE's NES reverse coverage test system only needs software upgrade on the base station side of the system to realize the dedicated measurement function, which has no impact on the existing network equipment. Together with the mobile launcher, the problem of limited dynamic range and sensitivity of the same drive frequency measurement at the receiving end of the traditional drive test tool (multi-transmission single-receive mode) is fundamentally avoided, providing a new idea and method for the acquisition of current network test data . Through further in-depth mining and application of the coverage data obtained by the NES reverse coverage test system, such as RF optimization combined with ACP, construction of interference matrix for network neighborhood, frequency and scrambling code optimization applications, can greatly improve coverage optimization efficiency And accuracy. ZTE will subsequently increase the application of the system in the field, give full play to its technical advantages as a new type of network coverage optimization tool, and provide operators with strong support for building TD quality networks.
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