Research on Match Test Method of Base Station Transmitting System
The base station transmission system is an important part of the mobile communication system, and its performance is critical to the overall mobile communication quality. According to the analysis of the statistical results of the operation quality of the mobile network, the main reason for the decline in the quality index of mobile communications comes from the antenna feeder system (about half of them), and the most important index in the antenna feeder system is matching (standing wave ratio). Therefore, operators must attach great importance to the inspection of the antenna feeder system during wireless network construction and daily maintenance, reduce the impact of the mismatch between antenna feeder system components on the system, and maximize the performance of the antenna feeder system. In addition, the power test of the transmitter, the matching test of online work, and the interference test of the wireless environment are of great significance for network maintenance and optimization.
Common failures of base station systems
A complete cellular base station is composed of transmitter and antenna feeder system. There are many physical connection points from the transmitter to the antenna, such as the output of the transmitter, the input of the combiner / filter, the output of the combiner / filter, any position of the feeder, the input of the antenna, etc. , A good match between each link is the key to ensure the normal operation of the system.
In the entire base station system, the output power amplifier of the transmitter and the antenna feeder system are more prone to failure. The amplifier is an active device, and its output S11 parameter (standing wave ratio) is not as close to the ideal value as the passive device, and changes in external conditions (such as power supply), its own stability, and device aging caused by long-term work will affect Its output power is especially stable for the standing wave ratio. In addition, most of the entire antenna feeder system is outdoors, which is also prone to failure.
There are three main causes of transmitter failure. First, the instability of the power supply and the ambient temperature cause changes in the amplifier output power and output standing wave ratio. Secondly, the aging of the high-power tube in the amplifier causes the output power to drop and the standing wave ratio to deteriorate. Third, the deterioration of the standing wave ratio of the antenna feeder system causes the operation of the protection circuit in the transmission system and causes a decrease in the transmission power.
There are five reasons for antenna failure. First, the damage caused by lightning, water and wind. Second, destruction from ultraviolet radiation. Third, the damage caused by cyclic changes in ice and long-term temperature. Fourth, corrosion caused by environmental pollution. Fifth, environmental conditions change the dielectric properties of the antenna shield, resulting in changes in antenna performance.
In addition, cables and connectors can also cause failures due to various reasons.
From the above analysis, it is not difficult to find that the launch system and the antenna feeder system are the key to determine the normal operation of the entire system, and the two parts are strongly related. This connection point is the RF output of the transmitter, that is, the input of the antenna feeder system. If the output standing wave ratio of the transmitting system is very ideal, and the antenna feeder system is in a mismatched state, the power of the system cannot be effectively radiated into the air. On the contrary, if the antenna feeder system is in an ideal matching state, and the standing wave ratio of the transmitting system is poor, the system power cannot be effectively radiated.
Therefore, to carry out the matching measurement of the cellular system, we must first have a correct understanding of the system matching, so that we can use the right equipment and do the right work. So far we can draw such a conclusion: in the matching test of the cellular base station, high-power measurement and standing wave ratio measurement are indispensable, and it must run through the test.
Commonly used on-site antenna feeder test methods
Antenna feeder system matching (standing wave ratio) test
The antenna feeder test can measure the standing wave ratio (VSWR) of the antenna input port, and can also use the fault point location (DTF) function in the antenna feeder analyzer to accurately measure the standing wave ratio of any physical point in the entire antenna feeder system To provide accurate information on the location of the fault point to the base station maintenance engineer.
The measurement and analysis steps of the antenna feeder system are as follows.
1. Measure the standing wave ratio of the antenna feeder system and save the test curve to judge whether the system is qualified.
2. Locate the fault point and save the test curve.
3. According to the location of the fault point marked by the fault location test curve, refer to the actual situation of the base station, combined with experience, to initially determine the cause and location of the fault.
4. Repair or replace the faulty parts when necessary.
5. Repeat steps 1 and 2 to check whether the fault is eliminated.
Transmitter matching measurement and power test
The pass-through power meter can test the power and standing wave ratio of the transmitter, and is also an essential tool for troubleshooting and changing the frequency of the base station. It has been learned from the above analysis that the matching measurement of the base station includes the transmitter and the antenna feeder system. The antenna feeder analyzer can accurately measure the matching condition of the antenna feeder system, but it is powerless to the transmitter, which means that the antenna feeder analyzer only completes half of the measurement work of the entire system. The correct solution is to use the power meter and antenna feeder analyzer to complete the matching measurement of the base station system.
Network interference test
Wireless frequency resources are scarce resources. More and more frequency bands are divided and more crowded. Interference between various frequency bands is inevitable. Interference is a permanent topic in the wireless field. Today's operators are also paying more and more attention to the monitoring of interference, and solving the interference problem is one of the key factors to provide network quality.
There are many ways to find interference, such as the use of high-performance swept-frequency receivers and spectrum analyzers. The traditional method of testing interference with spectrometers is to use a directional antenna to connect to the spectrometer and continuously test to confirm the interference source back and forth, but there is almost no way for intermittent interference sources, and the test time and labor costs are relatively large.
Using 3D spectrum to locate interference source
The so-called three-dimensional spectrum is based on the original two-dimensional frequency and field strength, adding a time factor, that is, recording spectrum information every minute, every second, that is, 7 × 24 spectrum information can be collected, thereby greatly reducing labor costs and Labor intensity is especially beneficial for finding intermittent interference.
In a certain optimization project, a handheld spectrometer was used to continuously monitor the downlink frequency band of the mobile network for three consecutive days. Intermittent interference can be clearly observed from the data recorded by the spectrometer, and then the directional antenna can be used again. It is easier to catch the source of interference.
Indoor distribution system optimization test
Due to changes in user habits, the majority of today ’s social mobile services occur indoors. According to Docomo ’s 3G operating experience, 69.7% of the traffic comes from indoors, and only about 30.3% of the traffic comes from outdoor. The indoor coverage is good or bad It directly affects the quality of the entire network. Therefore, major operators pay close attention to the quality of indoor networks, and also invest heavily in indoor coverage construction and optimization.
Indoor system testing usually uses CQT testing and indoor DT testing methods. The instruments used are usually frequency sweepers, test mobile phones, CQT testers, etc. After the test, the results are processed and analyzed to obtain an optimized solution.
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