Communication intermediate engineer

Discussion on lightning protection and grounding of mobile communication base station

This paper introduces the importance of lightning protection and grounding of mobile communication base station, the composition and basic requirements of lightning protection and grounding system, and the lightning protection and grounding of mobile communication base station.

Keywords: lightning protection and grounding of mobile communication base station

1, the importance of lightning protection and grounding for mobile communication base stations

Today, with the rapid development of mobile communication technology, usually, because the BTS antenna of mobile communication base station is located outdoors and set up relatively high, charged clouds will generate induced charges on the antenna. If there is a DC path between the antenna and the earth, the charge can be discharged through the earth without accumulation, so that the induced charge will not be discharged due to the high potential difference between the antenna and the earth.

In dry climate, the friction between sand, snow and antenna will also generate static electricity. Grounding is helpful to reduce lightning damage, electrostatic damage and man-made noise, so it is very important to ground all kinds of grounding communication equipment. Because the quality of grounding system is often the key to avoid lightning accidents, lightning protection is often an important issue in the installation and design of BTS equipment. For isolated mountain base stations in mountainous areas, lightning strikes are more frequent, and the design of lightning protection grounding system should be paid more attention.

2. Composition and basic requirements of lightning protection and grounding system

Lightning protection grounding system is a whole consisting of five parts: earth, grounding electrode, grounding lead-in, grounding bus and grounding wire. Among them: the earth has conductivity and infinite capacity, which is a good common reference potential; The grounding electrode is a metal belt that is in equal electrical contact with the earth. For spreading current to the earth; The grounding lead is a component that connects the grounding electrode and the indoor grounding bus. The grounding bus is a bus copper bar that collects grounding wiring; The grounding wire is the wire that connects the equipment to the grounding bus.

Grounding electrodes include rod-shaped grounding electrode group (made of flat steel or angle steel), steel plate grounding electrode group and horizontal radiation strip grounding electrode, and composite grounding network composed of these forms. Instead of breaking ground, it is better to drive vertically into the ground and connect them with wires. Because of the poor compactness of backfill soil, the grounding resistance is large. Besides. The grounding resistance under the tower should be as close as possible to the bottom of the tower.

Flat braided wires or stranded wires cannot be used as grounding leads, because they are easy to be corroded and oxidized, and have large inductance and mutual inductance, which is not conducive to discharging surge current. Therefore, it is best to use 16 ~ 18 galvanized flat iron or rebar. Welding is recommended for the connection with lightning rod and grounding body, and the length of welding contact seam should be more than 20cm, so as to prevent serious desoldering caused by small contact surface heating when large current passes through. It is best to use the same metal material for the whole lightning protection and grounding system, such as lightning rod, down conductor and grounding body, in order to prevent the grounding wire from being corroded due to long-term electrochemical reaction and poor grounding. In particular, direct contact between copper and galvanized iron parts should be avoided, because copper and zinc will form copper-zinc batteries at the contact surface, which will corrode quickly. When the grounding wire is led down from the roof, it should be prevented from being close to or arranged parallel to other conductors. Even if other conductors are in contact with the ground, they should be separated by more than 2m. When the grounding lead must pass through the metal tube, the down lead must be connected to the conductors at both ends of the conductor, which is also called the connecting wire of the grounding wire.

Generally, grounding rods are divided into indoor grounding rods and outdoor grounding rods. Indoor grounding rods are generally installed on the wall near BTS and power cabinet, and are the same height as the distribution frame. Outdoor grounding wire is generally near the water supply pipe window (within 1m). The grounding rod is made of copper rod. The connecting cables (called grounding wires) from the grounding bar to various devices should be as short as possible. Finally, the indoor grounding rod is led to the grounding electrode at the bottom of the building through a single black grounding wire. Outdoor grounding rod can be connected to the grounding body at the bottom of the building with black grounding wire (95mm2).

The requirements of lightning protection grounding system are mainly reflected in the following two aspects: ① Requirements of grounding resistance: grounding resistance mainly includes: soil resistance, contact resistance between soil and grounding electrode, resistance of grounding electrode itself, grounding down lead resistance, etc. Because the latter resistance is very small and generally negligible, grounding resistance mainly refers to soil resistance. Reducing grounding resistance is the key to realize lightning current leakage. The formula for calculating all voltage drops of lightning current passing through a single down conductor is

Where is the voltage drop in units; Is the lightning current, and the unit is: the resistance of the grounding device, and the unit is; Is the inductance per unit length, about1.5; Is the down lead length, and the unit is; Is the steepness of lightning current, in. According to the formula, the smaller the resistance value of grounding resistance in lightning protection grounding device, the smaller the instantaneous impact grounding voltage drop, and the less dangerous the facility is when lightning strikes. Different facilities have slightly different requirements for grounding resistance, such as mobile communication base station base ≤ 4Ω, antenna and feeder metal shield ≤ 4Ω, signal arrester ≤10Ω, power arrester ≤ 4Ω, safety protection place ≤ 4Ω and communication room ≤1Ω. When designing the system, it is necessary to plan correctly and meet the standard parameters. ② Requirements for common grounding: There is no separate grounding in the lightning protection design specifications of IEC (International Electrotechnical Commission) and ITU-T (International Telecommunication Union), but a public * * * grounding network is established for lightning protection, that is, the power supply grounding, workplace grounding and protective grounding are integrated on the public * * * grounding wire, and a zero potential reference level platform is established. In the mobile communication base station, lightning protection grounding is lightning protection for leakage grounding; Working grounding is grounded by DC power supply; Protective grounding is the grounding of indoor equipment shell.

3. Several practical situations of mobile communication base station BTS grounding.

3. 1 Use the existing lightning protection zone

When the building where BTS is located has reliable roof lightning protection belt, lightning protection grounding and working grounding, the existing grounding device of the building should be used for BTS grounding, but its grounding resistance value must be tested. If the test results do not meet the requirements. Grounding body should be added to make the grounding resistance meet the requirement of ≤ 5 Ω. If the lightning protection grounding of the building is separated from that of working grounding, the grounding resistance of the lightning protection grounding device is greater than that of working grounding, so the grounding body should be added to make its resistance equal to or smaller than that of working grounding. The antenna, antenna mast/tower, feeder and roof trolley shall be reliably connected with the roof lightning protection belt, and the connection points shall not be less than two points. If there is no lightning protection belt near the antenna, the down lead is specially designed to lead to the grounding body along the external wall, and the grounding rod in the computer room is not introduced.

3.2 There is no lightning protection zone in the building.

When there is no ready-made roof lightning protection zone in the building, a certain number of lightning rods should be erected, so that the top of the antenna is under the protection angle of the lightning rod, and the grounding wire of the lightning rod should be directly led to the grounding body downstairs.

3.3 BTS is equipped with antenna tower.

When BTS is equipped with an iron tower, a three-in-one (i.e. common grounding) system is usually adopted. In this case, the whole computer room is generally designed within the lightning protection range of the tower, and there is no lightning protection belt at the top of the computer room, but a closed grounding ring can still be buried around the computer room to make the ground potential of the computer room evenly distributed and shorten the grounding lead. The closed grounding ring is connected with the balanced grounding ring of the underground tower. The tower feet should also be connected with each other, and more points should be connected with equalizing rings. The coaxial cable of the antenna must be installed in the tower to prevent large current from passing through the coaxial cable. Grounding requires a conductor with large cross-section to meet the requirements of low resistance, high heating, small lead inductance and small skin effect.

4. Lightning protection and grounding of mobile communication base stations

4. 1 Lightning protection and grounding of power supply system

(1) The AC power supply of the mobile communication base station shall adopt the three-phase five-wire system.

(2) The mobile communication base station should be equipped with a special power transformer, and the power cord should be a cable with a metal sheath or an insulating sheath, which is introduced into the mobile communication base station through a steel pipe. Both ends of metal sheath or steel pipe of power cable shall be reliably grounded nearby.

(3) When the power transformer is located outside the station, for overhead high-voltage power lines in exposed areas with annual thunderstorm days of more than 20 days and earth resistivity of more than100Ω/m, it is advisable to erect lightning protection wires above them, and the length should not be less than 500m ... The power lines should be within the protection range of the lightning rod at a 25-degree angle, and each rod of the lightning rod (except the terminal rod) should be grounded once.

In order to ensure safety, a set of zinc oxide arresters should be installed on the front pole of the terminal pole of lightning rod.

(4) When the power transformer is located in the station, its high-voltage power line should use power cable to enter the station from underground, and the length of the cable should not be less than 200 m. The three-phase conductor at the joint of the power cable and the overhead power cable should be equipped with zinc oxide arrester, and the metal outer sheath at both ends of the cable should be grounded nearby. ,

(5) In the mobile communication base station, the three wires on the high-voltage side of the AC power transformer should be equipped with zinc oxide arrester to the ground nearby, and the three-phase wires on the low-voltage side of the power transformer should be equipped with gapless zinc oxide arrester to the ground respectively. The shell of the transformer, the AC zero line on the low voltage side and the metal outer sheath of the power cable connected with the transformer shall be grounded nearby. Lightning arresters should be installed at all power line exits in and out of the base station.

(6) The low-voltage power cable entering the mobile communication base station should be introduced into the computer room from underground, and its length should not be less than 50m. Lightning arresters should be installed at the place where power cables enter the AC screen of the computer room, and the zero line led from the screen shall not be grounded repeatedly.

(7) The normally uncharged metal parts of the power supply equipment of the mobile communication base station and the grounding terminal of the lightning arrester should be protected and grounded, and zero protection is prohibited.

(8) The DC working place of the mobile communication base station should be connected to the indoor grounding collector line nearby. The cross-sectional area of grounding wire should meet the requirements of maximum load, generally 35 ~ 95mm2, and the material is multi-strand copper wire.

(9) The power supply equipment of mobile communication base station shall meet the requirements of lightning impact resistance index in relevant standards and specifications, and the AC screen and rectifier shall be equipped with classified protection devices.

(10) Lightning impulse resistance indexes of power arrester and feeder arrester shall meet the requirements of relevant standards and specifications.

4.2 Lightning protection and grounding of iron tower

(1) The tower of the mobile communication base station should have a perfect lightning protection device to prevent direct lightning and secondary induction lightning.

(2) The tower of mobile communication base station adopts solar lighthouse. For aviation sign lights powered by alternating current, the power cord should be a cable with a metal sheath, and the metal sheath of the cable should be grounded outside the entrances of several engine rooms at the top of the tower. Lightning arresters shall be installed at the entrance of the machine room for each phase line of the lighthouse control line and power line, and the zero line shall be directly grounded.

4.3 Lightning protection and grounding of antenna feeder system

(1) The antenna of the mobile communication base station shall be within the protection range of the lightning receptor, and the lightning receptor shall be provided with a special lightning current downlead made of 40×40mm galvanized flat steel.

(2) The metal outer sheath of the coaxial cable feeder of the base station should be grounded nearby at the upper and lower parts and the entrance of the wire rack into the machine room, and the grounding at the entrance of the machine room should be correctly connected with the grounding wire led from the nearby grounding network. When the height of the tower is greater than or equal to 60m, the metal outer sheath of the coaxial cable feeder should also be indirectly in the tower.

(3) After the coaxial cable feeder enters the computer room, a feeder arrester should be installed at the connection with the communication equipment to prevent the induction lightning introduced from the antenna feeder. The grounding terminal of feeder arrester shall be connected to the ground wire at the entrance of nearby outdoor feeder. When selecting feeder arrester, the impedance, attenuation, working frequency band and other indicators should be considered to adapt to communication equipment.

4.4 Lightning protection and grounding of other equipment

(1) The construction of mobile communication base stations should have perfect lightning protection devices (lightning protection network, lightning protection network and connectors, etc. ) prevent direct lightning and inhibit secondary induction lightning.

(2) All kinds of metal facilities at the top of the machine room should be connected with the lightning protection belt on the roof nearby. The colored lights at the top of the computer room should be installed under the lightning protection belt.

(3) Wiring racks, hanging iron racks, racks or casings, metal ventilation pipes, metal doors and windows in the machine room shall be protected and grounded. Generally, multi-stranded copper wires with a cross-sectional area of not less than 35mm2 should be used for protective grounding leads.

5. Concluding remarks

With the continuous development of IT industry, the equipment and lightning protection measures of mobile communication stations are constantly innovating. As long as we continue to explore and optimize the research in engineering practice, fully understand the possible invasion ways of lightning, and adopt all-round and multi-level comprehensive protection, we can achieve effective lightning protection effect.

References:

[1] Code for Lightning Protection and Grounding Design of Mobile Communication Base Station (YD5068-98)

[2] Zhang Dianfu. Fundamentals of mobile communication. China Water Conservancy and Hydropower Press.

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On the Optimization of Mobile Communication Network

Network optimization is based on the principle that the network serves the market, providing solid technical support and guarantee for the business development of market operation, providing users with efficient and high-quality communication services, and finally realizing the real network optimization. Based on some maintenance experience of Hubei Unicom, this paper puts forward some ideas and methods to analyze and solve problems, which has certain reference value for engineers and technicians engaged in network maintenance.

Keywords: mobile communication network quality network optimization

order

With the development of the mobile communication industry, the scale of the network is getting larger and larger, and the number of mobile users is also increasing. The mobile communication network is facing severe challenges. On the one hand, with the rapid development of social economy and the acceleration of urban construction, the network environment is constantly changing, which leads to the increasingly complex structure of mobile communication network; On the one hand, the number of mobile users is amazing and the network scale is expanding, but the frequency resources are scarce; On the other hand, there are some remaining problems in the process of network construction and expansion, which leads to the decline of network quality. Many of the above problems need to be solved through network optimization. With the intervention of mobile communication competition mechanism, how to improve network performance and network quality has become an important bargaining chip for major operators, who are very concerned about the quality of mobile communication networks. Therefore, the work of network optimization can not be ignored, and its position and function are becoming more and more important for network operation and maintenance, network planning and engineering construction, which has positive guiding significance.

Since network optimization is so important in the communication industry, what is network optimization? Network optimization is a high-level maintenance work, which is to modify the parameters of the officially put into operation mobile communication network by adopting new technical means and optimization tools, rationally allocate network resources, and make the network reach the best operation state, thus improving the maintenance work of mobile network quality. Next, I will talk about my own views based on years of network maintenance experience.

The goal of network optimization

2. 1 expanded capacity

As a mobile communication user, I hope I can make a phone call anywhere with good call quality. But to do this, the network provided by operators must be able to provide enough business capacity. Service ability is related to the traffic of each user and the call loss of wireless channel. The call loss of foreign operators is generally 2%, while in China, due to economic reasons, the call loss is usually 5% in suburbs and 2% in urban areas.

2.2 Expand coverage

Coverage is a key factor that we need to consider in network optimization. If the coverage is not ideal, it will have adverse effects on many aspects of the system. Control coverage is the most important in optimization, so the mobile communication network should provide as large coverage as possible. In order to control the coverage, we can adjust the hardware and software. In terms of hardware, network quality can be improved by adjusting antenna angle, gain, azimuth, pitch angle and power, selecting the best site, adjusting carrier frequency configuration and balancing traffic distribution. Software? By modifying some cell parameters, such as access permission parameters, cell selection parameters, power parameters and handover parameters, the best coverage effect can be obtained.

2.3 provide good network services

The network spread of mobile communication determines that the coverage area cannot be covered by 100%, and it can only be hoped that the coverage area will have as few dead angles as possible. Speech quality depends on signal level and interference level. Sometimes the signal is very strong, but the quality is not good because of the interference problem. There are many reasons for dropped calls, which are related to signal level, interference level and switching level.

To achieve these goals, you can spend a lot of money, but a good network needs careful planning and design, and reasonable use of frequency and equipment to meet the above requirements at the same time.

Network optimization process

The process of network optimization is actually a cyclic process, and the whole process includes five steps: data collection, data analysis, making optimization scheme, implementing optimization scheme and adjusting optimization scheme.

As shown in the figure below:

3. 1 data acquisition

In order to optimize the network, it is necessary to fully understand the running state of the network, mainly to find the problems existing in the current network. This is data collection, which must be completed first and is a very important link in network optimization. At present, our data collection includes the following four ways:

3. 1. 1 DT data acquisition method:

DT, the abbreviation of English Driver Test, is translated as on-board test, that is, with the help of test instruments, mobile phones and other test tools in the test car, combined with geographic information map and network resource allocation, the wireless coverage, voice quality, handover relationship between cells and downlink wireless interference of the current network are tested. , so as to collect the problems existing in the current network and provide reliable data for the next data analysis.

3. 1.2 CQT data acquisition method:

CQT, the abbreviation of English Call Quantity Test, is translated as voice quality test, that is, multiple test points are selected for a certain number of calls within the current network coverage. It mainly tests the voice quality of the call, the reception level, whether the collection is frequently switched and dropped between communities, and the test points are generally selected in public places with relatively concentrated communication, such as airports, hotels, stations and office buildings.

3. 1.3 OMC data acquisition method:

OMC, the abbreviation of English operation management center, is translated into operation management center test, that is, the collected wireless traffic statistics report data and system hardware alarm information are obtained through the base station operation management center. By analyzing the indicators in the traffic statistics report (call success rate, dropped call rate, handover success rate, traffic per time slot, wireless channel availability, voice channel blocking rate, signaling channel availability rate, dropped call rate, blocking rate, etc.). ), you can know the traffic distribution and changes of wireless base stations and find abnormal problems. Combined with other means, we can also analyze the rationality of network logic or physical parameter design, the balance of traffic, whether there is frequency interference and hardware failure. These indicators can be used to analyze the working state and optimization direction of the cell base station.

3. 1.4 user declaration data collection method:

The data collection method of user declaration is to understand the network quality through user complaints or business complaints or user surveys. This method can timely understand the problems related to the quality of service in the network, and it is an important way for us to understand the status of network services. Through this collection method, we can understand the phenomena in the network, such as call failure, dropped call, crosstalk, one-way, echo, signal interval, voice interval and so on.

But in practical work, we will cooperate with each other, confirm each other and collect network problems.

3.2 Data analysis

Through three acquisition methods of DT, CQT and user notification, the network field strength coverage map, bit error rate map, packet loss rate map, effective neighbor cell map, neighbor base station frequency interference map, dual-frequency network evaluation, call process events and frequency statistical reports are obtained, so as to obtain the location of network coverage blind area. Network interference (uplink/downlink) location, handover analysis report, etc. Traffic statistics can be obtained by OMC acquisition method, and information such as connection rate, dropped call rate, handover success rate and handover failure rate can be obtained after processing.

3.3 Develop an optimization plan

According to various data analysis methods, obtain data, analyze effective data, judge the cause of the problem, and take corresponding measures to optimize the network.

Usually, the optimization scheme we make in network maintenance is generally the initial level optimization scheme. To further improve the operation quality of the network, we must carry out higher-level optimization, which needs to be carried out periodically and step by step, constantly improve the network requirements, and cycle the network optimization process according to the data analysis results, and finally get a good quality network.

3.4 the implementation of the optimization scheme

According to the established optimization scheme, the optimization scheme is implemented in strict accordance with the site, so that the network can achieve good quality. If you encounter steps that cannot be completed, you need to record them and return to the maintenance center to make a feasible plan again.

3.5 Adjust and optimize the scheme

When the expected network quality is not achieved after the implementation of the optimization scheme, that is to say, there are still problems in the optimization scheme we implemented. At this time, we will reanalyze the data according to the collected effective data and get a better solution. This is called adjusting and optimizing the scheme, and this process is usually repeated many times.

Network optimization method

At this stage, according to the optimization scheme, we mainly take the following measures in the process of network optimization: base station alarm investigation, base station patrol, frequency planning optimization, antenna adjustment, handover relationship modification and database modification. Achieve the purpose of optimization: reduce the congestion rate, drop call rate, improve the connection rate, improve coverage and improve call quality.

4. 1 Method 1: First, use planning optimization software to simulate and calculate the adjusted effect. If satisfied, adjust the antenna parameters, then conduct wireless test, and repeat the simulation, adjustment, test and comparison until it reaches a good service state.

4.2 Method 2: According to the statistical data obtained from the wired part test, analyze the reasons of poor network service quality. After modifying the central management system or equipment terminal database, statistics will be made. Try to modify only one parameter at a time, and get a better index through repeated modification, statistics and comparison.

4.3 Method 3: Adjust the angle, height, inclination, type, connection and transmission power of the terminal equipment according to the test data of blind spots and areas with poor voice quality. If necessary, use the standing wave ratio comprehensive tester to check whether the antenna feed system, such as wireless output power, feeder return loss, large line angle, model and height, is in line with the design. Use power meter, spectrometer and other instruments to check the output power, amplification gain, working level of test point, filter output waveform, etc. Base station hardware equipment module. This can deal with bad base stations, such as replacing faulty components, adjusting antennas, and even changing the location of base stations.

4.4 Method 4: By upgrading and repairing the software versions of the central control system and terminal equipment, the network can obtain new statistical functions, network services and better working conditions. At the same time, the adoption of perfect recording notification system, short message, voice mail and other new services is also conducive to reducing invalid calls and improving the connection rate.

Concluding remarks

In a sense, network optimization is also a process of constantly optimizing and adjusting various parameters in the network according to the changes of users' feelings and business requirements. With the development of market business, new technologies will be applied on the network, and new problems will appear constantly. Only through continuous learning and experience accumulation, especially the understanding of new technologies and knowledge reserve, can we keep up with the pace of technological development and improve the quality of mobile communication networks through network optimization.

The above discussion is only a small part of network optimization. In the process of network optimization, more and more complex problems will appear. We must proceed from the overall concept and never let go of any suspicious point, because some faults are often caused by many inconspicuous and seemingly unrelated equipment and parameters. Especially in fault analysis, we must clear our minds and find the fault point according to the process. We must never make a plan blindly without finding the fault point.

References:

[1] Huang Lunzhou. Analysis of GSM network optimization scheme in Suizhou [J]. Telecom Express, 2004;

[2] Dai Mattel, Wu Zhizhong. . Optimization of GSM mobile communication network [M]. Beijing: People's Posts and Telecommunications Press. 2003；

[3] Sun Minying. Telecommunications technology, issue 05, 2003;

[4] Wang Hongwei. Information Technology, Volume 30, No.4, 2006;

[5] Xiaolei Chen Xiangtan Mobile Communication Company (network resources).

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