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10.GSM扩容工程网络规划设计,10.,GSM,扩容,工程,网络,规划,设计
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Lee Kong Haw. Huawei Technologies Co., Ltd. 公司内部资料Antenna SelectionThe antenna selection is a very important part in a mobile communication network. The antenna must be selected according to the actual conditions, such as coverage requirement, traffic volume, interference, and the quality of service of the network. A proper antenna can enlarge coverage area, reduce interference, and improve the quality of service.Because antenna selection is closely related to coverage requirement, the antenna application environment can be divided into four types according to landforms or traffic distribution. They are: urban area, suburban area, rural area, and highroad.1、 Problems Present in Antenna SelectionThis section introduces the problem present in antenna application from the following perspectives:l The antenna is selected only based on the covered traffic distribution, but little consideration is given to the relationship between landforms and antenna directional diagram. For example, if all antennas used in a network are of the same type, when the antenna is installed at a high position, the phenomenon of blind under tower” will be present because the width of the beams in vertical plane is narrow.l Too large antenna mechanical tilt angle results in the distortion of the directional diagram. In this case, coverage problem or interference problem will occur. Emulation shows that the restrictions on tilt angles must vary in accordance with the antennas with different gains.l Too much attention is focused on the high gain performance of the antenna but little attention is given to its drawbacks. As a result, the gains of almost all the antennas used in a network are quite high. A high gain antenna has many drawbacks, including large size, great weight, high side lobe, deep zero lobe, and narrow vertical beams.l No consideration is given to the difference between the vertical polarization antenna and dual polarization antenna in terms of application. The dual polarization antenna is selected from the perspective of installation.2、 Principles for Selecting Base Station Antenna in Urban AreasBase stations are densely distributed in urban areas. Therefore, it is required that the coverage area of each base station is as small as possible so as to reduce cross coverage and interference among base stations, and enhance frequency reuse rate as well. In this case, an antenna must meet the following requirements in principle.I. Selection of antenna horizontal half power beam widthBecause a large number of base stations are distributed in urban areas, overlapping coverage and frequency interference rises as serious problems in a network. To reduce the overlapping areas of neighbor sectors and the interference between base stations, you can set the beam width of the antenna horizontal half power to a smaller value. Generally, antennas whose horizontal half power beam width is 65 are selected, but antennas whose horizontal half power beam width is above 90 are not selected.II. Selection of antenna gainThe base stations in urban areas are not required to cover a large area, so the antennas with medium gain are recommended. Thus the antenna vertical beam can be wider, which can improve the coverage quality within the areas to be covered. In addition, the size and weight of the antenna with medium gain are small, which is helpful for installing the antenna and reducing cost. According to present antenna specifications, antennas with a gain of 15dBi (900MHz) and 15-18 dBi (1800 MHz) are recommended in urban areas.For the base stations on the outskirt of a city, if it is required to cover a large distance, you can select the antennas with higher gains, such as 17dBi and 18dBi.In principle, when designing base station coverage in urban areas, you should select the antennas with a fixed electrical tilt angle. The degrees of the electrical tilt angle can be set according to actual conditions (the recommended value is 6 to 9).In urban areas, to enhance frequency reuse rate and reduce cross interference, you can select the shaped-beamed antenna with the first upper side lobe suppressed and the lower side lobe filled.Because space restriction is present in the antenna installation in urban areas, the dual polarization antenna is recommended. And it is better to select the antenna with a smaller size when the electrical specifications of the antennas are the same or nearly the same.3、 Principles for Selecting Base Station Antenna in Suburban AreasBecause the environment is suburban areas are largely different from that in urban areas, antennas used in suburban areas can be selected according to the required coverage area. Generally, in suburban areas, an antenna can be selected according to the following principles:l The antennas whose horizontal half power beam width is 65 or 90 can be selected according to actual conditions. If base stations are sparsely distributed, the antennas whose horizontal half power beam width is 90 is first considered.l If the base stations are densely distributed, the antennas are selected by referring to the principles for selecting base station antenna in urban areas.l Omni antennas are not recommended for the purpose of smooth expansion in the future.4、 Principles for Selecting Base Station Antenna in Rural AreasIn rural areas, traffic volume is small and base station are sparsely distributed, so some base stations are required to cover a large area. In this case, the antennas are selected based on the following principles:l Considering the construction cost, you are recommended to select an omni antenna for the base stations whose coverage area is small and traffic volume is low. However, because the gain of the omni antenna is low, the coverage of an omni antenna is shorter than that of a directional antenna. When the base station is required to cover a long distance, the directional antenna must be selected to realize the coverage. Generally, a high gain vertical polarization antenna whose horizontal half power beam width is 90 is recommended.l One point needs to be noted. That is, if the base station antenna is installed at a high position, but the area needs to be covered lies in a low location (the depression angle is greater than 5), when an omni antenna is used, the kind with a preset tilt angle or with zero point filling function are recommended to improve the coverage quality of this area. In this case, the phenomenon of “blind under tower” and the signal fluctuation caused by uneven coverage can be avoided. 5、 Principles for Selecting Base Station Antenna along HighroadsThe principles for selecting antennas along highroads are as follows:l For the base stations designed to cover the areas along railways and highroads, a directional antenna with narrow beams can be selected.l For the base station designed to cover the highroads and the villages scattered around the highroads, an omni antenna can be selected.l For the base station designed to cover highroads only, an 8-shaped antenna can be selected, because the 8-shaped antenna help realize the highroad coverage with only a few base stations.For the base station designed to cover the highroads and the towns on both sides of the highroads, the antenna whose horizontal half power beam width is 210 canl be selected according to actual conditions. It is recommended to give the priority to the 8-shaped antenna and the 210antenna for highroads coverage.Figure 4-1shows the application of a 210 antenna.Figure 4-1 Application of a 210 antennaFigure 4-2 shows the application of an 8-shaped antennaFigure 4-2 Application of an 8-shaped antenna6、 Other Considerations for Antenna SelectionApart from the basic principles for selecting the antenna in different places are provided in the previous parts, other factors, such as system expansion and equipment performance, must be considered for antenna selection.Hereunder is an example:If the 210 antenna and used to cover the highroads nearby a small town, and only a cell is used to promise the coverage requirements, you should consider whether the traffic of this area will increase in the future and whether to meet the expansion requirements by adding carriers. Generally, once a carrier is added to the base station, the combiner loss will increase, so the coverage distance will decrease after the expansion. Therefore, when selecting an antenna, you should consider these problems beforehand and work out a good plan for the selection of antenna gain and base station type.7、 Antenna Selection Reference1 lists the antenna selection references.1. Antenna selection referenceLandformStation typeReferenceUrban areasDirectional stationGenerally, select the antennas with low or medium gains and preset electrical tilt angle dependi
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