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2 Definition and classification of repeaters Repeaters are a two-way amplifier that can simultaneously amplify the signals of base stations and mobile stations, also known as relay stations. The repeater in the downlink picks up the signal from the existing coverage area of ​​the donor antenna, excellently isolates the out-of-band signal through the band-pass filter, and then amplifies the filtered signal by the power amplifier and transmits it to the standby Cover the area. In the uplink, the signals of the mobile stations in the coverage area are processed by the uplink amplification link in the same working mode and then transmitted to the corresponding base station, so as to realize the signal transmission between the base station and the mobile station.
There are many classification methods for repeaters. According to different transmission methods, repeaters can be divided into fiber optic repeaters and RF repeaters. According to different channel bandwidths, repeaters can be divided into channel selection and broadband repeaters. According to the different signal access methods, it can be divided into GSM, CDMA, WCDMA and TD-SCDMA repeaters. According to different installation scenarios, it can be divided into outdoor repeaters and indoor repeaters.
3 Application Features of Repeater Stations 3.1 Features and Application Principles of Repeater Stations In mobile communication networks, the solutions are different according to the equipment type of the repeater station and different application scenarios.
The radio frequency repeater uses the wireless transmission method, with a short construction period, low investment, low transmission requirements, but high signal isolation requirements. The wireless repeater receives signals from space, and it is bound to require the space signal to be as pure as possible. In areas where the base station is dense, the difficulty of separating the signals of different base stations or sectors will greatly increase, and it is easy to increase the interference of the repeater to the base station. Therefore, in areas where the base station is relatively dense, it is recommended to use fiber optic repeaters as much as possible. In places where the conditions for using fiber optic repeaters are not available, only wireless repeaters can be used, but the donor antenna must have sufficient directional selectivity.
Optical fiber repeaters use optical fiber as the transmission medium, with low transmission loss and long transmission distance, but need to set up optical fiber, and there is no advantage in investment compared with the use of microcellular or outdoor integrated base stations. Repeaters can play a role in expanding coverage and absorbing traffic, and can significantly increase the total traffic of some base stations, thereby improving network resource utilization.
Whether it is a fiber optic repeater or an RF repeater, you must pay attention to the radius of the repeater's service area and the distance between the repeater and the donor base station during the application must not exceed the TA (time advance) limit. For ordinary repeaters, the distance should not exceed 35 km. For code division multiple access systems, it is best not to exceed 10 km.
When planning the construction of repeaters, three issues should be paid attention to:
(1) The overall principle is to use the repeater reasonably without affecting the quality of the existing network.
(2) To ensure that the signal of the serving cell plays a leading role, the donor antenna should adopt a high-gain antenna with a narrow beam in the horizontal direction.
(3) Prevent self-excitation Because the repeater's sending and receiving are of the same frequency, it is easy to cause self-excitation, thus causing interference to the network. Generally, the isolation between the donor antenna and the cover antenna is greater than 15 dB greater than the overall gain (including the antenna). In actual operation, on the one hand, try to choose antennas with different heights; on the other hand, there should be high shielded obstacles or a certain distance between the two antennas.
For different geomorphic environments, it is recommended to refer to the following construction principles:
(1) Dense urban area In the dense urban area, indoor repeaters are often used as the signal source of the indoor distribution system. In some places where the distribution of buildings that need to be covered is concentrated, a base station may be configured with multiple repeaters.
The wireless environment in dense urban areas is very complex. The application of outdoor repeaters will cause interference to the network, causing pilot pollution and co-channel interference. Therefore, it is generally not recommended to use outdoor repeaters in dense urban areas. Repeaters with low power (preferably below 1 w) should be used.
(2) The edge of the city The number of base stations on the edge of the city is often relatively small, but there is a need for coverage in emerging residential quarters and development zones. At this time, network problems are mainly reflected in signal coverage. Repeater equipment with a power of about 10 w can be used in this area.
(3) Suburbs, rural suburbs, and villages mainly solve coverage problems. In areas where fiber is laid, it is best to use high-power fiber repeaters (10/20 W) to expand coverage.
For areas that do not have fiber optic resources but can receive base station signals, wireless repeaters can be used to solve coverage problems. In special cases, frequency-shift repeaters can also be used to increase the coverage distance.
3.2 The main purpose of the repeater (1) The coverage of the blind zone The repeater is an extension of the coverage of the base station, and the base station signal is amplified and transmitted to a larger area to provide services for areas with poor original signal coverage. This is also the most common application method of repeaters at present, and it is mostly used to provide coverage for marginal towns, transportation trunk lines, outdoor special terrain and tourist attractions with low demand for dialogue services.
(2) Indoor coverage in some deep buildings (such as shopping malls, office buildings) or shadow areas (such as tunnels, basements, etc.) can also receive good results by setting repeaters.
(3) Traffic balance The extended features of repeaters are used to introduce the services of idle base stations into the coverage area of ​​busy base stations, which can play a guiding role and help the entire system to further achieve traffic balance.
(4) Network optimization Due to various reasons, there is still a weak signal in the local area between certain service areas. Because the area is small or there is no high traffic demand, it is not suitable to build a base station. The repeater improves the signal condition in the area.
3.3 Comparison between repeater and outdoor small base station Outdoor small base station mainly refers to outdoor microcell and integrated small base station. Compared with outdoor small base stations, repeaters have their own characteristics.
(1) The investment and construction period of building an outdoor small base station are relatively large, while the repeater station has a small investment and is simple and flexible to install.
(2) The repeater can be used to absorb traffic. When a cell is idle, the traffic introduced by the repeater can be used to improve the utilization rate of the equipment, while the outdoor small base station can increase the total capacity of the system and share the surrounding base stations. Traffic pressure.
(3) The use of outdoor small base stations requires the allocation of new frequency points or PN codes, which may be difficult in some cases, and the repeater does not need to allocate new frequency points or PN codes, but it needs to control its generation to other cells interference. 4 Typical applications of repeaters 4.1 Dense urban indoor coverage signal sources Repeaters are commonly used as indoor coverage signal sources, but in dense urban areas, due to the large number of buildings, the number of repeaters required is also relatively large Many, it is easy to have multiple repeaters in one base station or even one sector, but introducing too many repeaters will cause relatively large interference on the signal of the donor base station, on the other hand, it will increase the donor base station ’s signal. The amount of traffic will cause difficulties in accessing the donor base station. In the code division multiple access network, due to the self-interference characteristics of the system, introducing too many repeaters will cause more serious damage to the donor base station. This is an inevitable problem of using repeaters as indoor coverage signal sources in dense urban areas.
For example, during network optimization in a city, an operator found that some areas have relatively serious reverse interference alarms, which caused network quality degradation and user complaints. After investigation and analysis, it is believed that the causes of the above problems are in these areas The original macrocell introduced too many optical fiber repeaters.
After analysis and demonstration, in order to solve the above problems, a set of base station equipment can be used alone as the donor base station of the indoor coverage optical fiber repeater. This equipment is not used for outdoor coverage. It shares the site, power, transmission and Grouped equipment. After the implementation of this method, the original reverse alarm of the network disappeared, and all other network indicators have been improved to varying degrees. After many experiments, this method can solve similar problems in mobile communication networks of various standards (GSM, CDMA, WCDMA, etc.).
4.2 Incorporate fiber optic repeaters into the network management system In rural areas, transportation roads and other areas that require wide coverage and low capacity, operators often use high-power repeaters to meet coverage from the perspective of construction cost, network quality indicators and operational benefits. demand. Normally, these repeaters are not included in the network management system, and the stability of repeater equipment is often lower than outdoor microcells or integrated base stations. It is difficult to be found in time when a fault occurs, and it is easy to cause user complaints.
Taking into account the characteristics of optical fiber repeater stations, in the construction of the project, some important optical fiber repeater stations can be included in the network management system, and additional equipment such as UPS or small-capacity batteries and outdoor switching power supplies can be added. Although the construction cost is increased, there is no investment advantage compared to the construction of outdoor microcells or integrated small base stations, but it can effectively improve the stability and resource utilization of the network.
4.3 Micro-zones in dense urban streets In some areas of dense urban areas, landforms and landforms often show the characteristics of dense (high) -story buildings with small intervals between buildings. In these areas, low-rise buildings and road coverage have always been difficult for mobile network construction. Building a single macro base station is difficult to achieve the expected coverage effect. Building multiple base stations not only requires a large investment, but also damages the network quality because the distance between the stations is too small. Consider using repeaters at this time.
In these areas, the rooftop signal is usually strong and the signal is single. You can choose a repeater with appropriate power to install on the rooftop. The service antenna is placed in the middle of the building group. The isolation of the building can effectively control the repeater ’s cover. This application method can be regarded as a construction method of the street micro cell, but the setting of the transmission power and the selection of the antenna installation position in this construction method are complicated. When the signal leaks from the micro cell, it is easy to The quality of the network is disrupting.
4.4 Coverage of Highway A section of a highway is far away from nearby base stations, the signal is weak, and the communication is on and off, the effect is very bad. Because the roads at the front and back of the station are relatively straight, you can choose a suitable station on the road section to install a fiber optic repeater, and equipped with smaller front and rear antennas with larger gains. , Using one antenna can meet the coverage requirements of the road section.
4.5 The coverage extension of the tortuous terrain often encounters such situations in mountainous areas. The coverage target is located in the valley, which is very close to the base station, but the signal cannot be reached because it is blocked by the mountain. At this time, you can follow the valley and choose a suitable location at the inflection point to install the repeater. Since the direction of the repeater receiving the signal and the direction of the transmitting signal are at a certain angle, it is equivalent to a turn of the base station signal at the repeater. The donor antenna and the service antenna of the repeater are placed on both sides of the mountain, and the mountain is used to form a natural barrier. The performance of the repeater can be fully exerted.
5 Conclusion In the mobile communication network, the reasonable use of repeater equipment can play a role in expanding the coverage of the base station, absorbing traffic, and improving the utilization rate of network resources. In engineering practice, it is necessary to avoid or reduce the negative impact of the repeater on the network according to the characteristics of the repeater.
Application of Repeater in Covering Blind Area of ​​Mobile Communication Network
1 Introduction In mobile communication networks, due to various reasons, the network cannot achieve complete seamless coverage. For operators, sometimes due to cost, transmission conditions and other considerations, it is difficult to build a base station in some coverage blind areas. At this time, the repeater is usually used as an auxiliary means for base station coverage. Because the repeater can effectively allocate the traffic of different base stations while expanding the communication coverage, using the repeater is still one of the important means to achieve the goal of "small capacity and large coverage". Due to the characteristics of repeater equipment itself, the introduction of repeater equipment inevitably has some negative effects on the network. In engineering practice, how to use wireless network planning methods flexibly according to the characteristics of repeater equipment, maximize the performance of repeater equipment, and solve network problems is a problem that communication designers need to face.