A mobile communication repeater is a communication device designed to eliminate a local range signal dead zone or weak signal zone of a mobile communication network. There are two types of repeaters: RF repeaters and fiber optic repeaters. Compared with the base station, it has the advantages of simple structure, low price, convenient installation, etc. By setting up the repeater, not only can the coverage effect be improved, but also the investment cost can be greatly reduced. The repeater station is widely used in signal blind spots that cannot be reached by base station signals such as shopping malls, parking lots, airports, subways, highways, stadiums, etc., and at the same time, to eliminate outdoor shadows or remote suburbs of outdoor areas caused by high-rise buildings. The weak signal areas of individual villages and towns also have quite good coverage. The repeater itself does not generate capacity, it simply extends or extends the coverage of the donor base station. There are also some problems with the repeater. For example, repeater interference becomes one of the most common interferences in mobile communication networks. If not handled properly, it will have a negative impact on network performance.
The forward amplifier of the repeater amplifies the downlink signal from the base station to the mobile station, and the reverse amplifier amplifies the uplink signal of the mobile station to the base station, and the gain is generally 40-80 dB, and the noise figure is 8-10 dB. Since the uplink and downlink signal frequencies have an interval, the duplexer and the front-end filter conveniently separate the two signals. The antenna facing the base station is called a donor antenna or a source antenna, and functions to communicate the link between the base station and the repeater. Therefore, a directional antenna with strong directivity is generally used, and the gain is generally greater than 20 dBi. The service antenna (retransmission antenna) or working antenna of the repeater functions the same as the base station antenna. The antenna isolation of the RF repeater, that is, the interval between the donor antenna and the overlay antenna, should be at least 10-15 dB higher than the amplifier gain, otherwise the system may self-excitation. If the downstream amplifier gain of the RF repeater is 70 dB, the required interval should be at least 85 dB.
Indoor coverage antennaWith the development of the economy, the density of high-rise buildings in the city is increasing, and the underground facilities are also increasing, which causes the signal transmission of mobile communication to be seriously affected, thus forming many blind spots and dead zones of mobile communication. The use of mobile terminals indoors has exceeded 60%, and users have higher and higher requirements for the quality of mobile communication networks, so indoors need good mobile signal coverage. If the indoor macrocell is covered by the outdoor macrocell and the deep coverage is required in the dense urban area, sufficient penetration loss margin needs to be reserved, which inevitably reduces the coverage radius of the cell, which leads to an increase in the number of outdoor stations. In addition, the outdoor macrocell is too dense, and there will be a large number of cross-regional coverage, which affects the quality of the outdoor network. Therefore, a special indoor coverage system is needed to solve the indoor coverage problem. For indoor coverage systems, antennas are an indispensable part of the system.
The indoor distributed antenna system transmits the base station signal to an area where radio waves are difficult to reach through a transmission medium such as an optical fiber or a cable, and then transmits it through the antenna. The signal source can be a microcell, or it can be a macrocell or wirelessly coupled to obtain signals from the macrocell. The key to the design is to consider the isolation between indoor and outdoor. When the indoor and outdoor systems use the same frequency, the penetration loss of the building provides a certain degree of natural isolation. The design goal is still to meet the indoor coverage and capacity requirements. Minimize the leakage of indoor signals as much as possible.
Indoor antenna users can choose different antenna types depending on the frequency band and the location of the coverage. The indoor antenna should work in a special environment such as indoors. Therefore, the basic requirements for the antenna are small size, light weight, and beautiful appearance. The indoor antenna has an omnidirectional antenna (mounted on the roof) or a directional antenna (mainly installed on the wall). The size of the antenna depends on the actual requirements. The gain is generally between 2 and 7 dBi. When selecting the installation, it should be avoided as much as possible. The electronic equipment is close to prevent interference. At the same time, the antenna should be installed at a position other than 1 m away from the handset to avoid blocking the transmission power of the mobile phone to the base station due to the too close of the antenna. The antenna should be placed. Create a line-of-sight propagation environment wherever possible, without obstructions or areas far enough away from walls, pillars, etc.
Tunnel coverage antennaThe tunnels are mainly divided into railway tunnels, highway tunnels and subway tunnels. No matter what kind of tunnel, there are different conditions. Short tunnels are only a few hundred meters, while long tunnels are more than a dozen kilometers. Therefore, the solution for each tunnel may be different, and the coverage solution must be selected according to the actual situation.
A shorter length tunnel can be covered with a single antenna. This is a simple and economical solution. In actual engineering, the tunnel can be covered by selecting an antenna with a suitable gain according to the installation conditions of the tunnel port and the length of the tunnel. A high gain antenna can be selected when the installation conditions permit. In addition, when a single antenna is insufficient to cover the entire tunnel, it is possible to use one antenna at both ends of the tunnel to cover the tunnel at the same time. In general, the internal coverage of the tunnel and the coverage outside the tunnel can be considered together, and the same cell is used to cover both the inside and the outside of the tunnel.
For medium length tunnels, one solution is to install different numbers of bidirectional antennas and amplifiers in the tunnel depending on the length of the tunnel.
For a relatively long tunnel, the loss of the signal during transmission is also relatively large. At this time, the signal transmitted to the transmitting antenna is weak, and it is difficult to ensure coverage. In this case, the remote connection of the fiber optic repeater can be used as the coverage of the long tunnel. The advantage is that the signal is amplified once every time, and the loss of the signal can be reduced as much as possible.
Leaky cables are another option for tunnel coverage. The electromagnetic wave radiates electromagnetic waves to the outside through the slot while transmitting longitudinally in the leaking cable, and the external electromagnetic field can also be sensed through the slot to the inside of the leaking cable and transmitted to the receiving end. The leakage cable has a large transmission loss and is only suitable for scenarios where coverage is high and uniform. Since the linear loss has a great influence on the signal strength at the head end of the feeder, the coupling loss results in good coverage in the cable signal leakage area, but there is almost no coverage in the area exceeding 50 m.
Sea area covered antennaSome provinces along the coast of China have long coastlines. The coverage of this special scenario requires not a capacity but a low-cost wide-area coverage. Remote coverage base stations are the best solution to provide this special scene coverage. The coverage effect of the remote base station is very related to the terrain conditions, and it is necessary to have an ideal height control point for the coast to set up the antenna.
For sea coverage, coverage is required to be as far as possible, but the propagation of electromagnetic waves is affected by the curvature of the Earth. If the user enters the shadow area of ​​the earth's convex surface, it is impossible to improve the coverage by increasing the power or sensitivity. Therefore, it is necessary to overcome the influence of the curvature of the earth by increasing the height of the antenna. If the radius of the Earth is calculated according to 6400km and the top of the coast with a height of 400m can be used, the coverage can reach 72km if only the direct path is considered. If the atmospheric refraction is taken into consideration, the sea surface coverage of the remote base station can reach about 100km. . If the top of the coast has a 500m peak, the sea surface coverage of the remote base station can reach about 110km after considering factors such as atmospheric refraction.
In addition, in order to expand the coverage of the sea area, adding a tower amplifier is also a commonly considered method. Increasing the height of the antenna will inevitably lead to longer feeders and increased losses. In this case, it is necessary to increase the tower to compensate for the loss of the feeder.
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