Tunnel wireless intercom system solution

Nowadays, the society is developing rapidly, and transportation is a major focus of social development. In order to facilitate transportation, people dug the mountain and opened the tunnel project. Then, how to communicate smoothly in the tunnel has become a major problem in the project.

Most of the tunnels are narrow and narrow tubular structures. Due to the obstruction of the environment such as mountain trees, the signal shielding is very strong, and it is generally a signal blind zone. When the long tunnel coverage is solved and the fiber link is provided, the fiber base station signal enhancer can be installed to effectively solve the problem that the network coverage in the tunnel is not enough. Since the optical fiber has the characteristics of low cost and low loss, the farthest can be pulled 20 Kilometers, so you don't have to worry about isolation.

When solving the coverage of the short tunnel wireless intercom system, if the tunnel does not have the fiber connection, the Yagi antenna can be used to cover the tunnel near the tunnel entrance. This scheme has the characteristics of simple engineering installation and low cost. When solving the problem of bending the network coverage in a long tunnel or tunnel, it is necessary to perform passive antenna distribution on the tunnel; it can also be covered by a scheme of leaking cables.

Networking technology solution

The split type repeater has a near-end machine and a remote machine, and can be divided into a fiber base station signal booster and a radio frequency base station signal booster according to the link mode between the near-end machine and the remote machine.

After receiving the base station signal, the donor antenna of the optical fiber base station signal amplifies the signal by the low-noise amplifier module of the near-end machine, converts the electrical signal into an optical signal through the optical fiber module, and transmits the optical signal to the remote machine through the optical fiber link, and the remote end The machine converts the received optical signal into a radio frequency signal and then amplifies it, and finally radiates the enhanced signal to the service area through the retransmission antenna to improve the quality of the local call.

Scope of application: Extend the coverage of base stations, eliminate signal blind spots, shadow areas, and improve call quality in service areas.

Requirements: The base station to the service area should have a fiber link, and the total length of the link does not exceed 20 kilometers.

Main features: wireless receiving base station signal, signal stability; using optical fiber transmission, low loss, low cost; fiber can be pulled up to 20 kilometers between near and far-end machines, effectively improving antenna isolation; a near-end machine can be used up to Even with 4 remote units, it can achieve a larger coverage of the star network: suitable for narrow tunnel coverage or indoor signal coverage.

For a special tunnel, you can use a near-end machine with multiple remote machines to achieve coverage.

(1) Composition of a communication system using a directional antenna for tunnel coverage

As shown in the figure, the coverage is relatively simple, and the introduction of the signal source may be introduced by wireless or by wire. This method is mainly for the case where the tunnel and the underground passage are relatively straight and the tunnel distance is not very far. When the tunnel distance is long, as the distance increases, the attenuation of the signal in the tunnel increases, resulting in uneven distribution of the signal field strength in the entire tunnel, which is prone to call drop.

(2) Composition of a tunnel communication system using a leaky cable (LCX)

The communication system also has several signal introduction methods such as wired introduction and wireless introduction. This type of coverage is mainly for tunnels with long distances and curved paths. The leaky coaxial cable is laid across the entire tunnel, and the field strength of the entire line is very stable, providing a high-quality communication link.

The structure of the space wave and the leaky coaxial cable in the tunnel is shown in Figure 2. The signal booster near-end machine is installed at the tunnel port, and the spatial wave energy is amplified and transferred to the leaky coaxial cable. The leaky coaxial cable passes through itself. The slot radiates the received signal and forms a leakage electromagnetic field around it to enable communication between the mobile stations.

If the tunnel is far away, there will be non-uniform energy leakage along the leaking cable. A large amount of energy may leak out from the first arriving slot. In order to compensate for the drop in leakage level caused by the continuous drop of the level in the cable during transmission, several leakage cable routes may be connected in series by several cables with different coupling losses. Thus, fluctuations in the received signal level along the line can be reduced.

The specific tunnel radio communication signal coverage project is actually a relatively complicated task, and it is necessary to formulate specific coverage plans according to different tunnels in the field measurement.