Many friends have repeatedly asked about the wireless bridge, and today we have a comprehensive understanding of the wireless bridge knowledge.
First, what is a wireless bridge
As the name suggests, wireless bridges are the bridges of wireless networks. They use wireless transmission to bridge the communication between two or more networks. Wireless bridges are divided into circuit-type bridges and data-type bridges from the communication mechanism.
Wireless bridges can generally be divided into 2.4G and 5.8G. Other frequency bands require additional application and can be used after authorization.
1, 2.4G bridge:
The advantages are low frequency, large wavelength and strong diffraction ability. Simply put, the propagation performance is good, and the propagation path is slightly blocked or not. Then the cost is relatively low.
The disadvantage is that there are many devices using the 2.4G frequency band, and the electromagnetic wave signals transmitted by the bridge are easily interfered by signals transmitted by other devices, resulting in a decrease in transmission quality. Then it is limited by the transmission bandwidth of the 2.4GHz band itself, generally not exceeding 300Mbps.
2. 5.8G bridge:
The advantages are high frequency, relatively pure channel and large transmission bandwidth. The transmission bandwidth starts at 433 Mbps and can easily reach more than 1 Gbps. Suitable for scenarios with high data transmission requirements.
The disadvantage is that the frequency is high, the signal wavelength is short, the penetration is poor, and there is no occlusion during the propagation. The 5.8G equipment cost is higher than 2.4G and is still in the popularization stage.
Second, the working principle of the bridge
A wireless bridge transmission system usually consists of two or more wireless devices. Each device needs to have the ability to transmit and receive wireless signals due to the two-way transmission of data.
The working principle of the wireless bridge is actually that the bridge uses air as a medium to propagate signals. Simply put, the one-end bridge converts the signal in the network cable into a wireless electromagnetic wave signal and emits it in the air. The bridge at the other end acts just the opposite. It receives the wireless electromagnetic wave signal in the air and converts it into a wired signal.
Wireless electromagnetic wave signals can be transmitted with air as the transmission medium, which can solve many difficult problems in wired deployment: such as highways, rivers, mountain barriers, or road hardening, and difficult cable deployment.
Wireless bridge networking has obvious advantages, enabling point-to-point or point-to-multipoint network connections over distances of up to 50 kilometers, with data transmission speeds of up to 108 Mbps. Effectively solve the problem of network connectivity in the interval. As long as the client can easily access the network in the wireless signal coverage area, the system can be integrated without any wiring, and the wireless terminal can achieve zero configuration access, so network maintenance and expansion are very easy. .
Bridges are generally used in the following scenarios: wireless data collection, monitoring data transmission (outdoor and elevator), outdoor wireless coverage, outdoor long-distance wireless bridging, private ISP wireless broadband, unattended monitoring station data backhaul.
Third, how to choose the right bridge
A wireless bridge is a wireless monitoring transmission device commonly used in the field of wireless monitoring. Although it is a wireless device like a wireless AP or a wireless router, it is not used to build wifi coverage, but is used to wirelessly transmit video data. Like switches in wired monitoring, wireless bridges are important transmission devices in wireless surveillance, and are widely used in outdoor surveillance video transmission and elevator surveillance video transmission.
There are so many different types of wireless bridges on the market, how to choose a bridge that suits your needs? We will answer you from the following aspects.
1, transmission distance
Wireless monitoring projects need to transmit at different distances. There are many transmission distances for wireless bridges. Some transmissions are 1~3 kilometers, some are transmitted 3~5 kilometers, some are transmitted 5~10 kilometers, and some are transmitted 20 More than the kilometer, it must be determined according to the monitored transmission distance. As far as possible, the maximum transmission distance of the bridge is greater than the monitoring transmission distance, because the rain, fog, snow and other weather in the actual application environment will lead to the degradation of the bridge transmission performance. Leave plenty of performance margins.
2, transmission bandwidth
There are many transmission rates for wireless bridges, such as 150Mbps, 3000Mbps, 450Mbps, 600Mbps, 900Mbps, etc. Which rate is selected can be determined according to wireless monitoring requirements. What the user actually needs to consider is the transmission performance of the bridge at a certain distance, not the theoretical bandwidth data. For example, the theoretical transmission bandwidth of the IP-COM AP625 bridge is 433 Mbps. At a distance of 2 km, the point-to-point transmission bandwidth can be measured up to 200 Mbps, and 25 200W cameras are loaded without pressure.
3, working frequency
There are two main types of wireless bridge operating frequencies, 2.4G and 5.8G. The characteristics of the two bridges are different. In general, the 2.4G wireless bridge is the current mainstream frequency band, with good compatibility and good diffraction capability, but the anti-interference is relatively poor, especially in urban areas, which are susceptible to interference from wireless signals transmitted by other WiFi devices. The channel of 5.8G is relatively pure, the anti-interference ability is better, the transmission distance is far, but the diffraction ability is poor.
Urban area, downtown, long-distance transmission, camera code stream is large, 2.4G interference is more, choose 5.8G wireless bridge. Others use 2.4G wireless bridge if the transmission distance is relatively close, relatively remote, and the same frequency interference is less.
4, the antenna
The antenna is an important accessory for wireless bridges. It is used to transmit and receive wireless signals. Without an antenna, the wireless bridge cannot communicate. There are many types of antennas, including omnidirectional antennas and directional antennas. Omnidirectional antennas are used for close coverage and transmission. Long-distance bridging should select directional antennas and the larger the antenna gain, the better the performance of the wireless bridge.
5, power supply mode
The working environment of a wireless bridge usually involves some complicated outdoor environments, such as forests, ports, tunnels, reservoirs, etc., so power supply is a more troublesome problem. Selecting a wireless bridge that supports POE cable power supply can solve this problem well. The IP-COM bridges all support PoE injectors and supply distances up to 60 meters.
6, protection level
The wireless bridge works mostly outdoors, and the environment is changeable. The following are rain, rain, snow, high temperature, etc. The first requirement is waterproof, dustproof, heat resistant and anti-condensation. A "quality" is a must for a qualified wireless bridge.
7, matching method
Currently, there are three types of matching methods for the mainstream of the bridge: button pairing, dial pairing, and automatic pairing. In terms of the simplicity of engineering applications, especially for projects that install tens of hundreds of bridges at a time, automatic pairing is undoubtedly the best choice. The IP-COM bridge supports the automatic matching of the two bridges when they are powered on, which greatly reduces the workload.
Fourth, the installation requirements of the wireless bridge
The wireless bridge is an important transmission device in wireless monitoring, and is widely used in two fields of outdoor surveillance video transmission and elevator monitoring video transmission. In addition to selecting the right wireless bridge, we also need bridge equipment to fully exploit its performance advantages after installation to assist users in engineering. Therefore, for some installation requirements and precautions of wireless bridges, we must pay more attention to avoid any problems in the later stage.
1, the installation height
In the process of wireless transmission of wireless bridges, obstacles such as trees, buildings and large steel buildings will weaken the blocking of wireless signals. In order to improve the wireless transmission performance and prevent the signal from being damaged and the signal is weak, the user should try to ensure that there is no obstacle blocking in the transmission route of the wireless bridge, and the transmission conditions that are visible to each other are satisfied.
The two ends can not be simply understood as point-to-point visual, which means that there can be no obstacles or potential obstacles in the Fresnel zone (radio wave terminology) where the antenna propagates. The primary RF energy between the antennas is transmitted in this area, so the transmitting antenna must be above the obstacle at a sufficient height to maintain a line of sight between it and the receiving antenna to ensure that the communication link is working properly.
2, angle and signal debugging
Since the quality of the wireless bridge signal is directly related to the bandwidth and stability of the link, the wireless bridge signal must be further debugged after the installation is completed (you can adjust the signal strength by adjusting the direction of the two antennas, the elevation angle, etc.). ). The signal strength indicator can be viewed according to the signal status indicator of the bridge device (three lights, three signals are ideal, two are generally, one is poor) or software. Outdoor wireless AP detailed installation steps
3, lightning rod requirements
When the wireless bridge is installed in the field, if there is no tall building or lightning rod protection nearby, lightning protection measures need to be taken into account. Lightning rods are usually used. Generally, when lightning protection is installed in the urban area or surrounded by lightning rods, the lightning rods may not be separately provided.
It can be seen from the characteristics of the lightning rod that the lightning rod is for lightning, and the lightning rod will discharge on the grounding path when subjected to lightning strike. Therefore, the lightning rod and the protected equipment need to be insulated and insulated, otherwise the lightning rod is a lightning strike effect on other equipment when discharging. Because the lightning rod has a tip discharge characteristic, it is easy to cause lightning strike discharge than the general equipment. Therefore, if the lightning rod cannot be insulated from the protected equipment, the probability of lightning strike of other equipment is increased. Therefore, the lightning rod grounding needs to be separated from the equipment grounding and cannot share a grounding.
4, power supply requirements
The PoE power supply module of the bridge has a normal input voltage of 100V~240V and the output voltage is 24V-48V. Below or above this voltage will affect the normal operation of the device or cause abnormal damage to the PoE power supply module. In view of the unstable power supply voltage and high voltage in the field, it is necessary to design a PoE power supply solution (such as regulated power supply and UPS power supply) that can adapt to the working voltage.
Since the bridge belongs to precision electronic equipment, it has high requirements for power supply and is vulnerable to the impact and influence of other power supply equipment. Therefore, the power supply of the bridge power supply should be taken separately from other high-power equipment such as pumping units and oil pumps. When power is taken at the same position, UPS, regulated power supply or isolation transformer should be installed to filter out the influence and interference of the power supply when working with high-power motors.
When using a PoE module to power the bridge through a network cable, the recommended distance is no more than 60 meters. Beyond this distance it is recommended to move the transmission line to the vicinity of the bridge to meet the recommended power supply distance requirements.
5, equipment grounding requirements
The wireless bridge should be grounded. If the equipment is not grounded, it will cause abnormal operation and damage. The grounding resistance of the equipment should be less than 4 ohms, and it should not be grounded with lightning rods and high-voltage lines. Grounding is also required if a PoE power ground is used. Users can connect to the PoE adapter with a grounded Category 5 (or above) shielded network cable for grounding, which can easily and effectively prevent static electricity and lightning strikes. The grounding wire and grounding point should be waterproofed with waterproof tape and waterproof rubber to prevent the grounding point from being grounded due to long-term exposure to the air, causing oxidation and rust.
Five, wireless bridge installation considerations
Wireless bridges are generally used in pairs, with a transmitting end and a receiving end. The transmitting bridge is mainly connected to the front camera and the PoE adapter; the receiving end is mainly connected to the switch and the PoE adapter. This is relatively simple. Connect the power supply with the word POWER, and connect the data with the word DATA.
Do a good job of rain, dust and insulation. Although the wireless bridge itself is waterproof and sealed, the wireless bridge needs to be connected to other equipment and components. These connectors or connectors (the connector of the network cable and the wireless bridge, the connection between the network cable and the network camera, and the feeder connector) must be To be waterproof, use a waterproof tape to wrap 2 to 3 layers; all power connectors are insulated as much as possible.
It must be stable when it is fixed. Whether it is a bracket or a wireless bridge, if the wind is unstable due to strong wind, it will directly affect the stability of microwave signal transmission. When installing the bracket and the wireless bridge, it is necessary to put a rubber band on the bracket and then closely contact with the U-shaped clamp to prevent the bracket from rusting.
If an external antenna is used, the direction and angle of the antenna should be adjusted during installation; the built-in antenna type bridge is used, and the angle between the transmitting end and the receiving end should also be selected.
Since the wireless bridge generally uses a PoE adapter for PoE power supply, it is necessary to control the quality and length of the network cable. In addition to selecting a good (super five or more) network cable, the cable length between the wireless bridge and the PoE adapter is guaranteed to be 25 meters.
When the pole is installed, the selected poles should not be too thin or too thick to ensure that the standard cable tie can be installed directly.
When connecting to the network port of the device, you need to strictly follow the installation instructions of the bridge. If the operation of the network port is improper, the interface may be burnt out or the circuit board may be short-circuited.
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