The Influence of Weather on Wireless Network

The electromagnetic wave of wifi can only travel in a straight line, and the diffraction phenomenon is very weak. Rainy days and foggy days have great influence on the absorption and scattering of radio waves. The attenuation of rainy days is mainly due to the scattering and absorption of radio waves by raindrops, and the absorption of radio waves in foggy days plays a more important role than scattering.

The weather in nature is unpredictable, such as lightning, rain, wind, fog and snow. Wireless communication will be affected by the weather under certain conditions. Generally speaking, lightning and rainstorm have great influence, while other weather has little influence on microwave communication.

I. Lightning

Wireless communication belongs to the category of electronic communication, and lightning has great destructive power to electronic equipment. Because the antenna installation position of wireless communication is relatively high, it is necessary to do a good job of lightning protection for equipment. Generally speaking, the probability of being struck by lightning is extremely low. Even if the building is struck by lightning, it is also the lightning rod of the building. Powerful current will instantly flow into the ground, generating induced voltage on the wireless device, and the current will be pumped into the ground through the radio frequency lightning arrester. Baseband cables will also be affected. By installing network arrester, the instantaneous high voltage of baseband cable is eliminated.

Second, the rainstorm.

When radio waves pass through the rain area, raindrops will absorb and scatter the radio waves, thus causing attenuation. The magnitude of rain attenuation is closely related to the ratio of raindrop radius to wavelength, and raindrop radius is related to rainfall rate. The measured results show that the raindrop radius is about 0.025 cm ~ 0.3 cm, but the closer the radio wavelength is to this wavelength, the greater the rain attenuation. The influence of rain attenuation on radio waves is mainly absorption attenuation, most of which is heat loss. 2.4Ghz？ The wavelength of is about 12.5 cm, and the wavelength of 3.5Ghz is 8.3 cm. The wavelength of 5.8Ghz is about 5.5 cm, and the wave wavelength of Ku band (1 1G~ 12Ghz) is about 2.5cm. From the above wavelengths, it can be seen that the rain attenuation of Ku band is close to the physical model of raindrops, and the rain attenuation of other frequencies is generally estimated as? 40 km 6dbi？ Adopting high gain antenna and high transmission power is an effective means to resist rain attenuation. Wireless communication needs the net gain reserve of signals, which is generally 2.4Ghz? The requirements must be above 10dbi, and 5.8Ghz must be above 15dbi. When designing wireless links, we usually design the net gain reserve to be above 30dbi. Even if there is a rainstorm minus the loss of 6dbi, the gain reserve of the system is above 20dbi, so the wireless communication system will not be affected by rainy days.

3. How to calculate the net gain reserve of the system according to the specific requirements of users for wireless link design: All networking nodes are designed to meet the link transmission rate required by customers, and the system margin is at least 15bm. The overall scheme design is combined with the overall design idea of the scheme design and the principle of establishing wireless positioning system _ positioning scheme based on WiFi signal _ information technology, relevant data provided by users, one-to-multipoint networking mode and different products. ?

First of all, we can calculate the transmission distance of different antenna configurations in free space by theoretical calculation on the premise of satisfying the 15dBm margin. The known parameter is -9 1dBm. When the LB product is 6Mbps, Pout=27dBm is the output power of the equipment, Gt is the gain of the antenna at the transmitter, Gr is the gain of the antenna at the receiver, ct is the feeder loss at the transmitter, Cr is the feeder loss at the receiver, PL is the attenuation of the signal in space, and 0.66 is the attenuation of Andrew cable of 1/2 inch. The signal intensity received by the receiving end is Si; ? Because the indoor unit/outdoor unit of LB series products are connected by baseband cable, and the maximum allowable length is 90 meters, the baseband cable can be directly used for sockets with feeder length less than 90 meters, and will not cause loss to wireless signals. Therefore, the feeder loss in the above calculation formula is zero, while in the design scheme, the feeder length without station exceeds 90 meters, resulting in the feeder loss being zero. ?

The signal receiving intensity at the receiving end is (see attached figure):? Si=Pout-Ct+Gt-PL+Gr-Cr？ The calculation formula of signal power attenuation of electromagnetic wave in space transmission is: 32.4+20xLogFmhz+20xLogRKm? At 5.8GHz: PL= 108+20LogD[km]? Bring this formula into the above formula: si = pout-CT+gt-108-20 logd [km]+gr-Cr? According to this formula, the transmission distance of antennas with different gains can be calculated under the premise of meeting the conditions:? Take the monitoring center and each monitoring point as an example: the gain of the monitoring center 120 sector antenna is 15dBi, and the remote station adopts an external 28dBi directional antenna with the distance of 15 km when only the baseband cable is used. Receiving sensitivity = 27-0+15-(108+20logd [km])+28-0 =-61DBM? Compared with the receiving sensitivity of 6Mbps -9 1dBm, the received signal strength is greater than 30dBm.