Wi-Fi technology and application(2)Luis
Immediately after the last article, we continue to discuss the speed and signal problems of WiFi.
Why is your home WiFi signal weak?
It is well known that Wi-Fi signals are mainly transmitted through radio waves, because there will be interference and loss in the air propagation path of wireless signals.
What is the specific interference loss method? Let’s take a look:
- The wireless router is far away, which will greatly weaken the wireless signal.
The Wi-Fi standard has strict restrictions on the transmit power of the device, and the antenna gain for indoor use cannot exceed 5dBi. Moreover, the propagation of Wi-Fi signals in space decreases exponentially, and the signal strength decreases by 20dBm for every 10 times increase in free space distance.
Since the gain of indoor antennas is within 5dbi, is the longer the antenna, the stronger the signal?
You are right! The gain of the antenna largely depends on the size, there are 1dBi, 3dBi, 5dBi. Even if they are both 5dBi, the longer one can increase some receiving sensitivity even if the gain cannot be increased. Now I know why sometimes there is still a Wi-Fi signal, but the Internet is no longer available? That is because the receiving sensitivity of the antenna is not enough.
Because although the signal can be sent to the mobile phone, the signal sent back by the mobile phone is not received by the router!
(The router has been designed to avoid this blind spot as much as possible, but different mobile phones have different transceiver antennas, so it cannot be completely avoided…)
So is it that the more antennas, the stronger the signal?
It can be understood in this way, but it is not a simple 1+1=2 sub-signal that becomes stronger, but multiple antennas use MI-MO (Multiple-Input Multiple-Output) technology. MIMO technology has combining gain, which enhances the signal quality.
Obstacles can cause a large drop in the wireless signal
The objects that cause signal attenuation are mainly metal objects, walls (especially load-bearing walls). Large furniture/appliances, etc.
|reinforced concrete partition wall||20-40dB|
|plain concrete wall||10-18dB|
|Hollow drilling wall||4-6dB|
|glass doors and windows||2-4dB|
|Coated glass doors and windows||12-15dB|
In addition, the actual penetration loss of the WLAN signal when it penetrates the wall obliquely is much greater than the penetration loss when the signal is directed directly, which seriously reduces the signal quality. Therefore, when planning the installation location of the AP, the incident angle of the signal passing through the wall should also be minimized~