Hey guys, thanks for coming back to Wi Fi fundamentals with location and analytics. This course will help you to muster the air. Alright, so we are continuing our adventure in the air. And in this part we will look at the phenomenon that happens to our wave as it hits physical objects. The first phenomenon is reflection. It happens when an RF wave is being reflected from different services in its surrounding.
Reflection happens when the signal bounces off a matter that is non absorptive. As metal, it is quite common in furniture, windows, walls and mirror. The signal will change its direction. absorption happens when this hates a dense object and gets absorbed in it. It is common in concrete walls bricks, different types of doors and even in people, the signals amplitude is reduced. Another phenomenon is Catherine.
It happens when the signal hits a surface that is not even, and is being reflected all over. It is quite common in furniture roofs and metal object. The result is increased paths. It is more common in high frequency waves due to their short wavelength. Another phenomenon refraction. It happens when the signal hits the surface with a different density then the air that will bend its path as it moves in it.
It is very common in glass, water and the result is a changing path and attenuation. So what is the outcome? Well, the outcome of a wave that changes his path and comes in different direction, polarity and time is phase shift. Remember we have spoken of phase shift of the wave, it causes it sometimes to be canceled, and sometimes to be a stronger, vital wave. So what do we do? Well, we're quite ahead of our learning curve.
And this topic is an advanced topic. But just bear in mind that in today's Wi Fi network, we use different techniques to deal with such phenomenons. One of them is guards. Wi Fi frames are actually sliced into tiny symbols, tiny frames There are sent in with a bit of a delay, one after the other. Why it is done to compensate the delay between the time of the transmitted signal and the reflected signal as it approached an obstacle in its way. Our floss can also happen with interferences that come from other RF sources in our surrounding.
It doesn't always happen due to physical phenomenons or obstacles. It can come from other 802 11 devices, or other RF emitting devices such as a microwave or a cordless phone. The result is the same frames are lost and damaged. So our signal has lost its power due to interferences and path loss and when it hits our device, we will like to know how much power Is the left so we use a measurement known as the rssi received signal strength indicator, it is expressed in a dBm format which we will look into in the coming course. It usually starts from zero to minus 100. The closer the value to zero the stronger the signal.
Another term that you may have heard of is SNR signal to noise ratio and it is directly related to RF loss. It is actually the measurement of the intended signal or RF signal in relation to the background noise. What is the background noise? It is actually any electrical device that radiates in the air. Our signal has to be at least 20 to 25 deep higher than the noise in our surrounding. Otherwise, we will suffer from frame loss and our data rate will decrease.
Next up RF met in the form of dB m