Eli5:Why is it that cell phones , with their tiny antenaes are able to download files at LTE speeds inside concrete buildings from cell towers kilometers away yet getting wifi to work behind a corner is an exercise in frustration?
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All wireless communication suffers from something called “attenuation”. Attenuation means a reduction in signal strength. Many things can cause attenuation, but physical objects are one of the more common causes of attenuation when we’re talking about electromagnetic waves.
A physical object can be anything: a wall, a person, a mountain, you name it. Our world is full of them, and they all attenuate the radio waves we use for wifi and cellular communications, not to mention broadcast television signals and radio stations.
An interesting characteristic of radio waves though, is that waves of different frequencies are attenuated different amounts by different physical objects. As a general rule, the higher the frequency, the greater the attenuation a radio wave will suffer from a given object.
WiFi uses 2.4 GHz (2,400 MHz) and 5 GHz (5,000 MHz) bands exclusively. There are no lower frequency bands for it to choose from. Both of these bands are easily attenuated by common building materials, so the walls in your home attenuate your WiFi signal easily. Per the rule of thumb I mentioned earlier, the higher frequency 5 GHz band is more easily attenuated than the lower 2.4 GHz band.
Cellular devices have multiple bands to choose from. Some examples are 700 MHz, 850 MHz, 1,900 MHz (1.9 GHz), and 2,100 MHz (2.1 GHz). Newer wireless technologies like 5G utilize frequencies as high as 52.6 GHz. When you are outside, the device will use a higher frequency band for maximum performance, while switching to lower bands for better indoor performance.
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