Electronics > RF, Microwave, Ham Radio

Are mobile phones magic?

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OK I'm spoiled enough to complain that 4G is slow and crap :-DMM :-- but really I know it's magic :clap:. How does it work at all? With the inverse square law and every cheesebrain carrying arround one of these devices it seems like making a phone call would be like looking for half a bees dick with your name on it in a barn full of half bee dicks.  :scared: :scared:

Can you explain it in a way that doesn't need intelligence to understand? Like if I had a sort of cottage cheese in my head  |O, it would just make sense?   O0

If you liked this question I will set up a Patreon for future questions.  :palm:

Ok, I know i will get called up on these approximations but oh well,

First off, the towers, these you probably see but don't look for every day, likely big long grey rectangles on poles, they are what send and receive data between the phones and the general internet.

These towers each have a maximum possible bandwidth or speed, note this is not a per person speed, but the maximum that everyone connected to that tower has to share from, this is why you may see a pole with multiple antennas, to increase the speed in areas where many people are likely to connect.

If many people are connected to a tower, or a few people are doing high speed downloads like Netflix on a particular tower it means there is less bandwidth or speed left when you try and do something, This is partly a first come first serve issue, so if you are doing something like streaming your likely to keep a similar speed if other people try and hop one, making them suffer a slow connection until your stream is interrupted,

The further away from a tower you are, the weaker the signal, each time you double your distance away, the signal is 4 times weaker, if the signal is weak enough it means either the phone or the tower may not hear it, and need to resent slowing things down, equally if your signal is too weak for the fastest technology (4G) your phone may drop down to 3G or even 2G data, as slower connections tend to be more stable over longer distances, equally there is likely to be less people to share with on these bands.

More bits to the puzzle. 

The original layout of the system envisioned towers every 6 miles or so.  No one would be more than three miles from a tower.  That layout has changed over time but that is still within a few dB of the spacing.  By radio standards you are usually not that far from each other.

Everyone and their brother has one of these, but most of them aren't using all of the bandwidth they could all the time.  Many are resting quietly in a purse or pocket.  Many, many more are streaming audio, which is relatively low data rate.  Only a few at any given moment are streaming video or doing big file downloads.  So most of the time it works.  And sometimes you find yourself thumping on your phone in disgust as it puts up a buffering message or spends forever cycling through the download symbol while a group of people are all doing high bandwidth stuff at the same time.  That is why all of the carriers put data limits on their plans.  It keeps people from doing the high bandwidth stuff as much.

One other magic thing about mobile phones is how they manage to find you. Suppose my girlfriend calls me, how does the network know to route the call to tower WXYZ which is my closest tower? Also, how does the network route the call through foreign towers when I am over the border in Austria?

The magic happens in the network. Not on your phone! Even the transmission power of your MS (mobile station) is controlled by the BTS (base transceiver station) the same for when to switch to another antenna, it's not your phone that takes decision.
If you want to know more search on google, there are at least documents and lecture notes on GSM from 10 different universities which can be found easily.
Unfortunately I am not allowed to redistribute the documents which the university where I study uses. :-(


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