how do they make it so you can have thousands of phones in close proximity all sending and receiving signals at the same time without the airwaves getting clogged up into completely unreadable noise?
In: 2654
There are several ways.
Each cell can have multiple basestations in the same place overlayed on separate frequencies, in addition they split each frequency up in to lots of very small time slots. (TDMA).
When things get too busy for even all the available slots, like in town centres or at large events, they can split cells up into smaller and smaller areas, down to individual office sized cells if needed.
This is a great 20 minutes video which goes on to a reasonable amount of detail, but in a easy to explain way. Highly recommended and very interesting
(https://youtu.be/0faCad2kKeg)
It does get clogged.
It’s not a free for all where the phones just transmit whenever they want. The cell phone system controls the phones and tells them when it’s ok for them to transmit and when not to transmit. It does this based on need so that phones not using a lot of data get less time. This means it’s not always obvious how busy the system is. But this sharing system has its limits, if there are lots of phones all trying to use the network at once then everyones connection slows down.
In really heavily loaded situation connections will drop out. The system tries to do this in a smart way so that data fails first allowing voice calls to still go through. And if there are too many phone calls emergency calls get priority over normal calls.
Edit: getting a little over 5 year old level here but there are several ways to share radio time. A lot of people are talking about each phone talking at a different time (TDMA, time division multiple access). Some are talking about different frequencies (FDMA). And there is also CDMA, code division multiple access, where the signals are encoded in a way to allow them to be separated out at the receiver.
Cell phone systems initially used either TDMA or CDMA depending on the type of network. The newer standards are horrendously complicated and use a combination of these simultaneously.
Wireless communication is transported over certain frequencies of electromagnetic waves, i.e. light. Different technologies use different ranges of frequencies, and antennae are tuned to some desired frequency, ignoring everything else. This is similar to how our eyes are ‘tuned’ to see visible light (a specific range of frequencies of the electromagnetic spectrum), but are blind to all other frequencies, like radio waves and infrared waves.
Not only do different technologies like cellular, bluetooth, wifi, radio, etc use different frequency ranges, or bands, but each technology also has many separate frequencies they can choose from within their band, called channels.
Depending on the technology, algorithms are used to automatically choose less busy channels. When multiple devices are using a single channel, each device is simply given its own slice of time in which it’s allowed to communicate.
tl;dr wireless communication is isolated and organized by frequency and time
In short, a technology called ‘filter circuits’. Each cell phone has a unique frequency that it communicated on and since there are so many phones, you have to get pretty narrow to service all of them. This is, incidentally, why cell phone companies wanted that bandwidth purchase that Ajit Pai sold them. Anyway, anyone who has ever operated a radio knows that there is bleed over, to avoid this we have filter circuits that make the phone use *only* the frequency it is assigned and it blocks out everything else.
This is actually what the 3g, 4g, 4g LTE, 5G is all about.
Wendover did a recent video about it [here](https://youtu.be/0faCad2kKeg)
TL;DR – you clever condense the signals of those 1000 phones into a unique signal representing all 1000 individual signals
To keep it simple, the cell tower you’re connected to isn’t the only one your phone can hear. It’s not even the only one your phone can hear well. It just has the best quality signal at the moment. You’re phone keeps a running list of what towers it can hear best and their level of quality, so if it needs to switch from one to the other it knows where to go.
So while you’re on your current tower, you’re on the same frequency as everyone else, but your phone is assigned a “timeslot,” meaning it only gets to talk at specific times, and the signals meant for it only come in at specific times, as well. Now, these times have several times per second, so you as the user don’t notice that your phone isn’t broadcasting or receiving constantly, even when in a voice or video chat. When your phone isn’t taking it’s turn, everybody else is taking theirs. This is known as “Time Division Multiple Access.”
Now, there *are* limits to how many phones you can have on one channel. When the tower hits that limit, your phone gets moved to another tower to help handle the load.
Sometimes they DO get mixed up or garbled
When they don’t it is because of many technologies at the same time
The basic principle at work is called the principle of superposition. Superposition means you can combine two signals to make a new signal. Later, we use math to pick out the parts we want.
An easy analogy is sound. Sound obeys the principle the principle of superposition.
Imagine you are recording people talking and a train comes by. If you have good recording equipment you can isolate certain signals (noises) and separate them to remove the train horn from coming by using math. Then maybe you would raise the minimum volume level the microphone will pick up to ignore the noise of the train whooshing by but still hear the talking. Finally you may need a special program or technique to remove the sound of the train rattling over the tracks while someone is speaking.
Our phones use these techniques also: isolating signals based on certain markers like frequency, signal noise, signal strength, etc.
The best frequencies for fast data are the very high ones, like 5G.
And the higher the frequency the least is the range.
Coincidentally, trying to move more data has the side effect of having short range and this is super helpful. Each cell can cover its area with enough band but at the same time the short range prevents it to overlap with transmissions in the cells further away.
I might add that each phone, device, etc., has its very own address. The MAC address may look like letters and numbers but in reality, the number is the hexidecimal notation for the truly binary code of the device. Your phone transmits this code that is superimposed on an electromagnetic wave (CDMA, TDMA, Etc) The cell tower antenna “catches” your phone’s analog electromagnetic wave signal digitizes it and forwards to the home base for processing and re-routing to/from destinations. Probably got most of this wrong but it’s close considering how many years it’s been sine I learnded this stuff.
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