How does my tiny phone communicate with a cell tower so far away? How does it transmit my data to the cell tower?
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Your phone has a radio in it. The cell tower has a radio in it. The radio in the phone connects to the radio in the tower via radio waves. When the radios are connected data is transmitted.
We are still receiving radio communications from small spacecraft that have left the solar system.
Cell towers are very sensitive, and the signals they are detecting/listening for are very distinct. Your phone will also adjust its transmitting power based on how close it is to the cell tower. If you are right at the edge of reception, your phone will transmit at its highest power and drain the battery faster.
Over the last 100 years, humans have become very good at shaping radio waves to squeeze more data and range out of weaker signals.
How we transmit data on a radio wave affects how much data we can encode in it, and how easy it is to “hear it” against the background noise.
Early radio was Amplitude Modulated “AM”. AM signals are encoded in the power of the radio wave. It was very easy to create AM signals with primitive transmitters. And the receiver was very, very simple, consisting of essentially three core electronic components.
AM is very susceptible to noise, and you can hear it on AM radio today. We go around that by making AM transmitters very powerful, so the signal is much higher than the noise further away. High the power, the higher the Signal to Noise Ratio “SNR” will be at a given distance.
We eventually moved to Frequency Modulated “FM” radio receivers and transmitters. FM works by changing the frequency of the radio to encode the signal.
The circuits are still relatively simple but require transistors or vacuum tubes in the transmitter and receiver.
FM information isn’t tied to the transmitter’s power output and is less sensitive to interference from other electronics and the environment.
Another thing we do now, is encode the data as digital information instead of analog; using digital encoding, we can do error checking and improve SNR even more.
Today, more complex modulation techniques with digital data on modern communication radios improve signal-to-noise even more. These modulation techniques use properties like the phase of the wave and the shape of the wave to encode more data.
More advanced electronics let us send and receive vast amounts of data with very low power.
Cell towers must still be big and powerful and placed everywhere, sometimes only a mile apart. Towers still need to have big antennae and amplifiers to hear the small signal being sent by our low-power devices.
The advancements in how we squeeze data into radio waves let us increase the Signal to Noise ratio and get more data using less power.
The miniaturization of electronics has allowed us to use very advanced algorithms to manipulate radio waves in ways that would look like magic 100 years ago.
Cell towers operate in the UHF frequency band (300Mhz – 3Ghz) and are strictly line of sight. Thats why when you’re in a mountainous terrain service is bad, but in a building it’s still good.
To further extrapolate, cell towers utilize TDMA (Time Division Multiple Access) technology so that everyone can use the same towers simultaneously. Think of a time when you were in a very public area where everyone is using their phone. You’d notice your service is very slow. That’s because bandwidth is very limited if the area hasn’t seen that much traffic. TDMA gives you a specific ‘slot’ of time to receive/send traffic. Typically in the milli/nanoseconds.
This differs from your WiFi connection as that operates in the 2.4Ghz or 5Ghz band. This network is yours and yours alone, however it can be interrupted by something like a microwave, that also works in the 2.4Ghz band, but just way higher power.
The key point is that the tower is **NOT** far away. A **”cell”** is the area that each tower covers, and there are many, many towers everywhere. As you travel around, you’re moving from cell to cell, and your cellular phone switches its connection to the closest tower that covers each cell. That’s the #1 reason why your cell phone doesn’t need a large antenna. A CB/walkie-talkie two-way radio, on the other hand, **does** need a large antenna because it broadcasts directly from device to device.
And it’s not like your phone is waiting for you to input something for the radio waves to start. The radio waves are always going, and your phone is always constantly listening and sending its own info.
Don’t need much light to see something far away. You can very easily see car headlights from an airplane or a star from a billion miles away. Radio can be “seen” from a long way very easy.
It’s a combination of sensitive receivers on the cell towers and the nature of radio waves.
To begin, radio waves travel at the speed of light and will technically travel for infinity until they hit something that can disrupt their path. Air can slow them down and disrupt them a little, but not a whole lot.
So you don’t need a lot of power to send an RF signal blasting off in every direction for infinity. You just need enough power to ensure the signal is recognizable data and not just noise on that frequency and not have too much stuff between you and the destination. This is how we are able to communicate with the Voyager probes that aren’t even in our solar system anymore.
All you need is just a really good listener to pick up the signal. You can do this by eliminating the noise and focusing on a very specific band of frequencies to listen for.
Where the signal will finally become too weak is when there’s too much crap between you and the tower, OR, your far enough away that the signal is getting so spread or weak that the tower can’t distinguish the data from the noise floor on that frequency. Your phone may try to boost it’s power to compensate or look for more towers, but then say goodbye to your battery.
Wow, my phone is like a tiny astronaut communicating with Earth from space! Should I start calling it ‘Neil Armstrong’?
Not just cell towers. Now your tiny phone can communicate with satellites in low earth orbit:
https://www.businesswire.com/news/home/20230621154227/en/AST-SpaceMobile-Confirms-4G-Capabilities-to-Everyday-Smartphones-Directly-From-Space
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