How do wireless signals get to its destination?


There are billions of mobile phones all communicating with each other sending wireless signals across the globe. How does each signal know where to go exactly, and how are they not intercepted by other signals?

In: 9

One thing to know is that they’re only sending wirelessly to the nearest cell tower. From there it’s land-based, wires and fiber optic etc, connecting to a tower at the other end where your friend’s phone is connected wirelessly.


Each phone has a unique code/number assigned. Let’s say you’re in California and you call your friend in New York. Your phone is in the area of a cell tower, not too far away (if it wasn’t, got would have no signal), and it tells that tower, “I’m here, here’s my number and carrier information.” Your friend in New York’s phone does the same thing with his closest tower.

When you make your call, your phone tells the tower, “Connect me to the phone with number xxx.” Your service provider knows where all its towers are, and all the phones that are connected to each. It says, okay that phone is connected to a tower in New York, I’ll connect them. The service provider has your friend’s local tower reach out to his phone and say “Lauty_6 wants to talk to you” and his phone shows your number as incoming. If he accepts the call, then the service provider makes the connection for you.

Lots of cool ways. I’ll go over just the radio part between a cell phone and tower. The rest of it is the phone companies problem, and mostly uses the internet nowdays anyway.

At the most basic if you have two signals overlapping the receive strength is usually wildly different at the receiver. The receiver adjusts it’s gain to deal with different levels of power receiver even if just one signal is received. With multiple it adjusts to the loudest signal and the weaker signal just show up as noise and is ignored.

So the trick is mostly to keep all your transmitters in sync to avoid ending up with overlapping signals at the receiver. There’s lots of different types of segregation that can be used to achieve this.

Temporal segregation. If you think of like HAM radios where they say over, before someone else can speak. You can do the same with digital stuff. Digital signals compress data so that 1 second of sound might only take a few milliseconds to transfer and by careful coordination they don’t overlap.

Frequency segregation. Receivers and transmitters need to take up a certain range of frequencies to transmit data as a result of the carrier frequency getting deformed as part of encoding, but can pick different ranges within a wider range to avoid overlap. Those are called channels. Modern stuff to avoid getting stuck on any particular channel with lots of interference will jump between channels at different points in time called frequency hopping, and again takes careful coordination to keep all the devices from trying to transmit at the same time.

Spatial segregation. At it’s most basic it’s just adjusting transmit power to the minimum required. Basically just being polite to others, though maximum transmit power is also regulated by law. Two different systems won’t interfere with each other if they are quiet enough and spaced far away enough. Then you can have directional antennas like satellite dishes. You beam your signal in a line and use the dish to receive only in that direction. Beamforming antennas can do this with software/hardware that combines inputs from several antennas in an array with slightly different time delays and filtering depending on the antenna position in the array. This amplifies signals coming from certain directions without the hassle of physically pointing a dish in a direction. You can even control for specific location rather than just direction to a degree.

Wireless transceivers use antennas, analog filtering, and digital signal processing to talk on the right frequencies. Sometimes the transceivers are point-to-point, and the antennas are aimed at each other. Sometimes like cellphones, it’s a point to multipoint system, when one side provides coverage to a certain area and the subscribers have an antenna that works in all directions.

The signals are part of the electromagnetic spectrum, where the power comes from the transmitting side.

Now a really good question is, what are EM waves and how do they travel through space? Ask your mom..