How does a wireless adapter know which signals are intended for it, rather than another nearby device?

Question

(Let me know if you think this question fits the EE site better.)

If I'm on a Wi-Fi network using my laptop, and someone else is nearby on a laptop, also using the Wi-Fi, how do our respective devices separate out the signals and know which is intended for whom?

To my device, there would be signals coming out from the wireless router for both me and for other person, and it has to sort those out. Likewise, there would be signals coming from the other person's device and intended for the router, which my computer would also want to ignore.

How does the adapter tell which is which? Why don't these signals interfere with one another if multiple devices are in proximity to one another? How is it possible to have more than two devices (one router, one user) using Wi-Fi in the same area?

Answer 1

Wi-Fi is both a layer-1 (the radio waves) and a layer-2 set of protocols. Each layer-2 frame has layer-2 source and destination addresses (MAC addresses, in the case of Wi-Fi), and the layer-2 addresses tell each host which frames are for that host.

This is how many layer-2 protocols work. For instance, ethernet was also originally designed for a shared medium, and an ethernet switch will still send frames for which is doesn't know a destination interface to all the switch interfaces, and each host will ignore frames not destined for it.