how do radio signals (4G, WiFi etc.) manage to retain their information after passing through trees, buildings and other obstacles? And how are they not mixed up, intertwined?
In: Technology
First the not intertwined bit:
Different types of radio signals are allocated to certain bands. Some bands are a free for all (like 2.4 GHz for cordless phones, bluetooth and early wifi routers), others are strictly regimented. In the states this is by the FCC. You (as a device manufacturer or a broadcaster) send waves out in a frequency band you aren’t supposed to you get slapped big. Fines or even revoke your device licence. Each band of frequency is allocated for specific purposes (this band is UHF old school TV, this band is FM radio channels 97-108), another band is radar, another air traffic control, another is CDMA old school cell, another is 4G EDGE GSM whatever cell traffic. Other countries have same or similar, and have their own FCC and “spectrum” allocation which may or may not be similar.
So within each band, it may be further broken into channels. Most cell, radio, ATC communication is like this. AM/FM and broadcast TV too. Groups like the FCC make sure that one station on a channel doesn’t clobber or cross talk with another by ensuring geographical separation. Two cities may both have a 107.9 FM station, but they won’t be geographically near one another… or it is ensured that on most days the broadcast transmitter of one doesn’t reach the broadcast area of another.
For communication channels, more traffic gets stacked into a single channel using digital multiplexing. There’s various ways to do this but its akin to letting phone 1 talk during timeslot 1, phone 2 during timeslot 2 and so on (thats time division multiplexing).
Next passing through stuff:
Different frequency signals travel through different things to different degrees. Low frequency waves generally travel very far thru stuff, high frequency waves travel shorter distances or are “attenuated” more by various mediums. Whales use low frequencies and can hear each other over hundreds of miles. The loudest chipmunk in the world will only be heard a few hundred yards. AM signals are lower than FM signals, thus can be heard hundreds of miles away, only a few dozen miles for FM; given the same height of tower and strength of transmitter (and atmospheric conditions etc. etc.).
Now add in error correction etc. – analogue signals travelling through walls, trees etc., well not much you can do to correct that – you get static. Digital signals however, you can use error correction. For broadcast signals, again, you can’t ask for the last second to be rebroadcast, but perhaps there is some extra redundant data being sent and you can reconstruct part of the msg that is missing. Or, in the case if digital wifi or cell signals, if you didn’t get a msg correctly you can ask for it again.
Also don’t discount that a lot of these signals can travel through windows and bounce down hallways and around corners. [Here’s a map someone did that shows how wifi signals get weaker as you move further away from the router in an apartment.](https://i.dailymail.co.uk/i/pix/2014/08/27/1409153044123_wps_3_How_To_Perfectly_Locate_Y.jpg) Note that some signal is getting around corners but further and the more corners, less straight line you are the weaker the signal.
In wider area networks, this is where devices called repeaters come in. All they do is take the wifi or wireless signal and “repeat” it. Like all those relay fires in LoTR, signalling Gondor for aid. Emergency radio networks and public internet and cell networks all use repeaters to deep inside things like tunnels, the subway, really large buildings etc.
A bit more on traffic congestion in certain frequency bands: there are some frequency bands where traffic is largely unregulated. The 2.4GHz band is one. Anyone who wants to broadcast there, go right ahead. No FCC van will pull up and give you a fine (within limits). So thats why in this band we have: cordless phones, baby monitors, early wifi routers, bluetooth runs here (I think)… and really cheap microwaves. My wifi would go down everytime I microwaved something. There are “channels” that you can change your device to, like your wifi things… if your wifi traffic sucks, try changing your router away from “auto” to use a particular wifi channel (0-11), see if it helps.
Latest Answers