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It's been awhile since I had to think about Wifi on a serious level. Last I knew: Due to the nature of the medium (radio waves), wifi was a 'circuit-switched'
by mmooss 2y ago
It's been awhile since I had to think about Wifi on a serious level.
Last I knew: Due to the nature of the medium (radio waves), wifi was a 'circuit-switched' network - any two devices communicating monopolized the entire network. That is, unlike a switched wired network, only two devices can communicate at once (usually an endpoint and a base station).
More devices using the network, which of course was usually necessary, required some sort of time-division multiplexing - the network needed to slice up circuit access by time. The only other solutions were multiple networks, which were created with multiple radios on different frequencies, and [edit: beam forming], which created different networks to different physical locations - if that actually worked in practice.
Has anything changed? Are there new solutions to the circuit-switching limitation? Has someone managed to turn wireless into a packet-switched network?
- kbolino 2y agoWiFi is a shared medium, but shared medium and circuit-switched are not the same thing. WiFi uses packets and conforming devices do not block other devices for any longer than the time to send a packet.
- aeonik 2y agoYou can multiplex by frequency as well. Also, modern wireless systems can even multiplex by location, using phased arrays, it will beam a spotlight of radio to your direction, and can noisy data from receiving phase information as well.
- mmooss 2y agoHow are those different than the multiple radios and beam forming (oops, I see I wrote something else) that I mentioned? I'm not being snarky; I'm trying to learn what I'm missing. Thanks.
- aeonik 2y agoI think you could approximate the phased array and frequency multiplexing with a bunch of dish antennas connected to separate radios, but the dishes would need to be connected to motors to follow moving targets. It would also require a lot more physical space. The neat thing about phased arrays is that they are solid state, aka no moving parts, so they have a much faster response. Here is a really good presentation on how they work and how to build one. https://youtu.be/ytBmoL2wZLw?si=f7aTFNfeUbvbbqVe https://youtu.be/ytBmoL2wZLw?si=f7aTFNfeUbvbbqVe
- mmooss 2y agoSorry, I wasn't clear with what I was saying - but now I understand what you meant anyway. Thanks.
- aeonik 2y agoGlad it helped, I just now see you are talking beamforming. Beamforming is achieved using phased arrays. I'm not sure if all beam forming uses phased arrays, but one of the terms is just talking about the wave itself (beamforming), while phased array is talking about how the beamforming is achieved. That being said, I don't want to presuppose that you can't beamform form without phased arrays.
- simonm21 2y agoTo complete what is has been said by the community, I suggest to look at the CWNA certification to begin your Wi-Fi journey. It explains perfectly all the base knowledge that all guys working on Wi-Fi should have. It's independent and not related to any vendors, that's why this certification is the best to begin with.
- varenc 2y agoThat's a bit of an oversimplification. Access Points coordinate communication to ensure clients take turns, and Wi-Fi avoid collisions by having clients listen for an idle channel before transmitting and exponentially backing off if it's busy (CSMA/CA). So even when clients share the same frequency, it’s not 'circuit-switched' since transmissions are managed dynamically. Clients wait for the AP to respond before sending additional data. And there's QoS features to ensure things like live voice take priority over a bulk download. Wi-Fi 6 adds OFDMA, which splits channels into sub-channels so multiple clients can transmit simultaneously, and MU-MIMO allows simultaneous streams to different clients. Beamforming helps too with directional signals. tl;dr; it is a shared medium but with lots of tech on top of it that mitigate much of the issues!
- mmooss 2y agoThanks ... but one thing I don't understand: > MU-MIMO allows simultaneous streams to different clients That's great, but the question is the same: how? How does it solve what I called the circuit-switching problem (i.e., each tranmission utilizing the channel 100%)?
- evil-olive 2y agostarting with 802.11ax ("Wifi 6") [0] they've started doing frequency-division [1], in addition to time-division. as I understand it, a channel can be effectively divided into K separate sub-channels, and then in a crowded space with N active users, your time-division only needs to contend with N/K other users. this dovetails well with Wifi 6E expanding to the 6ghz range, and Wifi 7 (among other things) expanding channel bandwidth to as large as 320mhz. (compare this to classic 2.4ghz having only 3 non-overlapping channels of 20mhz width each) 0: https://en.wikipedia.org/wiki/Wi-Fi_6 https://en.wikipedia.org/wiki/Wi-Fi_6 1: https://en.wikipedia.org/wiki/Orthogonal_frequency-division_multiple_access https://en.wikipedia.org/wiki/Orthogonal_frequency-division_...
- mmooss 2y agoThanks. > starting with 802.11ax ("Wifi 6") [0] they've started doing frequency-division How does that differ from multiple radios running multiple connections? Is it that there are many more frequencies, closer together, dynamically allocated?