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Comment by kbirkeland | Hacker News Reader

The larger problem with the 2.4 GHz ISM band is the lack of non-overlapping channels along with only one station being able to transmit at a time per channel (in pre 802.11ax). There are only three non-overlapping 20 MHz channels in the 2.4 GHz unlicensed spectrum, where 5 GHz spectrum has about 21 (although some require active radar avoidance).

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> The larger problem with the 2.4 GHz ISM band is ... only one station being able to transmit at a time per channel

Is there any Wifi tech for which that isn't true, sans beam-shaping and other tech that effectively puts stations on different physical networks? How do 5 GHz technologies handle multiple simultaneous broadcasts on the same channel? How will 802.11ax do it? Signal processing?

My impression, based on only a little research, is that it's impossible with any tech. Even cell providers need CDMA, TDMA, etc. Maybe that understanding is out of date?

Maybe this?

https://en.wikipedia.org/wiki/IEEE_802.11ax#Technical_improv...

> Spatial frequency reuse

> Coloring enables devices to differentiate transmissions in their own network from transmissions in neighboring networks.

> Adaptive Power and Sensitivity Thresholds allows dynamically adjusting transmit power and signal detection threshold to increase spatial reuse.

> Without spatial reuse capabilities devices refuse transmitting concurrently to transmissions ongoing in other, neighboring networks. With coloring, a wireless transmission is marked at its very beginning helping surrounding devices to decide if a simultaneous use of the wireless medium is permissible or not. A station is allowed to consider the wireless medium as idle and start a new transmission even if the detected signal level from a neighboring network exceeds legacy signal detection threshold, provided that the transmit power for the new transmission is appropriately decreased.

Those along with downlink multi-user MIMO from 802.11ac allowed an AP to send to multiple clients at one time using spatial division multiplexing.

That makes good sense to me, but it's still basically keeping stations on separate networks - it's managing the networks' transmission power carefully so they can run in closer proximity.

Still I don't know a solution to concurrent broadcasts on the same network, as the GGP comment seemed to imply.

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