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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 (i

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).

forapurpose 8y ago
> 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 Maybe that understanding is out of date?
- kalleboo 8y ago
  Maybe this? https://en.wikipedia.org/wiki/IEEE_802.11ax#Technical_improvements 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.
  - kbirkeland 8y ago
    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.
  - forapurpose 8y ago
    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.

forapurpose 8y ago

> 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?

kalleboo 8y ago
Maybe this? https://en.wikipedia.org/wiki/IEEE_802.11ax#Technical_improvements 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.
- kbirkeland 8y ago
  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.
- forapurpose 8y ago
  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.