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back to article WTF is … MU-MIMO?

With 802.11ac Wave 2 due for ratification in December, El Reg had a talk to Cisco's Andrew Myles, Manager of Protocols in the Borg's Wireless Network Business Unit, to get a handle on one of its more interesting characteristics: MU-MIMO. Along the way, there were some handy reminders. Myles, who's been around the wireless scene …

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I love innovation

However this still doesn't get over the problem that we actually need more frequencies for WiFi. My typical suburban home has a good 10-12 networks in range on any given evening, there has got to be a least 2-3 devices on each.

The 5Ghz band is useless at getting through a house with sturdy walls, although I would imagine these modern wooden framed homes would be easier on the signal.

The congestion is just killing the network, its like when you try and scale a token ring network.

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Bronze badge

Re: I love innovation

To be fair, if the beam forming works as advertised reducing signal in the direction where you're not located, then neighbourhoods may become "quieter" as access points aim their signal at their clients rather than just blasting out a big spherical signal, which could reduce leakage.

That said, I doubt it's going to get good enough to make an appreciable difference in an apartment block, so especially high-density environments will still struggle with congestion, but if of the 10-12 networks you can see, the 2 or 4 furthest away can beam-form and don't leak as far as you, then that's 20+% improvement.

As people upgrade their kit and increasingly use 5GHz though, one would hope that congestion also eases, as people migrate to a band that naturally resists leakage (admittedly sometimes resisting leaking from the hallway into the lounge, which is inconvenient), so geographically you should see less of the neighbourhood's traffic pouring in through your windows. If your wifi only propagates next door rather than halfway down the street (and if everyone else's does the same), then you've suddenly got a lot less congestion.

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Re: I love innovation

If your wifi only propagates next door rather than halfway down the street...

...then you have a problem when sitting in the garden (shed).

Not really an issue for those in apartment blocks, but it is an issue for others.

I'd like someone to come up with a small, portable (cheap) dual-band Wi-fi extender that could be placed in, say, a window that has a pointable, directional aerial so it can be used as a booster in such cases.

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Anonymous Coward

Re: I love innovation

2.4GHz only has (this depends on the country as well) eleven channels. 5GHz (also depends on the country) has 21 channels. Now if people start take 160MHz to get those high speeds, then you start having issues again as 21 channels is 21 channels at 20MHz. Using 8 of them for 160MHz is useless for home use unless you are doing large transfers to a local server. With the propagation of 5GHz being less than 2.4GHz that will help as well. I have two AP's that sit in my attic running back to a Wireless LAN Controller (WLC) and have 2.4GHz and 5GHz both running. Wall penetration is not an issue as the signal has to go through the ceiling and 24 inches of insulation. The MCS Index is usually 15 but does drop down to 13 at times but 99% of the time it is 15.

Under 5GHz the RSSI is -46 and under 2.4GHz it would be -33. So 2.4GHz is still the stronger signal coming from the same AP but given that both provide an MCS of 15 and that 5GHz supports channel bonding the 5GHz is faster and currently has less interference. With where I have the AP's I can actually see 20 networks around me. The most popular channels are 1, 6 and 11. There are seven AP's that use channel 6, three that use channel 1 and currently only one that uses channel 11. If you want the most out of your AP, make sure it never uses 1, 6 and 11.

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Re: I love innovation

@AC 15:38

The reason most APs use 1, 6 or 11 is because those frequencies, 2.412, 2.437 & 2.462 GHz, don't overlap with 20 MHz wide channels given the 5 MHz channel separation. In short, it's impossible to make sure your AP "never uses 1, 6 and 11" because there aren't any other non-overlapping channels in between. Note that channels are typically 20 MHz wide in the 5 GHz range so overlap isn't as much of a problem

Currently where I am, according to inSSIDer, there are 6 APs on channel 1, 5 APs on channel 6 and 8 APs on 11 so my best bet would be channel 1 except there are also one AP on each of channels 2, 3, 4 and 7 plus a pair on channel 9. Yes, there really are 25 APs. That means there are 9 APs working at least partly on channel 1, 11 APs working in the frequency range of channel 6 and 11 APs operating in the range of channel 11.

Now lets look at the channels that "avoid" these three major channels. There are 14 devices working in the 20 MHz band around channel 2, 15 devices in each band for channels 3 & 4, 16 devices in channel bands 9 & 10, 17 devices overlapping in the "empty" channel bands 5 & 8 and a peak of 18 devices overlapping channel 7. Notice that each of these are worse than the 9 or 11 devices working on channels 1, 6 and 11 and in fact channel 1 would be my best bet but I'm running at 5 GHz and have it all to myself since the neighbor, who was also on 5 GHz, moved a few months ago.

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Re: I love innovation

Ok, pretend the last sentence in the first paragraph above reads "Note that channels are typically separated by 20 MHz in the 5 GHz range so overlap isn't as much of a problem."

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Meh

Alas: MU-MIMO only works in the download direction,

Which is going to be over 90% of the traffic with tablets/phones anyway....

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