New MU-MIMO Standard Could Allow For Gigabit WiFi Throughput

MojoKid (1002251) writes "Today, Qualcomm is announcing full support for a new wireless transmission method that could significantly boost performance on crowded networks. The new standard, MU-MIMO (Multiple User — Multiple Input and Multiple Output) has a clunky name — but could make a significant difference to home network speeds and make gigabit WiFi a practical reality. MU-MIMO is part of the 802.11ac Release 2 standard, so this isn't just a custom, Qualcomm-only feature. In SU-MIMO mode, a wireless router creates time slices for every device it detects on the network. Every active device on the network slows down the total system bandwidth — the router has to pay attention to every device, and it can only pay attention to one phone, tablet, or laptop at a time. The difference between single-user and multi-user configurations is that where SU can only serve one client at a time and can therefore only allocate a fraction of total bandwidth to any given device, MU can create groups of devices and communicate with all three simultaneously."

Comments

Cool, but

[rossdee]

WE have a combined Wifi Router and cable modem that is owned by the cable company, but at least they fix it when there is a problem

Anyway it means we have to wait for them to update us to new WiFi standards. Which of course they will charge more for...
 

Re:Cool, but

[rossdee]

But it was still fast enough to get first psot

Re:Cool, but

[Anonymous Coward]

And whats stopping you from plugging in your own WIFI router? Which you should have done anyway.

Re:Cool, but

[a-zarkon!]

Are they providing you a Gig Internet connection? If not, then it doesn't really matter so much if you have a Gigabit-capable wireless connection. On the other hand, if you need Gig wireless connectivity between devices/systems within your network - you might consider springing for a wireless infrastructure to support that kind of connectivity.

Re:Cool, but

[Anonymous Coward]

Just having a gbit speed in LAN is quite nice too even if you don't have that speed to internet.

Re:Cool, but

[mlts]

What would be interesting is if the groups of devices could have their own individual WPA2 encryption key. That way, one wireless segment can use multiple keys in PSK mode. This way, if a smartphone is lost or changed out, just one password needs deleted rather than rekeying every device on the subnet.

Re:Cool, but

[Anonymous Coward]

You are completely forgetting people with a NAS. There are more uses for WiFi, than just your Facebook page.

Re:Cool, but

[bws111]

Couldn't make it all the way to his third sentence, eh?

Re:Cool, but

[rb12345]

You can do that easily enough as it is. One way is to set up multiple SSIDs per radio with separate PSKs. Another way is to use WPA2 Enterprise with one username/password pair per device.

Re:Cool, but

[AvitarX]

They did that to me too, no longer offering modem purchases, or modem only.

I was able to get it into bridging mode, but it was a big pain on the phone (they asked for a reason, and I just said work VPN equipment, and every rep I spoke too (I talked to 3 because switching modes revealed the one they shipped me was broken and I had to get a new one) knew what I meant and was super helpful, but I was kinda cranky that they locked the ability to bridge from the admin interface. The Modem / AP where I work allows the customer to turn on bridge mode.

Of course I haven't RTFA but...

[Anonymous Coward]

I wonder if this would help alleviate the step down problem when older/compliant devices connect (EG if an 802.11b connects on an 802.11g router the router automatically downgrades everyone to 802.11b speeds)

Sooo, TDMA for Wifi

[drrck]

I guess I thought this kind of thing was already out there, if not sounds solid to me.

Re:Sooo, TDMA for Wifi

[Phreakiture]

Your understanding is reversed.

TDMA for WiFi is what we have now.

MU-MIMO is simultaneous comms with each device.

The title is a bit misleading

[YoopDaDum]

The title could lead some to believe that MU-MIMO is increasing the peak throughput, which is not the case. Spatial multiplexing (SM) MIMO allows to have as many independent concurrent streams as there are antennas on receiver and transceiver (the min of both sides actually). So with 4 antennas on the AP and 3 on the station for example, you can have 3 streams. With SU-MIMO, all three streams are used between the AP and a single station. With MU-MIMO the AP can use its streams with more stations: for example 1 stream to station A, and 2 streams to station B. There is a little bit of degradation of course compared to single use. It's a win when you have for example a 4 antennas AP and only 2 antennas stations, then instead of leaving half the capacity on the floor you can make use of all the streams. But it doesn't increase the peak rate possible with SU-MIMO, it increases the AP capacity when devices do not have as many antennas as the AP, which is the usual case.

Re:The title is a bit misleading

[wonkey_monkey]

Slow down, science boy. Can I haz more lolcats, or what?

Re:The title is a bit misleading

[wonkey_monkey]

I do apologise. I meant, of course, "or wut?"

Re:The title is a bit misleading

[George_Ou]

MU-MIMO does effectively offer higher speeds than SU-MIMO in practice. Since most client devices are single antenna devices and only a few that are dual-antenna, MU-MIMO effectively increases the per-client throughput by improving overall capacity. If four single-antenna clients can be concurrently served by a MU-MIMO access point with 4 antennas, each client can have up to 4 times more throughput than the same 4 clients being served by a 4-antenna SU-MIMO access point. The SU-MIMO 4-antenna AP can't speed up operation for a single 1-antenna client.

Re:The title is a bit misleading

[YoopDaDum]

Absolutely, and that's why I'm talking about "peak throughput" above and not only throughput. Increasing capacity allows to either offering higher average throughput, or offering the same average throughput to more devices concurrently, or any mix in between. It does matter, and actually changing field a bit capacity in the wireless cellular world is what really matters: stretching things a bit to make a point you could say that in cellular peak throughput is for marketing, capacity improvements are for real life concerns (increasing average throughput / reducing cost per bit). Unfortunately the later is more complicated to sell so is often not put forward, but that's where the real work is.

Still, it's too bad that on a geek site one has to pass a capacity improvement as a peak improvement to make it more sexy. Let's learn to love capacity for its own sake ;)

Re:The title is a bit misleading

[George_Ou]

Capacity matters a lot in Wi-Fi as well as cellular data. Very rarely will you see mobile devices be able to leverage 2x MIMO or better because they only have one antenna. Capacity is effective peak performance for most situations. Peak throughput is great for marketing benchmarks and occasionally real life performance when it comes to wireless bridging.

rental

[Anonymous Coward]

I'm sure they charge out a monthly rental fee for that item as well. Likely if people are using a combo wifi router / cable modem from their provider, they don't have any need for gigabit wifi anyway.

A rare sight

[wulfhere]

What a great, informative reply! I learned something. So rare on Slashdot lately. :-/

So, is 802.11ac a polling MAC layer?

Re:A rare sight

[YoopDaDum]

Thanks! The MAC layer principles are the same in 802.11ac than in 802.11n. The MU-MIMO feature is really made for the AP to stations direction (downlink). The AP can decide on the combined transmission on its own, based on queued packets: if the AP has packets buffered for several stations that can be sent using MU-MIMO, it can merge them into a single PHY access. There's a gotcha for the ACK part, you don't want the receiving stations to ACK at the same time but for this block ACK is used for all stations but one. So those other stations will wait for a block ACK request from the AP, and the AP makes sure there is no collision.

For more details I can recommend "Next Generation Wireless LANs" by E. Perahia and R. Stacey. I have no relation to the authors, but I've used their book and found it good. Warning: it's only if you really want to go into the details (but it beats the IEEE spec handily on readability ;)

Re:A rare sight

[wulfhere]

I'm a wireless engineer (but not a WiFi engineer), so I might just check out that book. Thanks!

So.....

[Lab Rat Jason]

...Token Ring is back?

Re:So.....

[Anonymous Coward]

WIFI is like a hub and if you don't want collisions, you need a way to negotiate when a device can speak. Not exactly token ring because tokens can be held onto while TDMA is strict definitions on when you can send.

Wireless will still never compete with wired

[Anonymous Coward]

If you really *need* gigabit throughput chances are you've already run the hardline necessary to get it. Anything else is just hobby work.

Cool but...

[grumpyman]

...what we need more is connectivity and reliability.

Clunky name

[Art3x]

The new standard, MU-MIMO (Multiple User — Multiple Input and Multiple Output) has a clunky name — but could make a significant difference...

I thought clunky names were an engineering tradition, like CSMA/CD (Carrier Sense Multiple Access with Collision Detection), which means, Listening Among Others for a Chance to Speak.

Re:Clunky name

[Anonymous Coward]

Which would inevitably turn into LAOCS. It's also less informative. CSMA/CD describes nearly the whole algorithm with the exception of the random transmit backoff. LAOCS doesn't really describe anything to do with radio systems; sounds like some cooky old proverb.

Nice ... but no clients until 2016

[ras]

MU-MIMO is part of wave 2 of the 802.11ac standard. Right now every shipping product is wave 1.

If we are lucky the routers will get wave 2 this year, or if not this year definitely next. Apart from allowing more devices to share the same cell MU-MIMO is nice in that it reduces power consumption of devices like phones, as they only see the packets for their stream. Wave 2 also bring doubling of the bandwidth (if the spectrum is available) and other efficiences which translates to 2..3 times the speeds of wave 1. This means unlike wave 1, wave 2 should be able get 1Gb/s in the real world.

All very nice. The only issue is we won't see wave 2 client chips in laptops, phone and the like until 2016 at the earliest. So unless you are doing back to back routers or range extending, don't expect this shiny new Qualcomm chip to make see any measurable improvement in any of your existing 802.11ac devices, or in any you buy in the next 2 years.

They must have taken a page from Nokia on the name

[Anonymous Coward]

Maemo, meego, finding nemo.

Or the Laughing Cow: MooMIMO

Uninformed question.

[Anonymous Coward]

A number of things. For example, this may be in an office space or an airport or any other place that you don't own. You have a lot more freedom at home than you do when you're out and about.

Also, even at home, the whole point of the technology is that they're changing what happens between your router and the clients. Your question really doesn't make any sense.