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