Now, you might ask, "So what? 802.11ac has been around for a few years now. What's so special about Wave 2 and Multi-User MIMO?"
That's a very good question, one which I hope to be able to easily answer.
There have been a number of challenges that the Wi-Fi industry has been trying to address over the last ten years. First and foremost is the issue of 2.4Ghz spectrum saturation.
If you live in a crowded apartment complex, or in a suburban neighborhood of sufficient size, many of which use broadband/telco provided Wi-Fi router devices, you're bound to see a lot of SSIDs in the 802.11g and 802.11n 2.4Ghz band, using a lot of overlapping channel space.
That isn't good, because it creates a lot of interference and degrades signal quality for the endpoint devices accessing Wi-Fi networks.
The initial solution to this problem was to add a second band, the 5Ghz spectrum. 5Ghz has the advantage of having a lot more channels, but to truly take advantage of the higher speeds of technologies such as 802.11ac, your endpoint device needed to have multiple antennas (MIMO) in order to combine multiple "spatial streams" for bandwidth aggregation.
That's fine if you use something like a stationary media bridge with two or more antennas on it to connect your video game console or streaming device from your living room or bedroom to take advantage of 802.11ac's extremely high wireless throughput (1Gbps+). But a lot of the advantages of 5Ghz 802.11ac are lost when your device, such as a smartphone or a tablet, only has a single antenna. That's where 802.11ac Wave 2 with Multi-User MIMO comes in.
Multi-User MIMO in 802.11 Wave 2 works effectively the opposite way the Single-User MIMO solutions work with current 802.11ac devices on the market. Instead of the spatial streams being aggregated at the endpoint, the router/access point is doing the "mixing" of the spatial streams and then beam-forming to a 802.11ac Wave 2-compatible client device.
MU-MIMO is a software technology, whereas the 802.11ac standard itself is a hardware technology. The software improvements in MU-MIMO include the following:
MU-MIMO is able to group/schedule what type of traffic each device should get, determine if the device is stationary or moving, and the number of antennas/streams supported by each client.
MU-MIMO Rate adaptation dynamically adapts modulation and coding on a client-by-client level and uses past performance and current channel conditions to optimize throughput for each client connection.
MU-MIMO Sounding rate control is used to determine how often data rates should be adjusted for rapidly moving devices.
So there's a lot more heavy lifting in terms of processing on the router/AP. This requires more powerful SoCs, and a lot more intelligence on the router/AP side as well.
So why do we need MU-MIMO technology now? Unlike five or ten years ago, there's much more competition for shared Wi-Fi bandwidth.
According to studies done by Machine Research in 2014 and ABI Research in 2015, the average US home is expected to have 20 connected devices by 2020. In my own home, I have approximately 40 devices connected to my 2.4Ghz and 5Ghz networks.
The total installed base of Wi-Fi enabled devices is also expected to surpass 5 billion devices by the end of 2015. Single-antenna devices dominate that population, with smartphones making up over 50 percent of annual Wi-Fi shipments. These single-antenna devices also have a heavy focus on power efficiency, size, and cost.
Ultimately, what 802.11ac Wave 2 and Multi-User MIMO means for the industry is that it will help Wi-Fi networks scale, and to increase capacity, even when predominantly single-antenna devices are in use. Cost and complexity is added to the router/AP as opposed to the client device, and it increases network performance without additional cost, power and size on client devices.
And obviously, with more new devices, there's more opportunity to combine transmissions to multiple stations.
For legacy client devices, Dual-band 802.11ac Wave 2 routers will be backward-compatible with the existing 802.11ac standard. But ultimately we'll have to see what the device manufacturers are going to do in order to embrace the newer chipsets so that they can take advantage of the new standard's capabilities.
Is 802.11ac Wave 2 Multi-User MIMO a godsend for improving Wi-Fi scalability or is it just an evolutionary improvement? Talk Back and let me know.