What is Second Wave Wi-Fi?

wave wifi

The second wave of 802.11ac is coming ashore and the new MU-MIMO technology (Multi-User, Multiple Input Multiple Output) is going to make a splash. It’s one of the biggest improvements to Wi-Fi we’ve seen to date with the potential to greatly increase wireless network throughput and make a huge difference in dense, high capacity networks.

We saw MU-MIMO technology in action at a recent Qualcomm event. Instead of increasing the speed of just one Wi-Fi client, MU-MIMO improves the entire network, even delivering better results for unsupported devices.

+ ALSO ON NETWORK WORLD: 7 free WI-FI stumbling and surveying tools +

Previous wireless standards and technologies have greatly increased data rates, but until now the increase only applied to one user at a time. For instance, SU-MIMO (Single-User MIMO) with 802.11n allows up to four streams of data to be simultaneously sent and received between a single user and the access point.

However, MU-MIMO with 802.11ac allows access points to simultaneously send one or more streams to multiple users, which has a greater impact across the entire network.

This graphic shows how SU-MIMO can only communicate with clients individually, whereas MU-MIMO allows simultaneous communication with multiple clients.

This graphic depicts how MU-MIMO can send three times the amount of data compared to SU-MIMO in the same amount of time, more than doubling the data rate of each device.

Visualizing how MIMO works

Imagine waiting in line to enter an event or arena that has four different entrance doors. The waiting line would resemble an access point, the people would resemble the data, and the doors resemble the receivers, the Wi-Fi clients.

Without MIMO, a random number of people (data) would be allowed to enter one of the doors (Wi-Fi devices) at a time. That door would close and the next group would enter through a different door (Wi-Fi device). This isn't the best approach as only one door (Wi-Fi device) is open at once, slowing down how quickly the people (data) in the waiting line (access point) enter.

With MIMO, there are four big waiting lines (four data streams) leading up to the entrance of the event, again with four different doors or gates. Each waiting line resembles a data stream and the group of lines altogether resemble the access point. Again, the four doors represent the receivers of the data, the Wi-Fi clients.

If you’re running SU-MIMO, a random number of people (data) from each of the four waiting lines (data streams) enters into just one of the doors (Wi-Fi clients), which remains open all the time. This increases the speed at each waiting line entering into the event; however, it still doesn't make use of all four doors.

With MU-MIMO, people (data) from each waiting line (data streams) simultaneously enter through all the doors. Everyone enters faster because each line can enter through a different door.

Remember, right now MU-MIMO only works for the downlink connection: for example, from the access point to your phone, laptop, and other Wi-Fi devices. Thus devices will still have to contend with each other when transmitting to the access point. This would be like allowing people (data) from all waiting lines (data streams) to enter simultaneously into all the doors (Wi-Fi devices) but alternate which doors are used when exiting (sending back to the access point).

Helps with user density and capacity

Wi-Fi has always suffered from density and capacity issues, especially in the small and crowded 2.4GHz band. Using 802.11n or 802.11ac in the 5GHz band helps by providing many more channels and faster data rates. However, MU-MIMO helps even more as multiple devices can be served simultaneously. This leads to increased throughput, frees up more airtime, and allows access points to serve larger crowds of devices.

+ ALSO ON NETWORK WORLD Gigabit Wi-Fi adapters +

It's important to note that MU-MIMO can increase throughput as described without requiring channel bonding, although it can be utilized with any of the channel widths. Back with 802.11n, two 20MHz channels could be bonded, regardless of using SU-MIMO, enabling more data to be transferred at once. These 40MHz channels could be acceptable in the 5GHz band where there's more frequency space, however it's pretty much out of the question for the small and crowded 2.4GHz band. Then with Wave 1 of 802.11ac we had the ability to use 80MHz channels in 5GHz, again with or without SU-MIMO. Now with Wave 2 that number doubles again, giving us up to 160MHz wide channels, that can be used with SU-MIMO, MU-MIMO, or neither.

You might not want to utilize 160MHz channels since it greatly reduces the amount of channels you have to use in the 5GHz band, but you might consider using 40 or 80MHz to help increase throughput rates even more.

Doesn’t require advanced client device

SU-MIMO required both end-user devices and access points to support the technology and contain multiple antennas. Furthermore, for the client to receive the multiple concurrent streams it had to perform signal processing. The more antennas and streams a device supports, the more power, size, and cost it requires, which is why many end-user devices are still single stream. This isn’t a problem with MU-MIMO, as the client isn’t the one performing the signal processing; the burden falls on the access point.

Although MU-MIMO still requires end-user devices to support the technology in addition to the access point, they can have as little as one antenna and still be served their single stream simultaneously with other devices.

You actually see the biggest difference with MU-MIMO when there are devices that support fewer data streams, versus those that support more. For instance, a four-stream MU-MIMO access point will send data at the same rate that a four-stream SU-MIMO access point would; MU-MIMO doesn’t directly help in this situation. The access point wouldn’t be able to serve other clients.

Not requiring multi-antenna clients also helps the adoption of MU-MIMO on public Wi-Fi hotspots. SU-MIMO isn't as present as much on access points and hotspot gateways as we’ll likely see with MU-MIMO, because more devices will likely support the newer technology due to the eased requirements. Thus we can basically expect better performing public Wi-Fi networks as more devices adopt the technology.

Older clients can see higher data rates

Although MU-MIMO requires support by both the access point and end-user devices, older or simpler clients that lack support still indirectly benefit from the technology, similar to how the technology helps on dense and high capacity networks. Again, when supported devices are served simultaneously, there’s more free airtime for other devices to be served. This applies whether it’s more multi-antenna devices or single-antenna devices. Generally, when devices are served quicker, the higher the data rates you’ll see. This is why unsupported devices can still see increased throughput.

MU-MIMO provides an indirect security benefit. The way the data is encoded when sent from an access point to a device prevents other devices, even those connected to the same access point, from reading the packet’s actual contents, including any sensitive data. Any eavesdroppers performing packet capturing of MU-MIMO transmissions will see limited identification details, such as the MU Group, modulation used, and client MAC address. Remember, MU-MIMO only works on the downlink. Any eavesdroppers can certainly still see unencrypted packets flowing from MU-MIMO devices to the access point. However, any security improvement is welcomed.

It’s coming soon

We’re already starting to see the first MU-MIMO devices shipping, such as the Linksys EA8500 router and Acer Aspire E-series laptops. Through the rest of the year, we should see more products supporting the technology as well, such as business-class access points and smartphones. According to Qualcomm, one of the largest wireless chipset manufacturers, they actually started including the technology in mobile devices starting in 2013, now requiring just software updates to activate.

Eric Geier is a freelance tech writer—keep up with his writings on Facebook or Twitter. He’s also the founder of NoWiresSecurity providing a cloud-based Wi-Fi security service, and On Spot Techs providing RF site surveying and other IT services.


Copyright © 2015 IDG Communications, Inc.

The 10 most powerful companies in enterprise networking 2022