The following post originally appeared in Human Infrastructure magazine, a weekly newsletter about life in IT. Human Infrastructure is free with your subscription to Ignition, the Packet Pushers’ professional development site.
Wi-Fi 6 is the latest industry standard for wireless networking. Also known as IEEE 802.11ax and “High Efficiency” wireless, this emerging standard is an opportunity for your favorite WLAN vendors to come knocking to talk about upgrades.
This is a brief technical overview of Wi-Fi 6 to help get you up to speed and ask the right questions.
In next week’s issue I’ll examine the business case for Wi-Fi 6 and share opinions on whether to deploy now or hold off.
A Technical Introduction To Wi-Fi 6
Wi-Fi 6 improves throughput for wireless networks by enabling a high client density. Wi-Fi 6 efficiencies include breaking up channels into sub-channels and longer sleep intervals for low-power devices.
Wi-Fi 6 is not focused on higher maximum speeds or wider channels. Rather, Wi-Fi 6 enables multiple wireless clients to transmit data simultaneously. A stated goal of Wi-Fi 6 is a 4x throughput improvement for clients in high-density environments.
Wi-Fi 6 access points will be backwards compatible with 802.11a/b/g/n/ac clients. However, maximum network efficiency will only be reached with Wi-Fi 6 clients.
Perhaps you just yawned. If that’s what’s notable about the Wi-Fi 6 specification, is it really that interesting? I believe it is.
Meet OFDMA
The cornerstone technology of Wi-Fi 6 is orthogonal frequency-division multiple access (OFDMA). OFDMA is what makes Wi-Fi 6 compelling. OFDMA subdivides a channel into Resource Units (RUs). Those RUs can be allocated to different wireless clients, giving them the ability to communicate at the same time.
OFDMA is the multi-user version of orthogonal frequency division multiplexing (OFDM), which is used in 802.11a/g/n/ac.
The OFDMA tradeoff is in performance. Wireless communications use radio waves to push data. One way to send more data through the air is via radio channel width. The wider the channel, the more data you can send. Therefore, if a channel is subdivided, a client only get a fraction of the channel, and can only send a fraction of the data it could otherwise send if it had the whole channel to itself.
So why is OFDMA a positive feature? Because wireless clients don’t always have a lot to say. We networkers tend to think in terms of maximum throughput, but most of the time, network clients don’t need big bandwidth.
Activities like browsing a web site, using social media, or sending a text message need relatively small chunks of data. Just like most wired desktops could get away with 100Mbps or less most of the time, most wireless clients don’t need entire channels most of the time.
OFDMA means multiple clients can transmit simultaneously, rather than waiting for the air to clear before they get a turn. OFDMA will reduce collisions in dense environments and should go a long way toward the 4x throughput improvement goal.
Wi-Fi 6 Means Faster Speeds, Right?
While I was sitting on a Wi-Fi 6 industry panel at Cisco headquarters, one of the other panelists said Wi-Fi 6 means faster speeds, just like all previous iterations of the Wi-Fi spec.
That’s sort of true. One key issue is quadrature amplitude modulation (QAM). QAM increases throughput in Wi-Fi networks by encoding more bits in a transmission by changing the angle of a wave and the amplitude of a wave relative to a center point. Unique angles and amplitudes are spread over a quadrant grid, creating a constellation. Wireless QAM schemes include 4-, 16-, 64-, and 256-QAM.
The challenge with high-density QAM constellations is that the air must be clear and the signal strength strong between client and AP to experience the throughput benefit. Poor signal quality means that the tiny distinctions between the various angle and amplitude combinations can’t be communicated clearly.
Wi-Fi 6 introduces 1024-QAM, which should result in a higher theoretical maximum throughput, but only under ideal conditions. Ideal, as in, there’s no one else on the air, the spectrum is pristine, and the client and AP are within a few feet of each other.
This is why I contend that faster speeds in Wi-Fi 6 are only sort of true. The spec is there to facilitate faster speeds, but in real-world conditions, faster speed in Wi-Fi 6 is closer to fake news.
Target Wait Time Reduces Battery Consumption
An understated feature of Wi-Fi 6 is Target Wait Time (TWT). TWT is a power saving mechanism that schedules a wake time for clients that are sleep capable. The goal of TWT is to optimize how often the client needs to wake up to determine if it has network communication to attend to.
The big idea is to keep clients asleep as long as possible to reduce battery use. Scheduling a specific wake time means the client doesn’t have to cycle the radio up as often.
BSS Coloring Puts Others On Ignore
Basic service set (BSS) coloring is a Wi-Fi 6 feature that should improve throughput. The idea is to color your wireless world with a number–a digit for identification. The client will look to determine if it’s a part of the BSS indicated in the frame. If the client is not a part of the BSS indicated by the “color,” the client knows it’s okay to send.
In theory, BSS coloring will increase throughput. The wireless speaker won’t be waiting as long for the air to clear before sending in a busy wireless environment with a large number of BSS’s. I found this counterintuitive, because two wireless transmissions happening at the same time can clobber each other, forcing a retransmission–the opposite of increased throughput.
A wireless friend explained to me that there’s an assumption built into BSS coloring. The assumption is that the different wireless systems will be physically far enough apart that one system will be much quieter than the other. In that scenario, it’s safe to have simultaneous transmissions, because the local, shouty transmission will drown out the whispering transmission from far away. Therefore, if you hear a different BSS color in the air, it’s safe to be inconsiderate and shout away.
In that assumption, there is a catch. BSS coloring won’t help in scenarios where different wireless systems are right on top of each other. Apartment complexes and multi-floor, multi-tenant business parks could have systems just as loud as one another and potentially disrupt each other’s transmissions. BSS coloring won’t replace careful channel planning.
For More Technical Information On Wi-Fi 6
I recommend Clear-To-Send’s 802.11ax podcast series very highly. I listened to Rowell Dionicio talk through the Wi-Fi 6 overview episode in detail, taking lots of notes to get up to speed on this topic. The series is a fantastic resource, and I hope I got most of my information right.
I also found this article from Aerohive to be a cut above most of the flotsam turned up by Internet search. The piece is in a Q&A format and is grounded in technology as opposed to marketing puffery.
And I’d be remiss not to mention the Packet Pushers’ own episode, Inside The Pros And Cons Of 802.11ax, with guests Devin Akin and David Coleman.
