Wi-Fi .11AX – What’s It All About?

Cees Links was the founder and CEO of GreenPeak Technologies, which is now part of Qorvo. Under his responsibility, the first wireless LANs were developed, ultimately becoming household technology integrated into PCs and notebooks. He also pioneered the development of access points, home networking routers, and hotspot base stations. He was involved in the establishment of the IEEE 802.11 standardization committee and the Wi-Fi Alliance. He was also instrumental in establishing the IEEE 802.15 standardization committee to become the basis for the Zigbee sense and control networking. Since GreenPeak was acquired by Qorvo, Cees has become the General Manager of the Low Power Wireless Business Unit in Qorvo.

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Is Wi-Fi Running Out of Steam?

Despite the fact that nobody could keep track of the array of acronyms underlying Wi-Fi (IEEE 802.11b, .11a/g, .11n, .11ac), the good news was that each new version was a clear step forward in raw data rate. In four generations, that rate went from 11 Mb/s to 6.9 Gb/s – an increase of more than 650 percent!

After all, raw data rate is the “name of the game.” This comes as no surprise, since Wi-Fi is about pure data communication.

Now there is the imminent arrival of IEEE 802.11ax, with a maximum raw data rate of 9.6 Gb/s. But given its slow appearance (ratification is now planned for late 2018) and marginal improvement, one might wonder if this is an indication that Wi-Fi is running out of steam.

But don’t be fooled! Underneath the acronym, there is a real shift going on from raw data rate toward multi-channel capacity and improved spectral reuse. This means that the real-life throughput experience of .11ax may be an increase of as much as four times that of .11ac. Let’s explore, because this has consequences for consumers, as well as for product builders.

“For the consumer, there are always two important points with Wi-Fi. The first is performance. The second is range.”

Interference

For the consumer, there are always two important points with Wi-Fi. The first is performance (data rate). The second is range (e.g., “how can I get the highest speed in every corner in my house and backyard or basement, etc.?”).

In urban areas these days, consumers have grown accustomed to what is now a common scenario – turning on a laptop, for example, and having to weed through the many routers or access points that are visible when trying to find a Wi-Fi network. Many of the routers use the limited number of overlapping channels, which means users are sharing those channels. Or to put it another way, there is interference on those channels.

When two devices are talking through each other, over the same channel at the same moment, it means that the messages are getting garbled and both need to be sent again. It’s no surprise, then, that the throughput in dense environments can collapse in continuous retransmissions. Again, this is a form of interference.

What happens if two devices are “talking through each other?”

Smart phones, computers, tablets and routers communicating with each other on the same channel sometimes “talk through each other.” Not surprisingly, this jumbles the communication.

A sending device usually knows that a packet has not arrived, because it does not receive an acknowledgement back from the receiving device within a certain time frame (we are talking milliseconds here).

The “mechanism” with which devices communicate is called a protocol, which describes how proper communication needs to be handled, including what to do when “talking through each other.” A simple part of a protocol is “listen-before-talk,” which means that before a device starts to send a data packet, it listens to ensure that nobody else is “on the air.” But, if two devices both listen and, both conclude that the “air is clear” and start communicating at the same time, it creates a “collision.” Some devices can “hear” the interference and will “back-off,” or stop and wait (again, milli-seconds) before
sending again.

So, typically what happens in dense environments is that more packets collide, more packets need to be retransmitted with now higher chances of another collision, and the consequence is that the performance of the network as a whole can break down. This is what happens, for example, with too many people on a single hotspot.

This form of interference is made worse by the fact that routers and access points have attempted to improve range via the highest output power possible. Anyone who has ever been to a crowded party can understand this scenario. The more everyone speaks louder to be heard, the overall noise goes up and any real opportunity to communicate goes down. In the same way, more output power just causes more interference. In addition, higher output power in some channels of the band causes the signal to “bleed” from one channel into the channels next to it – another form of interference – causing the capacity of the band and the total Wi-Fi system to degrade. So, what to do?

Distributed Wi-Fi

This is where IEEE 802.11ax comes into play. The goal of this new standard is less about higher data rates, and more about the use of as many channels in the 2.4 GHz band or the 5 GHz band as possible – at the same moment in the same space.

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