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what-is-wifi-6

Introduction

What is Wifi 6? We all know that Wifi 6 is coming! Even though IEEE has not yet ratified the 802.11ax standard (target Q3 of 2019), many network vendors such as Cisco, Asus, AeroHive, Netgear etc have come up with product lines supporting this new standard.

If fact, just yesterday, Cisco announced new access points across their Catalyst and Meraki product lines that support this new standard.

Are you in the market looking to upgrade your Wifi infrastructure?

This article addresses the most commonly asked questions regarding Wifi 6 so that IT managers can decide whether this is the right time to upgrade or not.

What is Wifi 6? What happened to the other digits?

The “Technical term” for Wifi 6 is 802.11AX. Calling it Wifi 6, is an attempt made by the Wifi Alliance to simplify the naming used by 802.11 standards.

This means that the previous generations of wifi also get these numbers:

  • 802.11ac becomes Wifi 5
  • 802.11n becomes Wifi 4.

Here are the standards that saw the light of day, and the year they came out in:

  • 802.11b – Wifi 1 (1999)
  • 802.11a – Wifi 2 (1999)
  • 802.11g – Wifi 3 (2003)
  • 802.11n – Wifi 4 (2009)
  • 802.11ac – Wifi 5(2014)

How fast is Wifi 6? How much faster compared to 802.11ac Wave 2?

Since we now have an understanding of “What is wifi 6?” – let’s look at how fast it is.

The theoretical speed for AC wave 2 (Wifi 5), is 866 Mb/s for a single spatial stream on the 80 Ghz channel. For Wifie 6, it’s 1201 Mbps.

So, while Wifi 5 saw a 6X speed jump compared to Wifi 4 (150 Mb/s) – the speed jump from wifi 5 to wifi 6 isn’t that much. What the powers-that-be have focused on more is “efficiency”.

Please note that “theoretical speeds” are inaccurate. Real world performance varies and depends on range, obstavles, other signals in the air, and the quality of the radio on your Access point and device.

Will my 802.11ac / 802.11n / 802.11a/b/g devices still work if I upgrade my Access Points to Wifi 6? Is Wifi 6 backwards compatible?

Yes, the standard is backward compatible. That said, don’t expect a performance improvement by just upgrading the AP – the client devices need to be AX too.

How is Backwards compatibility achieved in 802.11ax?

Devices with 802.11ax radios will communicate with other 802.11ax radios using OFDM and/or OFDMA.

Devices with 802.11ax radios will communicate with older radios using OFDM or HR-DSSS.

When 802.11ax-only OFDMA conversations are taking place, RTS/CTS (Request to Send / Clear to Send) mechanisms will be used to defer legacy transmissions.

What problem does Wifi 6 solve?

Traditionally, WiFi performance becomes un-predictable under load. 802.11ax is more deterministic – both in terms of latency and throughput. The main focus behind 802.11ax isn’t speed. This standard addresses congestion and capacity to connect the “extremely large number of devices” to the network.

It provides four times more capacity compared to older standards.

Access points will be able to handle upto 12 simultaneous wifi streams.

How does Wifi 6 solve the problem of efficiency?

It gives the Access Point the ability to send and receive data from multiple devices at the same time. In older standards, the access point could only talk to one device at a time.

Traditionally, in 802.11, there is the concept of a DCF (Distributed Coordinated Function). This means, that, if you’re a radio ready to transmit data, you need to first see if someone else is using the channel. This means, that even if you’re a 802.11AC Wave 2 radio, you’ll still need to “Wait your turn” and contend for channel access with other, older 802.11 a/b/g devices. In other words, at any given point of time – For One Channel, Only One Frame can be on that channel within a certain signal strength range. Therefore, different devices habe to look for each other to see if some one else is talking before they can talk.

Another cool feature is the concept of “Target Wakeup Time” (TWT). This allows devices to negotiate that for how long and how often they’ll need to transmit and receive data. This allows the transponder on the device to sleep when transmission isn’t necessary. This “should” preserve battery life on devices once “wifi 6” devices become available. This is great news for IoT (Internet of Things) devices! 802.1ax IoT clients could potentially sleep for hours/days and conserve battery life.

My Wifi works just fine. Do I really need to upgrade to Wifi 6?

Depends on who you are, really. The problem that Wifi 6 solves is of “Dense Deployment Scenarios”. Places where there is a lot of CCI – Common Channel interference. Lots of client devices trying to access the Wifi medium at the same time. Lots of co-located access points. Places such as Airports, Stadiums, hotspots, etc. That’s where Wifi 6 really shines. It has mechanisms built in that make more efficient use of the wireless medium.

Please know that, there’s almost no benefit to upgrade your access points, if your clients don’t support the newer standard. 802.11ax provides enhancements to the PHY and MAC layers – that should improve operations in the limited frequency bandwidth available – but that’s only when it’s also available on the clients.

You’ll still get the benefit of MU-MIMO spatial streams – but our opinion is that, this may not justify the cost for the upgrade just yet.

That said, if you’re in the market deciding between 802.11ac and 802.11ax, we recommend that you go for the latest tech so as to future proof your investment.

I thought 2.4 Ghz was dead. Does 802.11ax add support for the 2.4 Ghz spectrum?

Yes, Wifi 6 is dual band, while it’s predecessor was 5 Ghz only. Some vendors tried to implement Wifi 5 on 2.4 Ghz – but the standard only ratified 5 Ghz radios.

I feel that the reason for 2.4 Ghz is financially driven. Almost all consumer devices, older or newer – support the cheaper 2.4 Ghz. And while 2.4 Ghz is more susceptible to interference, it does provider better receptivity. That is, it can be “received” at greater distances.

The power-that-be determined that even the “2.4 Ghz only” devices will benefit because of the new enhancements in Wifi 6, such as BSS Coloring.

Is Wifi 6 full duplex communication?

Afraid not. With OFDMA, you’re just dividing a 20 Mhz channel into 2 Mhz sub-channels. It’s still half duplex. Think of it as a half duplex switch with shared bandwidth.

While lot’s of big names are rooting for opening up the 6 Ghz band for unlicensed WiFi spectrum use, that’s still not happened. We’re still operating on 2.4 Ghz and 5 Ghz.

Is 802.11ax an official standard?

No, the IEEE is scheduled to ratify it somewhere in the quarter 3 of 2019. That said, vendors such as Cisco, Asus and Netgear have already started releasing 802.11ax products out to market.

When will 802.11ax devices come to market?

More than 70% of the client radios are made by merchant silicon mass producer, Broadcom. We expect that Wifi 6 devices will become common place somewhere around the Q2 of 2020.

There’s already talk of some phones made by Samsung and LG that will come out with 802.11ax compatible radios.

Here’s a Wiki link that tracks all 802.11ax devices.

What is OFDMA?

802.11 has been using OFDM (Orthogonal frequency-division multiplexing) since 1999, when 802.11a was launched. OFDMA (Orthogonal Frequency Division Multiple Access) is a “Multi User” version of OFDM.

In OFDMA, instead of using all of the frequency bandwidth for one frame / one communication, the device can do “sub-channelization”. This means that you can break up a channel into smaller “Resource Units” which can then be allocated to different devices. It can, then, transmit to, and receive from these multiple devices concurrently.

Refer the above figure, ODFM was “Time Domain” only. So, if you had a 20 Mhz channel in the frequency domain, each frame used all 20 Mhz of that channel. If you had a 40 Mhz channel, and “User 1” could only transmit on 20 mhz, the leftover 20 mhz would remain unused.

In OFDMA, more that one user can communicate with in the assigned time, with in the assigned channel. So, If it’s a 20 mhz channel, you could have users 1, 2 and 3 all communicating at some point at the same time.

What is BSS Coloring?

It’s a 802.11ax technique, whereby 802.11ax radios can differentiate between BSSs by adding a number (color) to the PHY header. Same color bit indicates an intra-BSS. Different color bits indicate inter-BSS.

This circumvents Common Channel interference. A “BSS Color” is attached to each data frame to indicate what wireless network it came from.

Access points typically wait before transmitting If there’s already someone transmitting another frame through the air. With BSS coloring, the Acccess Point can see if the frames are of another network, and if so, ignore them (as long as they’re below a threshold of RSSI weakness to prevent interference). This avoids unnecessary slow downs and should improve performance.

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Author

abi

Abhijit Singh Anand

Chief Evangalist

Zindagi Technologies LLP