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CTS 162: 802.11ax OFDMA Subcarriers

With OFDMA in 802.11ax, the size of the subcarriers has been divided by 4. Going from 312.5KHz wide with OFDM to 78.125KHz wide.

The symbol duration has been increased by 4 times in the meantime. Going from 3.2 microseconds with OFDM to 12.8 microseconds.

Zooming into the subcarriers of a 20 MHz channel width

View the full image here

Advantages of having more subcarriers

  1. Allow OFDMA to extend to small sub-channels. Each sub-channel requires at least one (usually two) pilot subcarriers, and with a 2 MHz minimum sub-channel size, a smaller subcarrier spacing loses a much smaller percentage of the overall bandwidth to pilots.
  2. The number of guard and null subcarriers across a channel can be reduced as a percentage of the number of usable subcarriers, again increasing the effective data rate in a given channel. The figures above show a ~10% increase in usable subcarriers compared to 802.11ac, after allowing for the 4x factor. Example: OFDM: 64 subcarriers, 12 GuardNull subcarriers = 18.75%, OFDMA: 256 subcarriers. 22 GuardNull subcarriers = 8.5%.
  3. The longer OFDM symbol allows for an increase in the cyclic prefix length without sacrificing spectral efficiency, which in turn enables increased immunity to long delay spreads, especially in outdoor conditions. The cyclic prefix can be reduced to a smaller percentage of the symbol time, increasing spectral efficiency even while more robust to multipath conditions. And it reduces the jitter-sensitivity of uplink multi-user modes.

The smallest sub-channel is composed of 26 subcarriers.

Type of subcarriers:

  • Data subcarriers
  • Pilot subcarriers
  • DC subcarriers
  • Guard subcarriers
  • Null subcarriers

A 26-tone RU consists of 24 data subcarriers and 2 pilot subcarriers.

A 52-tone RU consists of 48 data subcarriers and 4 pilot subcarriers.

A 106-tone RU consists of 102 data subcarriers and 4 pilot subcarriers.

A 242-tone RU consists of 234 data subcarriers and 8 pilot subcarriers.

A 484-tone RU consists of 468 data subcarriers and 16 pilot subcarriers.

A 996-tone RU consists of 980 data subcarriers and 16 pilot subcarriers.

DC (Direct Current) subcarriers are used for the subcarriers located in the center of the channel. Depending on the channel width and the number of tone used, the number of DC subcarriers can vary (Ex: 3 or 7 for a 20MHz wide channel). Most of the time it will be 7 for the 20MHz and 80MHz wide channels and 5 for the 40MHz wide channels.

A 20MHz wide channels has 11 guard interval: the first 6 and the last 5 of the channel.

Here are the diagrams extracted from the 802.11ax draft document detailing the structure of the subcarriers for each channel width using different RUs sizes:

Links & Resources

Meraki MR55 and MR45 802.11ax (Wi-Fi 6) access points
Meraki MR45 802.11ax (Wi-Fi 6) access point
Meraki MR55 802.11ax (Wi-Fi 6) access point

CTS 129: 5G Technology

Recorded at Cisco Live 2018 in Orlando, Florida. We speak to Mike Geller and Pramod Nair about 5G technology and what Wi-Fi professionals would know about.

5G Technology

Rowell Dionicio, François Vergès, Mike Geller, and Pramod Nair talking about 5G

We’ve been hearing a lot about 5G lately. But do many of you what is involved with 5G? We just know it’s the next number up from 4G 😉

We recorded an episode with Mike Geller and Pramod Nair, Cisco employees, at the Podcast Domain in Cisco Live Orlando, Florida. There’s some background noise from the attendees at Cisco Live but you’ll still be able to hear the conversation.

As Wi-Fi professionals, what should we know about 5G? What is it all about? Hopefully, Mike and Pramod can shed some light on this topic for us.

First thing to know, is 5G caters to a set of use cases. Pramod points out this is the first time we’ve seen something driven by use cases. Some of those use cases for 5G are low latency for IoT and fixed wireless access. There’s the vehicle to everything use case. It can include Wi-Fi transmission but doesn’t define what RF interface to use, regulated or not.

What we do know, spectrum is always going to be a scarce, finite, resource. There is a possibility to use Wi-Fi and LTE together. Possibly use Wi-Fi on specific IoT use cases so we can better use spectrum more efficiently.

More importantly, we will not see 5G replace Wi-Fi. Mike Geller and Pramod Nair do not consider them as competing technologies.

Wi-Fi has been there yesterday, Wi-Fi is there today, Wi-Fi will be there tomorrow. – Pramod Nair

If you listen around the 10:50 minute mark, Pramod makes a funny statement. 

The differentiator in 5G is the network has the capability to tell the device which slice of network resources it should follow. There can be a radio interface to cover your phone, your friends phone, and another phone. Each phone can have a different profile because of data packages. You can put any of those phones on a different slice all together. Here, it just becomes more flexible. The network is becoming more complex but the use case is becoming easier.

Listen to the episode to hear the full conversation.

Links and Resources

The Story Behind the Ekahau Hat

During Cisco Live 2018 in Orlando, Florida we were able to meet up with Jussi Kiviniemi from Ekahau. We were enamored with the Ekahau hat which was being given out at their booth.

The quality of the hat is exceptional. There’s even a little detail inside the hat with reference to the Simpsons. If you’ve received a Sidekick then you know what I mean.

Minimalism is key. If you’ve used Ekahau, you know what the bar represents on the hat and I think it’s a genius idea.

Another great detail about the Ekahau hat is the reflective sticker on the top.

François asks Jussi about the hat and the story.. just check out the video for yourself.

CTS 124: Wireless Session Quick List – Cisco Live Orlando

Clear To Send is headed to Cisco Live Orlando.

Cisco Live Orlando

One of the largest conferences is headed back to the East Coast – in Orlando, Florida. If you know anything about Cisco Live then you know there are a plethora of sessions to select from. But we’re passionate about Wi-Fi which is what we’re going to highlight in a list here.

These session’s we’re interested in attending and the ones you should keep an eye on. Even if you aren’t attending, most of the sessions will be made available weeks after the conference is finished.

#CLUS Giveaway

Participate in our Clear To Send Giveaway. Because François and Rowell are joining together for the first time for CTS episodes, we wanted to give back to our listeners. We’re offering two giveaways, a Ventev Mobile Device Accessory kit ($300 value!) and a Cisco Press book of the winner’s choice.

Here’s how to enter:

  1. Fill out the form below (United States entries only)
  2. For an extra entry, find Rowell or François at CLUS, take a photo with one or both of them, and share it by tagging @cleartosend on Twitter.

Contest is over!

Live Recordings

Come watch François and Rowell do a live recording of a Clear To Send episode. There are a total of three recordings:

  • Monday June 11th @ 1PM– WiFi Analytics with Christian Gauer at the Podcast Domain Booth #1059 in World of Solutions
  • Tuesday June 12th – Cisco Live WiFi Meetup at 6:30pm – RSVP and Location here
  • Wednesday June 13th at 4pm – 5G with Mike Geller at the Podcast Domain Booth #1059 in World of Solutions

Wireless Session Quick List

Monday June 11

Tuesday June 12

Wednesday June 13

Thursday June 14

 

CTS 113: The Wizarding World of Cisco Live 2018

Robert Boardman, of WiFi of Everything, joins the show to tell us his thoughts on the upcoming Cisco Live conference during the summer of 2018.

CTS 113

Figus making an appearance at Cisco Live

Cisco Live 2018: What To Expect

Cisco Live 2018 will be from June 10 – 14, 2018 in Orlando Florida. Robert and I are both Cisco Champions. We decided to get together and record two shows at the same time. This CTS episode will also air as a video for the WiFi of Everything Show.

This is our first time attending Cisco Live in Orlando. One of the most visible parts of this conference is the Customer Appreciation Event. Let’s just get that out of the way. This year, Cisco is having the biggest party ever. All attendees will have Universal Studios all to themselves! There are multiple musical performers lined up and Cisco Live attendees will have the chance to have unlimited rides at the park. In addition to that, there will be food and drinks available. We’re looking forward to that.

Okay, now for the serious stuff. Have you seen the sessions that will be at Cisco Live? Being this is a Wi-Fi focused show, we have highlighted just a few:

Anatomy of real-time wireless analytics and troubleshooting using DNA Assurance/AIRsense

I’d like to see how far DNA Assurance has come along after first seeing it last year at Cisco Live 2017. Unfortunately, I haven’t ran into anyone who has it implemented. Hopefully there are some real use cases this time.

Cisco Next-Gen Enterprise Wireless Architecture

This could mean one thing right? 802.11ax? Maybe or maybe not? Will there be a new access point announced? New controllers? One can assume.

Securely Designing Your Wireless LAN for Threat Mitigation, Policy and BYOD

Security. Often forgotten and implemented after the fact. With wireless being a main point of connection, it’s important to keep it secure.

Optimize your WLANs for iPhones and iPads

We run networks predominantly used by iOS devices. So it only makes sense to optimize it for them and plus we’d like to know what else is coming out of the Cisco + Apple partnership.

Social

Getting involved in the wireless community is one of the primary reasons we’re attending. We love meeting new people, learning about what they do, and making new friends. This year is no different from the last.

What’s new? We will be recording WiFi of Everything videos! Stay tuned for what’s to come. There will also be CTS episodes recorded. As we get closer to the conference we will announce days and times.

Look out for Figus! He’s the guy you see in the image above. He’ll be better than last year and ready for social interactions!

Links and Resources