CTS 167: 802.11ax 1024-QAM & HE-MCSs


Evolution of the modulation techniques we are using today with 802.11ax (256-QAM).

With 1024-QAM, we are now able to encode 10 bits per cycle on each subcarrier. The way we are able to do that is by increasing the number of different levels of amplitudes used to encode the data.

If you want to learn more about the different types of modulations used by Wi-Fi and how they work, there is a great video where Keith Parsons explains it on youtube: https://www.youtube.com/watch?v=W5DMfEuY2Vg&t=8s

Due to the addition of a new modulation technique (QAM-1024), 2 new MCS indexes are now available with 802.11ax:

  • Index 10: when the 1024-QAM modulation is used with a coding of 3/4
  • Index 11: when the 1024-QAM modulation is used with a coding of ⅚

FEC (Forward Error Correction). Send more than the data bits. If you lose some of the sequence, the remaining bits will help you to understand what you were supposed to be sent.

What is the challenge with more complex modulation techniques?

How well will 1024-QAM in real life?

Will we be able to take advantage to it?

Interesting talk on twitter around the subject (Troy Martin, Andrew, Hendrik Lüth & Jim Vajda). We tend to think that a smaller communication bandwidth will give us a better SNR. But it is not necessarily the case here since the receiver in 802.11ax will still be listening to the whole 20MHz wide channel even if its RU is smaller. Link here: https://twitter.com/VergesFrancois/status/1113779145731977216


Download the updated MCS Table

With 802.11ax, we are getting a whole new set of data rates (or MCSs). If we want to understand why, we need to understand how these data rates are calculated.

The amount of data we can transfer through a Wi-Fi link will depend on:

  • The channel width (or the number of subcarriers)
  • The modulation and coding use
  • The amount of spatial streams used
  • The guard interval used
  • The duration of the symbol

And we can actually take all these different variables and calculate the different data rates using the following formula:

802.11n/ac Data Rate Formula

You can take a look at the blog post and see which values can each of these variables can have for 802.11n and 802.11ac:

HT & VHT Parameters

Now, the reason why we have a new set of data rates for 802.11ax is because some of the key variables are changing:

  • A new symbol duration is used: 12.8µs
  • Different Guard Intervals are used: 0.8µs, 1.6µs and 3.2µs
  • The size and number of data subcarriers is not the same (especially with the different RU sizes introduced by ODFMA.

Also, with the introduction of OFDMA and the use of Resource Units, we might be using smaller numbers of subcarriers which impact the data rates.

This is why the draft identify the OFDMA and non-OFDMA MCS differently.

The draft even use specific variables related to each resource unit. And we can therefore define this new formula:

802.11ax ODFMA Data rate Formula

And here are the different values each of these variables can have for 802.11ax communications. The first table details the parameters used when OFDMA is not used. The second table details the parameters when OFDMA and resource units are used.

802.11ax OFDM Parameters
802.11ax OFDMA Parameters

Sections Talking about MCS in The Standards & Draft

  • 28.3.7 HE Modulation and coding schemes (HE-MCSs) (p.442)
  • 28.5 Parameters for HE-MCSs (p. 589)
  • 19.5 Parameters for HT MCSs
  • 21.5 Parameters for VHT-MCSs


CTS 166: 802.11ax HE Channel Access

There are multiple functions in which a client or AP can gain access to the channel. What we’re going to discuss is in addition to the HCF and DCF.

  • TXOP duration-based RTS/CTS
  • Intra-BSS or inter-BSS frame determination
  • SRG PPDU determination
  • Two NAVs
  • EDCA using MU EDCA parameters


It’s all new ways of thinking about channel access but with added complexity. You’re dealing with multi-access, TXOP, BSS coloring which complicates the channel access process.

TXOP Duration-based RTS/CTS

HE AP can use TXOP duration-based RTS/CTS exchanges to mitigate interference for dense environments.

RTS/CTS is now under TXOP Duration RTS Threshold.

There is a TXOP Duration RTS Threshold subfield within the HE Operation element. To disable TXOP Duration RTS Threshold, the AP can set this subfield to a value of 1023. A client receiving a non-zero value from the AP will set its TXOP Duration RTS Threshold to the value of the TXOP Duration RTS Threshold subfield.

A client shall use an RTS/CTS exchange to initiate a TXOP if the feature is enabled and:

  • The client intends to transmit unicast frames to the AP or to a TDLS peer client
  • The transmission opportunity duration is greater than or equal to 32 μs * RTS/CTS threshold. (Ex: RTS/CTS threshold = 300 & duration is 12345. Then 12345 μs > 32*300=9600)

The RTS and CTS frames contain a Duration field that defines the period of time that the medium is to be reserved to transmit the actual Data frame and the returning ACK frame.

The AP can also send a MU-RTS and simultaneous CTS responses by clients prior to the actual Data frames is another means of distribution of the medium reservation information.

Otherwise, the client follows the normal DCF rules used today by 802.11ac.

Intra-BSS and Inter-BSS Frame Determination

Client determines if received PPDU is an inter-BSS PPDU based on the following:

  • BSS_COLOR is not 0 and is not the same BSS color which the client is a member. Pretty much is the client doesn’t have the same BSS color.
  • BSS_COLOR is not 0 and if HE client is associated with a non-HE AP. If the client is not associated to a 802.11ax AP

Client determines if received PPDU is an intra-BSS PPDU based on the following:

  • BSS color is the same as the client
  • The frame carries an RA/TA/BSSID field value that is equal to the BSSID the client is associated with

Essentially, in order for a transmitter to determine whether it can obtain access to the shared medium, it must determine if a received frame is within its own BSS color or not.

SRG PPDU Identification

A client looks to the Spatial Reuse Parameter Set element to see if the SRG Information Present subfield has been set to 1. It’s used to identify BSSs that are members of the client’s SRG.

It will be used by the client to identify if the received inter-BSS frame is a SRG frame.

It is used during Spatial Reuse Parameter (SRP) OBSS (Overlapping Basic Service Set) PD operation. We will have a dedicated episode on Spatial Reuse.

Updating Two NAVs

HE clients must maintain two NAVs. A HE AP can maintain two NAVs. Those two NAVs are:

  • intra-BSS NAV
  • Basic NAV

Within the intra-BSS PPDU will be the intra-BSS NAV. The basic NAV, as we have known it previously, can be updated within the inter-BSS PPDU or a PPDU that is not classified as an intra-BSS or inter-BSS. That classification is covered under Intra-BSS or Inter-BSS frame determination – which we just talked about earlier.

The purpose of two NAVs is to protect frames from clients within the intra-BSS and inter-BSS in dense environments. It gives more control to the AP in order to decide which clients will contend to the channel within a given TXOP.

As HE AP obtains TXOP, the intra-BSS NAV prevents associated clients from contending for the channel. Because the basic NAV is not updated during AP’s TXOP, the client will not transmit even if it received a trigger frame from the AP.

If both NAVs equal zero, the medium is idle. If one of the two NAVs is nonzero, the virtual CS is that the medium is busy. EASY RIGHT? ^^

Intra-BSS NAV Updates:

The intra-BSS NAV will be updated if a client receives/sends a intra-BSS frame with a duration higher than the current value of the intra-BSS NAV within a given TXOP.

The intra-BSS NAV will also be updated if the client receives a trigger frame from the AP.

Basic NAV Updates

The basic NAV will be updated if the inter-BSS frame RA is not the address of the STA. Still using the Duration ID Field.

MU-RTS/CTS Procedure

The MU-RTS/CTS procedure allows an AP to initiate a TXOP and protect the TXOP frame exchange.

The AP transmits an MU-RTS/CTS trigger frame to solicit simultaneous CTS responses from one or more HE STAs.


The STA will send a MU-RTS and expect to receive a CTS from 1 or multiple STA. Interesting note about MU-RTS, if the STA’s CTS Timeout interval reaches 0 it will assume the MU-RTS Trigger frame has failed and will invoke a backoff procedure.

CTS Response to a MU-RTS

The client shall response if the following conditions are met:

  • The medium is idle
  • The RU allocation is specified in the User Info field
  • There is a User Info field addressed to the client

Otherwise, the client show not send the CTS response.

The CTS will be carried in a non-HE PPDU so everyone can understand it. The data rate used should be 6Mbps.

It should be transmitted on the 20MHz wide channel specified in the RU Allocation subfield of the User Info field of the MU-RTS Trigger frame.

It’s important to know in MU-RTS, an AP can receive simultaneous CTS responses from clients.

EDCA Operation Using MU EDCA Parameters

A MU-EDCA Parameter Set Element might be included in the beacon frames, probe response and re(association) frames.

It can be a copy of the EDCA Parameters and can also be updated.

This is mainly used for QoS purposes. There is a QoS Info field within the (MU-)EDCA Parameter Set Element.

A client receiving a basic trigger frame containing addressed for itself will update various contention window values for the respective access categories.

The client station shall use the parameters set in the mostly recently received MU-EDCA. Including CWmin, CWmax, AIFSN and MUEDCATimer.

Closing Note (From Cisco 802.11ax White Paper)

“Because of this preamble-level compatibility, there is no inherent need for 802.11ax devices to precede their 802.11ax transmissions by CTS-to-self or RTS/CTS, although devices may still choose to implement and send them to protect longer PPDUs. However, 802.11ax adds the capability of multiuser RTS/CTS which allows the access point to reserve the channel (set the NAV) for multiple STAs simultaneously with a single MU-RTS PPDU that is then confirmed with simultaneous CTS PPDUs from multiple STAs. This scenario overcomes the inherent inefficiency of single-user RTS/CTS still prevalent in 802.11ac networks while adding protection to 802.11ax transmissions.”

Sections in the 802.11ax Draft Talking about HE Channel Access

  • 27.2 – HE channel access (p.253)
  • 10.3.1 DCF General

This Week in Wireless

CTS 164: 802.11ax Target Wake Time

Objectives of TWT

Objectifs of 802.11ax

  • Increase the performance of the Wi-Fi network by a factor of 4 while improving or not impacting power requirements
  • Provide power saving mechanisms for new emerging IoT devices

All the current power saving mechanisms defined today remain usable with ax. In addition, the 802.11ax draft defines a new mechanism called Target Wake Time or TWT.

Target wake time (TWT) is used to help minimize contention between clients and reduce the amount of time a client in power save mode to be awake.

Clients will operate in non-overlapping times and/or frequencies and the frame exchanges are coordinated.

TWT was introduced in 802.11ah and is particularly useful for battery-powered devices that communicate infrequently.

TWT Modes of Operations

There are three modes of operation:

  • Individual TWT
  • Broadcast TWT
  • Opportunistic PS

TWT Power-save options in 802.11ax from Aruba 802.11ax White Paper:

TWT Power-Save options in 802.11ax

Individual TWT

Client will be assigned specific times to wake up and exchange frames. The schedule is determined and delivered by the AP. There is a different mode of TWT such as explicit TWT. A client doesn’t need to know about another client’s TWT values.

Simple process:

  • A client wants to establish a TWT agreement
  • A client communicates its waking schedule information to the AP
  • The AP devises a schedule and delivers TWT values to the client
  • The client wakes up and transmit a frame according to the schedule
  • The AP send the client the next TWT information on when to wake up again (explicit mode)
  • The client wakes up again at the next scheduled time to send a frame and receive a new TWT information
  • When TWT implicit is used, the client calculates the Next TWT by adding a fixed value to the current TWT value

A client can go off of the AP’s TWT parameters. Or a client can “demand” a TWT with indicated parameters for agreement. If agreed upon, the AP will respond with “Accept TWT”. The AP can counter the offer with an Alternate TWT.

A client wanting to utilize TWT will indicate what channel to use as a primary channel during a TWT SP.

Broadcast TWT

The AP will be in charge. The AP will send TWT parameters in the Beacon frame using the TWT Element. The TWT Element might be sent in other management frames as well such as the (Re)Association frame or the probe response frame.

The clients will use the TWT parameters from the most recently received TWT element carried in the Management frames of its associated AP. The client is also called “TWT Scheduled STA” in this case in the draft. The AP is called “TWT Scheduling AP”

The AP will provide the schedule to all the clients that supports broadcast TWT.

The AP will send a trigger frame to discover which clients are awake. The AP will then send frames to these clients that will, then, be able to doze again. This is called a trigger-based TWT SP (Service Period).

Clients can device to join or leave a broadcast TWT. This is done by an exchange of frame that carry TWT elements.

Find the information in 802.11ax Frames

Subfields to identify client support of TWT modes:

  • TWT Requester Support
  • TWT Responder Support
  • Broadcast TWT Support

TWT Element

The Control field will indicate the negotiation type: Individual, Broadcast or Wake TBTT interval.

When Individual TWT is used, the TWT parameter Information field will have this format:

When Broadcast TWT is used, the TWT Parameter Information field will have this format:

Sections Talking About TWT in the 802.11ax Draft – TWT Information field – p.118 – TWT element – p.139 – TWT Teardown frame format – p.185

10.43 – Target wake time (TWT) – p.234

27.7 – TWT Operation – p.312


Here is an example of a beacon frame coming from a 802.11ax Aerohive AP (AP630). If we look into the “HE Capabilities” information element, we can drill down into the “HE MAC Capabilities Information” and validate both the “TWT Requester Support” and “TWT Responder Support” flags. In this case, they are set to 0, which means that the feature is not yet supported by the firmware used on this AP.

Then, we can take a look at the “TWT Required” flag located in the “HE Operation Parameters”. Here again, it is set to 0.

We should be able to show you example of TWT being supported later on this year as vendors update their 802.11ax AP firmware and start enabling the feature.

This Week In Wireless

CTS 163: Cisco 802.11ax APs & Cisco Live

Cisco Live

We have an episode full of Cisco goodness. Recently, Cisco released the data sheets to two 802.11ax access points. We have the details on these two APs, their capabilities, and some of our opinions.

And speaking of Cisco, right around the corner is Cisco Live. We have our tips and the sessions we’re looking forward to.

Cisco Live Tips

The following Cisco Live tips were written on Rowell’s blog – Attendee Guide to Cisco Live 2019. It’s going to be hosted in San Diego, CA this year which should be a fun event. Check out the blog and register for Cisco Live if you haven’t done so already!

  • Bring a smile!
  • Meetups
    • Cisco Champions
    • Twitter
    • Friends
  • Exams – book early
  • Bring walking shoes.
  • Bring a jacket – sometimes the A/C is blasting inside the conference.
  • Portable battery packs – for your mobile devices.
  • Drink plenty of water – it’s best you bring your own reusable. I like to use my Hydro Flask. Empty out the contents before you pass through TSA.
  • Tylenol might be useful for those headaches. Either from learning so much by the fire hose or from partying the night before.
  • Book your sessions once they’re available. Some fill up quickly and you’ll be let on the waitlist.
  • Book your exam early! Schedule it on Saturday or Sunday before the chaos of the conference begins.
  • Download the Starbucks app. The lines for coffee get really long. Download the app and do mobile purchase. Skip the lines.
  • Don’t bring a backpack. You’ll get one at Cisco Live.
  • Leave room in your luggage. If you plan on grabbing swag, this is the conference that will fill up your bag, easily.
  • Hang around after each of your sessions and thank the presenter.
  • Check out DevNet Create and get hands on.

Sessions on Wi-Fi to Look Out For

Roadmap: Wireless and Mobility – CCP-120

Hear about the future of wireless, and how Cisco bridges 5G and WiFi 6. And, learn how our open platform delivers network and location analytics to support IT and business use cases.

Securely Designing Your Wireless LAN for Threat Mitigation, Policy and BYOD- BRKEWN-2005

The session will cover effective strategies to build a defence-in-depth security model and the role of network segmentation in implementing Software-Defined Access (VLANs, VRF and TrustSec) for wireless networks. Participants will learn the principles of secured wireless networks (encryption, 802.1X, guest access, etc.) and the latest identity services available to securely onboard different kinds of devices (laptops, tablets, smartphones, IoT etc.) and users (employees, guests, contractors, etc.). This session will guide you through designing a fabric-integrated wireless deployment enabled for security, mobility and policy.

Introduction to Next Generation Wireless Stack – BRKEWN-2010

This session will introduce the Next Generation Wireless Stack for enterprise and branch office WLAN deployments, i.e. the core technologies that drive and enable mobility services. Topics covered include protocol details like CAPWAP, deep-dives into new controller Catalyst 9800 features like High Availability, Security and integration with Cisco DNA Center and Cisco 11ax Access Points. We will also introduce Cisco DNA spaces and integration with the next generation stack.

Introduction to Catalyst 9800 Wireless Controllers – BRKEWN-2670

Your next generation Wireless controller is the Catalyst 9800, available as an appliance, cloud and embedded controller on switch form factor  with IOS XE 16.10 and later. In this introductory session, you will learn how to get your Wireless network up and running with the C9800 controller, from Day 0 provisioning, High Availability, Patching, Programmability, Telemetry to Simplified configuration and Migration. You will also learn about the capabilities of the new wireless controller appliances running the Catalyst 9800 Wireless software.

Advanced Troubleshooting of Cisco Catalyst 9800 Wireless Controller – BRKEWN-3013

The session will cover troubleshooting of new-generation Wireless LAN Controllers including real-life examples. Participants will learn how IOS-XE capabilities like packet tracing and radioactive tracing are replacing debugs. The session will cover the hardware and software architecture specifics and all the serviceability improvements pertaining to making the troubleshooting effortless in everyday scenarios. The session assumes general knowledge of Cisco Unified Wireless troubleshooting and focuses on the methods to troubleshoot the newer platform.

Design and Use Cases of a Location Enabled Wi-Fi Network Supported by Cisco DNA Spaces – BRKEWN-2012

WLAN location based services is opening a whole new ecosystem of applications applicable to numerous verticals such as retail, healthcare, hospitality, education and others. New capabilities in device silicon have improved the accuracy of the ‘blue dot’, the user experience and the networks ability to provide relevant services. This session will explain the fundamentals of WLAN location based services, architecture, design and best practices. RF triangulation and architecture will be explained in light of the AP, Controller and CMX. Several models will be covered, including: location mapping, analytics, and location based application integration.

Advanced Troubleshooting of Wireless LANs – BRKEWN-3011

This session discusses troubleshooting techniques and best practices for the Cisco Unified Wireless Network Architecture (CUWN). Major topics include RF Validation, Wireless Authentication, and Client Roaming. We will talk about common client problems by looking at the various WLC and AP information, tools, and debugs used by TAC to resolve issues. We will also discuss the best practices to ensure you keep your users online and working.

Cisco DNA Assurance for Next Generation WIreless: Isolate problems for faster troubleshooting – BRKEWN-2034

You do not have time to deal with network issues anymore. In the past you would design RF coverage, build the WLANs, hope for the best, and react to alarms and user complaints. This logic would force you to constantly react to fire drills, running every day to assess issues as they were reported to you. What if you could benefit from tools that would anticipate these issues, instead of simply reporting once they occurred? The logic of the Cisco Digital Network Architecture (Cisco DNA) is not only to provide an abstraction for automation and policies, but also provide a virtuous feedback loop, allowing you to visualize the consequences of your configurations. Intelligent analytics allows you to observe trends, work on what-if scenarios, and be warned about issues before they actually explode and collapse your network. In this session, you will get a deep dive exposure to the new Cisco DNA Center Assurance tool, to monitor trends in your network, anticipate issues, get intelligent (human readable), meaningful and synthetic messages on the state of your network, your clients and their applications, and easily troubleshoot issues once you identify an unsafe trend.

Optimize your WLANs for small and mobile devices (phones, tablets and alike) – BRKEWN-2003

Smartphones and tablets often represent 60 percent or more of your WiFi clients, and people use voice and video calls on these devices while roaming. Turn aroud, and their signal drops by 30 dBm in less than a second. Optimizing a WLAN for highly mobile devices running real-time applications requires careful design and specific configurations. Cisco has introduced new features to optimize WiFi experience for Apple iOS devices, and iOS comes with new settings to better associate, roam and optimize traffic in Cisco WiFi networks. Cisco also works with large Android and laptop system manufacturers to tailor the WLANs to these devices’ needs. In this session, you will learn how to configure both sides, and how to optimize your wifi design to offer a seamless experience to your mobile clients, especially with real time applications. At the end of this session, you should know how these different types of clients see the network, and how to deploy and configure your WLANs to offer an optimal quality of experience for these clients.

High Density Wi-Fi Design, Deployment and Optimization – BRKEWN-2013

This session will cover an array of detailed tips, tricks, and tools for configuring and optimizing High Density WiFi networks in today’s most challenging environments, including valuable real-world insights on how the Cisco Access Point and Antenna portfolio can be leveraged to deliver an unparalleled user experience. Attend this session to hear real-world hints directly from engineers who have deployed networks for some of the largest sports venues and events worldwide.

Understanding RAN Spectrum Co-ordination and Cisco RF Features – BRKEWN-3010

The RF Landscape continues to change…With 802.11ax now entering the market and 5G standard beginning to mature a paradigm shift is re-shaping the entire industry . This session will focus on how Cisco’s RRM and related tools will help you to keep pace with and manage the transition into the next generation of wireless networks. RRM, CleanAir, ClientLink and other tools, explaining how they work, and how to use them effectively to optimize your network. This use-case-driven session promises to help you put these tools into perspective, and solve and prevent issues related to changing network demographics like coverage vs capacity, 802.11ac and now 802.11ax and the Overlapping BSS (OBSS) channelization and deployment strategies. This is an advanced session, so a solid understanding of 802.11PHYbasics and a little exposure to the 802.11ax specification and a basic familiarity of RRM are advised.

Advanced Troubleshooting of Cisco Catalyst 9800 Wireless Controllers – BRKEWN-3013

The session will cover troubleshooting of new-generation Wireless LAN Controllers including real-life examples. Participants will learn how IOS-XE capabilities like packet tracing and radioactive tracing are replacing debugs. The session will cover the hardware and software architecture specifics and all the serviceability improvements pertaining to making the troubleshooting effortless in everyday scenarios. The session assumes general knowledge of Cisco Unified Wireless troubleshooting and focuses on the methods to troubleshoot the newer platform.

Advancements in Wireless Security – BRKEWN-2006

Recently, the Wi-Fi Alliance announced three new programs to advance wireless security: Wi-Fi CERTIFIED WPA3™, Wi-Fi Certified Enhanced Open™, and Wi-Fi Certified Easy Connect™. This session will explore the details around these programs, including the history of wireless security, its ties to other standards bodies, the problems they solve, and guidance on how and when to adopt them in an enterprise wireless network. Attendees will hear from and speak with Stephen Orr, the Wi-Fi Alliance’s® Security task group chairman, and Bob Sayle, a contributing member of the Wi-Fi Alliance’s® Device Provisioning Protocol task group.

Sessions on 5G

5G Technology Updates – BRKSPM-2017

The mobile industry is constantly evolving by building capabilities to enhance value to consumers. 5G technologies will not only provide higher throughput, low latency and enable connectivities to billions of devices but it will provide enable new use cases to drive industry growth. 5G will be deployed on virtualized platforms which will have big impact on infrastructures, security, automation and this will require network and operations transformation.

The speakers are doing hands-on work to build 5G use cases in Cisco laboratories and working with customers globally for 5G proof of concepts and trials. We will start with 5G industry updates and what has changed in last one year, Cisco 5G plan, use cases we are working and learning, 5G security landscape and how to manage. You will also see live demonstration of how we can auto-deploy 5G services using end-to-end automation platform.

5G Mobile Transport Design and Deployment

Mobile service providers seek a new approach to address the increasing traffic demands. They require solutions that can help them to: Lower operational expenditures Improve Time to Revenue and Average Revenue per User (ARPU) Profitably transport the massive increase in user bandwidth Provide ultra-HD video, virtual reality, and tactile internet services anywhere, anytime, to any Internet-enabled device. Cisco Mobile xhaul Solution combines best of class Mobile & IP technologies to provide a simplified programmable transport of Mobile services using High performance platforms. A converged IP/MPLS architecture greatly increases service agility and decreases Time-to-Revenue. With an Agile, open, and virtualized architecture supporting open standards, and programmatic APIs for services orchestration, the Cisco Mobile xhaul Solution is “SDN ready” today.

5G xHaul Transport – BRKSPM-2012

LTE was about connectivity, however 5G will be about immersive experience, led by new services enhanced mobile broadband access everywhere (1Gpbs per UE), massive Internet of things, tactile Internet, higher user mobility, ultra-reliable communications & enterprise use cases. These services have divergent latency and throughput requirement requiring network transformation in addition to radio evolution “5G NR”. It is critical to invest in backhaul, midhaul & fronthaul (xHaul) evolution otherwise RAN gains will not be realized This session will address transport transformation through Segment Routing, stringent synchronization through phase and frequency, CPRI evolution to address 5G fronthaul requirement, virtualization and split of packet core to bring data plane closer to the user, telemetry for network insight and proactive health monitoring and orchestration through Cisco Crosswork.

Voice Over 5G Mobile Packet Core – BRKSPM-2017

The 5G specifications developed by 3GPP have completed the specifications for voice support for both non-standalone (5G NSA) and 5G standalone (5G SA) networksThe completion of 5G NR specifications for standalone (SA) has been approved by 3GPP. Also, after the 5G NR specifications for NSA, standardization of 5G at the first stage is pretty ready. Although the main drivers for 5G evolution is data, voice and video servcies are still very important as SPs will not be able to keep the voice on their LTE netwrok for a long time. At the beginning, 5G uses the LTE voice network and to provide those services using existing IMS architecture. The 5G radio technology is NR and the voice services called VoNR in 5G. In this session, the presenters will speak about the various 5G architecture options that SPs are planning to use and the voice/video evolution over each option. Cisco packet core and 3GPP experts will provide a comprehensive view on those options including: 1-CSFB–>VoLTE–>VoNR for Option 3X, 2- EPS or RAT FB / VoLTE –>VoNR for option 4/4a, 3- EPS or RAT FB / VoLTE –>VoNR for option 2, etc. After this session, audience will walk out with a better understanding on Vo5G and the evolution path options that large service providers are taking during their journey for 5G Network

Links & Resources

Cisco Catalyst 9100 Access Points
Cisco C9115AX Data Sheet
Cisco C9117AX Data Sheet

IEEE 802.11be PAR (.docx file)
Tweet from Jim Vajda

WLPC EU in Prague

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