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IEEE 802.11ax-2021
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IEEE 802.11ax-2021 or 802.11ax is an IEEE standard for wireless local-area networks (WLANs) and the successor of 802.11ac. It is marketed as Wi-Fi 6 (2.4 GHz and 5 GHz) and Wi-Fi 6E (6 GHz) by the Wi-Fi Alliance. It is also known as High Efficiency Wi-Fi, for the overall improvements to Wi-Fi 6 clients under dense environments. It is designed to operate in license-exempt bands between 1 and 7.125 GHz, including the 2.4 and 5 GHz bands already in common use as well as the much wider 6 GHz band (5.925–7.125 GHz in the US). The main goal of this standard is enhancing throughput-per-area[lower-alpha 1] in high-density scenarios, such as corporate offices, shopping malls and dense residential apartments. While the nominal data rate improvement against 802.11ac is only 37%,:qt the overall throughput improvement (over an entire network) is 400% (hence High Efficiency).:qt This also translates to 75% lower latency. The quadruplication of overall throughput is made possible by a higher spectral efficiency. The key feature underpinning 802.11ax is orthogonal frequency-division multiple access (OFDMA), which is equivalent to cellular technology applied into Wi-Fi.:qt Other improvements on spectrum utilization are better power-control methods to avoid interference with neighboring networks, higher order 1024‑QAM, up-link direction added with the down-link of MIMO and MU-MIMO to further increase throughput, as well as dependability improvements of power consumption and security protocols such as Target Wake Time and WPA3. The IEEE 802.11ax-2021 standard was approved in February 9th, 2021.

802.11ax 802.11ac quadruplication

1. Rate Set

Table
Modulation and coding schemes for single spatial stream
MCS
index[1]		 Modulation
type		 Coding
rate		 Data rate (in Mbit/s)[2]
20 MHz channels 40 MHz channels 80 MHz channels 160 MHz channels
1600 ns GI[3] 800 ns GI 1600 ns GI 800 ns GI 1600 ns GI 800 ns GI 1600 ns GI 800 ns GI
0 BPSK 1/2 8 8.6 16 17.2 34 36.0 68 72
1 QPSK 1/2 16 17.2 33 34.4 68 72.1 136 144
2 QPSK 3/4 24 25.8 49 51.6 102 108.1 204 216
3 16-QAM 1/2 33 34.4 65 68.8 136 144.1 272 282
4 16-QAM 3/4 49 51.6 98 103.2 204 216.2 408 432
5 64-QAM 2/3 65 68.8 130 137.6 272 288.2 544 576
6 64-QAM 3/4 73 77.4 146 154.9 306 324.4 613 649
7 64-QAM 5/6 81 86.0 163 172.1 340 360.3 681 721
8 256-QAM 3/4 98 103.2 195 206.5 408 432.4 817 865
9 256-QAM 5/6 108 114.7 217 229.4 453 480.4 907 961
10 1024-QAM 3/4 122 129.0 244 258.1 510 540.4 1021 1081
11 1024-QAM 5/6 135 143.4 271 286.8 567 600.5 1134 1201

Notes

  1. ↑ MCS 9 is not applicable to all combinations of channel width and spatial stream count.
  2. ↑ A second stream doubles the theoretical data rate, a third one triples it, etc.
  3. ↑ GI stands for guard interval.

2. OFDMA

In the previous amendment of 802.11 (namely 802.11ac), Multi-user MIMO has been introduced, which is a spatial multiplexing technique. MU-MIMO allows the Access Point to form beams towards each Client, while transmitting information simultaneously. By doing so, the interference between Clients is reduced, and the overall throughput is increased, since multiple Clients can receive data at the same time. With 802.11ax, a similar multiplexing is introduced in the frequency domain, namely OFDMA. With this technique, multiple Clients are assigned with different Resource Units in the available spectrum. By doing so, an 80 MHz channel can be split into multiple Resource Units, so that multiple Clients receive different type of data over the same spectrum, simultaneously. In order to have enough subcarriers to support the requirements of OFDMA, four times as many subcarriers are needed than by the 802.11ac standard. In other words, for 20, 40, 80 and 160 MHz channels, there are 64, 128, 256 and 512 subcarriers in the 802.11ac standard, but 256, 512, 1024 and 2048 subcarriers in the 802.11ax standard. Since the available bandwidths have not changed and the number of subcarriers increases by a factor of 4, the subcarrier spacing is reduced by the same factor, which introduces 4 times longer OFDM symbols: for 802.11ac the duration of an OFDM symbol is 3.2 microseconds, and for 802.11ax it is 12.8 microseconds (both without guard intervals).

3. Technical Improvements

The 802.11ax amendment will bring several key improvements over 802.11ac. 802.11ax addresses frequency bands between 1 GHz and 6 GHz.[4] Therefore, unlike 802.11ac, 802.11ax will also operate in the unlicensed 2.4 GHz band. To meet the goal of supporting dense 802.11 deployments, the following features have been approved.

Table
Feature 802.11ac 802.11ax Comment
OFDMA Not available Centrally controlled medium access with dynamic assignment of 26, 52, 106, 242(?), 484(?), or 996(?) tones per station. Each tone consists of a single subcarrier of 78.125 kHz bandwidth. Therefore, bandwidth occupied by a single OFDMA transmission is between 2.03125 MHz and ca. 80 MHz bandwidth. OFDMA segregates the spectrum in time-frequency resource units (RUs). A central coordinating entity (the AP in 802.11ax) assigns RUs for reception or transmission to associated stations. Through the central scheduling of the RUs contention overhead can be avoided, which increases efficiency in scenarios of dense deployments.
Multi-user MIMO (MU-MIMO) Available in Downlink direction Available in Downlink and Uplink direction With Downlink MU MIMO an AP may transmit concurrently to multiple stations and with Uplink MU MIMO an AP may simultaneously receive from multiple stations. Whereas OFDMA separates receivers to different RUs, with MU MIMO the devices are separated to different spatial streams. In 802.11ax, MU MIMO and OFDMA technologies can be used simultaneously. To enable uplink MU transmissions, the AP transmits a new control frame (Trigger) which contains scheduling information (RUs allocations for stations, modulation and coding scheme (MCS) that shall be used for each station). Furthermore, Trigger also provides synchronization for an uplink transmission, since the transmission starts SIFS after the end of Trigger.
Trigger-based Random Access Not available Allows performing UL OFDMA transmissions by stations which are not allocated RUs directly. In Trigger frame, the AP specifies scheduling information about subsequent UL MU transmission. However, several RUs can be assigned for random access. Stations which are not assigned RUs directly can perform transmissions within RUs assigned for random access. To reduce collision probability (i.e. situation when two or more stations select the same RU for transmission), the 802.11ax amendment specifies special OFDMA back-off procedure. Random access is favorable for transmitting buffer status reports when the AP has no information about pending UL traffic at a station.
Spatial frequency reuse Not available Coloring enables devices to differentiate transmissions in their own network from transmissions in neighboring networks.

Adaptive Power and Sensitivity Thresholds allows dynamically adjusting transmit power and signal detection threshold to increase spatial reuse.

 Without spatial reuse capabilities devices refuse transmitting concurrently to transmissions ongoing in other, neighboring networks. With coloring, a wireless transmission is marked at its very beginning helping surrounding devices to decide if a simultaneous use of the wireless medium is permissible or not. A station is allowed to consider the wireless medium as idle and start a new transmission even if the detected signal level from a neighboring network exceeds legacy signal detection threshold, provided that the transmit power for the new transmission is appropriately decreased.
NAV Single NAV Two NAVs In dense deployment scenarios, NAV value set by a frame originated from one network may be easily reset by a frame originated from another network, which leads to misbehavior and collisions. To avoid this, each 802.11ax station will maintain two separate NAVs — one NAV is modified by frames originated from a network the station is associated with, the other NAV is modified by frames originated from overlapped networks.
Target Wake Time (TWT) Not available TWT reduces power consumption and medium access contention. TWT is a concept developed in 802.11ah. It allows devices to wake up at other periods than the beacon transmission period. Furthermore, the AP may group device to different TWT period thereby reducing the number of devices contending simultaneously for the wireless medium.
Fragmentation Static fragmentation Dynamic fragmentation With static fragmentation all fragments of a data packet are of equal size except for the last fragment. With dynamic fragmentation a device may fill available RUs of other opportunities to transmit up to the available maximum duration. Thus, dynamic fragmentation helps reduce overhead.
Guard interval duration 0.4 µs or 0.8 µs 0.8 µs, 1.6 µs or 3.2 µs Extended guard interval durations allow for better protection against signal delay spread as it occurs in outdoor environments.
Symbol duration 3.2 µs 12.8 µs Since the subcarrier spacing is reduced by a factor of 4, the OFDM symbol duration is increased by a factor of 4 as well. Extended symbol durations allow for increased efficiency.[5]

4. Wi-Fi 6 Products

4.1. Chipsets

  • On October 27, 2016, Quantenna announced the first 802.11ax silicon, the QSR10G-AX. The chipset is compliant with Draft 1.0 and supports eight 5 GHz streams and four 2.4 GHz streams. In January 2017 Quantenna added the QSR5G-AX to their portfolio with support for four streams in both bands.[6] Both products are aimed at routers and access points.
  • On February 13, 2017, Qualcomm announced their first 802.11ax silicon.[7][8][9]
    • The IPQ8074 is a complete SoC with four Cortex-A53 cores and supporting up to eight 5 GHz streams and four 2.4 GHz streams.
    • The QCA6290 chipset which supports two streams in both bands and aims at mobile devices.
  • On August 15, 2017, Broadcom announced their 6th Generation of Wi-Fi products with 802.11ax support.[10][11]
    • The BCM43684 and BCM43694 are 4×4 MIMO chips with full 802.11ax support.
    • The BCM4375 provides 2 × 2 MIMO 802.11ax and Bluetooth 5.0.
  • On December 11, 2017, Marvell announced 802.11ax chipsets consisting of 88W9068, 88W9064 and 88W9064S.[12][13]
  • On January 4, 2018, Intel Announces 802.11ax Chipsets for Faster Wi-Fi [14]
  • On February 21, 2018, Qualcomm announced the WCN3998, a 2x2 802.11ax chipset for smartphones and mobile devices.[15]
  • As of April 2018, Intel is working on an 802.11ax chipset for mobile devices, the Wireless-AX 22560 with Harrison Peak code-name.[16]
  • On October 23, 2018, Broadcom announced two new 2x2 802.11ax SOCs: the BCM6752 and BCM6755. Both providing multi-core CPUs and Gigabit Ethernet[17]
  • On January 8, 2019, MediaTek announced their 802.11ax chips being 2x2 and 4x4[18]
  • On February 25, 2019, Qualcomm announced the QCA6390, a 2x2 802.11ax/Bluetooth 5.1 combined chipset for mobile and computing devices[19]

4.2. Devices

  • On March 8, 2019, Samsung released the Galaxy Fold and Galaxy S10 family (S10e, S10, S10+ and S10 5G) supporting 802.11ax.
  • On August 23, 2019, Samsung released the Galaxy Note 10 series (Note 10, Note 10+, Note 10 5G and Note 10+ 5G) supporting 802.11ax.
  • On September 10, 2019, Apple announced the iPhone 11, iPhone 11 Pro and iPhone 11 Pro Max supporting 802.11ax.[20]
  • On 18 March 2020, Apple announced the iPad Pro (4th generation) supporting 802.11ax.[21]
  • On August 5, 2020, Samsung released the Galaxy Note 20 series family (Note 20, Note 20 Ultra) supporting 802.11ax.[22]
  • On November 10, 2020, Apple announced that the new MacBook Air, MacBook Pro and Mac mini based on the new Apple silicon processor all support 802.11ax.[23]
  • The Huawei Mate Xs, Huawei P40, Honor 30 Pro, Oppo Reno3 5G, Oppo A91, Oppo Ace2, Oppo Find X2, Xiaomi Mi 10 5G, Xiaomi Redmi K30 Pro Zoom, Xiaomi Poco F2 Pro, Xiaomi Black Shark 3, Lenovo Legion Pro, vivo iQOO 3 5G, vivo Z6 5G, vivo NEX 3S 5G, vivo iQOO Neo3 5G, ZTE nubia Red Magic 5G, ZTE Axon 11 5G, Realme X50 Pro 5G, OnePlus 8, Sony Xperia 1 II, LG V60 ThinQ 5G, and Motorola Edge+, all support 802.11ax.
  • Sony's PlayStation 5 supports the 802.11ax (Wi-Fi 6) standard.[24]
  • On April 20, 2021, Apple announced that the new iPad Pro 5th Generation and new iMac 24", both based on the new Apple M1 processor, as well as the 6th generation Apple TV 4K supported 802.11ax.[25][26][27]

Access points

  • On September 12, 2017, Huawei announced their first 802.11ax access point. The AP7060DN uses 8×8 MIMO and is based on Qualcomm hardware.[28][29]
  • On January 25, 2018, Aerohive Networks announced the first family of 802.11ax access points. The AP630, AP650, and AP650X are based on Broadcom chipsets. [30]
  • On July 17, 2018, Ruckus Networks announced an IoT- and LTE-ready 802.11ax (Wi-Fi 6) access point, also known as the R730. The R730 shipped in September 2018.[31]
  • On September, 2018 Ruijie Networks announced the launch of the industry's first tri-band 802.11ax wireless access point RG-AP860-I up to 10Gbit/s and in June 2019 released cost effective 802.11ax Access point RG-AP840-I up to 5.2Gbit/s.
  • On November 13, 2018, Aruba Networks announced their first 802.11ax access points, the AP510 series.[32]
  • On January 22, 2019, Extreme Networks announced their first 802.11ax access points, the 500 series.[33]
  • On April 29, 2019, Cisco announced their first 802.11ax access point. The ax enabled access points are Catalyst 9115, Catalyst 9117, Catalyst 9120, Catalyst 9130, Meraki MR45 and MR55.[34]
  • On June 25, 2019, Juniper Networks, through their Mist Systems subsidiary, announced their Wi-Fi 6 compatible AP-43 as part of its AI-driven enterprise initiative.[35]

Routers

  • On August 30, 2017, Asus announced the first 802.11ax router.[36][37] The RT-AX88U uses a Broadcom chipset, has 4×4 MIMO in both bands and achieves a maximum of 1148 Mbit/s on 2.4 GHz and 4804 Mbit/s on 5 GHz.
  • On June 4, 2018, Asus launches the ROG Rapture GT-AX11000 : world's first 10 Gbit/s SOHO-router.[38]
  • The TP-LINK Archer AX6000 supports 802.11ax.

5. Wi-Fi 6E Products

5.1. Chipsets

  • Broadcom (announced)
  • Qualcomm FastConnect 6900
  • Celeno (announced)
  • On May 28, 2020, Qualcomm announced its first chips with support for Wi-Fi 6E, including chips for phones and Wi‑Fi access points.[39]

5.2. Devices

  • Intel's AX210 module is shipping.[40]
  • On 14 January 2021, Samsung released the Galaxy S21 Ultra.[41]

Routers

  • Asus Rapture GT-AXE11000 Wi-Fi 6E Gaming Router
  • Netgear Nighthawk RAXE500 12 Stream Tri-Brand WiFi [sic] 6E Router (to be announced)
  • Linksys AXE8400 (to be launched)

References

  1. MCS 9 is not applicable to all combinations of channel width and spatial stream count.
  2. A second stream doubles the theoretical data rate, a third one triples it, etc.
  3. GI stands for guard interval.
  4. Aboul-Magd, Osama (2014-01-24). "P802.11ax". IEEE-SA. https://development.standards.ieee.org/get-file/P802.11ax.pdf?t=81645500003. ;
  5. Porat, Ron; Fischer, Matthew; Venkateswaran, Sriram; Nguyen, Tu; Erceg, Vinko; Stacey, Robert; Perahia, Eldad; Azizi, Shahrnaz et al. (2015-01-12). "Payload Symbol Size for 11ax". IEEE P802.11. https://mentor.ieee.org/802.11/dcn/15/11-15-0099-04-00ax-payload-symbol-size-for-11ax.pptx. ;
  6. "Quantenna Announces QSR5G-AX, an 802.11ax Dual 4×4 Wi-Fi Access Point Solution targeting the Mainstream Wi-Fi Segment" (in en). http://ir.quantenna.com/releasedetail.cfm?ReleaseID=1006628. ;
  7. "Qualcomm and 802.11ax Wi-Fi tech: Game-changing breakthrough for dense networks | Qualcomm" (in en). Qualcomm. 2017-02-13. https://www.qualcomm.com/news/onq/2017/02/13/qualcomm-and-80211ax-wi-fi-tech-game-changing-breakthrough-dense-networks. ;
  8. "Qualcomm Announces First End-to-End 802.11ax Wi-Fi Portfolio | Qualcomm" (in en). Qualcomm. 2017-02-13. https://www.qualcomm.com/news/releases/2017/02/13/qualcomm-announces-first-end-end-80211ax-wi-fi-portfolio. ;
  9. "Qualcomm made a new Wi-Fi chip for the next generation of Wi-Fi". The Verge. https://www.theverge.com/2018/2/21/17035620/qualcomm-802-11ax-wifi-chip-phones-tablets. ;
  10. "Broadcom Announces Availability of Industry's First Complete Ecosystem of 802.11ax Solutions" (in en). https://www.broadcom.com/company/news/product-releases/2293974. ;
  11. "Broadcom unveils MAX, better Wi-Fi based on 802.11ax | FierceWireless" (in en). https://www.fiercewireless.com/wireless/broadcom-unveils-max-better-wi-fi-based-802-11ax. ;
  12. "Wireless - 802.11AX - Marvell". https://www.marvell.com/wireless/80211ax/. ;
  13. "Marvell 88W9068 Product Brief". http://www.marvell.com/documents/hhwxuqolekqzohvrfvsp/. ;
  14. "Intel Announces 802.11ax Chipsets for Faster Wi-Fi" (in en-US). 2018-01-04. https://itpeernetwork.intel.com/intel-announces-802-11ax-chipsets/. ;
  15. "Qualcomm Introduces the Industry's First Integrated 802.11ax-ready Solution for Smartphones and Computing Devices | Qualcomm" (in en). Qualcomm. https://www.qualcomm.com/news/releases/2018/02/21/qualcomm-introduces-industrys-first-integrated-80211ax-ready-solution. ;
  16. "Intel® Wireless Products: Documents and Datasheets" (in en). https://www.intel.com/content/www/us/en/design/products-and-solutions/wireless-and-modems/wireless-products/technical-library.html. ;
  17. "Broadcom Expands Family of Wi-Fi 6 Solutions with New Mesh Networking Platforms" (in en). https://www.broadcom.com/company/news/product-releases/2372971. ;
  18. "MediaTek Launches Newest Combo Chip with Wi-Fi 6 and AP+Bluetooth" (in en). https://www.mediatek.com/news-events/press-releases/mediatek-launches-newest-combo-chip-with-wi-fi-6-and-ap-bluetooth. ;
  19. "Qualcomm Revolutionizes Smartphones and Computing Devices with Game-Changing Wi-Fi 6 and Bluetooth 5.1 Connectivity SoC" (in en). https://www.qualcomm.com/news/releases/2019/02/25/qualcomm-revolutionizes-smartphones-and-computing-devices-game-changing-wi. ;
  20. Crist, Ry (2019-09-16). "The iPhone 11 supports Wi-Fi 6. Here's what that means for you". https://www.cnet.com/how-to/the-iphone-11-supports-wi-fi-6-here-is-what-that-means-for-you/. ;
  21. Broussard, Mitchel (2020-03-18). "New iPad Pro Announced With A12Z Bionic Chip, Magic Keyboard With Trackpad, LiDAR Scanner, Ultra Wide Camera". https://www.macrumors.com/2020/03/18/new-ipad-pro-a12z-bionic-trackpad-keyboard/. ;
  22. "All Wi-Fi 6 compatible smartphones". 2020-02-20. https://www.techietech.tech/wi-fi-6-compatible-smartphones/. ;
  23. "Introducing the next generation of Mac". 2020-11-10. https://www.apple.com/newsroom/2020/11/introducing-the-next-generation-of-mac/. ;
  24. Barker, Sammy (August 26, 2020). "PS5 Uses Bluetooth 5.1, Wi-Fi 6 for Improved Performance". PushSquare. https://www.pushsquare.com/news/2020/08/ps5_uses_bluetooth_5_1_wi-fi_6_for_improved_performance. ;
  25. Upadhyay, Rishaj (21 April 2021). "Everything you need to know about the 2021 M1 iPad Pro". https://www.techietech.tech/m1-ipad-pro-2021-everything-you-need-to-know/. ;
  26. "iMac 24" - Technical Specifications". 2021-04-20. https://www.apple.com/imac-24/specs/. ;
  27. "AppleTV 4K - Technical Specifications". 2020-04-20. https://www.apple.com/apple-tv-4k/specs/. ;
  28. "X-Gen Wi-Fi". http://e.huawei.com/topic/X-GenWIFI-en/index.html. ;
  29. "Huawei Launches X-Gen Wi-Fi to Redefine the Agile Campus Network Era". http://www.huawei.com/en/news/2017/9/Huawei-X-Gen-Wi-Fi-Agile-Campus. ;
  30. "Aerohive Networks" (in en-US). https://www.aerohive.com/press_releases/aerohive-announces-industrys-first-family-of-enterprise-802-11ax-access-points/. ;
  31. Chirgwin, Richard (2018-07-18). "The crowd roars and Ruckus joins in with 802.11ax kit". The Register (Situation Publishing). https://www.theregister.co.uk/2018/07/18/ruckus_80211ax_iot_ap/. ;
  32. "Aruba Introduces New Secure, AI-Powered Mobility Innovations for the Experience Edge" (in en-US). https://news.arubanetworks.com/press-release/aruba-introduces-new-secure-ai-powered-mobility-innovations-experience-edge. ;
  33. "Extreme Networks Makes Stadium-Caliber Wi-Fi 6 Solution Available to Every Enterprise" (in en-US). https://investor.extremenetworks.com/news-releases/news-release-details/extreme-networks-makes-stadium-caliber-wi-fi-6-solution. ;
  34. "Catalyst 9100 Access Points" (in en). https://www.cisco.com/c/en/us/products/wireless/catalyst-9100ax-access-points/index.html. ;
  35. "Mist Systems Introduces New Products and Services to Bring Simplicity and Scale to the AI-Driven Enterprise" (in en-US). 2019-06-25. https://www.mist.com/news/press-releases/mist-brings-simplicity-scale-to-ai-driven-enterprise/. ;
  36. Dignan, Larry (January 8, 2018). "D-Link, Asus tout 802.11ax Wi-Fi routers, but you'll have to wait until later in 2018". ZD net. https://www.zdnet.com/article/d-link-asus-tout-802-11ax-wi-fi-routers-but-youll-have-to-wait-until-later-in-2018/. ;
  37. "ASUS Press Room" (in en). https://press.asus.com/release.php?id=114#.WayQB8gjGUk. ;
  38. "Asus launches the ROG Rapture GT-AX11000 : world's first 10Gbps router" (in en). 2018-06-04. https://www.trustedreviews.com/news/asus-rog-rapture-gt-ax1100-3480869. ;
  39. Kastrenakes, Jacob (2020-05-28). "Qualcomm's first Wi-Fi 6E chips are here - For phones and routers". https://www.theverge.com/2020/5/28/21271814/qualcomm-wifi-6e-6ghz-chips-phones-routers-announced-fastconnect. ;
  40. "Product Brief: Intel® Wi-Fi 6E AX210 (Gig+) Module" (in en). https://www.intel.com/content/www/us/en/products/docs/wireless/wi-fi-6e-ax201-module-brief.html. ;
  41. Gogia, Kanika (4 February 2021). "What is Wi-Fi 6E? All Wi-Fi 6E Compatible Devices". https://www.techietech.tech/wifi-6e-compatible-smartphones/. ;
  42. E.Khorov, A. Kiryanov, A. Lyakhov, G. Bianchi (2019). "A Tutorial on IEEE 802.11ax High Efficiency WLANs". IEEE Communications Surveys & Tutorials (IEEE) 21 (in press): 197–216. doi:10.1109/COMST.2018.2871099.  https://dx.doi.org/10.1109%2FCOMST.2018.2871099
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