802.11ax WiFi Wireless Networking

Overview of 802.11ax

The IEEE 802.11ax standard, also known as WiFi 6, represents a significant advancement over its predecessor, 802.11ac (WiFi 5). Designed to deliver faster speeds, greater range, and improved performance in dense environments, 802.11ax operates in the unlicensed 2.4 GHz and 5 GHz bands, offering a robust upgrade for modern wireless networks.

IEEE 802.11ax Wireless Networking
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Technical Summary

IEEE 802.11ax is a high-efficiency wireless local area network (WLAN) standard that enhances spectral efficiency, particularly in crowded deployment scenarios. While its nominal data rate is approximately 37% higher than 802.11ac, 802.11ax achieves up to a 4x increase in user throughput through optimised spectrum usage. Key features include support for Orthogonal Frequency Division Multiple Access (OFDMA), 1024-QAM modulation, and enhanced Multi-User MIMO (MU-MIMO), enabling top speeds of around 10 Gb/s.

The table below shows Modulation and Coding Schemes (MCS) for Single Spatial Stream

Modulation and coding schemes for single spatial stream
MCS
index		 Modulation
type		 Coding
rate		 Data rate (in Mb/s)
20 MHz channels 40 MHz channels 80 MHz channels 160 MHz channels
1600 ns GI 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 4 4 8 9 17 18 34 36
1 QPSK 1/2 16 17 33 34 68 72 136 144
2 QPSK 3/4 24 26 49 52 102 108 204 216
3 16-QAM 1/2 33 34 65 69 136 144 272 282
4 16-QAM 3/4 49 52 98 103 204 216 408 432
5 64-QAM 2/3 65 69 130 138 272 288 544 576
6 64-QAM 3/4 73 77 146 155 306 324 613 649
7 64-QAM 5/6 81 86 163 172 340 360 681 721
8 256-QAM 3/4 98 103 195 207 408 432 817 865
9 256-QAM 5/6 108 115 217 229 453 480 907 961
10 1024-QAM 3/4 122 129 244 258 510 540 1021 1081
11 1024-QAM 5/6 135 143 271 287 567 600 1134 1201

Technical improvements in 802.11ax

The 802.11ax amendment will bring several key improvements over 802.11ac. 802.11ax addresses frequency bands between 1 GHz and 6 GHz. 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.

802.11ax introduces several technical improvements that enhance performance over 802.11ac, making it ideal for both indoor and outdoor applications. These include:

  • OFDMA: Divides the spectrum into time-frequency resource units (RUs) of 26, 52, 106, 242, 484, or 996 tones per station, each with a subcarrier bandwidth of 78.125 kHz. This allows a central access point (AP) to dynamically assign RUs, reducing contention and improving efficiency in dense environments.
  • Multi-User MIMO (MU-MIMO)- Downlink and Uplink: Enables simultaneous transmission to or from multiple devices, using spatial streams to separate users, complementing OFDMA for enhanced capacity. The AP sends a Trigger control frame containing RU allocations, modulation and coding schemes (MCS), and provides synchronisation. Uplink transmission starts SIFS after the Trigger frame ends.
  • Trigger-Based Random Access: The Trigger frame includes scheduled RU assignments and random access RUs. Stations without direct assignments can use these for transmission. To reduce collisions, an OFDMA back-off procedure is used. Random access is ideal for sending buffer status reports when the Ap lacks information on a station’s uplink traffic.
  • Spatial Frequency Reuse: Colouring helps devices distinguish between transmissions from their own and neighbouring networks. Adaptive Power and Sensitivity Thresholds allow devices to dynamically adjust transmit power and detection thresholds, enabling simultaneous transmissions. With these features, a device may begin transmission even if it detects a neighbouring signal, provided the new transmission’s power is reduced, improving spatial reuse.
  • Dual NAV: Maintains two Network Allocation Vectors to prevent collisions in dense deployments. One NAV is modified by frames from the station’s own network, while the other is modified by frames from overlapping networks.
  • Target Wake Time (TWT): Reduces power consumption and contention by scheduling device wake-up times outside beacon periods, grouping devices to minimise simultaneous access.
  • Dynamic Fragmentation: Optimises data transmission by filling available RUs, reducing overhead compared to 802.11ac’s static fragmentation.
  • Extended Guard Intervals (0.8 µs, 1.6 µs, 3.2 µs): Provides better protection against signal delay spread, ideal for outdoor environments.
  • Longer Symbol Durations (3.2 µs, 6.4 µs, 12.8 µs): Increases efficiency by allowing more data per symbol.

OFDMA and Data Transmission

In 802.11ax, data is distributed across multiple carriers using OFDMA, with each carrier handling a portion of the payload, reducing the data rate per carrier. When the carrier spacing is the reciprocal of the symbol period, carriers complete an integer number of cycles, ensuring their contributions sum to zero and eliminating interference. This lower data rate mitigates interference from reflections, further enhanced by guard intervals (0.8 µs, 1.6 µs, or 3.2 µs) that ensure data is sampled only when the signal is stable, preventing disruptions from delayed signals.

Distributing data across many carriers also improves resilience. Nulls from multi-path effects or interference affect only a few carriers, leaving others intact. Error-coding techniques, which add redundant data to the signal, allow the receiver to reconstruct corrupted data, as the error correction codes are transmitted separately within the signal.

IEEE 802.11ax Wireless Networking
IEEE 802.11ax Wireless Networking

Applications of 802.11ax

802.11ax is a versatile upgrade for existing 802.11a, b, g, n, and ac networks, suitable for both indoor and outdoor use. Its ability to penetrate walls (unlike 802.11ay, which operates at 60 GHz) makes it ideal for fixed point-to-point or point-to-multipoint outdoor backhaul, especially as an alternative to costly fibre deployments by providers like Google and Verizon.

Early Adopters and Industry Support

Major vendors have embraced 802.11ax with chipsets like Quantenna’s QSR5G-AX and QSR10G-AX, Qualcomm’s IPQ8074 and QCA6290, and Broadcom’s BCM43684, BCM43694, and BCM4375. These support varying stream configurations for routers, access points, and mobile devices, with some integrating Bluetooth 5.0. The IEEE 802.11 Working Group, including representatives from leading equipment and chipset vendors, finalised the standard after addressing feedback from draft reviews, with public release occurring in 2020.

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