Why IEEE 802.11be and 802.11bn Extend Wi-Fi Frequency Range to 7.25 GHz

In the context of 6G trial frequencies from 6425 to 7125 MHz and co-channel services, we previously mentioned that since 2020, some countries globally have gradually begun to allow Wi-Fi to use the extended band of 5925-7125 MHz on an unlicensed basis. The operating frequency range defined in the 2020 IEEE 802.11ax (HE: Wi-Fi 6) standard amendment was also 1 GHz to 7.125 GHz. However, last year, it was inadvertently discovered that the draft standards for IEEE 802.11be (EHT: Wi-Fi 7) and 11bn (UHR: Wi-Fi 8) both mention that their applicable carrier frequency range is 1 to 7.250 GHz. Although the difference is merely 125 MHz, what exactly is the reason behind this subtle extension, and what is its underlying purpose?

01. Definition of IEEE 802.11

Let us first compare the IEEE 802.11ax, 11be, and 11bn standards. According to the abstracts of the following standards, it is evident that the 2020 11ax standard amendment still defined the frequency range according to the upper allocation limit of 7.125 GHz for the Wi-Fi 6 GHz band in most countries globally. 11ax:

Abstract: This amendment defines modifications to both the IEEE 802.11 physical layer (PHY)and the medium access control (MAC) sublayer for high efficiency operation in frequency bands between 1 GHz and 7.125 GHz.

However, in the draft standards for 11be in 2024 and 11bn in 2025, the applicable carrier frequency range has already been changed to 1 to 7.250 GHz.

11be:

Abstract: This amendment defines standardized modifications to both the IEEE Std 802.11 physical layers (PHY) and the Medium Access Control Layer (MAC) that enable at least one mode of operation capable of supporting a maximum throughput of at least 30 Gbit/s, as measured at the MAC data service access point (SAP), with carrier frequency operation between 1 and 7.250 GHz while ensuring backward compatibility and coexistence with legacy IEEE Std 802.11 compliant devices operating in the 2.4 GHz, 5 GHz, and 6 GHz bands. This amendment defines at least one mode of operation capable of improved worst case latency and jitter.

11bn:

Abstract: This amendment defines modifications to both the IEEE Std 802.11 physical layer(PHY) and the IEEE Std 802.11 medium access control (MAC). The amendment adds an ultra high reliability capability to a wireless local area network (WLAN). The ultra-high reliability capability is defined for both an isolated Basic Service Set (BSS) and overlapping BSSs as:

• at least one mode of operation capable of increasing throughput by 25%, as measured at the MAC data service access point, in at least one signal to interference and noise ratio (SINR) level (rate-vs-range), compared to the extremely high throughput MAC/PHY operation, and

• at least one mode of operation capable of reducing latency by 25% for the 95th percentile of the latency distribution compared to the extremely high throughput MAC/PHY operation and

• at least one mode of operation capable of reducing MAC protocol data unit (MPDU) loss by 25% compared to the extremely high throughput MAC/PHY operation for a given scenario, especially for transitions between BSSs.

This amendment provides a mechanism to reduce power consumption for access points (APs) (including mobile APs) and improved peer-to-peer (P2P) operation compared to the extremely high throughput MAC/PHY operation. This amendment applies to carrier frequency operation between 1 GHz and 7.250 GHz. This amendment shall ensure backward compatibility and coexistence with legacy IEEE 802.11 devices in the 2.4 GHz, 5 GHz and 6 GHz unlicensed bands.

02. Regulatory Definition by the FCC

According to FCC regulations, Part 15.407 applies to U-NII (Unlicensed National Information Infrastructure) devices in the 5 GHz band, specifying limits for in-band emission power and power spectral density, unwanted emission limits, Transmit Power Control (TPC) and Dynamic Frequency Selection (DFS), and Automatic Frequency Coordination (AFC) systems. Effective July 27, 2020, provisions for the 6 GHz band, specifically for 5925-7125 MHz U-NII devices, were added.

For example: For an indoor access point operating in the 5.925-7.125 GHz band, the maximum power spectral density must not exceed 5 dBm e.i.r.p. in any 1-megahertz band. In addition, the maximum e.i.r.p. over the frequency band of operation must not exceed 30 dBm.For transmitters operating within the 5.925-7.125 GHz band: Any emissions outside of the 5.925-7.125 GHz band must not exceed an e.i.r.p. of −27 dBm/MHz.

Furthermore, up to the present, Part 15.407 still covers 5925-7125 MHz and has not been extended to 7250 MHz. However, another regulation that is easily confused with it is Part 15.250, which pertains to the operation of wideband systems in the 5925-7250 MHz band:

The 5925-7250 MHz band defined in Part 15.250 happens to be exactly the extended band mentioned earlier in the IEEE Wi-Fi 7/8 draft standards. However, this is purely a coincidence and not the reason for the extension. The provisions for wideband system operation in Part 15.250 were defined over twenty years ago and have nothing to do with the Wi-Fi 6 GHz extended band. It targets low-power, wideband devices operating with characteristics similar to UWB, with a -10 dB bandwidth of no less than 50 MHz. Below are its EIRP power spectral density limits within a 1 MHz bandwidth, which are comparable to the EIRP spectral density limits for UWB. Moreover, such devices are prohibited from operating on aircraft/satellites, prohibited for use in toys, and strictly restricted from use in outdoor fixed infrastructure.

03. The Actual Reason

To further explore the reasons, let us first look at the figure below, which illustrates the channel number allocation for the Wi-Fi extended band of 5925-7125 MHz under different bandwidths (20 MHz, 40 MHz, 80 MHz, 160 MHz, 320 MHz). Within the 6 GHz band of 5925-7125 MHz, the Wi-Fi channel numbering follows a fixed formula:

Center Frequency (MHz) = 5940 + Channel Number × 5

The upper cutoff frequency of 7125 MHz, although it has already expanded the bandwidth by 1.2 GHz, is somewhat awkward. If it could be further extended to 7250 MHz, then:

For a 320 MHz bandwidth, the number of channels could increase from 3 to 4; for a 160 MHz bandwidth, it could increase from 7 to 8; for an 80 MHz bandwidth, it could increase from 14 to 15; and so on.

Therefore, although this 125 MHz is just a small segment of spectrum, its impact should not be underestimated. This means that enterprise Wi-Fi deployments, which need to deploy a large number of APs across multiple different channels to avoid interference, can use 160 MHz channels more flexibly, thereby achieving significant improvements in speed and capacity. The theoretical peak speed of a 160 MHz channel in Wi-Fi 7 reaches up to 23 Gbps. This may sound somewhat exaggerated, and some might think such high rates are not yet needed, but that is not the case.

Currently, the 6 GHz band might support about 10 users equipped with AR/VR head-mounted display (HMD) devices simultaneously, whereas 160 MHz could support approximately 50 HMDs running concurrently in an office. This is preparing for the future of Wi-Fi, ensuring support for ultra-high-density scenarios.

Therefore, Intel and Broadcom jointly demonstrated to the FCC the advantages brought by this additional spectrum allocation, namely 7125-7250 MHz. They believe that while the current 6 GHz spectrum allocation in the United States extends to 7.125 GHz, the small segment of spectrum between 7.125 GHz and 7.250 GHz above it also has the potential to be allocated for Wi-Fi.

Today, the Wi-Fi industry is striving to incorporate this "parked band" into the existing 6 GHz Low Power Indoor (LPI) rules for use as a Wi-Fi band. Thus, chip manufacturers have already integrated the extended band up to 7.250 GHz into their chip designs, which can be realized merely through a software upgrade. This is because hardware planning typically requires a four-year lead time, so they must stay ahead of regulatory policies.

As a non-governmental organization of scientists, the IEEE naturally reserves technical space for the future and conducts forward-looking research based on the needs of the industry. Regardless of whether spectrum regulatory agencies in various countries will actually open up 7.125 to 7.250 GHz for Wi-Fi use in the future, it does not affect the IEEE's decision to implement this established capability limit in its standards.

Note: All images in this article are from R&S.