Features and benefits

Wi-Fi 7 is a Wi-Fi Alliance certification program based on the IEEE 802.11be amendment aiming to improve latency, reliability, and performance over previous Wi-Fi generations. Work on the specification began in 2019, and the certification program launched in January 2024.

This generation targets use cases requiring high data bandwidth, low latency, and reliability, such as extended reality (VR/MR/AR), real-time applications, gaming, and cloud computing.

Wi-Fi 7 introduces a key feature called multi-link operation (MLO) for improved link reliability, 4096-QAM for higher peak PHY data rates, wider channel widths in 6 GHz, and enhanced QoS with features like stream classification service (SCS).

Like previous generations, Wi-Fi 7 uses techniques to ensure backward compatibility across all bands to provide connectivity for previous generations of clients.

Key features

Wi-Fi 7 builds and extends on the capabilities of previous generations to increase throughput, reduce latency, and enhance reliability.

• Wi-Fi 7 can also leverage the 6 GHz band introduced by Wi-Fi 6E.

• Multiple link operation (MLO) enables channel aggregation and failover, enabling clients connecting to Wi-Fi 7 access points to combine or alternate between links across multiple frequency bands (can also be two links in the same band). Traffic can be sent over the link with lower latency or traffic could be split between links for parallel transmission. If one of the links is congested or interference occurs, traffic can be shifted seamlessly to another more stable link to improve the connection robustness.

• 4096 QAM (quadrature amplitude modulation) provides potentially higher peak data rates by enabling a 12-bit symbol to more densely embed greater amounts of data than before through MCS 12 and 13.

• Channel bonding up to 320 MHz bandwidth in 6 GHz doubles the capacity of 160 MHz supported by Wi-Fi 6. The increase in bandwidth can reduce delays and improve overall transmission rates.

• Improvements to OFDMA introduced in Wi-Fi 6 through Multi Resource Units (MRU).

• Preamble puncturing helps accommodate and co-exist with interference in wide channels by allowing the 20 MHz subchannels containing interference to be disabled within wide channels. This is sometimes called a punctured transmission. Puncturing helps work around interference or other requirements while still enabling the remainder of wide channels to function for transmit and receive.

• QoS improvements with triggered uplink access (TUA) using the stream classification service (SCS) framework.

• Power saving enhancements to target wake time with restricted target wake time (r-TWT) providing a level of medium access protection in a restricted service period (SP).

Technology comparison

6 GHz support

Like Wi-Fi 6E, Wi-Fi 7 also uses the 6 GHz band to increase capacity by using up to 1200 MHz of unlicensed spectrum depending on regulatory.

20 MHz-only operation

Wi-Fi 7 allows for 20 MHz-only operation which is aimed at IoT markets similarly as the same feature in Wi-Fi 6. 20 MHz-only operation allows for reduced implementation complexity, leading to low-power, lower-cost chips. Such clients can operate in 2.4 GHz, 5 GHz, and 6 GHz bands and support most of the mandatory Wi-Fi 7 features.

Increasing modulation complexity

Payloads in Wi-Fi are encoded using a technique called quadrature amplitude modulation (QAM) which encodes data by manipulating both the amplitude and phase of carrier waves. Each point in the QAM constellation represents a distinct symbol, with each symbol encoding multiple bits of information. Higher-order schemes allow more bits to be encoded per symbol, thus increasing spectral efficiency.

Building on digital modulation schemes in 802.11ax of up to 1024-QAM, 802.11be supports up to 4096-QAM. This means that each RF symbol represents one of 4096 possible combinations of amplitude and phase. The move from 1024-QAM to 4096-QAM increases number of bits carried per OFDM symbol from 10 to 12. This can result in up to a 25% increase in PHY data rates depending on environmental and capability support on both sides of the link.

Modulation and coding

802.11be adds a 12-bit symbol for 4096-QAM with coding rates of 3/4 and 5/6. The previous PHY rates remain available and are used during rate shifting when signal quality is insufficient to sustain higher rates.

Note both 3.2 μs guard interval and BPSK-DCM are excluded from the table.

320 MHz channel width

Wi-Fi 7 adds support for 320 MHz channel width. Support is advertised in the control field of the EHT operation information element. Inside this element there is an operating class field which defines radio parameters such as channel width. The operating class for 320 MHz channel width is 137.

Note the out-of-band reduced neighbor report element in 2.4 GHz or 5 GHz may report operating class of 131 (20 MHz), 132 (40 MHz), 133 (80 MHz) or 134 (160 MHz) instead of 137. This is for interoperability with legacy clients which do not know of operating classes introduced in newer generations.

To better line up with differing countries regulatory spectrum allocations, there are two sets.

1. 320 MHz-1 with channels 31, 95, and 159.
2. 320 MHz-2 with channels 63, 127, and 191.

Technology advancements

• EHT MU PPDU format used for all non-triggered transmissions.

• EHT TB PPDU format used for all triggered transmissions.

• New universal SIG (U-SIG) field to bring forward compatibility to the EHT preamble via new version independent fields. Duplicated in every 20 MHz sub-channel. U-SIG includes version-independent and version-dependent bits.

• DL/UL OFDMA are adopted from Wi-Fi 6 as is.

• Dynamic MU Spatial Multiplexing Power Save (SMPS) to allow clients to turn off a receive chain to reduce power consumption.

• Packet extension gives additional Rx processing time for features like 4096-QAM.

• Wi-Fi 7 adds support for multiple resource units (MRU) in orthogonal frequency division multiple access (OFDMA). This enables small or large multiple RUs to be allocated to the same client. The ability for clients to use MRUs enables more efficient and flexible usage of the available channel when using OFDMA.

• Preamble puncturing with static and dynamic puncturing to disable 20 MHz subchannels for wide channel bandwidths when there is narrow interference. This feature along with MRU enables punctured transmissions around the disabled subchannels.

• Compressed BA (C-BA) 256/512 bits to provide the ability to acknowledge (ACK) multiple MPDUs in a single block ack (BA).

• Restricted target wake time (r-TWT) enables restricted service periods for clients to have better medium access for latency sensitive traffic. r-TWT provides more precise wake-up intervals and shorter durations to improve power consumption.

• Triggered uplink access (TUA) optimization provides improved channel access through a scheduled period for latency sensitive uplink (UL) traffic. APs use the stream classification service (SCS) request frames from clients to schedule according to the requested QoS parameters.

• BPSK-DCM (dual carrier modulation) provides a 1-bit low rate MCS (14 and 15) with higher range, robustness, and interference mitigation at the cost of speed. These are optional rates.

Multiple link operation

Multi-link operation (MLO) is a key mandatory feature of Wi-Fi 7 enabling, for the first time in Wi-Fi, clients to associate and transmit and/or receive over more than one link or band at a time to a single AP.

A MLO-capable device is referred to as a multi-link device (MLD). In the MLD framework, the links can be across multiple bands or with-in the same band.

The primary benefit of multi-link operation is communication between to multi-link devices on non-overlapping frequency.

• Improved reliability and robustness. A client can seamlessly alternate between links when one of the links degrades without re-associating.
• Improved support for lower latency by fast failover between links or aggregating links.
• Higher aggregate throughput. Certain, optional, MLD types can leverage and combine multiple links at the same time, potentially improving throughput.

All Wi-Fi 7 clients are required to support basic multi-link operation (MLO) over multiple links with the ability to discover, authenticate, (re)associate, (re)setup of links, and support of multi-link control (MLC) frames.

Architecture

Multi-link operation (MLO) architecture splits the multi-link device (MLD) into two MAC layers.

Upper MLD (U-MAC) functions:

• (Re)association is at this layer
• Security association (PMKSA)
  • SN/PN assignments for unicast frames
  • Unicast encryption/decryption
• Link selection based on TID mapping
• Block ACK score boarding for unicast frames

• Channel access
• Control frames such as RTS and CTS
  • Block ACK (BA) sent in sync with upper MLD score boarding
• Beacons
• Broadcast frame transmission, encryption, decryption
• Power save state

MLO management

For any disruptive AP operations (link removal, new configuration, etc.) there are 2 methods available to manage MLO operation.

1. Multi-link reconfiguration (AP removal)

   • Multi-link reconfiguration is stateless and enables the stop and restart data traffic activity on one or more links. This may lead to client reassociation to the same AP with ‘other links’ and depends on the client implementation.

2. Advertised traffic identifier (TID) to link mapping (T2LM)

   • Advertised TID-to-link mapping is stateful and can disable data traffic on a link for a short duration after which the link is reenabled and maintains client association.
   • Used when AP needs to temporarily disable a link in a multi-link setup
   • Similar idea to multi-link reconfiguration, client can use remaining link to avoid reassociation.
   • When the AP brings the link back. The client can reuse.

Load balancing

AP MLDs can help influence link usage through BSS transition management frames (query, request, response) where the AP recommends one or more links for the client to operate on. This link recommendation feature provides clients the option to more quickly switch to links with less interference and spend less time contending for the medium on a link with more interference.

Multi-link BSS updates

The AP MLD must signal BSS critical updates (operational parameters) to client MLDs through a BSS parameters change count (BPCC). This update framework enables the client to track updates on all links by monitoring management frames on one link. Thus, clients can determine if they need to look for updated parameters on the link where a critical update occurred.

Examples of critical updates include:

• Channel switch announcements (CSA)
• Broadcast target wake time (b-TWT)
• Modification of HT, VHT, HE, or EHT operation elements

MLO MAC addressing

MLO devices have two types of MAC addresses. A MLD MAC and a per-link MAC.

The client (STA) MLD MAC (p) address and AP MLD MAC (m) address are addressable over the local network meaning they are used for resolving ARPs.

The MAC addresses for each link, (w), (x), (y), (z) are ’link local’ and not used to populate address fields in frames sent beyond their respective boundaries.

Certain HPE Aruba Networking CLI show commands are enhanced to show both MLD and per-link MAC addresses.

show ap association mlo
show ap debug client-table mlo

Device types

There are different types of MLD operation device types offer varying capabilities. The MLD type a client supports can be influenced by the bands presented by the ESS. For example, if all three 2.4 GHz, 5 GHz, and 6 GHz bands are presented, the client could support one type when setting up a MLD with 2.4 GHz and 6 GHz links, but a different type when setting up a MLD with 5 GHz and 6 GHz.

Multi-link single radio

A multi-link single radio (MLSR) device is a MLD which switches links to operate on any one link at a time. A MLSR MLD is not able to do carrier censing on multiple links at once. The MLSR client MLD controls the link for downlink traffic from the AP mld using power save (PS) polling.

Enhanced multi-link single radio

An enhanced multi-link single radio (EMLSR) device is a MLD which can only transmit (Tx) to or receive (Rx) data frames from another MLD on a single link. The enhanced part of EMLSR is the ability to carrier sense on multiple links at the same time.

Carrier sense on each link is accomplished using a single spatial stream (radio chain). If the AP MLD needs to transmit a data frame to an EMLSR device on one of the links, the AP initiates a control frame exchange (RTS, MU-RTS). While the AP MLD receives the CTS frame on the target link, the EMLSR device reconfigures the radio to switch over the spatial streams from other links to be ready for data reception.

Simultaneous transmit receive multi-link multi-radio (STR MLMR)

No need to reconfigure or transition radio chains between links.

Security requirements

The following security parameters for Wi-Fi 7 are required in all bands for Wi-Fi 7 connections:

• Security modes
  • WPA3-SAE-GDH (AKM:24/FT AKM:25) when using WPA3-Personal
  • Hash-to-element (H2E) for SAE PWE derivation required when using WPA3-Personal
  • Enhanced open when using open networks
• Beacon protection to enable clients to verify the integrity of beacon frames
• GCMP-256 ciphers
• PMF (802.11w)

Beacon protection

The december 2020 update of WPA3 introduced an optional feature called beacon protection to protect against active attacks attempting to exploit clients through forged signaling information to nudge clients to rogue APs. Wi-Fi 7 requires beacon protection to enable the AP to provision clients with integrity keys during security association.

A beacon integrity group temporal key (BIGTK) is used for beacon frame protection. The beacon integrity packet number (BIPN) is the BIGTK packet number used to calculate the MIC in the MME.

The BIGTK is then distributed to the client in message 3 of the 4-way handshake and group key handshake. The client is then enabled with information to validate, and further act on, integrity checks.

The management MIC (MME) element is appended to the beacon frame as the last element preceding the FCS providing message integrity to protect group addressed management frames and protected beacon frames from forgery and replay.

GCMP-256

GCMP is based on the GCM of the AES encryption algorithm. GCM protects the integrity of the MPDU and provides data confidentiality, integrity, and replay protection. AES processing used with-in GCMP-256 uses AES with a 256-bit key, hence GCMP-256. Wi-Fi 7 clients must support GCMP-256 as a unicast cipher.

PMF

PMF was introduced in 802.11w-2009 as an optional feature to provide integrity and encryption mechanisms for certain management frames. Wi-Fi 7 connections must use PMF. Learn more about PMF.

SAE-GDH

When using WPA3-Personal and Wi-Fi 7, the client must use simultaneous authentication of equals (SAE) with group dependent hashing (SAE-GDH) in all bands. The AKM selectors for SAE-GDH are AKM:24 and Fast Transition (802.11r) AKM:25.

The Diffie-Hellman (DH) group used will determine the hash algorithm / elliptic curve. Group selection is determined by support on both sides of the link and client preference during the commit phase of SAE.

Comparatively, previously WPA3-Personal with AKM:8 used the same SHA-256 hash algorithm for all DH groups.

MLD security

After association, the client (STA) MLD and AP MLD derive keys via the 4-way handshake. The entire handshake performed on a single link.

The pairwise master key (PMK) is derived using the MLD MAC addresses on both, the client MLD and the AP MLD. The PMK is used for generating PTK which is used for encrypting unicast frames. Same PTK is used across all the links setup in an multi-link association between an AP MLD and a client (STA) MLD.

Groupwise Transient Key (GTK) is unique per-link for all the links in the AP MLD. Each link uses its own GTK to encrypt groupcast frames.

There are new elements added in Message 2 and 3 of the existing 4-way key handshake to convey MLD MAC address to generate keys and per-link GTKs. Encryption of data frames does not require knowledge of link selection.

Multiple resource units

802.11be adds support for multiple resource units (MRU) where the previous generation only supports single resource units (RU). In Wi-Fi 6, clients could only use one resource unit at a time. In Wi-Fi 7, clients can use multiple adjacent or non-adjacent resource units.

Preamble puncturing

Preamble puncturing was introduced in IEEE 802.11ax (Wi-Fi 6) as an optional method to more efficiently use wider channel widths in the presence of narrow interference.

There are two types of puncturing.

1. Static puncturing
2. Dynamic puncturing

Wi-Fi 7 introduces static puncturing as mandatory in the 6 GHz band. Puncturing requires a minimal channel width of 80 MHz enabling clients to avoid using portions of 80 MHz, 160 MHz, or 320 MHz channels. Puncturing is not supported when the AP is operating on 20 MHz or 40 MHz channel widths.

Puncturing along with multiple resource units (MRU) enables flexible use of the remaining non-punctured channel bandwidth. OFDMA MRU distribution is then allocated in the available subchannels around the punctured subchannel.

The AP includes a disabled subchannel bitmap present in the EHT operation parameters and disabled subchannel bitmap in the EHT operation element.

Puncturing removes the PHY preamble which is normally duplicated for each 20 MHz subchannel of the bonded set. The resolution of puncturing is always in 20 MHz channel width increments e.g., 20 MHz or 40 MHz.