On the heels of Wi-Fi 6E, the 7th generation of WiFi technology (also known as IEEE 802.11be or Wi-Fi 7) is coming! It will be the fastest Wi-Fi technology ever and will be a game changer to provide a better user experience for the web and online activities in our daily lives. It will support and accelerate many demanding applications such as 8K video streaming, fully immersive AR/VR, gaming and cloud computing. This article will review the key features supported in 802.11be Release 1 and learn about the benefits of Wi-Fi 7 and how it will enable future connectivity.
Key Features of Wi-Fi 7
320MHz channel bandwidth
As the 6 GHz band opens up to Wi-Fi applications, Wi-Fi 7 supports up to 320 MHz channel bandwidth on the 6 GHz band, 20/40/80/160 MHz channel bandwidth on the 5 GHz and 6 GHz bands as well as 20 /40 MHz in the 2.4 GHz band. The 320 MHz channel bandwidth alone doubles the maximum speed of Wi-Fi 7 compared to existing Wi-Fi 6/6E.
Figure 1: 320 MHz channel bandwidth
Quadrature Amplitude Modulation (QAM) is a widely used Wi-Fi modulation scheme that simultaneously mixes amplitude and phase changes in the carrier. Wi-Fi-6 supports up to 1024 QAMs – the constellation points on the left in Figure 2 represent 10 bits of data (symbols). Wi-Fi-7 supports 4096 QAM – each right constellation point represents 12 bits of data (symbols). In other words, each point modulated with QAM in Wi-Fi7 can carry 2 more bits of information than Wi-Fi6, which is 20% faster.
Figure 2: 1024 QAM vs 4096 QAM
Multilink Operation (MLO)
Multi-Link Operation (MLO) is an important and useful feature in Wi-Fi-7. It enables devices to transmit and receive simultaneously across multiple bands and channels. It is similar to the link aggregation or clustering function of wired (ie Ethernet) networks, but is more complex and flexible. It creates a bundle or bond of multiple links (radios) in different bands and channels as one virtual link between connected peers. Each link (radio) can work independently and simultaneously with other links, or coordinate optimal aggregate speed, latency, range (coverage) or power saving. Wi-Fi-7 MLO is a MAC layer solution that can use multiple links simultaneously and is transparent to upper layer protocols and services. MLO can improve throughput, link robustness, roaming, interference mitigation and reduce latency.
Figure 3. Multilink operation
For example, in a home mesh network consisting of tri-band (6GHz, 5GHz, 2.4GHz) mesh nodes or APs, MLO can form a high-speed, low-latency wireless backbone for the home network and Devices connected to the AP provide loopback. If each mesh node supports a 4×4 tri-band concurrent configuration, the aggregated backhaul (backbone) speed can reach 21.6 Gbps. With MLO, the backhaul (backbone) is also more robust and reliable. When the 5GHz link is interrupted by DFS (radar), traffic can be automatically switched to the 6GHz and 2.4GHz links without business interruption and QoS (Quality of Service) degradation. Compared to Wi-Fi-7’s MLO-based backhaul, today’s Wi-Fi-6 and 6E mesh solutions use 4×4 radios to make up wireless backhaul, delivering only 4.8 Gbps speeds. If this link is disturbed or interrupted, the entire backhaul (backbone) will be affected or interrupted, resulting in degraded or interrupted QoS.
When client devices (such as smartphones, laptops, etc.) support multiple radios, MLO creates a larger pipe between the device and the AP for higher speeds, lower latency, and higher reliability and improve the user experience for seamless roaming.
Multiple Resource Unit (MRU)
Wi-Fi-7 adds a new RU resource allocation mechanism. In Wi-Fi-6, the AP can only allocate one RU to each user (non-AP user), while Wi-Fi-7 allows multiple MRUs (resource units) to be set as a non-AP user. The MRU further improves spectrum utilization efficiency, provides users with more flexible bandwidth (QoS) control as needed, and enhances the anti-jamming capability and coexistence capability of existing devices operating on the same frequency band or channel.
Figure 4. RU and MRU for 320 MHz OFDMA PPDU
This MRU mechanism supports Orthogonal Frequency Division Multiple Access (OFDMA) and non-OFDMA (ie MU-MIMO) modes. OFDMA mode supports small MRU and large MRU, allowing more flexible allocation of RU/MRU without complicated MAC and scheduler design. The non-OFDMA mode provides the most flexibility in the preamble puncturing of the subchannels.
For example, any 20 MHz sub-channel can be intercepted in the 320 MHz bandwidth, except the main channel or the 40/80 MHz channel. This allows transmissions to maximize the use of the channel's spectrum in the presence of interference and provides optimal coexistence when there are incumbent devices operating on a specific spectrum segment of the channel.
Wi-Fi 7 has a lot of new features and improvements. These features include: Preamble, Target Wake Time (TWT), Restricted Traveling Wave Time (rTWT), Extended Range (MCS 14 and MCS 15), and more. Other features, such as multi-AP coordination (coordinated beamforming, coordinated OFDMA, coordinated spatial reuse, joint transmission), 16 spatial streams, and HARQ, etc., may be supported in Release 2 and will not be covered in this article.
How will Wi-Fi-7 benefit end users?
very high throughput
Wi-Fi-7 supports lightning-fast speeds. Building on its predecessor Wi-Fi-6 (aka 802.11ax), Wi-Fi-7 supports Extremely High Throughput (EHT) with raw data rates of up to 46 Gbps and 16 spatial streams as defined in the standard specification. This is much faster than 10 Gbps Ethernet running on Cat 6/6a/7 cable. The closest access and connectivity technologies are Thunderbolt 3/4, USB 4 and HDMI 2.1, offering maximum raw data rates of 40Gbps or higher.
Wi-Fi-7 will support 320MHz channel bandwidth, twice that of Wi-Fi-6. Wi-Fi 7 also increases the QAM granularity from 1024 (1K) to 4096 (4K), a 20% increase in speed compared to Wi-Fi 6/6E or Wi-Fi 5 Wave 3. In addition, Wi-Fi-7 doubles the maximum number of spatial streams, which in some cases is tradeable with the number of antennas, from 8 to 16. So Wi-Fi 6/6E supports up to 9.6 Gbps with 8 spatial streams, Wi-Fi 7 supports up to 46 Gbps with 16 spatial streams (9.6 Gbps x2 (dual bandwidth) x1.2 (QAM improvement) x2 (spatial stream) )).
At this extremely high speed, users can achieve speeds of up to 5.8 Gbps per second on commonly used devices such as smartphones, laptops, etc., using two Wi-Fi antennas (two spatial streams). Due to strict power or form factor constraints, many devices using one antenna can also support data rates up to 2.9 Gbps. Users can get more than twice the speed without paying for additional antennas or higher electricity bills, as no additional power amplifiers or front-end modules are required—a paradigm shift for many future applications.
Ultra low latency
Latency is another key parameter for quality of service (QoS) and user experience. It is especially critical for real-time applications. Many multimedia applications, such as high-resolution live video streaming, virtual reality, augmented reality, cloud gaming, and real-time programming, require less than 20 milliseconds of latency. Achieving such low latency in a wireless environment is not easy. For fiber access, on the WAN side, the latency between the modem and the cloud/server is about 10ms or more. With this in mind, the latency budget between the WAN modem and the endpoint client device should be around 10ms or less for a good user experience. Wi-Fi-6 achieves 10-20ms latency. And, Wi-Fi 6E can achieve lower latency in a much less contentious environment. Wi-Fi-7 will help reduce latency to below 10ms and eventually to the sub-1ms range with deterministic boundaries by using various tools in the 802.11be standard. These tools include MLO, traveling wave transform (TWT) and rTWT, improved trigger transmission, and eventually integrated time-sensitive networking (TSN) capabilities.
As mentioned earlier, MLO provides a dynamic mechanism to accommodate connections between multiple links. MLO can dynamically balance the transmission load between two link peers (such as AP and client devices) based on metrics such as link performance and robustness, that is, load balancing. If there is interference on one link or a link is lost (for example, due to range), the connection can still operate on the remaining links, and transmissions can seamlessly switch from the failed link to the good link (also known as fail-fast transfer). MRU/RU and preamble puncture also contribute to the robustness of the connection. For example, when certain sub-channels of the operating channel or a certain segment of the spectrum are interfered, the AP can avoid using these interfered sub-channels or RU/MRU and optimize transmission according to the current environmental conditions and channel conditions. In addition, MCS 14 and MCS 15 are defined to improve the signal-to-noise ratio and also improve the robustness of the connection when the distance between link peers increases.
Better interference reduction and coexistence
Wi-Fi-6 and Wi-Fi-6E build on Wi-Fi-5 with many enhancements to reduce interference and coexist with existing devices. Wi-Fi-6 offers more flexible subchannel puncturing modes, and can utilize RUs in OFDMA mode to avoid finer-grained interference down to 2 MHz (the smallest RU has 26 tones). Wi-Fi 6E supports Automatic Frequency Coordination (AFC) for coexistence with existing equipment. Wi-Fi-7 features MRU and preamble puncturing for maximum flexibility, supporting all possible sub-channels and high-resolution puncturing modes in OFDMA and non-OFDMA (MU-MIMO) modes, providing better interference mitigation for different Types of services provide the best QoS.
Figure 5. Mitigation of interference and coexistence with Preamble Puncturing, MRU/RU, and AFC
Better roaming user experience
MLO also improves the user experience for seamless roaming. It provides built-in roaming enhancements defined in the 802.11be standard. For example, MLO preserves the ML (mulTI-link) connection between the AP and the device when the device is far away from the AP, and can automatically operate in the 2.4 GHz band without switching bands. Conversely, if the device is close to the AP, MLO can automatically and dynamically operate in the 5 GHz and 6 GHz bands for higher performance. Today's Wi-Fi-6 and 6E APs must rely on application-layer band-steering or client-steering features to force-steer clients to different bands. It doesn't always work as expected because the AP has no control over the client device; the client device decides whether to switch bands or not. Additionally, compatibility between providers is another major challenge for seamless roaming.
Figure 6. Leveraging MLO for a seamless roaming experience
higher spectral efficiency
From the perspective of spectrum utilization, Wi-Fi-7 provides higher efficiency than Wi-Fi 6/6E. Additional efficiency can benefit from multiple Wi-Fi-7 capabilities, MRU, preamble puncture, MLO, 4096 QAM, future 16 spatial streams, and coordinated multi-AP capabilities such as coordinated beamforming, coordinated OFDMA, joint transmission, and more.
Higher power efficiency and more energy savings
By taking advantage of higher speeds, Wi-Fi 7 delivers data with greater power efficiency thanks to wider 320 MHz channel bandwidth, 4096 QAM, and lower latency. Building on the power saving features of Wi-Fi-6, Wi-Fi-7 improves these features in a number of ways for optimal power saving.
With MLO, client devices do not need to listen for every Delivered Traffic Indication Map (DTIM) beacon frame and do not perform Group Time Key, Integrity Group Time Key, or Beacon Integrity Group Time Key (GTK/IGTK/BIGTK) updates . Clients can maintain one link for DTIM beacon updates, traffic indications, and BSS critical updates, and put other links into deep sleep without periodically waking up for DTIM beacon updates.
In addition to Wi-Fi 6's most promising power-saving feature, TWT, Wi-Fi 7 supports what's called a Triggered Transmission Opportunity (TXOP) sharing feature for further power savings. It allows the AP to allocate a portion of the time within the acquired TXOP to the associated client device for transmission, so that the AP does not need to wake up in the next service period (SP).
Onsemi also supports a number of proprietary dynamic adaptive power saving features based on actual application, real-time throughput and environmental (eg temperature) needs.
More Emerging Wi-Fi Sensing Applications
In recent years, Wi-Fi sensing applications, such as motion detection, Wi-Fi Channel State Information (CSI)-based positioning (especially indoors), and Fine Time Measurement/Round Trip Time (FTM/RTT), have caused service providers and Great interest from end users.
Wi-Fi channels are susceptible to interference, have strong dynamics and frequency selectivity, and CSI contamination will greatly reduce the accuracy of motion detection. Thanks to the 320 MHz channel bandwidth, Wi-Fi-7 supports richer CSI data up to 3984 tones, improving the accuracy of motion detection. Furthermore, since so much CSI data can be captured in a 320 MHz transmission, enough non-interfering CSI blocks can be selected for motion detection while avoiding noisy CSI data.
With 2x or 4x oversampling and upsampling techniques, the RTT timestamp and measurement accuracy can reach sub-nanosecond resolution for 320 MHz signals. That said, Wi-Fi-7 supports ranging and indoor positioning with sub-meter (ie, 30 cm) accuracy, which will enable many exciting new applications for Wi-Fi sensing.
Wi-Fi-7 will significantly improve the user experience in many ways and become more cost-effective. It can enable and enhance many demanding applications such as cloud gaming, immersive AR/VR, 8K video streaming, Industry 4.0 and more. Users can expect Wi-Fi 7 to offer higher speeds, lower latency and more robust performance than existing Wi-Fi 6/6E.
Editor: Huang Fei