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This post was last edited by btty038 on 2022-7-16 19:26
Hot 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! This will be the fastest Wi-Fi technology ever and will be a game changer, providing 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 enables the future of connectivity.
With the 6 GHz band open to Wi-Fi applications, Wi-Fi 7 supports a maximum channel bandwidth of 320 MHz on the 6 GHz band, 20/40/80/160 MHz on the 5 GHz and 6 GHz bands, and 20/40 MHz on the 2.4 GHz band. Compared with the existing Wi-Fi 6/6E, the 320 MHz channel bandwidth alone doubles the maximum speed of Wi-Fi 7.
Figure 1: 320 MHz channel bandwidth
Quadrature Amplitude Modulation (QAM) is a widely used Wi-Fi modulation scheme that mixes amplitude and phase changes in the carrier. Wi-Fi-6 supports up to 1024 QAM - each constellation point on the left in Figure 2 represents 10 bits of data (symbols). Wi-Fi-7 supports 4096 QAM - each constellation point on the right 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
Multi-Link Operation (MLO)
Multi-Link Operation (MLO) is an important and useful feature in Wi-Fi-7. It enables devices to transmit and receive across multiple bands and channels simultaneously. It is similar to the link aggregation or clustering capabilities of wired (i.e. Ethernet) networks, but more sophisticated and flexible. It creates a bundle or bond of multiple links (radios) in different bands and channels that act as one virtual link between connected peers. Each link (radio) can work independently and simultaneously with the other links, or coordinate for the best aggregate speed, latency, range (coverage), or power savings. Wi-Fi-7 MLO is a MAC layer solution that enables the use of multiple links simultaneously and is transparent to upper layer protocols and services. MLO can improve throughput, link robustness, roaming, interference mitigation, and latency reduction.
Figure 3. Multi-link operation
For example, in a home mesh network composed of tri-band (6GHz, 5GHz, 2.4 GHz) mesh nodes or APs, MLO can form a high-speed, low-latency wireless backbone for the home network and provide backhaul for devices connected to the mesh nodes/APs. If each mesh node supports a 4×4 tri-band concurrent configuration, the aggregate 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 automatically switch to the 6GHz and 2.4 GHz links without causing business interruption and QoS (quality of service) degradation. Compared with Wi-Fi-7's MLO-based backhaul, today's Wi-Fi-6 and 6E mesh solutions use 4×4 radios to form a wireless backhaul, which only provides 4.8 Gbps speed. If this link is interfered or interrupted, the entire backhaul (backbone) will be affected or interrupted, resulting in QoS degradation or interruption.
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 greater reliability, and improves the user experience for seamless roaming.
Multiple Resource Unit (MRU)
Wi-Fi-7 adds a new RU resource allocation mechanism. Compared with Wi-Fi-6, where AP can only allocate one RU to each user (non-AP user), Wi-Fi-7 allows multiple MRUs (resource units) to be set for one non-AP user. MRU further improves spectrum utilization efficiency, provides users with more flexible bandwidth (QoS) control as needed, and enhances the anti-interference and coexistence capabilities 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 both Orthogonal Frequency Division Multiple Access (OFDMA) and non-OFDMA (i.e. MU-MIMO) modes. OFDMA mode supports both small MRU and large MRU, allowing for more flexible allocation of RU/MRU without complex MAC and scheduler design. Non-OFDMA mode provides maximum flexibility in preamble puncture of subchannels.
For example, any 20 MHz sub-channel can be intercepted within the 320 MHz bandwidth in addition to the primary channel or 40/80 MHz channels. 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 many new features and improvements. These features include: preamble pulse, target wake-up time (TWT), restricted travel time (rTWT), extended range (MCS 14 and MCS 15), etc. Other features, such as multi-AP coordination (coordinated beamforming, coordinated OFDMA, coordinated spatial reuse, joint transmission), 16 spatial streams and HARQ, may be supported in Release 2 and will not be introduced in this article.
How will Wi-Fi-7 benefit end users?
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 up to 46 Gbps raw data rates and 16 spatial streams defined in the standard specification. This is much faster than 10 Gbps Ethernet running on Cat 6/6a/7 cables. The closest access and connection technologies are Thunderbolt 3/4, USB 4, and HDMI 2.1, which offer maximum raw data rates of 40Gbps or more.
Wi-Fi-7 will support 320MHz channel bandwidth, double that of Wi-Fi-6. Wi-Fi 7 also increases QAM granularity from 1024 (1K) to 4096 (4K), which is 20% faster than 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 traded off with the number of antennas, from 8 to 16. Therefore, Wi-Fi 6/6E supports up to 9.6 Gbps for 8 spatial streams, and Wi-Fi 7 supports up to 46 Gbps for 16 spatial streams (9.6 Gbps x2 (dual bandwidth) x1.2 (QAM improvement) x2 (spatial streams)).
At these extremely high speeds, users can achieve speeds of up to 5.8 Gbps per second on common devices such as smartphones and laptops when using two Wi-Fi antennas (two spatial streams). Many devices using a single antenna can also support data rates up to 2.9 Gbps due to strict power or form factor limitations. Users can get more than twice the speed without paying for additional antennas or higher electricity bills because no additional power amplifiers or front-end modules are required - a paradigm shift for many future applications.
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 latency of less than 20 milliseconds. It is not easy to achieve such low latency in a wireless environment. For fiber access, on the WAN side, the latency between the modem and the cloud/server is about 10 milliseconds or slightly more. After taking this into account, 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. Moreover, Wi-Fi 6E can achieve even lower latency in a much less contentious environment. Wi-Fi-7 will help reduce latency to below 10 milliseconds and eventually reach the sub-1 millisecond range with deterministic boundaries by using various tools in the 802.11be standard. These tools include MLO, traveling wave transform (TWT) and rTWT, improved triggered transmission, and eventually integrated time-sensitive networking (TSN) capabilities.
As mentioned earlier, MLO provides a dynamic mechanism to adapt the connection between multiple links. MLO can dynamically balance the transmission load between two link peers (such as AP and client device) based on indicators such as performance and robustness of the links, i.e., load balancing. If there is interference or link loss on one link (for example, due to range), the connection can still operate on the remaining links and the transmission can be seamlessly switched from the failed link to the good link (also known as fast failover). MRU/RU and preamble puncture also benefit the robustness of the connection. For example, when specific subchannels of the operating channel or a certain segment of the spectrum are interfered, the AP can avoid using these interfered subchannels or RU/MRU and optimize the transmission based on the current environmental situation and channel status. In addition, MCS 14 and MCS 15 are defined to improve the signal-to-noise ratio, which also improves the robustness of the connection when the distance between link peers increases.
Better interference reduction and coexistence
Wi-Fi-6 and Wi-Fi-6E have enhanced many features to reduce interference and coexist with existing devices based on Wi-Fi-5. Wi-Fi-6 provides more flexible sub-channel puncture modes and can utilize RU in OFDMA mode to avoid interference at a finer granularity, down to 2 MHz (the smallest RU has 26 tones). Wi-Fi 6E supports automatic frequency coordination (AFC) and coexists with existing devices. Wi-Fi-7 has MRU and preamble puncture with maximum flexibility, supports all possible sub-channels and high-resolution puncture modes in OFDMA and non-OFDMA (MU-MIMO) modes, provides better interference mitigation, and provides the best QoS for different types of services.
Figure 5. Interference and coexistence mitigation through Preamble Puncturing, MRU/RU, and AFC
Better roaming user experience
MLO also improves the user experience of seamless roaming. It provides built-in roaming enhancements defined in the 802.11be standard. For example, when the device is away from the AP, MLO retains the ML (multi-link) connection between the AP and the device 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 band steering or client steering features at the application layer to forcibly guide clients to different bands. It does not always work as expected because the AP cannot control the client device; the client device decides whether to switch bands. In addition, compatibility between vendors is another major challenge for seamless roaming.
Figure 6. Seamless roaming experience using MLO
Higher spectral efficiency
From the perspective of spectrum utilization, Wi-Fi-7 provides higher efficiency than Wi-Fi 6/6E. The additional efficiency can benefit from multiple Wi-Fi-7 features, MRU, preamble puncture, MLO, 4096 QAM, future 16 spatial streams, and coordinated multi-AP features such as coordinated beamforming, coordinated OFDMA, joint transmission, etc.
Higher power efficiency and more energy saving
By leveraging 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 on these features in a number of ways to achieve optimal power savings.
With MLO, client devices do not need to listen to every Delivery 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. The client can maintain one link for DTIM beacon updates, traffic indications, and BSS critical updates and put other links into a deep sleep state without waking up periodically to get DTIM beacon updates.
In addition to TWT, the most promising power saving feature in Wi-Fi 6, Wi-Fi 7 also supports the so-called Triggered Transmission Opportunity (TXOP) sharing feature to further save power. It allows the AP to allocate a portion of the time within the obtained TXOP to the associated client devices for transmission, so that the AP does not need to wake up in the next service period (SP).
Onsemi also supports many proprietary dynamic adaptive power saving features based on actual application, real-time throughput and environmental (such as temperature) requirements.
More emerging Wi-Fi sensing applications
In recent years, Wi-Fi sensing applications such as motion detection, positioning based on Wi-Fi channel state information (CSI) (especially indoors), and fine time measurement/round-trip time (FTM/RTT) have attracted great interest from service providers and end users.
Wi-Fi channels are susceptible to interference, are highly dynamic and frequency selective, and CSI pollution can significantly 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. In addition, because so much CSI data can be captured in a 320 MHz transmission, enough interference-free CSI blocks can be selected for motion detection while avoiding noisy CSI data.
Through 2x or 4x oversampling and upsampling technology, for 320 MHz signals, RTT timestamp and measurement accuracy can reach sub-nanosecond resolution. In other words, Wi-Fi-7 supports sub-meter (i.e. 30 cm) accuracy ranging and indoor positioning, which will make many exciting new Wi-Fi sensing applications possible.
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, etc. Users can expect Wi-Fi 7 to provide higher speeds, lower latency, and more powerful performance than the existing Wi-Fi 6/6E.
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