A New Wi-Fi Innovation Technology – Wi-Fi 7

NOVEMBER, 2022

In the previous article, we discussed a new band – 6 GHz – available in Wi-Fi 6E technology, which means faster data transferring can be achieved. Wi-Fi 6E also contains extra bandwidth to increase throughput in congested areas. However, due to ongoing supply chain shortages and slow automatic frequency coordination (AFC) system establishment by regulatory bodies, Wi-Fi 6E compatible products have seen slow adoption but are also facing the next generation Wi-Fi 7 getting closer to readiness. Wi-Fi 7, also known as IEEE 802.11be is targeting emerging applications that have higher requirements on throughput and latency, such as 4K and 8k videos (transmission rates up to 20 Gbps), Wi-Fi 6 is insufficient in spite of its dedication to improving user experience in high-density scenarios. As a result, Wi-Fi 7 will employ new features to reduce latency, increase network capacity, and improve efficiency. The revolutionary features included in Wi-Fi 7 technology include 320 MHz bandwidth, enhanced multiple-input multiple-output (MIMO) operations, multi-link operations, and multi-access point (AP) coordination. Let’s discuss how each feature can bring benefits to users’ network experience.

Wi-Fi 7 allows us to operate at a maximum transmission rate of 30 Gbps which, compared with Wi-Fi 6, it only supports a 9.6 Gbps transmission rate. In Wi-Fi 6, the 2.4 GHz and 5 GHz frequency bands are congested and have limited unlicensed spectrums. Thus, when running emerging applications, existing Wi-Fi networks generally encounter low quality of service. On the other hand, Wi-Fi 7 will enhance the support of the 6 Ghz frequency band further by extending new bandwidth modes on top of the advantages discussed in the previous Wi-Fi 6E article. The new bandwidth modes in new generation Wi-Fi include contiguous 240 MHz, non-contiguous 160+80 MHz, contiguous 320 MHz, and non-contiguous 160+160 MHz. One of the mechanisms to achieve higher throughput is called preamble puncturing. That is, when some of the channels used by the Access Point have some interference, then the AP will transmit a “punctured” section of the channel illustrated in the figure below to avoid the noisy channels. While this technique will reduce the overall bandwidth, it should still provide better performance than trying to fight over the interference. Since most countries will have overlapping channels especially in 6 GHz band, preamble puncturing can potentially allow more usage of wider channels which lead to greater throughput.

Wi-Fi 7 will be increasing the maximum number of MIMO spatial streams from 8 to 16. This feature particularly benefits indoor operations since they have a rich scuttering environment with high angular spreads, and an increasing number of MIMO spatial streams can easily allow information streams to separate in the spatial domain. With multi-antenna Access Point (AP), multi-user MIMO will send a trigger frame to each station and receive an acknowledgement frame from them; thus, it ensures transmitted power control, frequency alignment, and time synchronization. However, the bottleneck of explicit channel state information (CSI) is that acknowledgement frames are transmitted sequentially and do not scale well as the number of stations increases. To overcome this limitation, Wi-Fi 7 will use implicit CSI acquisition where AP will estimate devices’ location based on uplink signals transmitted by the stations. As a result, 16 data streams can be accomplished by multiple APs simultaneously and double the theoretical physical transmission rate by more than twice on Wi-Fi 6.

One of the challenges that industries often confront is that they need new spectrum management, coordination, and transmission mechanisms in order to efficiently utilize the use of multiple channels between 2.4 GHz, 5 GHz, and 6 GHz frequency bands. For current 802.11ax, a device can only select either 2.4 GHz or 5 GHz or 6Ghz for every connection; this means that bands go unused or limits network speeds if the slower band is chosen. In Wi-Fi 7, multi-link operation (MLO) enables devices to simultaneously send and receive data across different frequency bands and channels. With MLO, Wi-Fi 7 can establish multiple links between the stations such as your phone and Wi-Fi AP, which take the advantage of the greater capacity, higher peak speeds, and lower congestion of the high bands. There are two main modes in MLO: simultaneous transceiver mode (STR) or non-simultaneous transceiver mode (NSTR). In STR, two or more links work completely independently and don’t interfere with each other. In NSTR, all links can only receive or send data at a single time. Each mode has its pros and cons in terms of latency, depending on different scenarios. Nevertheless, multi-link technology still lowers latency in congested environments.

Last but not least, multi-AP coordination is supported in Wi-Fi 7. In the current 802.11 protocol framework, coordination between APs is minimal. WLAN functions such as smart roaming are mostly vendor-defined features. A set of APs in Wi-Fi 7, however, can form a system in which channel access and transmission schedules are tightly communicated. There are different types of multiple APs coordination: orthogonal frequency division multiple access (OFDMA), time division multiple access (TDMA), spatial reuse (SR), beamforming (BF), and joint processing (JP). OFDMA is that APs transmit to station on different resource units; whereas for TDMA, different APs take turns in transmitting to stations using the same resource units. With coordinated SR, different APs transmit simultaneously to stations on the same resource unit. Coordinated BF is that APs will recognize the sound channels from its own stations so that BF transmissions can occur on the same resource unit while nulling the interference towards adjacent APs. Coordinated JP establishes a distributed multi-MIMO system that allows a single station to receive from multiple APs. Multi-AP coordination helps APs to optimize channel selection and adjust load between them to achieve efficient utilization and balanced allocation of radio resources.

New Wi-Fi 7 compatible equipment will bring a novel experience over the next two to five years. For example, Extended Reality (XR) applications demand extremely low latency metrics, high quality video with high refresh rates, which are heavily dependent on connectivity and bandwidth. Other forms of entertainment like Metaverse will test the boundaries of wireless technology such that Wi-Fi 7 will deliver ample performance. In industry networks, digital transformation is becoming the major trend where low latency and high bandwidth Wi-Fi becomes vital to enterprises. As a result, Wi-Fi 7 is destined to quickly become a prerequisite to support heavily internet accessible use cases in the near future.