Since its inception, Wi-Fi technology has brought huge social and economic benefits to the world and has become one of the driving forces for social and economic development. Especially during the epidemic period, Wi-Fi kept users connected and entertained, promoted changes in education models, and enhanced health care businesses. Wi-Fi technology has also made outstanding contributions to bridging the digital divide in rural and remote areas around the world. According to a study, the global economic value of Wi-Fi in 2021 is estimated at US$3.3 trillion and continues to grow, and is expected to grow to US$4.9 trillion by 2025.

Overview of Wi-Fi technology evolution

        For nearly 20 years, Wi-Fi has efficiently used available unlicensed spectrum to establish a distributed connection architecture that has allowed Wi-Fi to enter various fields while using security technology to protect users. The main advantages of Wi-Fi technology include:

- Affordable performance;

- Unlicensed spectrum services;

- Ease of use;

- Self-service deployment;

- Long-term compatibility.

        Wi-Fi technology has evolved for many generations. For ease of understanding, WFA (Wi-Fi Alliance) named 802.11n (2009), 802.11ac (2013), and 802.11ax (2019) based on different PHY technologies as Wi-Fi 4, Wi-Fi 5, and Wi-Fi 6 respectively.

        The reliability, security, interoperability, and high-capacity, high speed, and low latency provided by Wi-Fi technology enable it to support next-generation use cases, including virtual reality (VR), augmented reality (AR), ultra-high definition (UHD) video, multi-party games, Internet of Things (IoT), etc. Wi-Fi 6 can provide greater capacity and higher performance;WiGig (Wireless Gigabit) provides extremely high rates in the 60GHz band; and Wi-Fi HaLow™ (short for the IEEE 802.11ah standard) can provide energy-saving use cases in scenarios such as IoT. Because Wi-Fi 6 can meet the needs of next-generation use cases, it reduces the pressure and urgency on operators to deploy expensive cellular networks. Research reports believe that Wi-Fi reduces 60% of cellular network traffic. Wi-Fi 6 and 5G are complementary technologies, both helping to expand the richness of wireless networks and the power of the entire wireless connection fabric.

Wi-Fi 6E expands to the 6GHz band, improving Wi-Fi spectrum shortage

        Demand for Wi-Fi networks has been growing steadily over the past 20 years, but until 2020, the amount of available unlicensed spectrum remained unchanged. The industry has pushed regulators in various countries to open up 6GHz as a new unlicensed frequency band for Wi-Fi. The FCC in the United States has taken the lead in approving the use of 1200MHz spectrum in the 6GHz frequency band, which has almost tripled the available spectrum. As shown in Figure 1, after 6GHz was added to the unlicensed spectrum, the available spectrum and channels were greatly expanded.

              Figure 1 6GHz expands the unlicensed spectrum range including 2.4 GHz and 5 GHz

The following three factors make the 6GHz band particularly attractive for the deployment of Wi-Fi technology:

- continuous spectrum

The 6GHz frequency currently under consideration is adjacent to existing 5GHz Wi-Fi frequencies, which helps reduce the incremental cost of adding 6GHz capabilities to Wi-Fi devices that already support the 5GHz band. The propagation characteristics of radio signals in the 6GHz band are similar to those of 5 GHz, making it easier to upgrade existing equipment in the field. Similar propagation characteristics allow reuse of original 5GHz network coverage maps and metrics.

- Wider channels

Up to 1200MHz of continuous spectrum allows for wider channels, supporting demanding applications that require high throughput and low latency, such as high-definition video delivery, AR/VR, and Telepresence.

- interference reduction

The 6GHz band is relatively less crowded and will be used only by Wi-Fi 6 and future generations of Wi-Fi devices. Migrating performance-critical applications to the 6GHz band will reduce congestion in the 2.4GHz and 5GHz bands, improving the overall capacity and performance of already deployed Wi-Fi devices.

Wi-Fi 6E devices are Wi-Fi 6 devices running in the 6GHz band and naturally have the advantages of using 6GHz spectrum. The combination of these features at 6GHz enables Wi-Fi 6E devices to provide 10Gbps rates, extremely low latency and greater network capacity.

Although some countries and regions (such as the United States and the European Union) have approved 6GHz medium or wide or narrow frequency bands for Wi-Fi, the adoption of 6GHz also needs to consider the following scenarios that may occupy 6GHz and cause conflicts:

- 5G NR-U (5G New Radio in Unlicensed Spectrum) is defined in the 3GPP R16 version that the 5G air interface can work in unlicensed frequency bands. In some regions, such as the United States, NR-U will also be used for services deployed in the 6GHz band. In addition, NR-U Sidelink based C-V2X services will also occupy part of the 6GHz bandwidth if deployed.

- The United States has allocated 20MHz of 5.9GHz to 5G C-V2X, and deployment needs to consider coexistence issues.

The 2023 World Wireless Conference WRC-23 will discuss whether to license 6GHz spectrum to 6G.

Wi-Fi 6E still provides the following Wi-Fi 6 standard certification features:

- Multi-user multiple-input multiple-output (MU-MIMO): allows more downlink data to be transmitted simultaneously and enables access points to send data to a large number of devices simultaneously;

- 160MHz channel: Increased bandwidth provides higher performance with low latency;

- Target Wake-Up Time (TWT): Significantly extends the battery life of Wi-Fi devices such as Internet of Things (IoT) devices;

- 1024 Quadrature Amplitude Modulation Mode (1024-QAM): Improve the throughput of Wi-Fi devices by encoding more data in the same amount of spectrum;

- Transmit beamforming: Supports higher data rates within a given range, providing greater network capacity;

- Orthogonal Frequency Division Multiple Access (OFDMA): Effectively share frequency channels to improve network efficiency and reduce latency for uplink and downlink traffic in demanding environments;

- Increased symbol duration supports reliable outdoor performance;

- Improved MAC signaling to improve efficiency;

- Higher security for WPA3;

- Spatial reuse, which uses BSS Coloring technology to improve the efficiency of high-density scenes;

- 4×longer OFDM symbol (Symbol), the subcarriers are reduced from 312.5kHz in Wi-Fi 5 to 78.125kHz, improving efficiency.

Wi-Fi 7, focusing on improving speed

The name of the Wi-Fi 6 protocol group is IEEE 802.11axHEW (High Efficiency WLAN), and its main goal is to improve efficiency; while the name of the Wi-Fi 7 protocol group is IEEE 802.11be EHT (Extremely High Throughput), an important goal is to improve speed. In particular, video traffic remains the dominant traffic type in many WLAN deployments. Due to the emergence of 4K and 8K video (uncompressed rates of 20Gbps), throughput requirements continue to increase. New high-throughput, low-latency applications will emerge in large numbers, such as virtual or augmented reality, games, remote offices and cloud computing. Therefore, the goals of the Wi-Fi 7 (802.11be) standard are:

- Configure at least one operating mode capable of supporting a maximum throughput of at least 30Gbps;

- Support the 1GHz~7.125GHz band (2.4GHz/ 5GHz/6GHzbands);

- Backward compatibility with 11a/b/g/n/ac/ax defines at least one operating mode that improves worst-case latency and jitter.

- Work on the Wi-Fi 7 standard was launched in 2019, and TGbe (Task Group be) was established. It is planned to release the standard in 2024. The milestones in standard advancement are shown in Figure 2.

                Figure 2 Milestones in Wi-Fi7 standard advancement

The main technical characteristics of Wi-Fi 5, 6, and 7 generations of Wi-Fi are compared in Table 1.

In Wi-Fi 7 (802.11be), the main candidate technical characteristics include:

- It can support up to 16 spatial streams, with a total rate that is twice that of Wi-Fi 6, and enhances the MIMO working mechanism;

- The maximum bandwidth supports 320MHz, the single stream rate is doubled compared to Wi-Fi 6, and discontinuous channels are allowed to be aggregated;

- Supports 4096QAM, which improves performance by 20% compared to Wi-Fi 6 1024QAM, and enhances MIMO working mechanism;

- MLO (Multi-Link Operation) and Multi-RU (Preamble Puncturing) allow aggregation and cooperation at the link level between different frequency bands and channels; perform traffic steering and Load Balancer under multiple frequency bands/channels, and utilize multiple frequency bands/channels for concurrent transmission and repeated transmission to increase reliability;

- Multi-AP Coordination adopts coordination and joint transmission technology among multiple APs to significantly improve network performance in a multi-AP environment by avoiding interference and collisions between BSSs, multiple APs sending the same data frame, and APs collecting CSI information of non-associated STAs., especially used to improve the increasing number of Mesh APs in home or commercial deployments;

- Adopt enhanced link adaptation and transmission protocols, such as HARQ (hybrid automatic repeat request) technology;

- To enhance low-latency capabilities, in order to support RTA (Real-time Application), TGbe analyzed the main findings of IEEE802 TSN and discussed how to improve EDCA, Enhanced UORA, etc.; the ongoing discussions in the Standards Committee include backoff procedures, AC (Access Categories), and message service policies.

              table 1   Characteristics comparison of three generations of Wi-Fi technologies

        802.11be is an important milestone for the next generation of Wi-Fi. Its goal is to provide extremely high throughput and support low-latency services. The standard is still in its infancy. Several innovations have been introduced above. In theory, the goals of high throughput and low latency can be achieved through EHT PHY (4096 QAM, 320MHz, 16×16 MU-MIMO, EHT Preamble). However, in practice, due to unlicensed spectrum, interference and huge overhead, EHT PHY alone cannot provide significant output and delay gains to end users. This is why TGbe also explored other important innovations such as improved EDCA, flexible OFDMA, multi-link, and reduced channel sounding. Finally, TGbe discussed advanced PHY methods that can improve spectral efficiency, such as Hybrid Automatic Repeat Request (HARQ), Non-Orthogonal Multiple Access Technology (NOMA), and Full Duplex FD (Full Delay), as well as various Multi-AP cooperation methods. In this set of recommendations, we see another paradigm shift from mitigating interference by separating transmissions in time/frequency/space or power to joint transmissions in distributed large-scale antenna systems. Although TGbe may delay many of the Advanced PHY and Multi-AP collaboration features in the next Wi-Fi release, these technologies point us to further development beyond Wi-Fi 7.

         ZTE actively participated in the formulation of Wi-Fi 7 technical specifications, providing theoretical support and engineering verification in terms of OFDMA operating performance, RU allocation mechanism, MAC support technology for RU allocation, multi-Link low latency support technology, channel access mechanism, and coordinated operations between MLDs, measurement and optimization of delay statistical indicators for low latency.

        As Wi-Fi technology continues to innovate, continues to provide a variety of solutions to meet the growing needs of users and maintain users 'high-quality connections anytime and anywhere, the social and economic value of Wi-Fi to the world will continue to increase.