Lorenzo Galati-Giordano#, Giovanni Geraci*, Marc Carrascosa*, and Boris Bellalta*
#Nokia Bell Labs, Stuttgart *Universitat Pompeu Fabra, Barcelona
You do not need to be tech-savvy to know Wi-Fi. With twice as many devices as people, Wi-Fi technologies carry two thirds of the world’s mobile traffic and underpin our digital economy. This generation will not easily forget what it could have meant to undergo Covid lockdown without Wi-Fi from social, economic, and safety standpoints. And even now that traveling to places is possible once again, many of us reach for the Wi-Fi password first thing upon arrival, as this is often the means to ordering a meal and sending news back home.
Wi-Fi has come a long way since its introduction in the late nineties. The easiest way to appreciate the technology’s improvement is by reading peak data rates specifications on commercial Wi-Fi access point (AP) boxes. These rates have grown roughly four orders of magnitude in two and a half decades, from the mere 1 Mbps of the original 802.11 standard to the near 30 Gbps of the latest 802.11be products (alias WiFi 7) scheduled to hit the shelves as early as 2024. This giant leap allowed Wi-Fi to move beyond email and web browsing and progressively conquer crowded co-working spaces, airports, and even the hearts of many parents who can now video-call their children without worrying about phone bills. But how many of us have complained at least once about Wi-Fi not functioning when we most need it? Unreliability would be the Achilles heel for any technology meant to be affordable, pervasive, and operating in license-exempt bands subject to uncontrolled interference. Wi-Fi is no exception.
And while it only takes patience to cope with a buffering video or to repeat our last sentence in a voice call, a lack of Wi-Fi reliability will not be tolerated by its new users: machines. In future manufacturing environments, Gbps communications between robots, sensors, and industrial machinery will demand reliability—with at least three (but sometimes many more) ‘nines’—in terms of both data delivery and maximum latency. Rest assured that these requirements will not get any looser for use cases involving humans. Many of us may not even want to think about undergoing robotic-assisted surgery with an unreliable Wi-Fi connection. But even just for holographic communications, a key building block of the upcoming Metaverse, excessive delays experienced by just 0.01% of the packets could trigger nausea and user distress. As it takes up ever more challenging endeavors to fuel industrial automation, digital twinning, and tele-presence, next-generation Wi-Fi is bound to step out of its comfort zone and set reliability as its first priority.
The IEEE 802.11bn Ultra High Reliability (UHR) Study Group was established in 2022 to define the set of objectives, frequency bands, and technologies to be considered beyond the present Wi-Fi standard, 802.11be. The current plan is to form the UHR Task Group by 2023, with a traditional single release standardization cycle that will last until 2028. This activity will define the protocol functionalities of future Wi-Fi 8 products. Although discussions are ongoing on the specific performance targets, Wi-Fi 8 will mark the first generation aimed at enhancing the reliability of the protocol, with a primary focus on improving service availability and ensuring minimal delays. Three critical aspects are currently being investigated: seamless connectivity, determinism, and controlled worst-case delay. In the sequel, we will briefly discuss the main opportunities and challenges associated with each of these aspects.
Seamless connectivity: While previous Wi-Fi standards did not prioritize mobility support, the unreliable nature of Wi-Fi links is often attributed to devices moving between APs. To address this issue, the newly introduced Wi-Fi multilink operation (MLO) provides a high degree of flexibility that can greatly improve mobility in Wi-Fi 8. One approach to leverage this is through the implementation of a new distributed MLO framework, allowing logical APs controlled by the same entity to be located separately rather than being confined to a single physical device. Although this approach requires coordination and communication among the distributed APs, it may effectively create a distributed virtual cell, so that a nomadic device can seamlessly stay connected to at least one link, thereby embedding native roaming support.
Determinism: Wi-Fi 8 may incorporate several PHY/MAC enhancements, including the adoption of hybrid automatic repeat request (HARQ) and an increase in the number of supported spatial streams from 8 to 16. The utilization of HARQ would enable devices to combine corrupted data units with their corresponding retransmissions, thereby increasing the likelihood of correct decoding and reducing latency in challenging channel conditions. The availability of additional spatial streams would allow for the simultaneous servicing of more users, thereby reducing their channel access time. Additionally, new features building upon the existing TXOP (Transmission Opportunity) sharing functionalities and R-TWT (Restricted Target Wake Time) may allow APs to share a portion of their acquired TXOPs with associated stations, should a latency-sensitive transmission require it.
Controlled worst-case delay: Providing performance guarantees in the presence of random access has proven to be challenging. Indeed, inter-BSS interactions are subject to contention principles, even when the APs belong to the same administrative domain, resulting in unpredictable worst-case delays. Wi-Fi 8 aims to address this issue by introducing multi-AP coordination to achieve higher reliability and prevent channel access contentions, particularly in dense and heavily loaded environments. To achieve this, new protocols and frames will be necessary for the discovery and management of multi-AP groups, sharing channel and buffer state data between APs, and triggering coordinated multi-AP transmissions. These measures aim to minimize inter-BSS collisions and achieve a more efficient use of the spectrum through dynamic inter-AP resource management. AP coordination schemes in Wi-Fi 8 will vary from basic to advanced, depending on the amount of data exchange required between APs and the level of implementation complexity. One intermediate approach—coordinated beamforming (CBF)—involves collaborative APs using some of their spatial degrees of freedom to place radiation nulls to and from neighboring non-associated stations. This approach makes the AP and its neighboring stations mutually invisible, avoiding channel access contention, allowing concurrent collision-free transmissions, and improving worst-case latency as a byproduct.
Wi-Fi has undoubtedly become a vital technology in our modern world, enabling seamless connectivity, powering our digital economy, and connecting billions of devices worldwide. As we rely more and more on Wi-Fi for essential tasks and experiences, the need for reliability has become paramount. The planned making of Wi-Fi 8, with its proposed new features aiming at enhancing the protocol’s reliability, marks a significant step forward in addressing this challenge. We hope this overview article will foster new research and breakthroughs, bringing the Wi-Fi community one step closer to making unlicensed wireless the new wired.
Full article: L. Galati Giordano, G. Geraci, M. Carrascosa, and B. Bellalta, “What Will Wi-Fi 8 Be? A Primer on IEEE 802.11bn Ultra High Reliability,” arXiv preprint 2303.10442, 2023.
About the authors:
Lorenzo Galati Giordano (SM’20) is Senior Research Engineer at Nokia Bell Labs, Germany. He has more than 15 years of academic and industrial experience in communication systems, protocols, and standards, resulting in tens of commercial patents, publications in prestigious books, journals, conferences, and standard contributions.
Giovanni Geraci (SM’19) is an Associate Professor at Univ. Pompeu Fabra in Barcelona and he was previously with Nokia Bell Labs. He holds a dozen patents on wireless technologies, and he received the IEEE ComSoc EMEA Outstanding Young Researcher Award as well as Best Paper Awards at IEEE PIMRC’19 and IEEE Globecom’22.
Marc Carrascosa is currently a Ph.D. candidate in the Wireless Networking group at Universitat Pompeu Fabra (UPF). His research interests are related to performance optimization in wireless networks. He obtained B.Sc. (2018) and M.Sc. (2019) degrees from UPF.
Boris Bellalta (SM’13) is a Full Professor at Universitat Pompeu Fabra (UPF). His research interests are in the area of wireless networks and performance evaluation, with emphasis on Wi-Fi technologies, and Machine Learning-based adaptive systems.
Acknowledgments:
This work was supported by the Spanish Research Agency through grants PID2021-123995NB-I00, PRE2019-088690, and PID2021-123999OB-I00, by the “Ramón y Cajal” program, and by the Fractus-UPF Chair on Tech Transfer and 6G.