# A Survey of Wi-Fi 6: Technologies, Advances, and Challenges
### Contribution  
In this paper, we consider publications about Wi-Fi 6 since 2015. To the best of our knowledge, the current paper is the first comprehensive literature review of IEEE 802.11 ax based on the latest version of the standard. There are already several tutorials describing novel features of Wi-Fi 6, which are listed in Table 2. Several papers present Wi-Fi 6 based on the early stages of the standardization [6; 7; 8] and are no longer up to date. Other tutorials focus on specific features such as resource allocation [9] or the MAC layer [10]. The most complete tutorial on Wi-Fi 6 is the one by [PERSON] et al. [11] with a focus on spatial reuse and random Orthogonal Frequency Division Multiple Access (OFDMA). In Sections 2 and 3, we provide a detailed description of Wi-Fi 6 for the benefit of non-expert readers, which may be skipped by expert readers familiar with Wi-Fi 6. In this article, we present a detailed survey of the studies of Wi-Fi 6. We identified the following surveys that have been published in this field (Table 3):  
* [PERSON] [12] summarized the related works for spatial reuse in Wi-Fi 6;
* [PERSON] [13] focused on energy efficiency for low-power devices;
* [PERSON] [14] focused on scheduling and resource allocation;
* [PERSON] [15] presented a novel simulator for next-generation wireless networks and identified a few contributions to the field. According to Tables 2 and 3, each of these tutorials and surveys has only a few references in common with our paper. Therefore, our paper covers a large number of references that were not considered by other tutorial and review papers. Moreover, none of these surveys focus on modulation techniques and MU MIMO. Although OFDMA is \begin{table}
\begin{tabular}{c c c} \hline \hline
**Amendment** & **Year Released** & **Target** \\ \hline IEEE 802.11b & 1999 & Wi-Fi 1 \\ IEEE 802.11a & 1999 & Wi-Fi 2 \\ IEEE 802.11g & 2003 & Wi-Fi 3 \\ IEEE 802.11e & 2005 & QoS enhancements \\ IEEE 802.11n & 2009 & Wi-Fi 4 \\ IEEE 802.11 ac & 2013 & Wi-Fi 5 \\ IEEE 802.11 ah & 2017 & Low-power WLAN \\ Extended range \\ IEEE 802.11 ax & 2021 & Wi-Fi 6 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Wi-Fi amendments relevant to Wi-Fi 6.  
investigated in [14], our survey is more comprehensive with more than 70 references in this field. In addition, we explore other topics in more detail than the other surveys. The ambition of the current paper is a comprehensive survey of all the features of Wi-Fi 6. Its target and level of explanation focus on the networking aspect of the enhancements rather than on the signal processing field so it is of most interest to researchers in networking. In each section, it focuses on a specific feature of Wi-Fi 6 to survey the corresponding related works. Figure 1 visualizes the categorizations of the related works by feature and facilitates a fast lookup of the relevant references. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Paper** & **Date** & **References** & **Focus** & **\#Common References with Current Paper** \\ \hline [PERSON] [6] & 2016 & 15 & All features & 0 \\ [PERSON] [7] & 2016 & 12 & All features & 4 \\ [PERSON] [8] & 2017 & 9 & All features & 0 \\ [PERSON] [9] & 2018 & 117 & Resource allocation & 4 \\  & & & All features mainly: & \\ [PERSON] [11] & 2018 & 79 & random OFDMA and & 18 \\  & & & spatial reuse & \\ [PERSON] [10] & 2020 & 17 & MAC layer & 3 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Tutorials on Wi-Fi 6. The current paper is based on the official standard (May 2021), whereas earlier papers rely on, e.g., Draft 3.0 (2018) or Draft 4.0 (2019). Figure 1: The related works are categorized according to the features of Wi-Fi 6. The main contributions of this paper are the following:  
* It explains the main features of Wi-Fi 6 based on the latest released standard. Thereby, it describes the improvements and differences compared to earlier Wi-Fi standards. * It provides a comprehensive review of the related works exploiting the new features.