  Dealing with massively crowded scenarios is one of the most ambitious goals
of next-generation wireless networks. With this goal in mind, the IEEE 802.11ax
amendment includes, among other techniques, the Spatial Reuse (SR) operation.
The SR operation encompasses a set of unprecedented techniques {that are
expected to significantly boost Wireless Local Area Networks (WLANs)
performance in dense environments}. In particular, the main objective of the SR
operation is to maximize the utilization of the medium by increasing the number
of parallel transmissions. Nevertheless, due to the novelty of the operation,
its performance gains remain largely unknown. In this paper, we first provide a
gentle tutorial of the SR operation included in the IEEE 802.11ax. Then, we
analytically model SR and delve into the new kinds of MAC-level interactions
among network devices. Finally, we provide a simulation-driven analysis to
showcase the potential of SR in various deployments, comprising different
network densities and traffic loads. Our results show that the SR operation can
significantly improve the medium utilization, especially in scenarios under
high interference conditions. Moreover, our results demonstrate the
non-intrusive design characteristic of SR, which allows enhancing the number of
simultaneous transmissions with a low impact on the environment. We conclude
the paper by giving some thoughts on the main challenges and limitations of the
IEEE 802.11ax SR operation, including research gaps and future directions.
