# Improving Spatial Reuse of Wireless LAN Uplink Using BSS Color and Proximity Information
## 1 Introduction  
In recent years, WLANs have become an essential part of everyday life in most places. The density of users has grown at a fast rate, because most people use phones, pads, laptops, and other devices that connect to WLANs whenever available, mostly while indoors. The traffic demand of each user is also rapidly increasing due to applications such as video streaming, video conferencing, and automatic backup services. On the other hand, the density of WLAN APs has also increased in recent years. We can easily find tens of WLAN APs accessible from a single indoor location. The cost of WLAN APs has become cheap enough to equip many APs in a room in order to support users in a crowded place. However, deploying more APs does not translate into providing more bandwidth, because the available bandwidth is decided by the frequency spectrum, not the density of APs. To support the ever-increasing traffic demand, an efficient use of frequency resource is very important. The earlier versions of the IEEE 802.11 WLAN standard did not pay much attention to supporting dense scenarios due to natural reasons. The DCF (Distributed Coordination Function), which is the fundamental medium access control protocol of WLANs, suffers from significantly degraded performance in dense environments due to collisions and hidden/exposed terminal effects. In the latest and upcoming versions of the standard such as IEEE 802.11 ax and 802.11 be, efficient utilization of the medium is gaining much attention due to increased traffic demand and network density [1, 2]. The goal of efficient channel utilization is to maximize \"spatial reuse\", or number of parallel transmissions in a given area. IEEE 802.11 ax, the most recent WLAN standard, incorporates a feature called BSS coloring [3], as well as two spatial reuse methods called OBSS/PD and PSR (Parameterized Spatial Reuse) [4]. Although these mechanisms can help increase spatial reuse and thus improve the overall performance in dense environment, they have their limitations as discussed in the next section. In this paper, we propose a method called PSC-UL (Proximity-based Sensitivity Control for UL) which uses BSS color and proximity information to dynamically control the carrier sense threshold of the nodes. In addition to differentiating between intra- and inter-BSS communication, the idea of PSC-UL is to locate the position of OBSS AP using the BSS color. Furthermore, proximity information is used to predict the position of the transmitting STA. Using this information, a node receiving a preamble can estimate whether its transmission can take place in parallel to the ongoing transmission. This method leads to a more accurate decision compared to OBSS/PD and PSR, and thus can improve spatial reuse further. Simulation results show that the proposed method achieves increased UL throughput compared to existing methods such as OBSS/PD, both for STAs close to the APs as well as STAs in the edge of their BSSes. Packet delivery ratio is also improved, showing that the proximity information can be used to more accurately determine whether a node can successfully transmit a packet in parallel to the ongoing transmission. In the following are the contributions of this paper. * We show that the BSS color can be used to predict the location of other APs, which can be used to estimate the interference received by the other AP when the node transmits a packet. Furthermore, we introduce the \"proximity information\" that can be included in the preamble. This proximity information together with the BSS color can be used to determine whether a node receiving the preamble can start a parallel transmission or not. * We propose a new method called PSC-UL that uses the BSS color and proximity information to dynamically control carrier sense threshold of the STAs. The proposed method improves spatial reuse for UL communications.