Outdoor Long-Range WLANs: A Lesson for IEEE 802.11ah

Several service applications have been reported by many who proposed the use of wireless LANs (WLANs) over a wide variety of outdoor deployments. In particular, the upcoming IEEE 802.11ah WLAN protocol will enable a longer transmission range between WLAN access points (APs) and stations (STAs) up to multiple kilometers using carrier frequencies at 900 MHz. However, limitations of WLAN outdoor installations have been found of the plethora of WLAN protocols in experimental studies. This article summarizes the challenges and provides a comprehensive overview of suggested improvements. As the standardization of the IEEE 802.11ah is reaching its final stage, important protocol aspects as well as new features are to be outlined. Interference problems and issues with the WLAN configuration, the physical layer (PHY), and media access control (MAC) are of paramount importance in outdoor WLAN networks, and thus, are discussed in detail. Further, we examine the reported upper boundaries in throughput and link reliability of long-range WLANs in different environments, including sea-surfaces, unmanned aerial vehicles (UAVs), and tunnels. At the end of this study, we reflect on the major issues regarding sub-1 GHz (S1G) WLANs and propose avenues for further research.