Link Setup Time Reduction by FILS on IEEE 802.11-Based Inter-Vehicular Communications

This paper reports the performance of link setup time reduction outlined by IEEE 802.11ai, which is also known as Fast Initial Link Setup (FILS), in real intermittent inter-vehicular communications. Fast link establishment is a significant concern in communications between mobile devices with high mobility, such as passing vehicles on roads, because short link setup times enable vehicles to transfer larger amounts of application data. However, secure links are also important because they prevent both unauthorized access by unauthenticated users and misinformation circulation by malicious persons. Conventional security protocols such as IEEE 1609.2 and IEEE 802.11i/IEEE 802.1X, which is also known as the Wi-Fi Protected Access 2 Extensible Authentication Protocol (WPA2-EAP), archive user authentication in vehicular networks but often take several seconds to establish a secure link due to numerous frame exchanges. In contrast, FILS is designed to establish a secure WPA2-EAP link in 100 ms using cached authentication information. However, since the effectiveness of FILS in real vehicular networks has not yet been reported, this paper describes experiments that clarify its setup time reduction abilities in 2.4GHz IEEE802.11n-based inter-vehicular communications by measuring the initial link setup times between two passing vehicles in a real environment. The results show that FILS significantly reduces the initial link setup times between the passing vehicles to around 150ms and increases the size of application data transferred between vehicles. Additionally, it is demonstrated that FILS always establishes a secure link, while Protected EAP (PEAP) sometimes fails. Finally, in communications between vehicles passing each other at the relative speed of 80km/h, we confirm that the FILS link setup time reduction effectively increases transferrable application data sizes by 10MB compared with WPA2-PEAP.