If you can't Beat Them, Augment Them: Improving Local WiFi with Only Above-Driver Changes

The basic MAC mechanisms in IEEE 802.11 (WiFi) have remained largely unchanged for over 20 years. In this paper, we argue that the prevalence of WiFi makes it almost impossible to improve its performance through changes that require modifying hardware, firmware, or drivers. New applications, however, continue to exert novel performance demands. We suggest that changes should be developed as augmentation-only solutions through above-driver, kernel-level software modifications. An augmentation-only solution needs to maintain inter-operability and afford transparency in performance to existing WiFi devices, as well as enable minimum overhead upgradability. Our goal is to demonstrate the feasibility of MAC augmentation according to these principles. To this end, we leverage soft scheduling, where nodes are asked for a best-effort attempt to adhere to a given schedule. We allow the soft scheduler to coexist with and work at a different time scale from WiFi's Distributed Coordination Function (DCF); allowing it to reduce the time nodes spend contending for the medium while allowing DCF to handle only missed schedule slots and schedule divergence. We present a new Soft Token Passing Protocol (STPP) as an instance of this family of Soft Scheduling Protocols. We then show how STPP can be made part of a MAC protocol with specific performance improvement goals by developing the Wireless Low-Latency Local Links (WL4) system. We evaluate WL4 on a five node microbenchmark and quantify the system's overhead on network throughput and latency. We show that soft scheduling, via STPP, enables WL4 to adhere to our augmentation principles while improving the latency within the system.