Physical Interference Modeling for Transmission Scheduling on Commodity WiFi Hardware

The demand for capacity in WiFi networks is driving a new look at transmission scheduling-based link layers. One basic issue here is the use of accurate interference models to drive transmission scheduling algorithms. However, experimental work in this space has been limited. In this work, we use commodity WiFi hardware (specifically, 802.11a) for a comprehensive study of interference modeling for transmission scheduling on a mesh network setup. We focus on the well-known physical interference model for its realism. We propose use of the "graded" version of the model where feasibility of a link is probabilistic, as opposed to using the more traditional "thresholded" version, where feasibility is binary. We show experimentally that the graded model is significantly more accurate (80 percentile error 0.2 vs. 0.55 for thresholded model). We develop transmission scheduling experiments using greedy scheduling algorithms for the evacuation model for both interference models. We also develop similar experiments for optimal scheduling performance for the simplified one-shot scheduling. The scheduling experiments demonstrate clearly superior performance for the graded model, often by a factor of 2. We conclude by promoting use of this model for scheduling studies.