When are directional antennas useful in indoor environments

Directional antenna systems can provide two benefits 1) improve signal strength and increase communication range, and 2) improve spatial reuse. Recent work has drawn contradicting conclusions in terms of which of the two benefits dominates in indoor environments. These contradicting conclusions are in fact caused by different levels of contention within the environments used in these studies, i.e., noise-dominated vs. interference-dominated. In this paper, we first show that due to emerging applications and technologies, wireless networks are becoming interference-dominated, and thus the ability of the directional antennas to improve spatial reuse is becoming critical. Evaluating the benefits of spatial reuse, however, is difficult especially in indoor environments where multipath have both good and bad effect on spatial reuse. In this paper, we use the separation metric to estimate the effectiveness of directional transmission and guide the placement of directional APs in any particular environment. The separation metric summarizes both the angular and the distance separation for a collection of transmissions in a particular environment. We show that this metric, though simple, is powerful enough to capture the various properties of the deployment and the potential interactions among the directional transmissions. Our experimental results show in several scenarios that the separation metric works well in practice.