to collect and aggregate measurements at APs rather than wireless clients. A global view of wireless signals observed across infrastructure APs can be used to infer aggregate performance metrics like number of active wireless clients, interference, loss rates, and utilization [7], [8] and even infer missing packets [9]. These approaches are only able to account for received wireless signals. This does not include failed transmissions that are not overhead or events that lead to particular wireless client handoff decisions, and thus are orthogonal to our work.