Online Estimation of RF Interference

Nabeel Ahmed, Usman Ismail, Srinivasan Keshav and Konstantina Papagiannaki

In enterprise networks in which the thin access points are managed by a single controller, there is much room for optimization. As a example, interference between access points can be prevented if a conflict graph is available.

The authors implement a novel mechanism to build such conflict graph. Instead of using lengthy bandwidth probes, they introduce the concept of microprobes. The idea is to attempt transmission from two access points simultaneously. If one of the access points hold the transmission until the other has finished, it means that the two access points are in carrier-sense range, which is quite common in enterprise networks.

The lack of ack may indicate that the APs are hidden from one another, and the simultaneous transmission prevented the receiver to correctly decode the packet.

The implementation of the idea poses a variety of challenges. The APs have to be sychronized, and the delay ellapsing from the controller order to the actual probe has to be minimized. Further, the network has to be silenced before the probe. Then it is necessary to accurately measure the MAC service time. The authors solved all the problems and attained an accuracy comparable to the one obtained from traditional bandwidth probes.

The advantage of the microprobes is that they can be performed in a few ms, which allows to build the conflict graph during the network normal operation (no downtime required).

I am particularly interested in the possibility to tinker with the wlan card microcode, since it would allow me to build a testbed of my idea.