Measuring channel occupancy for 802.11 wireless LAN in the 2.4 GHz ISM band.

In this paper we focus on measuring channel occupancy in the 2.4 GHz ISM band in a way that transmissions from Wireless LAN stations and other spectrum users can be distinguished. Most current 802.11 hardware does not offer methods to capture channel occupancy caused by non-802.11 transmissions accurately. We therefore combine a commodity 802.11 Wireless LAN card with an inexpensive 2.4 GHz RF transceiver IC which we use for spectrum measurements. We build a probabilistic model which allows to calculate the overall channel occupancy and to determine the fractions of 802.11 and non-802.11 activity. Our model covers adjacent channel interference, detects both narrow-band and wide-band interferers, and adapts to different signal strengths. We evaluate our approach in a test bed with controlled interference, estimate the achievable precision, and identify open problems.