Variations in Wireless Indoor MIMO Channels

WLAN systems such as 802.11a/g are designed on the premise that the indoor channels, however frequency selective, vary slowly at Doppler frequencies of around 10Hz at most. In this paper we consider rapid channel variations on the order of 10 ms and less. We provide experimental evidence that the presence of fluorescent lamps creates an environment where reflections are being introduced and removed at twice the power line frequency (120 Hz in the US, 100 Hz in Europe). We propose a modification to an existing channel model that incorporates this phenomena. This change had been accepted into the IEEE 802.11n channel models. We then propose a super-resolution technique used to validate the proposed model on measured channels. We present capacity and instantaneous capacity examples measured in the 5 GHz band using a MIMO system. These capacities are also subject to the effect of fluorescent lamps. We present the results of an experiment, specifically designed to validate that the fast channel variations are caused by the existence of fluorescent lamps. We end up by using the proposed super-resolution analysis for separating the various reflections. This analysis clearly shows the validity of the proposed model.