Estimation of Ultra Wide Band Channel Degrees of Freedom

Multipath propagation effects encountered in mobile wireless channels provide additional degrees of freedom [Ganesan et al., 2000] that can be exploited via appropriate signaling and reception. In this work, based on a set of measurements conducted at Eurecom, we consider a novel approach of analyzing an Ultra Wide Band (UWB) indoor radio propagation channel by performing an eigen-decomposition and observing the scaling of the number of significant eigenvalues with the channel bandwidth by using the Akaike information criterion (AIC) and Minimum Description Length (MDL). These criterion are applied to estimate the number of degrees of freedom (DoF) of an UWB in an indoor environment. We evaluate our approach under both scenarios, line-of-sight (LOS) and non-line-of-sight (NLOS). Based on AIC and the MDL criterion, we find that this number is large; this has important consequences on the receiver design. We show also, that in opposition to the accepted idea in the literature, the number of Degrees of Freedom (DoF) does not increase linearly with the channel bandwidth. Hence, the results of the estimation of UWB channel entropy confirm that the number of DoF increases sub-linearly with the channel bandwidth.