Eigen analysis of wide-band fading channel impulse responses

An investigation of the complex path gain correlation properties of several types of wide-band channel impulse responses is presented. The correlation coefficients of the complex path gains of the channel's impulse responses exhibit a large range of values even for large path delay differences. This indicates that the autocorrelation matrix of the channel impulse responses is rarely diagonal, as often assumed in the study of frequency-selective fading channels. Also, using an eigendecomposition and subspace-based statistical signal processing on the autocorrelation matrix of the channel impulse responses, it is then shown that the propagation process is dominated by only a few orthogonal modes in many instances of channel propagation. The eigenvalues of the modes can be used as a measure of the actual diversity gain obtainable over the channels. From the receiver point of view, the dominant modes can be identified and used in the detection process to reduce the number of parameters to track. Among the channels studied, the wide-band conventional cellular and microcellular radio channels at 910 MHz for mobile applications and the wide-band indoor channels with fixed transmitter-receiver configurations at 950 MHz and 40 GHz are particularly important for today's and future applications. Several channel impulse response measurements have been analyzed to demonstrate these assertions.