Characterizing spatial correlation in indoor channels

The spatial correlation features of channel impulse responses for an indoor environment are presented. The wide-hand impulse responses of a rectangular enclosure are calculated using the method of images. Bandpass representations of the non line-of-sight multipath responses are obtained for 2.4 GHz ISM band and their spatial cross correlation estimated for various positions of the transmitter and receiver arrays. The receiver and transmitter correlations are shown to exhibit periodic features and a spatial dependence in the decay rate. The correlation minima decreases with transmitter-receiver (T-R) separation and peak-to-peak correlation amplitude exhibits larger values when the transmitter and receivers are positioned close to the corners of the room. The oscillatory features in the spatial correlation may be attributed to the distribution of multipath clusters in time. For certain configurations of the T-R arrays the clusters are well separated resulting in a slower rate of oscillation at the inter-cluster time scale. In the short or intra-cluster time-scale, the correlation can exhibit a slow decay rate. At the corners, these clusters appear at faster rate and individual clusters are of a shorter duration. This feature leads to a faster and more structured oscillation in the correlation features. These observations are important considerations in design and evaluation of the performance of multiple-output multiple-input wireless communications systems.