Modeling of Line-of-Sight 2 × 2 MIMO Channels: Spherical Versus Plane Waves

We investigate the influence of exact spherical wave propagation modeling and approximate plane wave propagation modeling on the properties of a pure line-of-sight 2 times 2 multiple-input multiple-output channel. As transmission distance increases, the properties of the true spherical wave model converge to the properties given by the more simple plane wave model. We present a new model evaluation tool based on an analysis of the rank and singular values of the channel matrix, which can be employed to find the region where spherical wave modeling is necessary. The derivation results in new exact analytical expressions for which of the two models that should be applied, and the results based on mutual information show that the spherical wave model should be applied in many practical scenarios, e.g. indoor WLAN scenarios, where plane wave modeling is most frequently used today