Estimation of Near-Field Line-of-Sight Channels: A Multidimensional Polynomial Phase Approach

As the frequency and array apertures grow large, and the transmission range shrinks, the far-field assumption ceases to hold and, with that, the wavefront curvature is revealed over the arrays. This paper deals with the estimation of multiantenna channels in the line-of-sight conditions that are prevalent in the near field. By expressing the curved wavefronts as a polynomial via a power series expansion of a sphere, the estimation of the channel over the array can be formulated as a multidimensional polynomial phase estimation problem. The application of a newly developed polynomial phase estimator, able of handling arbitrary dimensions and polynomial degrees, yields an excellent tradeoff between channel estimation accuracy and complexity.