Near-Field Signal Model for Large-Scale Uniform Circular Array and Its Experimental Validation

The usually considered far-field assumption may not hold anymore, as the array aperture increases to a certain extent with respect to the near-field outer boundary (NFB), i.e., R_NFB = 2D²/λ, with D being the array aperture and λ the wavelength. Under this circumstance, estimating channel parameters with the plane-wave model may result in severe error. In this letter, a near-field signal model was proposed for the uniform circular array to avoid the plane-wave model mismatch during channel estimation at its near-field region. The ability of the underlying model to estimate path parameters was investigated with its ambiguity function. Moreover, a distance threshold dependent on the conventional NFB was proposed, and for the cases where the sources or the scatterers are located outside the proposed distance threshold, the plane-wave model could still be used with little estimation error.