Overhead and spectral efficiency of pilot-assisted interference alignment in time-selective fading channels

Abstract

The spectral efficiency achievable by IA (interfer-/nence alignment) in a/nK/n-user MIMO (multiple-input multiple-/noutput) interference channel is studied in the face of time-/nselective continuous fading explicitly estimated through pilot-/nsymbol observations. The robustness of IA in such operationally/nrelevant conditions is assessed through a joint optimization/nof the pilot overhead and the IA update interval, which are/ncharacterized—in high-power conditions—as solutions of a fixed-/npoint equation. Variations of the formulation are given for/nboth FDD (frequency-division duplexing) and TDD (time-division/nduplexing), the former requiring explicit feedback of the fading/nestimates and the latter relying on fading reciprocity. For the/nFDD variation, analog feedback is considered. In addition to/narbitrary numbers of users and antennas, and arbitrary tem-/nporal fading correlation functions, the derivations accommodate/nforward and reverse links with asymmetric power levels.