DoF Maximization in Heterogeneous Networks Using BIA Under Limited Coherence Time

Abstract

This paper considers downlink (DL) heterogenous networks where macrocells with one user in each cause interference on femtocells (FCs). In each FC, blind interference alignment (BIA) is applied which requires that the channel does not change during one super-symbol. Therefore, coherence time is important to determine whether BIA can be used in an FC. This paper presents a general framework to maximize the achievable degrees of freedom of FCs under limited coherence time by selecting FC configurations via Pareto optimization, where configuration denotes the number of users and antennas in FCs. After FC configurations are determined, we propose a novel technique where interference from macrocell base stations on all femtocell users is aligned at each time slot on predetermined interference dimension set by BIA. It is shown that the proposed scheme can achieve more degrees of freedom in lesser coherence time than the existing schemes.