User Cooperation in Heterogeneous Cellular Networks for Improved Spectral Efficiency

In this paper we propose user cooperation in Heterogenous cellular networks (HCNs) for combating intra-cell interference and improving downlink spectral efficiency (SE). The main idea we put forward is to employ interference cancellation at users associated to the small cell, when the macrocell transmits simultaneously with the small cell base station (causing intracell interference). This allows the decoding of the small cell transmission at several users. Then, in a subsequent time slot, a distributed space time code (DSTC) is used from these users in order to increase the reliability of the transmitted information to the final user. The proposed cooperative transmission scheme is compatible with state-of-the-art resource allocation mechanisms for HCNs. Our results indicate that as the user density is increased, this scheme can improve significantly the SE when compared to a non-cooperative system that does not exploit higher user densities, or a classic cooperative system that operates only during the interference-free time slots.