  The paper studies the suppression of cross-tier inter-cell interference (ICI)
generated by a macro base station (MBS) to pico user equipments (PUEs) in
heterogeneous networks (HetNets). Different from existing ICI avoidance schemes
such as enhanced ICI cancellation (eICIC) and coordinated beamforming, which
generally operate at the MBS, we propose a full duplex (FD) assisted ICI
cancellation (fICIC) scheme, which can operate at each pico BS (PBS)
individually and is transparent to the MBS. The basic idea of the fICIC is to
apply FD technique at the PBS such that the PBS can send the desired signals
and forward the listened cross-tier ICI simultaneously to PUEs. We first
consider the narrowband single-user case, where the MBS serves a single macro
UE and each PBS serves a single PUE. We obtain the closed-form solution of the
optimal fICIC scheme, and analyze its asymptotical performance in ICI-dominated
scenario. We then investigate the general narrowband multi-user case, where
both MBS and PBSs serve multiple UEs. We devise a low-complexity algorithm to
optimize the fICIC aimed at maximizing the downlink sum rate of the PUEs
subject to user fairness constraint. Finally, the generalization of the fICIC
to wideband systems is investigated. Simulations validate the analytical
results and demonstrate the advantages of the fICIC on mitigating cross-tier
ICI.
