University of Paderborn
In this paper, the authors consider a heterogeneous two-tiered network where a tier of cognitive self-organizing small cells is deployed over the coverage area of a preexisting Orthogonal Frequency Division Multiple Access (OFDMA) macro cell. Neither cross-nor co-tier cooperation or communication is established, thus no joint signal processing techniques can be implemented by the Macro and Small Base Stations (MBS/SBS). They assume that each SBS disposes only of a perfect local Channel State Information (CSI) w.r.t. the interfering links towards the Macro and Small User Equipments (MUEs/SUEs) operating inside its coverage area. They design a novel cognitive Interference Alignment (IA) based scheme to protect the macro cell from the cross-tier interference, while mitigating the multi-user interference in the second tier.