Distributed Antenna aided twin-layer femto-and macro-cell networks relying on fractional Frequency-Reuse

Distributed Antenna Systems (DAS) and femtocells are capable of improving the attainable performance in the cell-edge area and in indoor residential areas, respectively. In order to achieve a high spectral efficiency, both the Distributed Antenna Elements (DAEs) and Femtocell Base Stations (FBSs) may have to reuse the spectrum of the macrocellular network. As a result, the performance of both outdoor macrocell users and indoor femtocell users suffers from Co-Channel Interference (CCI). Hence in this paper, heterogenous cellular networks are investigated, where the DAS-aided macrocells and femtocells co-exist within the same area. The outage probability is derived and the network is optimised for minimising the outage probability. Our analysis demonstrates that surprisingly, the Unity Frequency Reuse (UFR) based macrocellular system can be optimised in isolation, without considering the impact of femtocells. We found that the macrocells relying on hard-FFR as well as on soft-FFR tend to migrate to several small cells, illuminated by the DAEs, when the density of femtocells becomes high.