Orthogonally-filled subframes for optimum operation of co-channel LTE HetNets

In heterogeneous cellular networks (HetNets) for mobile communications, small cells (SC) are deployed within the coverage range of primary macro cells (MC) to provide for a localized capacity boost in traffic hotspots. Focusing on LTE systems and co-channel SC deployments reusing the communication channels of the hosting MCs, we show that the performance of the LTE control signaling - the main performance bottleneck under inter-tier interference due to an inflexible and interference-unaware resource allocation - can be significantly improved by optimizing the seeds of the standardized pseudo-random mapping algorithms - the physical cell identity (PCI) and user radio network temporary identifier (RNTI). As a generalized result, we propose the standard-compliant concept of orthogonally-filled subframes (OFS) that employs power-control/blanking of UE-specific (PDCCH) channels to ensure co-existence in LTE HetNets. Simulations of a 3GPP-compliant HetNet deployed in Dublin show that compared to the standardized subframe-blanking approaches, configuring OFSs allows (i) extending the SC coverage range up to 3-times, i.e. to offload better the MC traffic, and/or (ii) increasing the control-channel capacity up to 8-times, e.g. to enable high-load voice-over-LTE applications.