Inter-Cell Interference Coordination for Control Channels in LTE Heterogeneous Networks

In heterogeneous cellular networks for mobile communications, small cells are deployed within the coverage range of primary macro cells to provide for a localized capacity boost in traffic hotspots. The sharing of communication channels among the small-cell and macro-cell tiers is spectrally efficient, but causes failures of control signaling and data channels due to unmitigated co-channel interference. Consequently, the small-cell coverage range and capacity deteriorate. In Long Term Evolution (LTE) networks, the performance of control channels such as the physical downlink control channels (PDCCH) is of particular concern because they are protected only by simple interference averaging based on pseudo-random subcarrier allocation. Observing that the randomization algorithms are primarily seeded by the the physical cell identifiers (PCIs) and cell radio network temporary identifier (C-RNTIs), we show that optimized allocation of PCIs, C-RNTIs and PDCCH resources enable efficient interference-aware scheduling of control transmissions, as known from the LTE data plane. Simulations of a 3GPP-compliant HetNet in a Dublin scenario show that the small-cell size can be doubled for a better macro-cell traffic offload by trading the number of active PDCCHs for a higher small-cell expansion bias. Alternatively, the small-cell PDCCH capacity can be tripled for high-load applications such as Voice over LTE by using macro-cell PDCCH muting.