C-RNTI Management for Orthogonally-Filled Subframes 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 is reduced. In LTE networks, the performance of some control channels (namely, PDCCH) is of particular concern because the LTE standard does not allow interference coordination in those, but only allows for interference averaging based on pseudo-random subcarrier allocation. Observing that the randomization algorithms are primarily seeded by the UE cell identifiers (the so-called C-RNTI), we show that simple C-RNTI optimization and selective scheduling can be used to enable efficient frequency-selective interference-aware scheduling also in these control channels. If combined with our previously formulated concept of orthogonally-filled subframes [1], the control channel reliability and capacity can be significantly improved, especially under high cell-selection biases.