Efficient Use of the Spectrum in Small Cell Deployments for 5G Wireless Communications Networks

Abstract

Paired frequency division duplexing (FDD) bands are traditionally adopted at macro cells (MeNBs) but they tend to show inefficient occupancy of the uplink (UL) band due to the asymmetric traffic conditions and prevalence of downlink (DL)-centric applications. To improve spectrum utilization, one possibility is to allow time division duplexing (TDD) small cells (SeNBs) to operate in the underutilized FDD-UL spectrum. However, under an opportunistic access, TDD
SeNBs might reuse the same resources as the FDD MeNB to receive in UL and, hence, strong interferences may appear. In this paper, we investigate advanced transmit coordination strategies to allow interference decoding and suppression at the MeNB such that the macro user signal can be decoded interference-free. We propose a novel technique to limit the maximum transmission rate of TDD SeNBs as a function of their distance to the MeNB in a way such that interference decoding and suppression is feasible. Simulation results show that sum-rate gains are obtained when the SeNB is close to the MeNB or when the SeNB transmits at high power (i.e. high interference conditions) as compared to a fully opportunistic access, while the proposed approach allows maintaining normal MeNB operation.