SLNR Based Coordinated Multicell Beamforming in an Uplink-Downlink Configuration of Cellular Networks

Consider an Uplink-Downlink configuration of a two-cell dynamic time division duplexing (TDD) cellular network, in which simultaneously we have downlink transmission in one cell and uplink transmission in the other cell. We assume that both the base stations (BSs) and the user terminals (UTs) are multiple-input-multiple-output (MIMO). In this paper, we state the signal-to-leakage-and-noise-ratio (SLNR) for the UTs in the uplink cell, considering the intercell leakage and for the UTs in the downlink cell considering both the intercell and intracell leakages. Then we formulate a multi-objective optimization problem to maximize all these SLNRs and find the coordinated beamformers for the BS in the first cell and the UTs in the second cell. In addition, we perform a similar approach based on the modified SLNR (mSLNR), in which the leakages are evaluated after the receive filters. Simulation results show that the proposed coordinated beamforming approaches outperform the local SLNR approach in terms of the average sum rate. Moreover, we compare our proposed beamforming schemes with the case that only the downlink BS uses the coordinated beamformers; simulation results show that the proposed SLNR beamforming scheme improves the downlink sum rate and the mSLNR beamforming approach improves both the downlink and uplink sum rates.