Long-Term Channel Information-Based CoMP Beamforming in LTE-Advanced Systems

Coordinated multi-point (CoMP) transmission and reception is a network multiple-input multiple- output (MIMO) technology considered in 3GPP LTE- Advanced systems. In order to improve reliability and capacity of the services for the user equipments (UEs) at the cell edges, CoMP utilizes cooperation among neighboring enhanced node Bs (eNBs). Accordingly, backhaul delay for sharing control signals among eNBs should be carefully handled as UE mobility increases in a fading channel environment; otherwise, CoMP operations derived from inaccurate channel state information (CSI) of neighboring eNBs can severely degrade the system performance. We propose CoMP beamforming schemes using long-term CSI such as spatial correlation matrices instead of instantaneous CSI of neighboring cells. Since long- term CSI varies relatively slowly, the proposed scheme is inherently robust even when a UE moves at a high speed and/or the backhaul delay is large. Using a multi-cell simulator which reflects realistic CoMP system environments, the performance gain of the proposed schemes is evaluated and discussed.