ROBUST PRECODING FOR MULTIUSER MISO SYSTEMS WITH LIMITED-FEEDBACK CHANNELS

Abstract—In this paper we focus on Multi User Multiple Input Single Output (MU-MISO) systems where one centralized transmitter with multiple antennas serves several decentralized single-antenna receivers. Precoding is an attractive way to combat multiuser interferences because it reduces cost and power consumption in the user equipment. When implementing precoding, however, the Channel State Information (CSI) should be available at the base station. In Frequency Division Duplex (FDD) systems, the CSI is sent from the receivers by means of a feedback channel whose data rate is often severely limited. Thus, CSI is imperfect because it is affected by the errors caused by channel estimation, feedback delay, truncation, and quantization of the Karhunen-Loève coefficients. In this paper, we explain how to model these errors which is the basic premise to design both robust linear precoding and robust Tomlinson Harashima precoding, whose performance will be compared. I