Codebook Design Strategies for Mmo-ofdm Downlink Systems with Zf-bf

Using the Channel State Information (CSI) at the transmitter is fundamental for the precoder design in Multi-user Multiple Input Single Output (MU-MISO-OFDM) systems. In Frequency Division Duplex (FDD) systems, CSI can be just available at the transmitter through a limited feedback channel [1], where we assume that each user quantizes its channel direction with a finite number of quantization bits. In this paper, we consider a scalar quantization (SQ) scheme of the Channel Direction Information (CDI). Although vector quantization (VQ) schemes [2], [3] still outperform this scalar scheme in terms of quantization error and Sum rate, the former scheme suffers from an exponential search complexity and high storage requirements at the receiver for high number of feedback bits.