Performance Analysis of a Hybrid Codebook for Downlink Relay Systems

In this paper, we propose a novel codebook for multiple-input multiple-output (MIMO) Rician fading channels. While the most conventional codebooks are designed in Rayleigh fading channels, we design a hybrid codebook which combines discrete Fourier transform matrix-based codebook for MIMO Rayleigh fading channels and array matrix-based codebook for MIMO line-of-sight channels. Especially, a backhaul link between base station and relay station can be a good target MIMO channels for the proposed codebook. Link-level simulations performed in a MIMO-OFDM system show that the proposed hybrid codebook outperforms the conventional codebooks when the K factor of Rician distribution is between 0.28 and 0.99. Moreover, the proposed codebook shows almost optimal link-level performances for MIMO Rayleigh fading channels.