Rank-Independent Codebook Design from a Quaternary Alphabet

Single-user as well as multi-user MIMO systems employ codebook-based feedback to customize the signal transmission to the current channel conditions. The two competing metrics for evaluating a codebook are packet-error-rate/throughput performance and codebook search complexity at the mobile. To address this issue structured unitary codebooks are proposed where each codebook entry is restricted to a power of i and a single codebook is optimized for all ranks. Such codebooks are shown to perform favorably with the best known (unconstrained) codebooks in terms of distance measures and are also shown to perform well in multi-user MIMO link-level simulations.