Optimum Reference Signal Structure for MIMO Multiplexing using Precoding in Evolved UTRA Downlink

This paper presents the optimum reference signal (RS) structure for channel estimation in MIMO multiplexing using precoding for OFDMA radio access in the Evolved UTRA downlink. In the evaluations, we compare common RSs and dedicated RSs from the viewpoint of the achievable throughput taking into account the overhead such as that for the respective RSs and Layer 1 (L1)/Layer 2 (L2) control signals related to precoding matrix information (PMI). Based on extensive simulations on the throughput in 2-by-2 and 4-by-4 MIMO multiplexing employing precoding, we conclude that channel estimation based on common RSs with L1/L2 control signaling of PMI achieves higher throughput compared to that using dedicated RSs when the number of available precoding matrices, i.e., the codebook size, is less than 16, which corresponds to a resolution of four bits.