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Abstract

The present invention proposes a hybrid spatial multiplexing (SM) and a space division multiple access (SDMA) technique in a frequency division duplex (FDD) massive multiple-input multiple output (MIMO) system using a two-dimensional planar array antenna, which effectively transmits a channel state information reference signal (CSI-RS) for estimating a downlink two-dimensional space channel using only a limited amount of downlink radio resources, and optimally selects and performs the SM and SDMA techniques in a two-dimensional space channel. To this end, the present invention proposes a technique which defines space resource blocks (SRB) by grouping space elements (SE) having a high spatial correlation between downlink channels in the horizontal dimension and corresponding SEs thereof in the vertical dimension, and transmits CSI-RSs for estimating channels in vertical dimension SEs corresponding to one selected horizontal SE in each SRB every transmit time interval (TTI). The present invention proposes a technique wherein user equipment (UE) estimates the spatial correlation between channels of different horizontal dimension SEs belonging to the same SRB received in different TTIs and the spatial correlation between channels of horizontal dimension SEs belonging to different SRBs received in the same TTI, and feeds information for changing the size of SRB of the corresponding UE to an optimal size back to eNodeB. The present invention proposes a technique wherein the UE estimates downlink channels through CSI-RSs transmitted from each SRB, and each UE feeds an index of a preferred SRB, a rank of the corresponding SRB in the vertical dimension, and channel quality information (CQI) back to eNodeB. When each UE determines the rank, it is possible to transmit the ranks to the fullest extent in the vertical dimension and only a single rank from each SRB in the horizontal dimension.

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