According to the present disclosure, behaviors of a Base Station (BS) and a User Equipment (UE) pertinent to Reference Signal (RS) transmissions are discussed. BS may configure RS corresponding to a set of antenna ports in two or more groups of Orthogonal Frequency Division Multiplexing (OFDM) symbols on a short Physical Downlink Sharing CHannel (sPDSCH), where subcarrier indices used for RS transmission are different between at least two groups of OFDM symbols. Then, BS may transmit the RS to UE. UE will receive RS and perform channel estimation based on the received RS.