A method for transmitting reference signals for eight antenna ports at a base station, the method comprising: transmitting common reference signals, CRSs, for one or two of the eight antenna ports in a downlink subframe including a first slot and a second slot and having a normal cyclic prefix, CP, wherein the downlink subframe has 14 orthogonal frequency division multiplexing, OFDM, symbols and the OFDM symbols are indexed starting from 0; and transmitting channel state information-reference signals, CSI-RSs, for the eight antenna ports, the CSI-RSs being mapped to the downlink subframe according to a predetermined pattern, wherein, based on the downlink subframe having the normal CP, the predetermined pattern defines the CSI-RSs for the eight antenna ports to be mapped to only two OFDM symbols per subcarrier in a data region of the downlink subframe, the two OFDM symbols being separated by only one OFDM symbol, wherein, the eight antenna ports are grouped into a total of four antenna port groups each having two antenna ports using same subcarrier in a frequency domain, wherein the four antenna port groups are multiplexed at different subcarrier locations using a frequency division multiplexing, FDM, scheme, and the CSI-RSs of each of the four antenna port groups are code division multiplexed using orthogonal codes in a time domain of the same subcarrier, wherein for each antenna port which is used for a CSI-RS that is mapped to one of the two OFDM symbols, the each antenna port is also used for a CSI-RS that is mapped to another of the two OFDM symbols at the same subcarrier, and wherein the two OFDM symbols are located at second and fourth OFDM symbol positions of the second slot in the downlink subframe not to overlap with OFDM symbols which the CRSs are located. transmitting common reference signals, CRSs, for one or two of the eight antenna ports in a downlink subframe including a first slot and a second slot and having a normal cyclic prefix, CP, wherein the downlink subframe has 14 orthogonal frequency division multiplexing, OFDM, symbols and the OFDM symbols are indexed starting from 0; and transmitting channel state information-reference signals, CSI-RSs, for the eight antenna ports, the CSI-RSs being mapped to the downlink subframe according to a predetermined pattern, wherein, based on the downlink subframe having the normal CP, the predetermined pattern defines the CSI-RSs for the eight antenna ports to be mapped to only two OFDM symbols per subcarrier in a data region of the downlink subframe, the two OFDM symbols being separated by only one OFDM symbol, wherein, the eight antenna ports are grouped into a total of four antenna port groups each having two antenna ports using same subcarrier in a frequency domain, wherein the four antenna port groups are multiplexed at different subcarrier locations using a frequency division multiplexing, FDM, scheme, and the CSI-RSs of each of the four antenna port groups are code division multiplexed using orthogonal codes in a time domain of the same subcarrier, wherein for each antenna port which is used for a CSI-RS that is mapped to one of the two OFDM symbols, the each antenna port is also used for a CSI-RS that is mapped to another of the two OFDM symbols at the same subcarrier, and wherein the two OFDM symbols are located at second and fourth OFDM symbol positions of the second slot in the downlink subframe not to overlap with OFDM symbols which the CRSs are located. <EOS>