Patent ID: 8885739

Claim:
A transmitter for transmitting reference signals in a wireless communication system, the transmitter comprising: a Channel State Information (CSI) reference signal (CSI-RS) generator configured to generate CSI-RSs for each of a plurality of antennas; a CSI-RS mapper configured to map the CSI-RSs to a resource region based on a CSI-RS pattern corresponding to a number of the plurality of antennas, the number of the plurality of antennas being eight, wherein the eight transmit antennas include two legacy antennas that can be used for Cell-specific Reference Signals (CRSs) and six additional antennas that can be used for the CSI-RSs with low density, wherein the CSI-RSs with low density for the six additional antennas are transmitted every subframe irrespective of a number of layers used for the CSI-RSs transmission, wherein the resource region is assigned to a subframe having two slots, wherein, if the two legacy antennas are used for the CRSs and the six additional antennas are used for the CSI-RSs and if the subframe has a normal Cyclic Prefix (CP), each slot of the subframe comprises 7 Orthogonal Frequency Division Multiplexing (OFDM) symbols and the CSI-RSs mapped at the resource region are at both an eleventh OFDM symbol and a last OFDM symbol of the subframe, wherein the eleventh OFDM symbol is calculated by an equation of (2N symbol −3) th , where the N symbol for the normal CP is seven, wherein, if the two legacy antennas are used for the CRSs and the six additional antennas are used for the CSI-RSs and if the subframe has an extended CP, each slot of the subframe comprises 6 OFDM symbols and the CSI-RSs mapped at the resource region are at both a ninth OFDM symbol and a last OFDM symbol of the subframe, and wherein the ninth OFDM symbol is calculated by the equation of (2N symbol −3) th , where the N symbol for the extended CP is six; and transmit circuitry configured to transmit a radio signal and the CSI-RSs, wherein the CSI-RS generator further generates additional CSI-RSs for tracking a time-varying channel for at least one of the antennas, wherein the additional CSI-RSs are configured by a signaling from a higher layer, and wherein the additional CSI-RSs are transmitted in both a subframe in which the CSI-RSs for said additional antennas are transmitted and a subframe in which the CSI-RSs for said additional antennas are not transmitted.