Method and apparatus for transmitting reference signal in time division duplex system

1. A method of transmitting a reference signal in a time division duplex (TDD) system, the method comprising:

generating a plurality of demodulation reference signals (DMRSs) for respective layers;

mapping the plurality of DMRSs to a downlink pilot time slot (DwPTS) region for downlink transmission within a special subframe; and

transmitting the plurality of DMRSs through a plurality of antennas,

wherein the special subframe is a subframe for separating uplink and downlink between an uplink (UL) subframe and a downlink (DL) subframe within a frame,

wherein the DwPTS region occupies only 10 to 12 orthogonal frequency division multiplexing (OFDM) symbols for the special subframe having a normal cyclic prefix (CP) structure according to the configuration of the special subframe and only 9 or 10 OFDM symbols for the special subframe having an extended CP structure according to the configuration of the special subframe in order to use both a code division multiplexing-time (CDM-T) method and a code division multiplexing-frequency (CDM-F) method based on the plurality of DMRSs, and

wherein the DwPTS region occupies only 9 orthogonal frequency division multiplexing (OFDM) symbols for the special subframe having a normal cyclic prefix (CP) structure according to the configuration of the special subframe and only 8 OFDM symbols for the special subframe having an extended CP structure according to the configuration of the special subframe in order to use only the CDM-T method based on the plurality of DMRSs.

2. The method of claim 1 , wherein the number of layers is 2 or 4.

3. The method of claim 1 , wherein the plurality of mapped DMRSs is multiplexed in accordance with a code division multiplexing (CDM) method using an orthogonal sequence.

4. The method of claim 3 , wherein the orthogonal sequence includes one of a Walsh code, discrete Fourier transform (DFT) coefficients, and a constant amplitude zero auto-correlation (CAZAC).

5. The method of claim 3 , wherein a length of the orthogonal sequence is 2 or 4.

6. The method of claim 1 , wherein some or all of the plurality of DMRSs for the respective layers are mapped to neighbor OFDM symbols within an identical subcarrier.

7. The method of claim 1 , wherein some or all of the plurality of DMRSs for the respective layers are mapped to neighbor subcarriers within an identical OFDM symbol.

8. The method of claim 1 , wherein each of the DMRSs is mapped at a certain subcarrier interval.

9. An apparatus for transmitting a reference signal in a time division duplex (TDD) system, the apparatus comprising:

a radio frequency (RF) unit; and

a processor, coupled to the RF unit, and configured to:

generate a plurality of demodulation reference signals (DMRSs) for respective layers,

map the plurality of DMRSs to a downlink pilot time slot (DwPTS) region for downlink transmission within a special subframe, and

transmit the plurality of DMRSs through a plurality of antennas,

wherein the special subframe is a subframe for separating uplink and downlink between an UL subframe and a DL subframe within a frame,

wherein the DwPTS region occupies only 10 to 12 orthogonal frequency division multiplexing (OFDM) symbols for the special subframe having a normal cyclic prefix (CP) structure according to the configuration of the special subframe and only 9 or 10 OFDM symbols for the special subframe having an extended CP structure according to the configuration of the special subframe in order to use both a code division multiplexing-time (CDM-T) method and a code division multiplexing-frequency (CDM-F) method based on the plurality of DMRSs, and

wherein the DwPTS region occupies only 9 orthogonal frequency division multiplexing (OFDM) symbols for the special subframe having a normal cyclic prefix (CP) structure according to the configuration of the special subframe and only 8 OFDM symbols for the special subframe having an extended CP structure according to the configuration of the special subframe in order to use only the CDM-T method based on the plurality of DMRSs.

10. The apparatus of claim 9 , wherein the number of layers is 2 or 4.

11. The apparatus of claim 9 , wherein the plurality of mapped DMRSs is multiplexed in accordance with a code division multiplexing (CDM) method using an orthogonal sequence.

12. The apparatus of claim 9 , wherein some or all of the plurality of DMRSs for the respective layers are mapped to neighbor OFDM symbols within an identical subcarrier.

13. The apparatus of claim 9 , wherein some or all of the plurality of DMRSs for the respective layers are mapped to neighbor subcarriers within an identical OFDM symbol.