Transmission scheme for wireless communication systems
A method of two-layer (Rank=2) demodulation reference signal (DMRS) based transmission scheme is proposed. The precoding matrix on a data RE can be represented as A×B. The precoding matrix on the UE-specific reference signal DMRS is A. Matrix B is the co-phasing cycling matrix. By applying the proposed co-phasing cycling matrix B for Rank=2 DMRS-based transmission scheme, the ratio of PDSCH EPRE to DMRS EPRE is equal to 0 dB, as required by the LTE specification. Further, when the DMRS power follows the precoding matrix A, UE channel estimation performance is improved.
1. A method comprising:
transmitting scheduling information from a serving base station to a user equipment (UE) for downlink transmission in a wireless communication network;
transmitting a UE-specific reference signal applied with a first precoding matrix, wherein the UE-specific resource signal is a demodulation reference signal (DMRS) configured for the UE and transmitted over predefined DMRS resource elements (REs); and
transmitting a data signal over data REs applied with a second precoding matrix, wherein the second precoding matrix can be represented by the first precoding matrix multiplied by a co-phasing cycling matrix, and wherein a ratio of an energy per resource element (EPRE) of data REs to an EPRE of the DMRS REs is 0 dB.
2. The method of claim 1 , wherein the scheduling information is carried by a physical downlink control channel (PDCCH).
3. The method of claim 1 , wherein the base station increases a transmit power of the DMRS REs through the first precoding matrix such that UE channel estimation performance is improved.
4. The method of claim 3 , wherein the first precoding matrix is defined in a codebook and scaled by a factor of 1/√{square root over (P)} and wherein P is defined as a number of ports for reference signals.
5. The method of claim 1 , wherein the co-phasing cycling matrix is predefined for each data RE based on a corresponding data RE index.
6. The method of claim 5 , wherein the co-phasing cycling matrix is a 2×2 matrix having co-phasing factor elements, and wherein the co-phasing cycling matrix is scaled by a factor of 1/√{square root over (2)}.
7. A method comprising:
receiving scheduling information from a serving base station by a user equipment (UE) for downlink transmission in a wireless communication network;
performing channel estimation by measuring a UE-specific reference signal applied with a first precoding matrix, wherein the UE-specific resource signal is a demodulation reference signal (DMRS) transmitted over predefined DMRS resource elements (REs);
decoding a data signal over data REs applied with a second precoding matrix, wherein the second precoding matrix can be represented by the first precoding matrix multiplied by a co-phasing cycling matrix; and
deriving the data signal by using the co-phasing cycling matrix, wherein a ratio of an energy per resource element (EPRE) of the data REs to an EPRE of the DMRS REs is 0 dB.
8. The method of claim 7 , wherein the scheduling information is carried by a physical downlink control channel (PDCCH).
9. The method of claim 7 , wherein the UE improves channel estimation performance when the DMRS is transmitted with an increased power through the first precoding matrix.
10. The method of claim 9 , wherein the first precoding matrix is defined in a codebook and scaled by a factor of 1/√{square root over (P)}, and wherein P is defined as a number of ports for reference signals.
11. The method of claim 7 , wherein the co-phasing cycling matrix is predefined for each data RE based on a corresponding data RE index.
12. The method of claim 11 , wherein the co-phasing cycling matrix is a two-by-two matrix having co-phasing factor elements, and wherein the co-phasing cycling matrix is scaled by a factor of 1/√{square root over (2)}.
13. The method of claim 7 , wherein the downlink transmission is a two-layer transmission with spatial multiplexing.
14. A User Equipment (UE) comprising:
a radio frequency (RF) receiver that receives scheduling information from a serving base station for downlink transmission in a wireless communication network;
a channel estimation circuit that performs channel estimation by measuring a UE-specific reference signal applied with a first precoding matrix, wherein the UE-specific resource signal is a demodulation reference signal (DMRS) transmitted over predefined DMRS resource elements (REs); and
a decoder that decodes a data signal over data REs applied with a second precoding matrix, wherein the second precoding matrix can be represented by the first precoding matrix multiplied by a co-phasing cycling matrix, and wherein the data signal is derived by using the co-phasing cycling matrix such that a ratio of an energy per resource element (EPRE) of the data REs to an EPRE of the DMRS REs is 0 dB.
15. The UE of claim 14 , wherein the scheduling information is carried by a physical downlink control channel (PDCCH).
16. The UE of claim 14 , wherein the UE improves channel estimation performance when the DMRS is transmitted with an increased power through the first precoding matrix.
17. The UE of claim 16 , wherein the first precoding matrix is defined in a codebook and scaled by a factor of 1/√{square root over (P)}, and wherein P is defined as a number of ports for reference signals.
18. The UE of claim 14 , wherein the co-phasing cycling matrix is predefined for each data RE based on a corresponding data RE index.
19. The UE of claim 18 , wherein the co-phasing cycling matrix is a two-by-two matrix having co-phasing factor elements, and wherein the co-phasing cycling matrix is scaled by a factor of 1/√{square root over (2)}.
20. The UE of claim 14 , wherein the downlink transmission is a two-layer transmission with spatial multiplexing.