Provided are a method of transmitting a dedicated reference signal (DRS), a method of receiving a DRS, and a feedback method of a terminal. The method of transmitting a DRS includes determining a DRS transmitting resource for at least one terminal which is a target of transmission, and transmitting the DRS using the determined transmission resource and notifying the terminal of information about layer used by the terminal. The method of receiving a DRS includes determining a DRS receiving resource, receiving information about layer used by a terminal from a serving cell base station, and receiving the DRS for the terminal using the determined reception resource and the information about layer. Accordingly, a terminal can find the position and sequence of its DRS. In particular, in the case of multi-user multiple input multiple output (MU-MIMO) or joint scheduling, it is possible to prevent or remove signal interference using the DRS of another terminal.
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0. 37. A communication method performed by a terminal, comprising:
receiving, from the base station, downlink control information (DCI), wherein the DCI includes first terminal-specific information;
receiving, from the base station, a reference signal; and
obtaining user data based on the reference signal, the first terminal-specific information and a physical layer cell identity (PCI) of a serving cell,
wherein the reference signal is a dedicated reference signal for the terminal.
0. 32. A communication device for a terminal, the communication device comprising:
a memory, and
a processor,
wherein the processor, when executing program instructions stored in the memory, is configured to:
cause the terminal to receive, from a base station, downlink control information (DCI), wherein the DCI includes first terminal-specific information;
cause the terminal to receive, from the base station, the reference signal; and
cause the terminal to obtain user data based on the reference signal, the first terminal-specific information and a physical layer cell identity (PCI) of a serving cell,
wherein the reference signal is a dedicated reference signal for the terminal.
0. 27. A terminal to receive a reference signal from a base station, the terminal comprising:
a memory, and
a processor operably coupled to one or more antennas to receive the reference signal,
wherein the processor, when executing program instructions stored in the memory, is configured to:
cause the terminal to receive, from the base station, downlink control information (DCI), wherein the DCI includes first terminal-specific information;
cause the terminal to receive, from the base station, the reference signal; and
cause the terminal to obtain user data based on the reference signal, the first terminal-specific information and a physical layer cell identity (PCI) of a serving cell,
wherein the reference signal is a dedicated reference signal for the terminal.
0. 1. A method for a base station to transmit a reference signal to a terminal, the method comprising:
transmitting, from the base station, a virtual terminal-specific information to the terminal;
generating a sequence for the reference signal for the terminal by using a physical cell identity (PCI) of a serving cell of the terminal and the virtual terminal-specific information; and
transmitting, from the base station, the reference signal using the sequence to the terminal,
wherein the virtual terminal-specific information is transmitted to the terminal by using downlink control information (DCI),
wherein the reference signal is a dedicated reference signal for the terminal.
0. 2. The method of
0. 3. The method of
0. 4. The method of
0. 5. The method of
0. 6. A method for a terminal to receive a reference signal from a base station, the method comprising:
receiving, from the base station, a virtual terminal-specific information from the base station;
generating a sequence for the reference signal for the terminal by using a physical cell identity (PCI) of a serving cell of the terminal and the virtual terminal-specific information; and
receiving, from the base station, the reference signal by using the sequence from the base station,
wherein the virtual terminal-specific information is received from the base station by using downlink control information (DCI),
wherein the reference signal is a dedicated reference signal for the terminal.
0. 7. The method of
0. 8. The method of
0. 9. The method of
0. 10. The method of
0. 11. A method for a base station to transmit a reference signal to a terminal, the method comprising:
transmitting, from the base station, a virtual cell-specific information and a virtual terminal-specific information to the terminal;
generating a sequence for the reference signal for the terminal by using the virtual cell-specific information and the virtual terminal-specific information; and
transmitting, from the base station, the reference signal using the sequence to the terminal,
wherein the virtual cell-specific information is transmitted to the terminal by using downlink control information (DCI),
wherein the reference signal is a dedicated reference signal for the terminal.
0. 12. The method of
0. 13. The method of
0. 14. The method of
0. 15. The method of
0. 16. The method of
0. 17. The method of
the virtual cell-specific information is identical to or different from a physical cell identity (PCI) of a serving cell of the terminal and
the virtual terminal-specific information is different from a radio network temporary identifier (RNTI) of the terminal.
0. 18. The method of
0. 19. A method for a terminal to receive a reference signal from a base station, the method comprising:
receiving, from the base station, a virtual cell-specific information and a virtual terminal-specific information from the base station;
generating a sequence for the reference signal for the terminal by using the virtual cell-specific information and the virtual terminal-specific information; and
receiving, from the base station, the reference signal by using the sequence from the base station,
wherein the virtual cell-specific information is received from the base station by using downlink control information (DCI),
wherein the reference signal is a dedicated reference signal for the terminal.
0. 20. The method of
0. 21. The method of
0. 22. The method of
0. 23. The method of
0. 24. The method of
0. 25. The method of
the virtual cell-specific information is identical to or different from a physical cell identity (PCI) of a serving cell of the terminal and
the virtual terminal-specific information is different from a radio network temporary identifier (RNTI) of the terminal.
0. 26. The method of
0. 28. The terminal of claim 27, wherein the reference signal is a user equipment specific (UE-specific) reference signal.
0. 29. The terminal of claim 27, wherein the DCI is also transmitted to a second terminal and the reference signal is also transmitted to the second terminal.
0. 30. The terminal of claim 27, wherein the processor is further configured to:
cause the terminal to receive a virtual cell identity of the serving cell from the base station;
cause the terminal to receive another reference signal from the base station; and
cause the terminal to obtain other user data based on the another reference signal, the first terminal-specific information and the virtual cell identity of the serving cell.
0. 31. The terminal of claim 27, wherein the terminal performs a single point reception from the base station.
0. 33. The communication device of claim 32, wherein the reference signal is a user equipment specific (UE-specific) reference signal.
0. 34. The communication device of claim 32, wherein the DCI is also transmitted to a second terminal and the reference signal is also transmitted to the second terminal.
0. 35. The communication device of claim 32, wherein the processor is further configured to:
cause the terminal to receive a virtual cell identity of the serving cell from the base station;
cause the terminal to receive another reference signal from the base station; and
cause the terminal to obtain other user data based on the another reference signal, the first terminal-specific information and the virtual cell identity of the serving cell.
0. 36. The communication device of claim 32, wherein the terminal performs a single point reception from the base station.
0. 38. The method of claim 37, wherein the reference signal is a user equipment specific (UE-specific) reference signal.
0. 39. The method of claim 37, wherein the DCI is also transmitted to a second terminal and the reference signal is also transmitted to the second terminal.
0. 40. The method of claim 37, further comprising:
receiving a virtual cell identity of the serving cell from the base station;
receiving another reference signal from the base station; and
obtaining other user data based on the another reference signal, the first terminal-specific information and the virtual cell identity of the serving cell.
0. 41. The method of claim 37, wherein the terminal performs a single point reception from the base station.
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Here, s denotes a symbol vector that has a magnitude of L×1 and is transmitted to a terminal by a serving cell, and n denotes a noise vector that has a magnitude of MR×1 and includes both of neighboring cell interference and Gaussian thermal noise.
When a channel covariance matrix is expressed by RS=HSHHS and a matrix consisting of eigenvectors having an eigenvalue other than 0 is indicated by VS1, VS1 can be obtained from an eigen decomposition RS=VSΛSVSH of RS=HSHHS or a singular value decomposition (SVD) HS=USΣSVSH (ΣSHΣS=ΛS) of HS.
When a transmitting side uses VS1 as a precoder, the reception signal of the terminal is expressed by y=HSVS1s+n. By multiplying the reception signal by a channel estimation value estimated from a DRS, the following valid reception signal can be obtained:
Such a transmitting and receiving method has been known as an excellent method capable of achieving a channel capacity. To enable the aforementioned single cell transmission and reception, the following can be used in particular as a feedback for precoding at a transmitting side among feedbacks that a terminal needs to transmit in a frequency-division duplex (FDD) system:
(i) a channel coefficient matrix HS
(ii) a channel covariance matrix RS=HSHHS
(iii) a main eigenmatrix VS1 of a channel.
While these three types of matrices are used for explicit channel feedback, a matrix that is the most similar to the eigenmatrix of (iii) is found from a predefined codebook, and the corresponding precoding matrix index (PMI) is fed back for implicit channel feedback. When the codebook is indicated by S(A)={wn, n=1, 2, . . . }, the PMI can be expressed as Equation 6 below.
Here, D(VS1, w) denotes a “distance” between VS1 and w.
(2) The Case of Coordinated Scheduling Transmission
When a terminal receives coordinated scheduling transmission from two cells as illustrated in
y=HSPSsS+HAPAsA+n [Equation 7]
When Hi (i=S, A) denotes the channel coefficient matrix of a terminal and cell i and Pi (i=S, A) denotes a precoder applied to cell i, an effective reception signal obtained by multiplying the received signal by a channel estimation value estimated from a DRS can be expressed by Equation 8 below.
When PS is an eigenmatrix consisting of eigenvectors of a channel HS, an intra-cell term
On the other hand, in order to cause little interference with the terminal, cell A can select PA to belong to a null space of HA or a space formed by eigenvectors corresponding to 0 or very small eigenvalues among eigenvectors corresponding to eigenvalues obtained by SVD of HA. In other words,
To implement the aforementioned coordinated scheduling transmission, the terminal can use one of the following as a feedback:
(i) channel coefficient matrices HS and HA
(ii) channel covariance matrices RS=HSHHS and RA=HAHHA and
(iii) main eigenmatrices VS and VA of a channel (obtained from eigen decompositions RS=VSΛSVSH and RA=VAΛAVAH).
These three types of matrices are used for explicit channel feedback, and the eigenmatrices of (iii) can be applied to codebook-based implicit channel feedback. In this case when the codebook is indicated by, S(i)={wn, n=1, 2, . . . } (i=S, A) a PMI can be expressed by Equation 9 below.
(3) The Case of Joint Processing Coherent Joint Processing
In coherent joint processing, cells participating in joint processing artificially adjust the phases of signals transmitted by the respective cells to obtain the maximum effect in consideration of the phases. On the other hand, in non-coherent joint transmission, a phase between internal antennas of each cell is adjusted without consideration of phase adjustment between cells.
When a terminal receives joint processing from two cells as shown in
y=HSPSs+HAPAs+n [Equation 10]
When Hi (i==S, A) denotes a channel coefficient matrix of a terminal and cell i, and Pi (i=S, A) denotes a precoder applied to cell i, an effective reception signal obtained by multiplying the received signal by a channel estimation value estimated from a DRS can be expressed by Equation 11 below.
The following two coherent precoding methods can be used.
(A) Global Precoding
An eigenvector matrix V is obtained from a joint channel
of two cells. V is used as a precoder.
Here, Rij=HiHHj, and the other transmission and reception process is similar to the case of single cell transmission.
(B) Local Precoding Plus Phase Correction
Cells participating in joint processing determine precoding in consideration of only wireless channels between the respective cells and the terminal. Phase correction is determined on the assumption of determined precoding of the respective cells in consideration of the wireless channels between all the cells participating in joint processing and the terminal. Precoding at cell i (i=S, A) can be expressed by Equation 13 below.
PS=VSDS
PA=VADA [Equation 13]
Here, DSHDS=1 and DAHDA=1 and (unitary). Intra-cell terms related to only the channels of respective individual cells become approximately diagonal matrices irrelevant to selection of DS and DA when DS and DA are limited to diagonal matrices. In other words, the intra-cell terms are expressed by Equation 14 below.
Likewise,
The matrices DS and DA for phase correction may be determined so that an inter-cell term
To implement the aforementioned joint processing, the terminal can use one of the following as an explicit channel feedback:
(i) channel coefficient matrices HS and HA
(ii) channel covariance matrices RS=HSHHS, RA=HAHHA, and an inter-cell matrix RSA=HSHHA.
(iii) a main eigenmatrix V (obtained from an eigen decomposition
(iv) main eigenmatrices VS and VA, and phase correction matrices DS and DA.
In the case of implicit feedback, (iii) and (iv) are corrected, precoders that are the most similar to the corrected matrices are found, and the corresponding indices are fed back. When a codebook for global precoding is indicated by S(SA), a codebook for local precoding of cell i is indicated by S(i)(i=S, A), and a codebook for phase correction is indicated by X(i)(i=S, A), an implicit feedback of the terminal can be expressed as follows:
(v) a precoding matrix for global precoding is
(vi) precoding matrices for local precoding and phase correction are
and
a matrix index for phase correction is
Here, R denotes an overall data transmission rate.
Preferable Feedback Structure of Terminal
Consequently, in a terminal employing a DM-RS transmitting method according to an exemplary embodiment of the present invention, feedback of the terminal for downlink transmission such as single cell transmission, coordinated scheduling transmission, and coherent joint processing has characteristics as described below.
First, coordinated scheduling transmission and non-coherent joint processing can use the same terminal feedback.
Second, when terminal feedback used for single cell transmission is simply scaled up to a plurality of cells, the terminal feedback can be used for coordinated scheduling and non-coherent joint processing.
Third, terminal feedback for coherent joint processing can be designed to include coordinated scheduling transmission or non-coherent joint processing. Local precoding and phase correction have the same content as terminal feedback for coordinated scheduling transmission or non-coherent joint processing except for a diagonal matrix for phase correction.
Terminal feedback may have the following two characteristics.
A first characteristic is scalability, which denotes that a transmitting side needs to be able to perform transmission using a part of content fed back by a terminal. For example, when a terminal performs feedback for joint processing in which three cells participate, a transmitting side may successfully receive feedbacks for only two cells. In this case, when the feedbacks have scalability, joint processing for the two cells can be performed using the feedbacks. Also, the transmitting side may use an additional terminal feedback to scale up the joint processing so that more cells can participate in the joint processing. For example, when a terminal transmits a feedback to a transmitting side for joint processing in which three cells participate and then additionally transmits a feedback for one cell, the transmitting side should be able to perform joint processing in which the four cells participate using the successfully received feedback information of the four cells.
A second characteristic is flexibility, which denotes that a plurality of transmission methods can be selected from a terminal feedback causing high overhead. For example, from a terminal feedback for coherent joint processing, a transmitting side should be able to select and perform coherent joint processing, non-coherent joint processing, coordinated scheduling transmission, or single cell transmission.
In Table 1 and Table 2, merits and demerits of the aforementioned explicit channel feedback and implicit channel feedback are arranged according to transmission methods.
TABLE 1
Explicit Channel Feedback
CoMP
Non-
Coherent
Explicit
Single Point
Coordinated
Joint
Coherent Joint
Feedback
Transmission
Scheduling
Processing
Processing
(i) Channel
HS
Hi(i = S, A, . . . )
Hi(i = S, A, . . . )
Hi(i = S, A, . . . )
High
Coefficient
HS
Overhead,
Matrix
Complete
Scalability
and
Flexibility
(ii) Channel
RS
Ri(i = S, A, . . . )
Ri(i = S, A, . . . )
Ri(i = S, A, . . . ) +
High
Covariance
RS
Rij(i≠j, i, j = S, A, . . . )
Overhead,
Matrix
Complete
Scalability
and
Flexibility
(iii)
VS
Vi(i = S, A, . . . )
Vi(i = S, A, . . . )
Vjoint
Low
Eigenmatrix
VS
Overhead,
for Global
Partial
Precoding
Scalability
and
Flexibility
(iv) Local
VS
Vi(i = S, A, . . . )
Vi(i = S, A, . . . )
Vi(i = S, A, . . . ) +
Medium
Precoding
VS
Di(i = S, A, . . . )
Overhead,
Eigenmatrix
Complete
and Diagonal
Scalability
Matrix for
and
Phase
Flexibility
Correction
TABLE 2
Implicit Channel Feedback
CoMP
Non-Coherent
Implicit
Single Point
Coordinated
Joint
Coherent Joint
Feedback
Transmission
Scheduling
Processing
Processing
(v) PMI for
WS
Wi(i = S, A, . . . )
Wi(i = S, A, . . . )
Wjoint
Multi-Cell
Global
Codebook
Precoding
Is Needed.
Partial
Scalability
and
Flexibility
(vi) PMI for
WS
Wi(i = S, A, . . . )
Wi(i = S, A, . . . )
Wi(i = S, A, . . . ) +
Single Cell
Local
Xi(i = S, A, . . . )
Codebook
Precoding
Is Needed.
and Phase
Complete
Correction
Scalability
and
Flexibility
Referring to Table 1 and Table 2 above, (i), (ii) and (iv) of Table 1 and (vi) of Table 2 satisfy both of scalability and flexibility. Also, (i) and (ii) of Table 1 increase the amount of feedback of a terminal, and, in comparison with (i) and (ii) of Table 1, (iv) of Table 1 has scalability and flexibility and maintains an appropriate amount of feedback. Furthermore, (vi) of Table 2 is based on the codebook of each cell and thus has scalability and flexibility while reducing the amount of feedback.
While the example embodiments of the present invention and their advantages have been described in detail, it should be understood that various changes, substitutions and alterations may be made herein without departing from the scope of the invention.
Ahn, Jae Young, Seo, Bangwon, Ko, Young-Jo
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