Method for determining precoding matrix indicator, user equipment, and base station evolved NodeB

Abstract

The present disclosure relates to a method for determining a precoding matrix indicator, a user equipment (UE), a base station (e.g., eNB), and a system. The method includes: receiving a reference signal sent by a base station; selecting, based on the reference signal, a precoding matrix from a codebook, where a precoding matrix W included in the codebook is a product of two matrices W.sub.1 and W.sub.2, where W.sub.1 is a block diagonal matrix, where each block matrix is a Kronecker product of a matrix A.sub.i and a matrix B.sub.i; and sending a precoding matrix indicator (PMI) to the base station, where the PMI corresponds to the selected precoding matrix, so that the base station obtains the precoding matrix according to the PMI.

Claims

1. A method for determining a precoding matrix indicator, the method comprising: sending, by a base station, a reference signal to a terminal device; and receiving, by the base station, a precoding matrix indicator (PMI) from the terminal device, wherein the PMI corresponds to a precoding matrix in a codebook, wherein each precoding matrix W comprised in the codebook is a product of two matrices W.sub.1 and W.sub.2, W=W.sub.1W.sub.2, wherein the matrix W.sub.1 is a block diagonal matrix, W.sub.1=diag{X.sub.1, . . . , X.sub.N.sub.B}, N.sub.B>1, each block matrix X.sub.i being a Kronecker product of a matrix A.sub.i and a matrix B.sub.i, X.sub.i=A.sub.i.Math.B.sub.i, 1≤i≤N.sub.B, wherein the matrix A.sub.i and the matrix B.sub.i are for channel state information quantization in two degrees of freedom of an antenna array respectively.

2. The method according to claim 1, wherein each column of the matrix A.sub.i and the matrix B.sub.i is a discrete Fourier transform (DFT) vector, and the two degrees of freedom of the antenna array comprise a degree of freedom in a horizontal direction and a degree of freedom in a vertical direction.

3. The method according to claim 1, wherein receiving by the base station the PMI from the terminal device comprises: receiving a third precoding matrix indicator PMI.sub.11, a fourth precoding matrix indicator PMI.sub.12, and a fifth precoding matrix indicator PMI.sub.2 from the terminal device, wherein the third precoding matrix indicator PMI.sub.11 is used to indicate the matrix A.sub.i, wherein 1≤i≤N.sub.B; the fourth precoding matrix indicator PMI.sub.12 is used to indicate the matrix B.sub.i, wherein 1≤i≤N.sub.B, and the fifth precoding matrix indicator PMI.sub.2 is used to indicate the matrix W.sub.2.

4. The method according to claim 1, wherein block matrices in the matrix W.sub.1 satisfy X.sub.2j−1=X.sub.2j, 1≤j≤N.sub.B/2.

5. The method according to claim 1, wherein the matrix W.sub.2 is used to select or weight and combine at least one column vector in the matrix W.sub.1 to form the matrix W.

6. The method according to claim 1, wherein the codebook comprises a codebook subset consisting of precoding matrices corresponding to a subset of the matrix A.sub.i and the matrix B.sub.i.

7. The method according to claim 6, further comprises: notifying, by the base station, the subset of the matrix A.sub.i and the matrix B.sub.i to the terminal device.

8. A device, comprising: a transmitter configured to send a reference signal to a terminal device; and a receiver configured to receive a precoding matrix indicator (PMI) from the terminal device, wherein the PMI corresponds to a precoding matrix in a codebook, wherein each precoding matrix W comprised in the codebook is a product of two matrices W.sub.1 and W.sub.2, W=W.sub.1W.sub.2, wherein the matrix W.sub.1 is a block diagonal matrix, W.sub.1=diag{X.sub.1, . . . , X.sub.N.sub.B}, N.sub.B>1, each block matrix X.sub.i being a Kronecker product of a matrix A.sub.i and a matrix B.sub.i, X.sub.i=A.sub.i .Math.B.sub.i, 1≤i≤N.sub.B, wherein the matrix A.sub.i and the matrix B.sub.i are for channel state information quantization in two degrees of freedom of an antenna array respectively.

9. The device according to claim 8, wherein each column of the matrix A.sub.i and the matrix B.sub.i is a discrete Fourier transform (DFT) vector, and the two degrees of freedom of the antenna array comprise a degree of freedom in a horizontal direction and a degree of freedom in a vertical direction.

10. The device according to claim 8, wherein receiving the PMI from the terminal device comprises: receiving a third precoding matrix indicator PMI.sub.11, a fourth precoding matrix indicator PMI.sub.12, and a fifth precoding matrix indicator PMI.sub.2 from the terminal device, wherein the third precoding matrix indicator PMI.sub.11 is used to indicate the matrix A.sub.i, wherein 1≤i≤N.sub.B; the fourth precoding matrix indicator PMI.sub.12 is used to indicate the matrix B.sub.i, wherein 1≤i≤N.sub.B, and the fifth precoding matrix indicator PMI.sub.2 is used to indicate the matrix W.sub.2.

11. The device according to claim 8, wherein block matrices in the matrix W.sub.1 satisfy X.sub.2j−1=X.sub.2j, 1≤j≤N.sub.B/2.

12. The device according to claim 8, wherein the matrix W.sub.2 is used to select or weight and combine at least one column vector in the matrix W.sub.1 to form the matrix W.

13. The device according to claim 8 wherein the codebook comprises a codebook subset consisting of precoding matrices corresponding to a subset of the matrix A.sub.i and the matrix B.sub.i.

14. The device according to claim 13, the transmitter is configured to notify the subset of the matrix A.sub.i and the matrix B.sub.i to the terminal device.

15. A non-transitory computer-readable storage medium storing instructions which, when executed by at least one processor in a base station, cause the base station to: send a reference signal to a terminal device; and receive a precoding matrix indicator (PMI) from the terminal device, wherein the PMI corresponds to a precoding matrix in a codebook, wherein each precoding matrix W comprised in the codebook is a product of two matrices W.sub.1 and W.sub.2, W=W.sub.1W.sub.2, wherein the matrix W.sub.1 is a block diagonal matrix, W.sub.1=diag {X.sub.1, . . . , X.sub.N.sub.B}, N.sub.B>1, each block matrix X.sub.i being a Kronecker product of a matrix A.sub.i and a matrix B.sub.i, X.sub.i=A.sub.i.Math.B.sub.i, 1≤i≤N.sub.B, wherein the matrix A.sub.i and the matrix B.sub.i are for channel state information quantization in two degrees of freedom of an antenna array respectively.

16. The non-transitory computer-readable storage medium according to claim 15, wherein each column of the matrix A.sub.i and the matrix B.sub.i is a discrete Fourier transform (DFT) vector, and the two degrees of freedom of the antenna array comprise a degree of freedom in a horizontal direction and a degree of freedom in a vertical direction.

17. The non-transitory computer-readable storage medium according to claim 15, wherein receiving the PMI from the terminal device comprises: receiving a third precoding matrix indicator PMI.sub.11, a fourth precoding matrix indicator PMI.sub.12, and a fifth precoding matrix indicator PMI.sub.2 from the terminal device, wherein the third precoding matrix indicator PMI.sub.11 is used to indicate the matrix A.sub.i, wherein 1≤i≤N.sub.B; the fourth precoding matrix indicator PMI.sub.12 is used to indicate the matrix B.sub.i wherein 1≤i≤N.sub.B, and the fifth precoding matrix indicator PMI.sub.2 is used to indicate the matrix W.sub.2.

18. The non-transitory computer-readable storage medium according to claim 15, wherein block matrices in the matrix W.sub.1 satisfy X.sub.2j−1=X.sub.2j, 1≤j≤N.sub.B/2.

19. The non-transitory computer-readable storage medium according to claim 15, wherein the matrix W.sub.2 is used to select or weight and combine at least one column vector in the matrix W.sub.1 to form the matrix W.

20. The non-transitory computer-readable storage medium according to claim 15, wherein the codebook comprises a codebook subset consisting of precoding matrices corresponding to a subset of the matrix A.sub.i and the matrix B.sub.i.

21. The non-transitory computer-readable storage medium according to claim 20, wherein the instructions which, when executed by at least one processor in the base station, cause the base station to notify the subset of the matrix A.sub.i and the matrix B.sub.i to the terminal device.

22. A communications device, comprising: at least one processor; and a memory configured to store computer operation instructions that, when executed by the at least one processor, cause the at least one processor to perform: sending a reference signal to a terminal device; and receiving a precoding matrix indicator (PMI) from the terminal device, wherein the PMI corresponds to a precoding matrix in a codebook, wherein each precoding matrix W comprised in the codebook is a product of two matrices W.sub.1 and W.sub.2, W=W.sub.1W.sub.2, wherein the matrix W.sub.1 is a block diagonal matrix, W.sub.1=diag{X.sub.1, . . . , X.sub.N.sub.B}N.sub.B>1 each block matrix X.sub.i being a Kronecker product of a matrix A.sub.i and a matrix B.sub.i, X.sub.i=A.sub.i.Math.B.sub.i, 1≤i≤N.sub.B, wherein the matrix A.sub.i and the matrix B.sub.i are for channel state information quantization in two degrees of freedom of an antenna array respectively.

23. The communications device according to claim 22, wherein each column of the matrix A.sub.i and the matrix B.sub.i is a discrete Fourier transform (DFT) vector, and the two degrees of freedom of the antenna array comprise a degree of freedom in a horizontal direction and a degree of freedom in a vertical direction.

24. The communications device according to claim 22, wherein receiving the PMI from the terminal device comprises: receiving a third precoding matrix indicator PMI.sub.11, a fourth precoding matrix indicator PMI.sub.12, and a fifth precoding matrix indicator PMI.sub.2 from the terminal device, wherein the third precoding matrix indicator PMI.sub.11 is used to indicate the matrix A.sub.i, wherein 1≤i≤N.sub.B; the fourth precoding matrix indicator PMI.sub.12 is used to indicate the matrix B.sub.i wherein 1≤i≤N.sub.B, and the fifth precoding matrix indicator PMI.sub.2 is used to indicate the matrix W.sub.2.

25. The communications device according to claim 22, wherein block matrices in the matrix W.sub.1 satisfy X.sub.2j−1=X.sub.2j, 1≤j≤N.sub.B/2.

26. The communications device according to claim 22, wherein the matrix W.sub.2 is used to select or weight and combine at least one column vector in the matrix W.sub.1 to form the matrix W.

27. The communications device according to claim 22, wherein the codebook comprises a codebook subset consisting of precoding matrices corresponding to a subset of the matrix A.sub.i and the matrix B.sub.i.

28. The communications device according to claim 27, the at least one processor is further caused to perform: notifying the subset of the matrix A.sub.i and the matrix B.sub.i to the terminal device.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a flowchart of a first embodiment of a method for determining a precoding matrix indicator according to the present invention;

(2) FIG. 2 is a flowchart of a second embodiment of a method for determining a precoding matrix indicator according to the present invention;

(3) FIG. 3 is a schematic structural diagram of composition of a system for determining a precoding matrix indicator according to the present invention;

(4) FIG. 4 is a schematic structural diagram of composition of a user equipment UE in FIG. 3; and

(5) FIG. 5 is a schematic structural diagram of composition of a base station eNB in FIG. 3.

DETAILED DESCRIPTION

(6) The following further describes the technical solutions of the present invention in detail with reference to the accompanying drawings and embodiments.

(7) According to embodiments of the present invention, a codebook scheme is designed for an actual network deployment and antenna configuration, and especially for a base station antenna configuration condition of an active antenna system. According to the codebook scheme, a UE selects and reports a PMI, and a NodeB performs precoding according to PMI information reported by the UE, so as to improve performance of a system with the foregoing antenna configuration and especially with the AAS base station antenna configuration. The base station antenna can not only use a degree of freedom in a horizontal direction, but also can use a degree of freedom in a vertical direction.

(8) FIG. 1 is a flowchart of a first embodiment of a method for determining a precoding matrix indicator according to the present invention. As shown in the figure, this embodiment specifically includes the following steps:

(9) Step 101: Receive a reference signal sent by a base station.

(10) Specifically, the reference signal sent by the base station may include a channel state information reference signal (CSI RS), a demodulation reference signal (demodulation RS, DM RS), or a cell-specific reference signal (cell-specific RS, CRS). A user equipment UE may obtain a resource configuration of the reference signal by receiving a notification (for example, RRC (Radio Resource Control) signaling or downlink control information DCI) from an eNB or based on a cell identity ID, and obtain the reference signal from a corresponding resource or subframe.

(11) Step 102: Select, based on the reference signal, a precoding matrix from a codebook, where a precoding matrix W included in the codebook is a product of two matrices W.sub.1 and W.sub.2, that is:
W=W.sub.1W.sub.2  (1)

(12) where W.sub.1 is a block diagonal matrix, that is:
W.sub.1=diag{X.sub.1. . . ,X.sub.N.sub.B}  (2)

(13) where each block matrix X.sub.i is a Kronecker product of a matrix A.sub.i and a matrix B.sub.i, that is:
X.sub.i=A.sub.i.Math.B.sub.i,1≤i≤N.sub.B  (3)

(14) the W.sub.1 includes at least one block matrix, that is, the number N.sub.B of block matrices is:
N.sub.B≥1  (4)

(15) Specifically, each column of the matrix A.sub.i or of the matrix B.sub.i in formula (3) may be a discrete Fourier transform (DFT) vector or may be a column vector of a Hadamard matrix, that is:
A.sub.i=[a.sub.0a.sub.1 . . . a.sub.N.sub.a.sub.−1]  (5)
B.sub.i=[b.sub.0b.sub.1 . . . b.sub.N.sub.b.sub.−1]  (6)
therefore:
a.sub.k∈{f.sub.0,f.sub.1, . . . ,f.sub.N.sub.f.sub.−1},k=0, . . . ,N.sub.a−1  (7)
or
a.sub.k∈{h.sub.0,h.sub.1, . . . ,h.sub.N.sub.h.sub.−1},k=0, . . . ,N.sub.a−1  (8)
or
b.sub.l∈{f.sub.0,f.sub.1, . . . ,f.sub.N.sub.f.sub.−1},l=0, . . . ,N.sub.b−1  (9)
or
b.sub.l∈{h.sub.0,h.sub.1, . . . ,h.sub.N.sub.h.sub.−1},l=0, . . . ,N.sub.b−1  (10)

(16) where N.sub.a and N.sub.b represent the numbers of columns of the matrix A.sub.i and the matrix B.sub.i, respectively; h.sub.m, m=0, . . . , N.sub.h−1 represents a column vector of the Hadamard matrix, where N.sub.h represents the number of columns of the Hadamard matrix; and f.sub.n=0, . . . , N.sub.f−1 represents a DFT vector, where N.sub.f is the number of DFT vectors, and the DFT vector f.sub.n may be represented as:

(17) $\begin{array}{cc}{f}_n={\left[e^{j\frac{2\pi .Math.0.Math.n}{N}}{e}^{j\frac{2\pi .Math.1.Math.n}{N}}.Math.e^{j\frac{2\pi .Math.\left(M-1\right).Math.n}{N}}\right]}^T& \left(11\right)\end{array}$

(18) where both M and N are integers.

(19) Specifically, the matrix A.sub.i or the matrix B.sub.i in formula (3) may also be a precoding matrix in a 2-antenna codebook or a 4-antenna codebook of an LTE R8 system, or in an 8-antenna codebook of an LTE R10 system.

(20) Further, the matrix W.sub.2 is used to select or weight and combine a column vector in the matrix W.sub.1, so as to form the matrix W.

(21) In an example in which the number of block matrices is N.sub.B=2 and there are 32 transmit antennas, matrices that form the precoding matrix W may separately be:
A.sub.i=a.sub.0,i=1,2  (12)
where:
a.sub.0∈{f.sub.0,f.sub.1, . . . ,f.sub.3}  (13)
[f.sub.0,f.sub.1,f.sub.2,f.sub.3]=diag{1,e.sup.jnπ/8,e.sup.jnπ/4,e.sup.jnπ/8}F.sub.4,n=0,1,2,3  (14)

(22) $\begin{array}{cc}{F}_4=\frac{1}{2}\times \left[\begin{array}{cccc}1& 1& 1& 1\\ 1& j& -1& -j\\ 1& -1& 1& -1\\ 1& -j& -1& j\end{array}\right]\mathrm{or}& \left(15\right)\end{array}$$\begin{array}{cc}{a}_k\in \left\{h_0,h_1,.Math.,h_3\right\},k=0,.Math.,3& \left(16\right)\end{array}$$\begin{array}{cc}\left[h_0,h_1,.Math.,h_3\right]=\frac{1}{2}\times H_4& \left(17\right)\end{array}$

(23) where H.sub.4 is a Hadamard matrix of order 4.

(24) $\begin{array}{cc}{B}_i\in \left\{\left[b_{\left(2k\right)\mathrm{mod}32}{b}_{\left(2k+1\right)\mathrm{mod}32}{b}_{\left(2k+2\right)\mathrm{mod}32}{b}_{\left(2k+3\right)\mathrm{mod}32}\right]:k=0,1,.Math.,15\right\},i=1,2& \left(18\right)\end{array}$$\begin{array}{cc}{b}_{\left(2k+l\right)\mathrm{mod}32}={\left[e^{j\frac{2\pi .Math.0.Math.\left(\left(2k+l\right)\mathrm{mod}32\right)}{32}}{e}^{j\frac{2\pi .Math.1.Math.\left(\left(2k+l\right)\mathrm{mod}32\right)}{32}}{e}^{j\frac{2\pi .Math.2.Math.\left(2k+l\right)\mathrm{mod}32}{32}}{e}^{j\frac{2\pi .Math.3.Math.\left(\left(2k+l\right)\mathrm{mod}32\right)}{32}}\right]}^T,l=0,1,2,3& \left(19\right)\end{array}$

(25) where x mod y represents an operation of x mod y; and j represents a unit pure imaginary number, that is, j=√{square root over (−1)}; or

(26) B.sub.i is a precoding matrix in a 4-antenna rank-4 codebook of an LTE R8 system.

(27) $\begin{array}{cc}{W}_2\in \left\{\frac{1}{\sqrt{2}}\left[\begin{array}{c}Y\\ Y\end{array}\right],\frac{1}{\sqrt{2}}\left[\begin{array}{c}Y\\ \mathrm{jY}\end{array}\right],\frac{1}{\sqrt{2}}\left[\begin{array}{c}Y\\ -Y\end{array}\right],\frac{1}{\sqrt{2}}\left[\begin{array}{c}Y\\ -\mathrm{jY}\end{array}\right]\right\}& \left(20\right)\end{array}$$\begin{array}{cc}Y\in \left\{{\tilde{e}}_1,{\tilde{e}}_2,{\tilde{e}}_3,{\tilde{e}}_4\right\}\mathrm{or}& \left(21\right)\end{array}$$\begin{array}{cc}{W}_2\in \left\{\frac{1}{\sqrt{2}}\left[\begin{array}{cc}{Y}_1& Y_2\\ Y_1& -Y_2\end{array}\right],\frac{1}{\sqrt{2}}\left[\begin{array}{cc}{Y}_1& Y_2\\ {\mathrm{jY}}_1& -{\mathrm{jY}}_2\end{array}\right]\right\}& \left(22\right)\end{array}$$\begin{array}{cc}\left(Y_1,Y_2\right)\in \left\{\left({\tilde{e}}_1,{\tilde{e}}_1\right),\left({\tilde{e}}_2,{\tilde{e}}_2\right),\left({\tilde{e}}_3,{\tilde{e}}_3\right),\left({\tilde{e}}_4,{\tilde{e}}_4\right),\left({\tilde{e}}_1,{\tilde{e}}_2\right),\left({\tilde{e}}_2,{\tilde{e}}_3\right),\left({\tilde{e}}_1,{\tilde{e}}_4\right),\left({\tilde{e}}_2,{\tilde{e}}_4\right)\right\}& \left(23\right)\end{array}$

(28) where {tilde over (e)}.sub.n, n=1, 2, 3, 4 represents a 4×1 selection vector in which all elements are 0 except the n.sup.th element being 1.

(29) In an example in which the number of block matrices is N.sub.B=2 and there are 32 transmit antennas, matrices that form the precoding matrix W may also separately be:
A.sub.i=[a.sub.0a.sub.l],i=1,2  (24)
a.sub.0,a.sub.1∈{f.sub.0,f.sub.1, . . . f.sub.3}  (25)

(30) where f.sub.i, i=0, . . . , 3 is shown in formula (14).

(31) or
a.sub.0,a.sub.1∈{h.sub.0,h.sub.1, . . . ,h.sub.3}  (26)

(32) where h.sub.i, i=0, . . . , 3 is shown in formula (17);

(33) the matrix B.sub.i, i=1, 2 is shown in formulas (18) and (19), or the matrix B.sub.i is a precoding matrix in a 4-antenna rank-4 codebook of an LTE R8 system;

(34) $\begin{array}{cc}{W}_2\in \left\{\frac{1}{\sqrt{2}}\left[\begin{array}{c}Y\\ Y\end{array}\right],\frac{1}{\sqrt{2}}\left[\begin{array}{c}Y\\ \mathrm{jY}\end{array}\right],\frac{1}{\sqrt{2}}\left[\begin{array}{c}Y\\ -Y\end{array}\right],\frac{1}{\sqrt{2}}\left[\begin{array}{c}Y\\ -\mathrm{jY}\end{array}\right]\right\}& \left(27\right)\end{array}$$\begin{array}{cc}Y\in \left\{e_1,e_2,e_3,e_4,e_5,e_6,e_7,e_8\right\}\mathrm{or}& \left(28\right)\end{array}$$\begin{array}{cc}{W}_2\in \left\{\frac{1}{\sqrt{2}}\left[\begin{array}{cc}{Y}_1& Y_2\\ Y_1& -Y_2\end{array}\right],\frac{1}{\sqrt{2}}\left[\begin{array}{cc}{Y}_1& Y_2\\ {\mathrm{jY}}_1& -{\mathrm{jY}}_2\end{array}\right]\right\}& \left(29\right)\end{array}$$\begin{array}{cc}\left(Y_1,Y_2\right)\in \left\{\left(e_1,e_1\right),\left(e_2,e_2\right),\left(e_3,e_3\right),\left(e_4,e_4\right),\left(e_1,e_2\right),\left(e_2,e_3\right),\left(e_1,e_4\right),\left(e_2,e_4\right)\right\}& \left(30\right)\end{array}$

(35) where e.sub.n, n=1, 2, . . . , 8 represents an 8×1 selection vector in which all elements are 0 except the n.sup.th element being 1.

(36) Specifically, the selecting, based on the reference signal, a precoding matrix from a codebook includes:

(37) obtaining, by the user equipment UE based on the reference signal, a channel estimate; and selecting, based on a predefined criterion such as a channel capacity or throughput maximization criterion, the precoding matrix from the codebook according to the channel estimate. Selecting, based on a predefined criterion, a precoding matrix is an existing technology, and details are not described herein.

(38) Further, the selecting, based on the reference signal, a precoding matrix from a codebook includes:

(39) selecting, based on the reference signal, the precoding matrix from a codebook subset, where

(40) the codebook subset may be a codebook subset that is predefined; or a codebook subset that is reported by the UE to the base station eNB, determined by the base station eNB based on the report from the UE, and notified to the UE; or a codebook subset that is determined and reported by the UE, for example, a latest reported codebook subset.

(41) Further, the codebook subset may include:

(42) a subset of the matrix W.sub.1, the matrix A.sub.i, the matrix B.sub.i, or the matrix W.sub.2.

(43) The selecting, based on the codebook subset, the precoding matrix can further reduce feedback overheads and implementation complexity.

(44) Further, the codebook subsets have a same subset of the matrix W.sub.1 the matrix A.sub.i, the matrix B.sub.i, or the matrix W.sub.2. In this way, the codebook subsets overlap each other, which can overcome an edge effect of channel state information quantization.

(45) Further, in the precoding matrix, block matrices X.sub.i and X.sub.j, i≈j may be unequal, or may also be equal. If there are multiple cases that X.sub.i and X.sub.j, i≈j are equal, for example, X.sub.i and X.sub.j, i≈j that are equal may appear in pairs, the feedback overheads can be further reduced.

(46) In addition, the foregoing matrix A.sub.i or matrix B.sub.i may also use another form, which is not further elaborated herein.

(47) It should be noted that, each of the foregoing matrices may further be multiplied by a scale factor, so as to implement power normalization or power equalization.

(48) Step 103: Send a precoding matrix indicator PMI to the base station, where the PMI corresponds to the selected precoding matrix, so that the base station obtains the precoding matrix according to the PMI.

(49) Specifically, the precoding matrix is included in a precoding matrix set or a codebook; and the PMI is used to indicate the selected precoding matrix in the precoding matrix set or the codebook.

(50) Specifically, sending a precoding matrix indicator PMI to the base station includes: sending the precoding matrix indicator PMI to the base station, where the PMI may include only one specific value. In this case, the PMI directly indicates the precoding matrix W. For example, if there are a total of 16 different precoding matrices, PMI=0, . . . , 15 may be used to respectively indicate precoding matrices W whose labels are 0, 1, . . . , 15.

(51) Specifically, sending a precoding matrix indicator PMI to the base station may also include: sending precoding matrix indicators PMI.sub.1 and PMI.sub.2 to the base station, where PMI.sub.1 and PMI.sub.2 are used to indicate the matrix X.sub.i=A.sub.i.Math.B.sub.i, 1≤i≤N.sub.B in formula (2) and the matrix W.sub.2, respectively; and in this case, the matrix X.sub.i=A.sub.i.Math.B.sub.i, 1≤i≤N.sub.B and the matrix W.sub.2 are respectively indicated by PMI.sub.1 and PMI.sub.2 in the codebook; or

(52) sending precoding matrix indicators PMI.sub.11, PMI.sub.12, and PMI.sub.2 to the base station, where PMI.sub.11, PMI.sub.12, and PMI.sub.2 are used to indicate the matrix A.sub.i, 1≤i≤N.sub.B, the matrix B.sub.i, 1≤i≤N.sub.B, and the matrix W.sub.2, respectively; and in this case, the matrix A.sub.i, 1≤i≤N.sub.B, the matrix B.sub.i, 1≤i≤N.sub.B, and the matrix W.sub.2 are respectively indicated by PMI.sub.11, PMI.sub.12, and PMI.sub.2 in the codebook.

(53) Further, the precoding matrix indicators PMI.sub.1 and PMI.sub.2, or the precoding matrix indicators PMI.sub.11, PMI.sub.12, and PMI.sub.2 have different time domain granularities or frequency domain granularities, for example, PMI.sub.1 and PMI.sub.2, or PMI.sub.11, PMI.sub.12, and PMI.sub.2 separately indicate different periods or bandwidth channel features, or are obtained based on different subframe periods or subband sizes.

(54) Alternatively, further, the precoding matrix indicators PMI.sub.11 and PMI.sub.12 are sent to the base station according to different time periods.

(55) Specifically, sending a precoding matrix indicator PMI to the base station may also include: sending precoding matrix indicators PMI.sub.1,i, 1≤i≤N.sub.B; and PMI.sub.2 to the base station, where PMI.sub.1,i, 1≤i≤N.sub.B and PMI.sub.2 are used to indicate the matrix X.sub.i=A.sub.i.Math.B.sub.i, 1≤i≤N.sub.B and the matrix W.sub.2, respectively; or

(56) sending precoding matrix indicators PMI.sub.11,i, PMI.sub.12,i and PMI.sub.2 to the base station, where PMI.sub.11,i, PMI.sub.12,i, and PMI.sub.2 are used to indicate the matrix A.sub.i, 1≤i≤N.sub.B, the matrix B.sub.i, 1≤i≤N.sub.B, and the matrix W.sub.2, respectively.

(57) Specifically, sending a precoding matrix indicator PMI to the base station may also include: sending precoding matrix indicators PMI.sub.1,i, 1≤i≤N.sub.B/2 and PMI.sub.2 to the base station, where PMI.sub.1,i, 1≤i≤N.sub.B/2 and PMI.sub.2 are used to indicate a matrix X.sub.2i−1=X.sub.2i=A.sub.2i.Math.B.sub.2i, 1≤i≤N.sub.B/2 and the matrix W.sub.2, respectively; and in this case, X.sub.2i−1=X.sub.2i, and the matrices appear in pairs; or

(58) sending precoding matrix indicators PMI.sub.11,i, PMI.sub.12,i, and PMI.sub.2 to the base station, where PMI.sub.11,i, PMI.sub.12,i, and PMI.sub.2 are used to indicate a matrix A.sub.2i−1=A.sub.2i, 1≤i≤N.sub.B/2 the matrix B.sub.2i−1=B.sub.2i, 1≤i≤N.sub.B/2, and the matrix W.sub.2, respectively; and in this case, A.sub.2i−1=A.sub.2i, B.sub.2i−1=B.sub.2i, and the matrices appear in pairs.

(59) Specifically, sending a precoding matrix indicator PMI to the base station may be sending, by the U, the precoding matrix indicator PMI to the base station through a physical uplink control channel (PUCCH) or a physical uplink shared channel (PUSCH).

(60) Further, sending a precoding matrix indicator PMI to the base station may be separately sending, by the UE by using different subframes or according to different periods, the foregoing PMI.sub.1 and PMI.sub.2; or PMI.sub.11, PMI.sub.12, and PMI.sub.2; or PMI.sub.1,i, 1≤i≤N.sub.B, and PMI.sub.2; or PMI.sub.11,i, PMI.sub.12,i, 1≤i≤N.sub.B, and PMI.sub.2; or PMI.sub.1,i, 1≤i≤N.sub.B/2, and PMI.sub.2; or PMI.sub.11,i, PMI.sub.12,i, 1≤i≤N.sub.B/2 and PMI.sub.2 to the base station.

(61) Further, sending a precoding matrix indicator PMI to the base station may also be separately sending, by the UE for different subbands or subband sizes in a frequency domain, the foregoing PMI.sub.1 and PMI.sub.2; or PMI.sub.11, PMI.sub.12, and PMI.sub.2; or PMI.sub.1,i, 1≤i≤N.sub.B, and PMI.sub.2; or PMI.sub.11,i, PMI.sub.12,i, 1≤i≤N.sub.B, and PMI.sub.2; or PMI.sub.1,i, 1≤i≤N.sub.B/2, and PMI.sub.2; or PMI.sub.11,i, PMI.sub.12,i, 1≤i≤N.sub.B/2 and PMI.sub.2 to the base station.

(62) In this embodiment of the present invention, a user equipment determines and sends a precoding matrix indicator PMI, where the PMI indicates a precoding matrix. The precoding matrix has a structure of W=W.sub.1W.sub.2, where W.sub.1 is a block diagonal matrix in which each block matrix on a diagonal line is X.sub.i=A.sub.i.Math.B.sub.i, and i=1, . . . , N.sub.B, where the matrix A.sub.i or the matrix B.sub.i effectively supports channel state information quantization in a horizontal direction or a vertical direction, respectively. This can fully use a degree of freedom of an active antenna system AAS in a horizontal direction and a vertical direction, thereby greatly improving channel state information feedback accuracy. In addition, multiple block matrices X.sub.i may separately correspond to antenna groups of different polarizations or at different locations, so that the foregoing precoding matrix matches multiple antenna deployments or configurations. The foregoing codebook structure greatly improves performance of MIMO, and especially that of MU-MIMO. Moreover, one or more PMIs are fed back based on a subset to indicate a precoding matrix, which fully uses time/frequency domain/spatial correlation of a channel, thereby greatly reducing feedback overheads.

(63) FIG. 2 is a flowchart of a second embodiment of a method for determining a precoding matrix indicator according to the present invention. As shown in the figure, this embodiment specifically includes:

(64) Step 201: Send a reference signal to a user equipment U.

(65) Specifically, the reference signal may include a channel state information reference signal (CSI RS), a demodulation reference signal (demodulation RS, DM RS), or a cell-specific reference signal (cell-specific RS, CRS). Abase station eNB may notify the user equipment UE of a resource configuration of the reference signal by using RRC (Radio Resource Control) signaling or downlink control information DCI), and instruct the UE to obtain the reference signal from a corresponding resource or subframe. The user equipment UE may also implicitly obtain, based on other information such as a cell identity ID, the resource configuration of the reference signal, and obtain the reference signal from the corresponding resource or subframe.

(66) Step 202: Receive a precoding matrix indicator PMI sent by the user equipment UE, where the PMI corresponds to a precoding matrix selected by the user equipment, based on the reference signal, from a codebook; and a precoding matrix W included in the codebook is a product of two matrices W.sub.1 and W.sub.2, and the precoding matrix has a structure shown in formulas (1) to (4).

(67) Specifically, each column of the matrix A.sub.i or of the matrix B.sub.i may be a DFT vector or is a column vector of a Hadamard matrix, as shown in formulas (5) to (11); or

(68) specifically, the matrix A.sub.i or the matrix B.sub.i may also be a precoding matrix in a 2-antenna codebook or a 4-antenna codebook of an LTE R8 system, or in an 8-antenna codebook of an LTE R10 system.

(69) Further, the matrix W.sub.2 is used to select or weight and combine a column vector in the matrix W.sub.1, so as to form the matrix W.

(70) In an example in which the number of block matrices is N.sub.B=2 and there are 32 transmit antennas, matrices that form the precoding matrix W may separately be those shown in formulas (12) to (23); or B.sub.i is a precoding matrix in a 4-antenna rank-4 codebook of an LTE R8 system.

(71) In an example in which the number of block matrices is N.sub.B=2 and there are 32 transmit antennas, matrices that form the precoding matrix W may separately be those shown in formulas (24) to (30); or B.sub.i is a precoding matrix in a 4-antenna rank-4 codebook of an LTE R8 system.

(72) Specifically, selecting, based on the reference signal, a precoding matrix from a codebook includes:

(73) selecting, based on the reference signal, the precoding matrix from a codebook subset, where

(74) the codebook subset may be a codebook subset that is predefined; or a codebook subset that is reported by the UE to the base station eNB, determined by the base station eNB based on the report from the UE, and notified to the UE; or a codebook subset that is determined and reported by the UE, for example, a latest reported codebook subset.

(75) Further, the codebook subset may include a subset of the matrix W.sub.1, the matrix A.sub.i, the matrix B.sub.i, or the matrix W.sub.2.

(76) Further, the codebook subsets have a same subset of the matrix W.sub.1, the matrix A.sub.i, the matrix B.sub.i, or the matrix W.sub.2. In this way, the codebook subsets overlap each other, which can overcome an edge effect of channel state information quantization.

(77) Further, in the precoding matrix, block matrices X.sub.i and X.sub.j, i≈j may be unequal, or may also be equal. If there are multiple cases that X.sub.i and X.sub.j, i≈j are equal, for example, X.sub.i and X.sub.j, i≈j that are equal may appear in pairs, feedback overheads can be further reduced.

(78) In addition, the foregoing matrix A.sub.i or matrix B.sub.i may also use another form, which is not further elaborated herein.

(79) It should be noted that, each of the foregoing matrices may further be multiplied by a scale factor, so as to implement power normalization or power equalization.

(80) Specifically, the precoding matrix is included in a precoding matrix set or a codebook; and the PMI is used to indicate the selected precoding matrix in the precoding matrix set or the codebook.

(81) Specifically, receiving a precoding matrix indicator PMI sent by the user equipment UE includes: receiving the precoding matrix indicator PMI sent by the user equipment UL, where the PMI may include only one specific value. In this case, the PMI directly indicates the precoding matrix W. For example, if there are a total of 16 different precoding matrices, PMI=0, . . . , 15 may be used to respectively indicate precoding matrices W whose labels are 0, 1 . . . 15.

(82) Specifically, receiving a precoding matrix indicator PMI sent by the user equipment UE may also include: receiving precoding matrix indicators PMI.sub.1 and PMI.sub.2 sent by the user equipment UE, where PMI.sub.1 and PMI.sub.2 are used to indicate the matrix X.sub.i=A.sub.i.Math.B.sub.i, 1≤i≤N.sub.B, in formula (2) and the matrix W.sub.2, respectively; and in this case, the matrix X.sub.i=A.sub.i.Math.B.sub.i, 1≤i≤N.sub.B, and the matrix W.sub.2 are respectively indicated by PMI.sub.1 and PMI.sub.2 in the codebook; or

(83) receiving precoding matrix indicators PMI.sub.11, PMI.sub.12, and PMI.sub.2 sent by the user equipment UE, where PMI.sub.11, PMI.sub.12, and PMI.sub.2 are used to indicate the matrix A.sub.i, 1≤i≤N.sub.B, the matrix B.sub.i, 1≤i≤N.sub.B, and the matrix W.sub.2, respectively; and in this case, the matrix A.sub.i, 1≤i≤N.sub.B, the matrix B.sub.i, 1≤i≤N.sub.B, and the matrix W.sub.2 are respectively indicated by PMI.sub.11, PMI.sub.12, and PMI.sub.2 in the codebook.

(84) Further, the precoding matrix indicators PMI.sub.1 and PMI.sub.2, or the precoding matrix indicators PMI.sub.11, PMI.sub.12, and PMI.sub.2 have different time domain granularities or frequency domain granularities, for example, PMI.sub.1 and PMI.sub.2, or PMI.sub.11, PMI.sub.12, and PMI.sub.2 separately indicate different periods or bandwidth channel features, or are obtained based on different subframe periods or subband sizes.

(85) Alternatively, further, the precoding matrix indicators PMI.sub.11 and PMI.sub.12 are sent to the base station according to different time periods.

(86) Specifically, receiving a precoding matrix indicator PMI sent by the user equipment UE may also include: receiving precoding matrix indicators PMI.sub.1,i, 1≤i≤N.sub.B, and PMI.sub.2 sent by the user equipment UE, where PMI.sub.1,i, 1≤i≤N.sub.B and PMI.sub.2 are used to indicate the matrix X.sub.i=A.sub.i.Math.B.sub.i, 1≤i≤N.sub.B, and the matrix W.sub.2, respectively; or

(87) receiving precoding matrix indicators PMI.sub.11,i, PMI.sub.12,i, and PMI.sub.2 sent by the user equipment UE, where PMI.sub.11,i, PMI.sub.12,i, and PMI.sub.2 are used to indicate the matrix A.sub.i, 1≤i≤N.sub.B, the matrix B.sub.i, 1≤i≤N.sub.B, and the matrix W.sub.2 respectively; or

(88) receiving precoding matrix indicators PMI.sub.1,i, 1≤i≤N.sub.B/2, and PMI.sub.2 sent by the user equipment UE, where PMI.sub.1,i, 1≤i≤N.sub.B/2 and PMI.sub.2 are used to indicate a matrix X.sub.2i−1=X.sub.2i=A.sub.2i.Math.B.sub.2i, 1≤i≤N/2, and the matrix W.sub.2 respectively; and in this case, X.sub.2i−1=X.sub.2i, and the matrices appear in pairs; or

(89) receiving precoding matrix indicators PMI.sub.11,i, PMI.sub.12,i, and PMI.sub.2 sent by the user equipment UE, where PMI.sub.11, PMI.sub.12,i, and PMI.sub.2 are used to indicate a matrix A.sub.2i−1=A.sub.2i, 1≤i≤N.sub.B/2, the matrix B.sub.2i−1=B.sub.2i, 1≤i≤N.sub.B/2, and the matrix W.sub.2, respectively; and in this case, A.sub.2i−1=A.sub.2i, B.sub.2i−1=B.sub.2i, and the matrices appear in pairs.

(90) Specifically, receiving a precoding matrix indicator PMI sent by the user equipment UE may be receiving, through a physical uplink control channel (PUCCI) or a physical uplink shared channel (PUSCH), the precoding matrix indicator PMI sent by the user equipment UE.

(91) Further, receiving a precoding matrix indicator PMI sent by the user equipment UE may be separately receiving, by the base station by using different subframes or according to different periods, the foregoing PMI.sub.1 and PMI.sub.2; or PMI.sub.11, PMI.sub.12, and PMI.sub.2; or PMI.sub.1,i, 1≤i≤N.sub.B and PMI.sub.2 or PMI.sub.11,i, PMI.sub.12,i, 1≤i≤N.sub.B, and PMI.sub.2; or PMI.sub.11,i, PMI.sub.12,i, 1≤i≤N.sub.B/2, and PMI.sub.2 that are sent by the user equipment UE; or

(92) may also be receiving the foregoing PMI.sub.1 and PMI.sub.2; or PMI.sub.11, PMI.sub.12, and PMI.sub.2; or PMI.sub.1,i, 1≤i≤N.sub.B and PMI.sub.2; or PMI.sub.11,i, PMI.sub.12,i, 1≤i≤N.sub.B, and PMI.sub.2; or PMI.sub.11,i, PMI.sub.12,i, 1≤i≤N.sub.B/2, and PMI.sub.2 that are sent for different subbands or subband sizes in a frequency domain by the user equipment U.

(93) In this embodiment of the present invention, a base station eNB receives a precoding matrix indicator PMI sent by a user equipment UE, where the PMI indicates a precoding matrix. The precoding matrix has a structure of W=W.sub.1W.sub.2, where W.sub.1 is a block diagonal matrix in which each block matrix on a diagonal line is X.sub.i=A.sub.i.Math.B.sub.i, and i=1, . . . , N.sub.B, where the matrix A.sub.i or the matrix B.sub.i effectively supports channel state information quantization in a horizontal direction or a vertical direction, respectively. This can fully use a degree of freedom of an active antenna system AAS in a horizontal direction and a vertical direction, thereby greatly improving channel state information feedback accuracy. In addition, multiple block matrices X.sub.i may separately correspond to antenna groups of different polarizations or at different locations, so that the foregoing precoding matrix matches multiple antenna deployments or configurations. The foregoing codebook structure greatly improves performance of MIMO, and especially that of MU-MIMO. Moreover, one or more PMIs are fed back based on a subset to indicate a precoding matrix, which fully uses time/frequency domain/spatial correlation of a channel, thereby greatly reducing feedback overheads.

(94) The following describes a system for determining a precoding matrix indicator, a user equipment UE, and a base station eNB in the present invention in detail.

(95) FIG. 3 is a schematic structural diagram of composition of an embodiment of a system for determining a precoding matrix indicator according to the present invention. The system according to this embodiment of the present invention includes a user equipment UE 11 and a base station eNB 12. For a structure of the user equipment UE 11, refer to FIG. 4; and for a schematic structural diagram of the base station eNB 12, refer to FIG. 5.

(96) FIG. 4 is a schematic diagram of a user equipment UE 11 for determining a precoding matrix indicator according to an embodiment of the present invention. As shown in the figure, the user equipment UE 11 includes: a receiving unit 111, a selecting unit 112, and a sending unit 113.

(97) The receiving unit 111 is configured to receive a reference signal sent by a base station.

(98) Specifically, the reference signal sent by the base station may include a channel state information reference signal (CSI RS), a demodulation reference signal (demodulation RS, DM RS), or a cell-specific reference signal (cell-specific RS, CRS). The user equipment UE may obtain a resource configuration of the reference signal by receiving a notification (for example, RRC (Radio Resource Control) signaling or downlink control information DCI) from an eNB or based on a cell identity ID, and obtain the reference signal from a corresponding resource or subframe.

(99) The selecting unit 112 is configured to select, based on the reference signal, a precoding matrix from a codebook, where a precoding matrix W included in the codebook is a product of two matrices W.sub.1 and W.sub.2; and the precoding matrix has the structure shown in formulas (1) to (4).

(100) Specifically, each column of the matrix A.sub.i or of the matrix B.sub.i may be a DFT vector or may be a column vector of a Hadamard matrix, as shown in formulas (5) to (11); or

(101) specifically, the matrix A.sub.i or the matrix B.sub.i may also be a precoding matrix in a 2-antenna codebook or a 4-antenna codebook of an LTE R8 system, or in an 8-antenna codebook of an LTE R10 system.

(102) Further, the matrix W.sub.2 is used to select or weight and combine a column vector in the matrix W.sub.1, so as to form the matrix W.

(103) In an example in which the number of block matrices is N.sub.B=2 and there are 32 transmit antennas, matrices that form the precoding matrix W may separately be those shown in formulas (12) to (23); or B.sub.i is a precoding matrix in a 4-antenna rank-4 codebook of an LTE R8 system.

(104) In an example in which the number of block matrices is A=2 and there are 32 transmit antennas, matrices that form the precoding matrix W may separately be those shown in formulas (24) to (30); or B.sub.i is a precoding matrix in a 4-antenna rank-4 codebook of an LTE R8 system.

(105) Specifically, selecting, based on the reference signal, a precoding matrix from a codebook includes:

(106) obtaining, by the user equipment UE based on the reference signal, a channel estimate and selecting, based on a predefined criterion such as a channel capacity or throughput maximization criterion, the precoding matrix from the codebook according to the channel estimate. Selecting, based on a predefined criterion, a precoding matrix is an existing technology, and details are not described herein.

(107) Further, selecting, based on the reference signal, a precoding matrix from a codebook includes:

(108) selecting, based on the reference signal, the precoding matrix from a codebook subset, where

(109) the codebook subset may be a codebook subset that is predefined; or a codebook subset that is reported by the UE to the base station eNB, determined by the base station eNB based on the report from the UE, and notified to the UE; or a codebook subset that is determined and reported by the UE, for example, a latest reported codebook subset.

(110) Further, the codebook subset may include a subset of the matrix W.sub.1 the matrix A.sub.i, the matrix B.sub.i, or the matrix W.sub.2.

(111) Selecting, based on the codebook subset, the precoding matrix can further reduce feedback overheads and implementation complexity.

(112) Further, the codebook subsets have a same subset of the matrix W.sub.1, the matrix A.sub.i, the matrix B.sub.i, or the matrix W.sub.2. In this way, the codebook subsets overlap each other, which can overcome an edge effect of channel state information quantization.

(113) Further, in the precoding matrix, block matrices X.sub.i and X.sub.j, i≈j may be unequal, or may also be equal. If there are multiple cases that X.sub.i and X.sub.j, i≈j are equal, for example, X.sub.i and X.sub.j, i≈j that are equal may appear in pairs, the feedback overheads can be further reduced.

(114) In addition, the foregoing matrix A.sub.i or matrix B.sub.i may also use another form, which is not further elaborated herein.

(115) It should be noted that, each of the foregoing matrices may further be multiplied by a scale factor, so as to implement power normalization or power balancing.

(116) The sending unit 113 is configured to send a precoding matrix indicator PMI to the base station, where the PMI corresponds to the selected precoding matrix, so that the base station obtains the precoding matrix according to the PMI.

(117) Specifically, the precoding matrix is included in a precoding matrix set or a codebook; and the PMI is used to indicate the selected precoding matrix in the precoding matrix set or the codebook.

(118) Specifically, sending a precoding matrix indicator PMI to the base station includes: sending the precoding matrix indicator PMI to the base station, where the PMI may include only one specific value. In this case, the PMI directly indicates the precoding matrix W. For example, if there are a total of 16 different precoding matrices, PMI=0, . . . , 15 may be used to respectively indicate precoding matrices W whose labels are 0, 1, . . . , 15.

(119) Specifically, sending a precoding matrix indicator PMI to the base station may also include: sending precoding matrix indicators PMI.sub.1 and PMI.sub.2 to the base station, where PMI.sub.1 and PMI.sub.2 are used to indicate the matrix X.sub.i=A.sub.i.Math.B.sub.i, 1≤i≤N.sub.B in formula (2) and the matrix W.sub.2, respectively; and in this case, the matrix X.sub.i=A.sub.i.Math.B.sub.i, 1≤i≤N.sub.B, and the matrix W.sub.2 are respectively indicated by PMI.sub.1 and PMI.sub.2 in the codebook; or

(120) sending precoding matrix indicators PMI.sub.11, PMI.sub.12, and PMI.sub.2 to the base station, where PMI.sub.11, PMI.sub.12, and PMI.sub.2 are used to indicate the matrix A.sub.i, 1≤i N.sub.B, the matrix B.sub.i, 1≤i≤N.sub.B, and the matrix W.sub.2, respectively; and in this case, the matrix A.sub.i, 1≤i≤N.sub.B, the matrix B.sub.i, 1≤i≤N.sub.B, and the matrix W.sub.2 are respectively indicated by PMI.sub.11, PMI.sub.12, and PMI.sub.2 in the codebook.

(121) Specifically, sending a precoding matrix indicator PMI to the base station may also include: sending precoding matrix indicators PMI.sub.1,i 1≤i≤N.sub.B/2 and PMI.sub.2 to the base station, where PMI.sub.1,i, 1≤i≤N.sub.B/2 and PMI.sub.2 are used to indicate a matrix X.sub.2i−1=X.sub.2i=A.sub.2i.Math.B.sub.2i, 1≤i≤N.sub.B/2 and the matrix W.sub.2 respectively; and in this case, X.sub.2i−1=X.sub.2i, and the matrices appear in pairs; or

(122) sending precoding matrix indicators PMI.sub.11,i, PMI.sub.12,i, and PMI.sub.2 to the base station, where PMI.sub.11,i, PMI.sub.12,i, and PMI.sub.2 are used to indicate a matrix A.sub.2i−1=A.sub.2i, 1≤i≤N.sub.B/2, the matrix B.sub.2i−1=B.sub.2i, 1≤i≤N.sub.B/2, and the matrix W.sub.2, respectively; and in this case, A.sub.2i−1=A.sub.2i, B.sub.2i−1=B.sub.2i, and the matrices appear in pairs.

(123) Further, the precoding matrix indicators PMI.sub.1 and PMI.sub.2, or the precoding matrix indicators PMI.sub.11, PMI.sub.12, and PMI.sub.2 have different time domain granularities or frequency domain granularities, for example, PMI.sub.1 and PMI.sub.2, or PMI.sub.11, PMI.sub.12, and PMI.sub.2 separately indicate different periods or bandwidth channel features, or are obtained based on different subframe periods or subband sizes.

(124) Alternatively, further, the precoding matrix indicators PMI.sub.11 and PMI.sub.12 are sent to the base station according to different time periods.

(125) Specifically, sending a precoding matrix indicator PMI to the base station may also include: sending precoding matrix indicators PMI.sub.1,i, 1≤i≤N.sub.B and PMI.sub.2 to the base station, where PMI.sub.1,i, 1≤i≤N.sub.B and PMI.sub.2 are used to indicate the matrix X.sub.i=A.sub.i.Math.B.sub.i, 1≤i≤N.sub.B and the matrix W.sub.2, respectively; or

(126) sending precoding matrix indicators PMI.sub.11, PMI.sub.12, and PMI.sub.2 to the base station, where PMI.sub.11,i, PMI.sub.12,i, and PMI.sub.2 are used to indicate the matrix A.sub.i, 1≤i≤N.sub.B, the matrix B.sub.i, 1≤i≤N.sub.B, and the matrix W.sub.2, respectively.

(127) Specifically, sending a precoding matrix indicator PMI to the base station may be sending, by the UE, the precoding matrix indicator PMI to the base station through a physical uplink control channel (PUCCH) or a physical uplink shared channel (PUSCH).

(128) Further, sending a precoding matrix indicator PMI to the base station may be separately sending, by the UL by using different subframes or according to different periods, the foregoing PMI.sub.1 and PMI.sub.2; or PMI.sub.11, PMI.sub.12, and PMI.sub.2; or PMI.sub.1,i, 1≤i≤N.sub.B, and PMI.sub.2; or PMI.sub.11,i, PMI.sub.12,i, 1≤i≤N.sub.B, and PMI.sub.2; or PMI.sub.1,i, 1≤i≤N.sub.B/2, and PMI.sub.2; or PMI.sub.11,i, PMI.sub.12,i, 1≤i≤N.sub.B/2 and PMI.sub.2 to the base station.

(129) Further, sending a precoding matrix indicator PMI to the base station may also be separately sending, by the UE for different subbands or subband sizes in a frequency domain, the foregoing PMI.sub.1 and PMI.sub.2; or PMI.sub.11, PMI.sub.12, and PMI.sub.2; or PMI.sub.1,i, 1≤i≤N.sub.B, and PMI.sub.2; or PMI.sub.11,i, PMI.sub.12,i, 1≤i≤N.sub.B, and PMI.sub.2; or PMI.sub.1,i, 1≤i≤N.sub.B/2, and PMI.sub.2; or PMI.sub.11,i, PMI.sub.12,i, 1≤i≤N.sub.B/2 and PMI.sub.2 to the base station.

(130) In this embodiment of the present invention, a user equipment determines and sends a precoding matrix indicator PMI, where the PMI indicates a precoding matrix. The precoding matrix has a structure of W=W.sub.1W.sub.2, where W.sub.1 is a block diagonal matrix in which each block matrix on a diagonal line is X.sub.i=A.sub.i.Math.B.sub.i, and i=1, . . . , N.sub.B, where the matrix A.sub.i or the matrix B.sub.i effectively supports channel state information quantization in a horizontal direction or a vertical direction, respectively. This can fully use a degree of freedom of an active antenna system AAS in a horizontal direction and a vertical direction, thereby greatly improving channel state information feedback accuracy. In addition, multiple block matrices X.sub.i may separately correspond to antenna groups of different polarizations or at different locations, so that the foregoing precoding matrix matches multiple antenna deployments or configurations. The foregoing codebook structure greatly improves performance of MIMO, and especially that of MU-MIMTO. Moreover, one or more PMIs are fed back based on a subset to indicate a precoding matrix, which fully uses time/frequency domain/spatial correlation of a channel, thereby greatly reducing feedback overheads.

(131) FIG. 5 is a base station eNB 12 for determining a precoding matrix indicator according to an embodiment of the present invention. As shown in the figure, the base station eNB 12 includes: a sending unit 121 and a receiving unit 122.

(132) The sending unit 121 is configured to send a reference signal to a user equipment UE.

(133) Specifically, the reference signal may include a channel state information reference signal (CSI RS), a demodulation reference signal (demodulation RS, DM RS), or a cell-specific reference signal (cell-specific RS, CRS). Abase station eNB may notify the user equipment UE of a resource configuration of the reference signal by using RRC (Radio Resource Control) signaling or downlink control information (DC), and instruct the UE to obtain the reference signal from a corresponding resource or subframe. The user equipment UE may also implicitly obtain, based on other information such as a cell identity ID, the resource configuration of the reference signal, and obtain the reference signal from the corresponding resource or subframe. The receiving unit 122 is configured to receive a precoding matrix indicator PMI sent by the user equipment UE, where the PMI corresponds to a precoding matrix selected, based on the reference signal, from a codebook by the user equipment; and a precoding matrix W included in the codebook is a product of two matrices W.sub.1 and W.sub.2, and the precoding matrix W has the structure shown in formulas (1) to (4).

(134) Specifically, each column of the matrix A.sub.i or of the matrix B.sub.i may be a DFT vector or may be a column vector of a Hadamard matrix, as shown in formulas (5) to (11); or

(135) specifically, the matrix A.sub.i or the matrix B.sub.i may also be a precoding matrix in a 2-antenna codebook or a 4-antenna codebook of an LTE R8 system, or in an 8-antenna codebook of an LTE R10 system.

(136) Further, the matrix W.sub.2 is used to select or weight and combine a column vector in the matrix W.sub.1, so as to form the matrix W.

(137) In an example in which the number of block matrices is N.sub.B=2 and there are 32 transmit antennas, matrices that form the precoding matrix W may separately be those shown in formulas (12) to (23); or B.sub.i is a precoding matrix in a 4-antenna rank-4 codebook of an LTE R8 system.

(138) In an example in which the number of block matrices is N.sub.B=2 and there are 32 transmit antennas, matrices that form the precoding matrix W may separately be those shown in formulas (24) to (30); or B.sub.i is a precoding matrix in a 4-antenna rank-4 codebook of an LTE R8 system.

(139) Specifically, the precoding matrix selected, based on the reference signal, from a codebook includes: the precoding matrix selected, based on the reference signal, from a codebook subset, where

(140) the codebook subset may be a codebook subset that is predefined; or a codebook subset that is reported by the UE to the base station eNB, determined by the base station eNB based on the report from the UE, and notified to the UE; or a codebook subset that is determined and reported by the UE, for example, a latest reported codebook subset.

(141) Further, the codebook subset may include a subset of the matrix W.sub.1, the matrix A.sub.i, the matrix B.sub.i, or the matrix W.sub.2.

(142) Further, the codebook subsets have a same subset of the matrix W.sub.1, the matrix A.sub.i, the matrix B.sub.i, or the matrix W.sub.2. In this way, the codebook subsets overlap each other, which can overcome an edge effect of channel state information quantization.

(143) Further, in the precoding matrix, block matrices X.sub.i and X.sub.j, i≈j may be unequal, or may also be equal. If there are multiple cases that X.sub.i and X.sub.j, i≈j are equal, for example, X.sub.i and X.sub.j, i≈j that are equal may appear in pairs, feedback overheads can be further reduced.

(144) In addition, the foregoing matrix A.sub.i or matrix B.sub.i may also use another form, which is not further elaborated herein.

(145) It should be noted that, each of the foregoing matrices may further be multiplied by a scale factor, so as to implement power normalization or power balancing.

(146) Specifically, the precoding matrix is included in a precoding matrix set or a codebook; and the PMI is used to indicate the selected precoding matrix in the precoding matrix set or the codebook.

(147) Specifically, receiving a precoding matrix indicator PMI sent by the user equipment UE includes: receiving the precoding matrix indicator PMI sent by the user equipment UE, where the PMI may include only one specific value. In this case, the PMI directly indicates the precoding matrix W. For example, if there are a total of 16 different precoding matrices, PMI=0, . . . , 15 may be used to respectively indicate precoding matrices W whose labels are 0, 1, . . . 15.

(148) Specifically, receiving a precoding matrix indicator PMI sent by the user equipment UE may also include: receiving precoding matrix indicators PMI.sub.1 and PMI.sub.2 sent by the user equipment UE, where PMI.sub.1 and PMI.sub.2 are used to indicate the matrix X.sub.i=A.sub.i.Math.B.sub.i, 1≤i≤N.sub.B in formula (2) and the matrix W.sub.2, respectively; and in this case, the matrix X.sub.i=A.sub.i.Math.B.sub.i, 1≤i≤N.sub.B and the matrix W.sub.2 are respectively indicated by PMI.sub.1 and PMI.sub.2 in the codebook; or

(149) receiving precoding matrix indicators PMI.sub.11, PMI.sub.12, and PMI.sub.2 sent by the user equipment UE, where PMI.sub.11, PMI.sub.12, and PMI.sub.2 are used to indicate the matrix A.sub.i, 1≤i≤N.sub.B, the matrix B.sub.i, 1≤i≤N.sub.B, and the matrix W.sub.2, respectively; and in this case, the matrix A.sub.i, 1≤i≤N.sub.B, the matrix B.sub.i, 1≤i≤N.sub.B, and the matrix W.sub.2 are respectively indicated by PMI.sub.11, PMI.sub.12, and PMI.sub.2 in the codebook.

(150) Further, the precoding matrix indicators PMI.sub.1 and PMI.sub.2, or the precoding matrix indicators PMI.sub.11, PMI.sub.12, and PMI.sub.2 have different time domain granularities or frequency domain granularities, for example, PMI.sub.1 and PMI.sub.2, or PMI.sub.11, PMI.sub.12, and PMI.sub.2 separately indicate different periods or bandwidth channel features, or are obtained based on different subframe periods or subband sizes.

(151) Alternatively, further, the precoding matrix indicators PMI.sub.11 and PMI.sub.12 are sent to the base station according to different time periods.

(152) Specifically, receiving a precoding matrix indicator PMI sent by the user equipment UE may also include: receiving precoding matrix indicators PMI.sub.1,i, 1≤i≤N.sub.B, and PMI.sub.2 sent by the user equipment UE, where PMI.sub.1,i, 1≤i≤N.sub.B and PMI.sub.2 are used to indicate the matrix X.sub.i=A.sub.i.Math.B.sub.i, 1≤i≤N.sub.B the matrix W.sub.2, respectively; or

(153) receiving precoding matrix indicators PMI.sub.11,i, PMI.sub.12,i, and PMI.sub.2 sent by the user equipment UE, where PMI.sub.11,i, PMI.sub.12,i, and PMI.sub.2 are used to indicate the matrix A.sub.i, 1≤i≤N.sub.B, the matrix B.sub.i, 1≤i≤N.sub.B, and the matrix W.sub.2, respectively; or receiving precoding matrix indicators PMI.sub.1,i, 1≤i≤N.sub.B/2, and PMI.sub.2 sent by the user equipment UE, where PMI.sub.1,i, 1≤i≤N.sub.B/2 and PMI.sub.2 are used to indicate a matrix X.sub.2i−1=X.sub.2i=A.sub.2i.Math.B.sub.2i, 1≤i≤N.sub.B/2, and the matrix W.sub.2, respectively; and in this case, X.sub.2i−1=X.sub.2i, and the matrices appear in pairs; or

(154) receiving precoding matrix indicators PMI.sub.11,i, PMI.sub.12,i, and PMI.sub.2 sent by the user equipment UE, where PMI.sub.11,i, PMI.sub.12,i, and PMI.sub.2 are used to indicate a matrix A.sub.2i−1=A.sub.2i, 1≤i≤N.sub.B/2, the matrix B.sub.2i−1=B.sub.2i, 1≤i≤N.sub.B/2, and the matrix W.sub.2, respectively; and in this case, A.sub.2i−1=A.sub.2i, B.sub.2i−1=B.sub.2i, and the matrices appear in pairs.

(155) Specifically, receiving a precoding matrix indicator PMI sent by the user equipment UE may be receiving, through a physical uplink control channel (PUCCI) or a physical uplink shared channel (PUSCH), the precoding matrix indicator PMI sent by the user equipment UE.

(156) Further, receiving a precoding matrix indicator PMI sent by the user equipment UE may be separately receiving, by the base station by using different subframes or according to different periods, the foregoing precoding matrix indicators sent by the user equipment UE, which are PMI.sub.1 and PMI.sub.2; or PMI.sub.11, PMI.sub.12, and PMI.sub.2; or PMI.sub.1,i, 1≤i≤N.sub.B and PMI.sub.2; or PMI.sub.11,i, PMI.sub.12,i, 1≤i≤N.sub.B, and PMI.sub.2; or PMI.sub.11,i, PMI.sub.12,i, 1≤i≤N.sub.B/2, and PMI.sub.2; or

(157) may also be receiving the foregoing PMI.sub.1 and PMI.sub.2; or PMI.sub.11 PMI.sub.12, and PMI.sub.2; or PMI.sub.1,i, 1≤i≤N.sub.B and PMI.sub.2; or PMI.sub.11,i, PMI.sub.12,i, 1≤i≤N.sub.B, and PMI.sub.2; or PMI.sub.11,i, PMI.sub.12,i, 1≤i≤N.sub.B/2, and PMI that are sent for different subbands or subband sizes in a frequency domain by the user equipment UE.

(158) In this embodiment of the present invention, the base station eNB receives a precoding matrix indicator PMI sent by the user equipment UE, where the PMI indicates a precoding matrix. The precoding matrix has a structure of W=W.sub.1W.sub.2, where W.sub.1 is a block diagonal matrix in which each block matrix on a diagonal line is X.sub.i=A.sub.i.Math.B.sub.i, and i=1, . . . , N.sub.B, where the matrix A.sub.i or the matrix B.sub.i effectively supports channel state information quantization in a horizontal direction or a vertical direction, respectively. This can fully use a degree of freedom of an active antenna system AAS in a horizontal direction and a vertical direction, thereby greatly improving CSI feedback accuracy. In addition, multiple block matrices X.sub.i may separately correspond to antenna groups of different polarizations or at different locations, so that the foregoing precoding matrix matches multiple antenna deployments or configurations. The foregoing codebook structure greatly improves performance of MIMO, and especially that of MU-MIMO. Moreover, one or more PMIs are fed back based on a subset to indicate a precoding matrix, which fully uses time/frequency domain/spatial correlation of a channel, thereby greatly reducing feedback overheads.

(159) A person skilled in the art may be further aware that, in combination with the examples described in the embodiments disclosed in this specification, units and algorithm steps may be implemented by electronic hardware, computer software, or a combination thereof. To clearly describe the interchangeability between the hardware and the software, the foregoing has generally described structures and steps of each example according to functions. Whether the functions are performed by hardware or software depends on particular applications and design constraint conditions of the technical solutions. A person skilled in the art may use different methods to implement the described functions for each particular application, but it should not be considered that the implementation goes beyond the scope of the present invention.

(160) In combination with the embodiments disclosed in this specification, method or algorithm steps may be implemented by hardware, a software module executed by a processor, or a combination thereof. The software module may reside in a random access memory (RAM), memory, a read-only memory (ROM), an electrically programmable ROM, an electrically erasable programmable ROM, a register, a hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art.

(161) The foregoing specific embodiments further describe the objectives, technical solutions, and beneficial effects of the present invention in detail. It should be understood that the foregoing descriptions are merely specific embodiments of the present invention, but are not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, or improvement made without departing from the spirit and principle of the present invention should fall within the protection scope of the present invention.