1. A method for determining a precoding matrix indicator, the method comprising: receiving, by a user equipment, a reference signal sent by a base station; selecting, by the user equipment, based on the reference signal, a precoding matrix from a codebook, wherein a precoding matrix W comprised in the codebook is a product of two matrices W 1 and W 2 , wherein W 1 is a block diagonal matrix, W 1 =diag{X 1 , . . . , X N B }, wherein each block matrix X i is a Kronecker product of a matrix A i and a matrix B i , X i =A i B i , and 1≦i≦N B , and the W 1 comprises at least one block matrix, N B ≧1; and sending, by the user equipment, a precoding matrix indicator (PMI) to the base station, wherein the PMI corresponds to the selected precoding matrix.
2. The method according to claim 1 , wherein each column of the matrix A i or the matrix B i in the block matrix X i =A i B i is a discrete Fourier transform (DFT) vector or is a column vector of a Hadamard matrix.
3. The method according to claim 1 , wherein the matrix A i or the matrix B i in the block matrix X i =A i B i is selected from a 2-antenna codebook, a 4-antenna codebook, or an 8-antenna codebook of a Long Term Evolution (LTE) system.
4. The method according to claim 1 , wherein selecting, based on the reference signal, a precoding matrix from a codebook comprises: selecting, based on the reference signal, the precoding matrix from a codebook subset that is predefined, or reported by a mobile terminal, or locally determined.
5. The method according to claim 1 , wherein sending a precoding matrix indicator (PMI) to the base station comprises: sending a first precoding matrix indicator PMI 1 and a second precoding matrix indicator PMI 2 to the base station, wherein the first precoding matrix indicator PMI 1 is used to indicate the matrix X i =A i B i and the second precoding matrix indicator PMI 2 is used to indicate the matrix W 2 ; or sending a third precoding matrix indicator PMI 11 , a fourth precoding matrix indicator PMI 12 , and a fifth precoding matrix indicator PMI 2 to the base station, wherein the third precoding matrix indicator PMI 11 is used to indicate the matrix A i wherein 1≦i≦N B ; the fourth precoding matrix indicator PMI 12 is used to indicate the matrix B i , wherein 1≦i≦N B , and the fifth precoding matrix indicator PMI 2 is used to indicate the matrix W 2 .
6. A method for determining a precoding matrix indicator, the method comprising: sending, by a base station, a reference signal to a user equipment (UE); and receiving, by the base station, a precoding matrix indicator (PMI) sent by the UE, wherein the PMI corresponds to a precoding matrix that is selected by the UE, based on the reference signal, from a codebook, wherein a precoding matrix W comprised in the codebook is a product of two matrices W 1 and W 2 , wherein W 1 is a block diagonal matrix, W 1 =diag{X 1 , . . . , X N B }, wherein each block matrix X i is a Kronecker product of a matrix A i and a matrix B i , X i =A i B i , and 1≦i≦N B , and the matrix W 1 comprises at least one block matrix, N B ≧1.
7. The method according to claim 6 , wherein each column of the matrix A i or the matrix B i in the block matrix X i =A i B i is a discrete Fourier transform (DH) vector or is a column vector of a Hadamard matrix.
8. The method according to claim 6 , wherein the matrix A i or the matrix B i in the block matrix X i =A i B i is selected from a 2-antenna codebook, a 4-antenna codebook, or an 8-antenna codebook of a Long Term Evolution (LTE) system.
9. The method according to claim 6 , wherein the precoding matrix that is selected, based on the reference signal, from the codebook comprises: selecting, based on the reference signal, the precoding matrix from a codebook subset that is predefined, or reported by the UE, or locally determined.
10. The method according to claim 6 , wherein receiving a precoding matrix indicator PMI sent by the UE comprises: receiving a first precoding matrix indicator PMI 1 and a second precoding matrix indicator PMI 2 , that are sent by the user equipment UE, wherein the first precoding matrix indicator PMI 1 is used to indicate the matrix X i =A i B i and the second precoding matrix indicator PMI 2 is used to indicate the matrix W 2 ; or receiving a third precoding matrix indicator PMI 11 , a fourth precoding matrix indicator PMI 12 , and a fifth precoding matrix indicator PMI 2 that are sent by the UE, wherein the third precoding matrix indicator PMI 11 is used to indicate the matrix A i , wherein 1≦i≦N B , the fourth precoding matrix indicator PMI 12 is used to indicate the matrix B i , wherein 1≦i≦N B , and the fifth precoding matrix indicator PMI 2 is used to indicate the matrix W 2 .
11. A user equipment (UE), comprising: a receiving unit, configured to receive a reference signal sent by a base station; a selecting unit, configured to select, based on the reference signal, a precoding matrix from a codebook, wherein a precoding matrix W comprised in the codebook is a product of two matrices W 1 and W 2 , wherein W 1 is a block diagonal matrix, W 1 =diag{X 1 , . . . , X N B }, wherein each block matrix X i is a Kronecker product of a matrix A i and a matrix B i , X i =A 1 B i , and 1≦i≦N B , and the W 1 comprises at least one block matrix, N B ≧1; and a sending unit, configured to send a precoding matrix indicator (PMI) to the base station, wherein the PMI corresponds to the selected precoding matrix.
12. The user equipment according to claim 11 , wherein each column of the matrix A i or the matrix B i in the block matrix X i =A i B i is a discrete Fourier transform (DE l′)) vector or is a column vector of a Hadamard matrix.
13. The user equipment according to claim 11 , wherein the matrix A i or the matrix B i in the block matrix X i =A i B i is selected from a 2-antenna codebook, a 4-antenna codebook, or an 8-antenna codebook of a Long Term Evolution (LTE) system.
14. The user equipment according to claim 11 , wherein the selecting unit is configured to select, based on the reference signal, the precoding matrix from a codebook subset that is predefined or locally determined.
15. The user equipment according to claim 11 , wherein the sending unit is configured to: send a first precoding matrix indicator PMI 1 and a second precoding matrix indicator PMI 2 to the base station, wherein the first precoding matrix indicator PMI 1 is used to indicate the matrix X i =A i B i , and the second precoding matrix indicator PMI 2 is used to indicate the matrix W 2 ; or send a third precoding matrix indicator PMI 11 , a fourth precoding matrix indicator PMI 12 , and a fifth precoding matrix indicator PMI 2 to the base station, wherein the third precoding matrix indicator PMI 11 is used to indicate the matrix A i wherein 1≦i≦N B , the fourth precoding matrix indicator PMI 12 is used to indicate the matrix B i , wherein 1≦i≦N B , and the fifth precoding matrix indicator PMI 2 is used to indicate the matrix W 2 .
16. A base station, comprising: a sending unit, configured to send a reference signal to a user equipment UE; and a receiving unit, configured to receive a precoding matrix indicator (PMI) sent by the UE, wherein the PMI corresponds to a precoding matrix that is selected by the UE, based on the reference signal, from a codebook, wherein a precoding matrix W comprised in the codebook is a product of two matrices W 1 and W 2 , wherein W 1 is a block diagonal matrix, W 1 =diag{X 1 , . . . , X N B }, wherein each block matrix X i is a Kronecker product of a matrix A i and a matrix B i , X i =A i B i , and 1≦i≦N B , and the matrix W 1 comprises at least one block matrix, N B ≧1.
17. The base station according to claim 16 , wherein each column of the matrix A i or the matrix B i in the block matrix X=A i B i is a discrete Fourier transform (DFT) or is a column vector of a Hadamard matrix.
18. The base station according to claim 16 , wherein the matrix A i or the matrix B i in the block matrix X i =A i B i is selected from a 2-antenna codebook, a 4-antenna codebook, or an 8-antenna codebook of a Long Term Evolution (LTE) system.
19. The base station according to claim 16 , wherein the selecting unit is configured to select, based on the reference signal, the precoding matrix from a codebook subset that is predefined, or reported by the UE, or locally determined.
20. The base station according to claim 16 , wherein the receiving unit is configured to: receive a first precoding matrix indicator PMI 1 and a second precoding matrix indicator PMI 2 that are sent by the UE, wherein the first precoding matrix indicator PMI 1 is used to indicate the matrix X i =A i B i , and the second precoding matrix indicator PMI 2 is used to indicate the matrix W 2 ; or receive a third precoding matrix indicator PMI 11 , a fourth precoding matrix indicator PMI 12 , and a fifth precoding matrix indicator PMI 2 that are sent by the UE, wherein the third precoding matrix indicator PMI 11 is used to indicate the matrix A i , wherein 1≦i≦N B , the fourth precoding matrix indicator PMI 12 is used to indicate the matrix B i , wherein 1≦i≦N B and the fifth precoding matrix indicator PMI 2 is used to indicate the matrix W 2 .
