A method for providing codeword index information to a base station from a user equipment, the base station being configured with N t directional antennas, the method comprising: determining by the UE, according to an estimated broadband and/or long-term channel matrix and based on a first predetermined criterion, a first codeword in a first codebook whose rank is r, wherein the first codeword indicates broadband and/or long-term channel characteristics of antenna pairs having the same of two polarization directions, and r∈{1,2,..., N t}; sending a codeword index of the first codeword to the base station; determining by the UE, for each sub-band according to an estimated sub-band and/or short-term channel matrix and based on a second predetermined criterion, a second codeword in a second codebook whose rank is r, wherein the second codeword indicates sub-band and/or short-term channel characteristics of each polarization direction and between the two polarization directions; and sending a codeword index of the second codeword to the base station, wherein the first codeword is a block diagonal matrix, a matrix on a diagonal block of the block diagonal matrix is a matrix with N t /2 rows and N b columns, the N b columns are N b different Discrete Fourier Transform vectors arbitrarily selected from N predefined DFT vectors, N is an integer power of 2, 1≤N b ≤N, and the length of each DFT vector is N t; and the second codeword is constructed based on column selection of the first codeword and co-phasing information between the two polarization directions, and each column corresponding to each data stream in the second codeword comprises an equal-length column selection vector for individually selecting from the N b columns in the first codeword the DFT vectors used in the two polarization directions and co-phasing information θ = 2 π m M between the two polarization directions, where M is an integer power of 2, and 0≤m≤M-1, wherein the N b columns comprise four columns, the DFT vectors in the first column and the second column and the DFT vectors in the third column and the fourth column are adjacent vectors, and the DFT vectors in the first column and the third column and the DFT vectors in the second column and the fourth column are orthogonal vectors. determining by the UE, according to an estimated broadband and/or long-term channel matrix and based on a first predetermined criterion, a first codeword in a first codebook whose rank is r, wherein the first codeword indicates broadband and/or long-term channel characteristics of antenna pairs having the same of two polarization directions, and r∈{1,2,..., N t}; sending a codeword index of the first codeword to the base station; determining by the UE, for each sub-band according to an estimated sub-band and/or short-term channel matrix and based on a second predetermined criterion, a second codeword in a second codebook whose rank is r, wherein the second codeword indicates sub-band and/or short-term channel characteristics of each polarization direction and between the two polarization directions; and sending a codeword index of the second codeword to the base station, wherein the first codeword is a block diagonal matrix, a matrix on a diagonal block of the block diagonal matrix is a matrix with N t /2 rows and N b columns, the N b columns are N b different Discrete Fourier Transform vectors arbitrarily selected from N predefined DFT vectors, N is an integer power of 2, 1≤N b ≤N, and the length of each DFT vector is N t; and the second codeword is constructed based on column selection of the first codeword and co-phasing information between the two polarization directions, and each column corresponding to each data stream in the second codeword comprises an equal-length column selection vector for individually selecting from the N b columns in the first codeword the DFT vectors used in the two polarization directions and co-phasing information θ = 2 π m M between the two polarization directions, where M is an integer power of 2, and 0≤m≤M-1, wherein the N b columns comprise four columns, the DFT vectors in the first column and the second column and the DFT vectors in the third column and the fourth column are adjacent vectors, and the DFT vectors in the first column and the third column and the DFT vectors in the second column and the fourth column are orthogonal vectors.