A communications apparatus, comprising: a transceiver, configured to receive indication information; and a processor, configured to determine, based on the indication information received by the transceiver, a second precoding matrix set from a first precoding matrix set whose rank is R, wherein each precoding matrix W in the first precoding matrix set satisfies W = W 1 × W 2, W is a matrix of N t rows and R columns, N t is greater than or equal to R, W 1 satisfies W 1 = X 0 0 X, X = [b k 0 ··· b k M-1], b k i is an N t /2×1 vector, b k i belongs to a vector set B = {b 0, b 1,..., b T -1}, T is a quantity of vectors in B, T ≥ M, T is an integer, W 2 is a matrix of 2M rows and R columns, an element W 2 ( x, y) in row x and column y of W 2 satisfies W 2 x y = p 0, y − 1, x − 1 0 × p 0, y − 1, x − 1 1 × p 0, y − 1, x − 1 2, an element W 2 ( x + M, y) in row x+M and column y of W 2 satisfies W 2 x + M, y = p 1, y − 1, x − 1 0 × p 1, y − 1, x − 1 1 × p 1, y − 1, x − 1 2, p z, y − 1, x − 1 0 is a first product factor, p z, y − 1, x − 1 1 is a second product factor, p z, y − 1, x − 1 2 is a third product factor, 0 < x ≤ M, 0 < y ≤ R, a value range of p z, y − 1, x − 1 0 is a set A 0, z belongs to {0,1}, 1 ≥ p z, y − 1, x − 1 0 ≥ 0, p z, y − 1, x − 1 0 is a real number, p z, y − 1, x − 1 1 = 1, and p z, y − 1, x − 1 2 is a complex number whose modulus is 1; the indication information comprises indication information of S sets D 0 to D S-1, Do to D S-1 are respectively in one-to-one correspondence with c 0 to c S -1 in a vector set C = {c 0, c 1,..., c S -1}, any vector c j in C belongs to B, D j is a proper subset of A 0, S - 1 ≥ j ≥ 0, and j is an integer; and the second precoding matrix set is a proper subset of the first precoding matrix set, and the second precoding matrix set does not comprise W = W 1 × W 2 that satisfies the following condition in the first precoding matrix set: an x th column vector comprised in X of W 1 is the vector c j, and a first product factor p z, y − 1, x − 1 0 of at least one of elements in row x and row x+M of W 2 belongs to D j. a transceiver, configured to receive indication information; and a processor, configured to determine, based on the indication information received by the transceiver, a second precoding matrix set from a first precoding matrix set whose rank is R, wherein each precoding matrix W in the first precoding matrix set satisfies W = W 1 × W 2, W is a matrix of N t rows and R columns, N t is greater than or equal to R, W 1 satisfies W 1 = X 0 0 X, X = [b k 0 ··· b k M-1], b k i is an N t /2×1 vector, b k i belongs to a vector set B = {b 0, b 1,..., b T -1}, T is a quantity of vectors in B, T ≥ M, T is an integer, W 2 is a matrix of 2M rows and R columns, an element W 2 ( x, y) in row x and column y of W 2 satisfies W 2 x y = p 0, y − 1, x − 1 0 × p 0, y − 1, x − 1 1 × p 0, y − 1, x − 1 2, an element W 2 ( x + M, y) in row x+M and column y of W 2 satisfies W 2 x + M, y = p 1, y − 1, x − 1 0 × p 1, y − 1, x − 1 1 × p 1, y − 1, x − 1 2, p z, y − 1, x − 1 0 is a first product factor, p z, y − 1, x − 1 1 is a second product factor, p z, y − 1, x − 1 2 is a third product factor, 0 < x ≤ M, 0 < y ≤ R, a value range of p z, y − 1, x − 1 0 is a set A 0, z belongs to {0,1}, 1 ≥ p z, y − 1, x − 1 0 ≥ 0, p z, y − 1, x − 1 0 is a real number, p z, y − 1, x − 1 1 = 1, and p z, y − 1, x − 1 2 is a complex number whose modulus is 1; the indication information comprises indication information of S sets D 0 to D S-1, Do to D S-1 are respectively in one-to-one correspondence with c 0 to c S -1 in a vector set C = {c 0, c 1,..., c S -1}, any vector c j in C belongs to B, D j is a proper subset of A 0, S - 1 ≥ j ≥ 0, and j is an integer; and the second precoding matrix set is a proper subset of the first precoding matrix set, and the second precoding matrix set does not comprise W = W 1 × W 2 that satisfies the following condition in the first precoding matrix set: an x th column vector comprised in X of W 1 is the vector c j, and a first product factor p z, y − 1, x − 1 0 of at least one of elements in row x and row x+M of W 2 belongs to D j.