Channel state information feedback method, communications apparatus, and system

A channel state information receiving method, comprising:

• receiving first frequency domain indication information and M1 pieces of precoding indication information, wherein the first frequency domain indication information is used to indicate L1 frequency domain subbands in T frequency domain subbands, the T frequency domain subbands are a system bandwidth or a part of a system bandwidth, 1≤L1<T, the T frequency domain subbands are in a one-to-one correspondence with T precoding matrices, and a precoding matrix wk corresponding to a kth frequency domain subband satisfies:
• Wk=W1×W2k, wherein
• w1 represents a matrix with Nt rows and R columns, and W2k represents a matrix with R rows and S columns;
• and
• determining T first elements based on the first frequency domain indication information and the M1 pieces of first precoding indication information, wherein a kth first element in the T first elements is a factor of an element in an rth row and an sth column of W2k and 1<M1<T.

A communications apparatus, comprising:

• a processor, configured to generate first frequency domain indication information and M1 pieces of first precoding indication information, wherein the first frequency domain indication information is used to indicate Li frequency domain subbands in T frequency domain subbands, the T frequency domain subbands are a system bandwidth or a part of a system bandwidth, 1≤L1<T, the T frequency domain subbands are in a one-to-one correspondence with T precoding matrices, and a precoding matrix wk corresponding to a kth frequency domain subband satisfies:
• Wk=W1×W2k, wherein
• w1 represents a matrix with Nt rows and R columns, and W2k represents a matrix with R rows and S columns;
• and
• the first frequency domain indication information and the M1 pieces of first precoding indication information are used to determine T first elements, a kth first element in the T first elements is a factor of an element in an rth row and an sth column of W2k, and 1<M1<T;
• and
• a transceiver, configured to send the first frequency domain indication information and the M1 pieces of first precoding indication information.

A communications apparatus, comprising:

• a transceiver, configured to receive first frequency domain indication information and M1 pieces of precoding indication information, wherein the first frequency domain indication information is used to indicate L1 frequency domain subbands in T frequency domain subbands, the T frequency domain subbands are a system bandwidth or a part of a system bandwidth, L1<T, the T frequency domain subbands are in a one-to-one correspondence with T precoding matrices, and a precoding matrix wk corresponding to a kth frequency domain subband satisfies:
• Wk=W1×W2k, wherein
• w1 represents a matrix with Nt rows and R columns, and W2k represents a matrix with R rows and S columns;
• and
• a processor, configured to determine T first elements based on the first frequency domain indication information and the M1 pieces of first precoding indication information, wherein a kth first element in the T first elements is a factor of an element in an rth row and an sth column of W2k, and 1<M1<T.