Method for precoding matrix indicator feedback and apparatus

1. A method, comprising:

receiving, by a terminal device, a reference signal from a base station;

based on the received reference signal, determining, by the terminal device, a precoding matrix W in a precoding matrix set corresponding to a rank indication, wherein W satisfies W=W 1 ×W 2 ×W 3 , W is a matrix of N t rows and R columns, N t is a quantity of antenna ports, R is a rank value corresponding to the rank indication, N t is an even number and N t is greater than or equal to R, wherein W 1 is a matrix of N t rows and 2M columns, W 2 is a matrix of 2M rows and 2K columns, W 3 is a matrix of 2K rows and R columns, K is less than M, wherein N t , R, M, and K are all positive integers, M is greater than or equal to 2, none of W 1 , W 2 , and W 3 is an identity matrix, and the 2M columns in W 1 comprise every column in W 1 ×W 2 , wherein a first precoding matrix indicator corresponds to the first precoding matrix W 1 , a second precoding matrix indicator corresponds to the second precoding matrix W 2 , and a third precoding matrix indicator corresponds to the third precoding matrix W 3 ;

sending, by the terminal device, the rank indication, the first precoding matrix indicator, the second precoding matrix indicator, and the third precoding matrix indicator to the base station; and

receiving, by the terminal device, data which is precoded using a precoding matrix determined by the base station based on the rank indication, the first precoding matrix indicator, the second precoding matrix indicator and the third precoding matrix indicator.

2. The method according to claim 1 , wherein

W 2 satisfies

W

2

=

[

X

2

0

0

X

2

]

,

 X 2 is a matrix of M rows and K columns, any column in X 2 is represented as e p , e p is an M×1 column vector, a p th element in e p is 1, the remaining elements in e p are 0, and p is an integer ranged from 1 to M.

3. The method according to claim 1 , wherein

W 1 satisfies

W

1

=

[

X

1

0

0

X

1

]

,

 X 1 is a matrix of N t /2 rows and M columns, X 1 =[v 0 . . . v m−1 ], v o is a column vector comprising N t /2 elements, and o is an integer ranged from 0 to M−1.

4. The method according to claim 1 , wherein a frequency domain resource corresponding to the first precoding matrix indicator is a downlink system bandwidth of the terminal device, the downlink system bandwidth comprises A first sub-bands and B second sub-bands, A and B are positive integers greater than 1, and A is less than or equal to B; and

wherein a frequency domain resource corresponding to the second precoding matrix indicator is one of the A first sub-bands, and a frequency domain resource corresponding to the third precoding matrix indicator is one of the B second sub-bands.

5. The method according to claim 1 , wherein a transmission period of the first precoding matrix indicator is P 1 , a transmission period of the second precoding matrix indicator is P 2 , a transmission period of the third precoding matrix indicator is P 3 , P 1 is greater than or equal to P 2 , and P 2 is greater than or equal to P 3 .

6. The method according to claim 1 , wherein T column vectors in 2K column vectors in W 2 are indicated by the first precoding matrix indicator, T is an integer greater than or equal to 2, and T is less than K; and

wherein 2K−T column vectors in W 2 except the T column vectors are indicated by the T column vectors and the second precoding matrix indicator.

7. The method according to claim 1 , wherein 2K column vectors in W 2 are indicated by a configuration parameter delivered by the base station and the second precoding matrix indicator.

8. An apparatus, comprising:

a receiver, configured to receive a reference signal from a base station;

a processor, configured to: based on the received reference signal, determine a precoding matrix W in a precoding matrix set corresponding to a rank indication, wherein W satisfies W=W 1 ×W 2 ×W 3 , W is a matrix of N t rows and R columns, N t is a quantity of antenna ports, R is a rank value corresponding to the rank indication, N t is an even number and N t is greater than or equal to R, wherein W 1 is a matrix of N t rows and 2M columns, W 2 is a matrix of 2M rows and 2K columns, W 3 is a matrix of 2K rows and R columns, K is less than M, wherein N t , R, M, and K are all positive integers, M is greater than or equal to 2, none of W 1 , W 2 , and W 3 is an identity matrix, and the 2M columns in W 1 comprise every column in W 1 ×W 2 , wherein a first precoding matrix indicator corresponds to the first precoding matrix W 1 , a second precoding matrix indicator corresponds to the second precoding matrix W 2 , and a third precoding matrix indicator corresponds to the third precoding matrix W 3 ; and

a transmitter, configured to send the rank indication, the first precoding matrix indicator, the second precoding matrix indicator, and the third precoding matrix indicator to the base station,

wherein the receiver is further configured to receive data which is precoded using a precoding matrix determined by the base station based on the rank indication, the first precoding matrix indicator, the second precoding matrix indicator and the third precoding matrix indicator.

9. The apparatus according to claim 8 , wherein

W 2 satisfies

W

2

=

[

X

2

0

0

X

2

]

,

 X 2 is a matrix of M rows and K columns, any column in X 2 is represented as e p , e p is an M×1 column vector, a p th element in e p is 1, the remaining elements in e p are 0, and p is an integer ranged from 1 to M.

10. The apparatus according to claim 8 , wherein

W 1 satisfies

W

1

=

[

X

1

0

0

X

1

]

,

 X 1 is a matrix of N t /2 rows and M columns, X 1 =[v 0 . . . v m−1 ], V o is a column vector comprising N t /2 elements, and o is an integer ranged from 0 to M−1.

11. The apparatus according to claim 8 , wherein a frequency domain resource corresponding to the first precoding matrix indicator is a downlink system bandwidth of the apparatus, the downlink system bandwidth comprises A first sub-bands and B second sub-bands, A and B are positive integers greater than 1, and A is less than or equal to B; and

wherein a frequency domain resource corresponding to the second precoding matrix indicator is one of the A first sub-bands, and a frequency domain resource corresponding to the third precoding matrix indicator is one of the B second sub-bands.

12. The apparatus according to claim 8 , wherein a transmission period of the first precoding matrix indicator is P 1 , a transmission period of the second precoding matrix indicator is P 2 , a transmission period of the third precoding matrix indicator is P 3 , P 1 is greater than or equal to P 2 , and P 2 is greater than or equal to P 3 .

13. The apparatus according to claim 8 , wherein T column vectors in 2K column vectors in W 2 are indicated by the first precoding matrix indicator, T is an integer greater than or equal to 2, and T is less than K; and

wherein 2K−T column vectors in W 2 except the T column vectors are indicated by the T column vectors and the second precoding matrix indicator.

14. The apparatus according to claim 8 , wherein the receiver is configured to receive a configuration parameter from the base station; and

wherein 2K column vectors in W 2 are indicated by the configuration parameter and the second precoding matrix indicator.