Method for precoding matrix indicator feedback and apparatus
A method and apparatus for precoding matrix indicator feedback reduce a quantity of bits in the feedback. In the method, a terminal device receive a reference signal from a base station, determines a precoding matrix W in a precoding matrix set corresponding to a rank indication. W satisfies W=W 1 ×W 2 ×W 3 , W 1 , W 2 and W 3 and matrices and respectively corresponding to a first, second and third precoding matrix indicator. 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 . The terminal device transmits the rank indication, the first precoding matrix indicator, the second precoding matrix indicator, and the third precoding matrix indicator to the base station. Therefore, a quantity of to-be-selected vectors is reduced by using a first-stage feedback and a second-stage feedback, thereby reducing calculation complexity of third-stage feedback, and reducing a quantity of bits in the third-stage feedback.
1. A method for wireless communications, comprising:
receiving, by a network device, a rank indication, a first precoding matrix indicator, a second precoding matrix indicator, and a third precoding matrix indicator from a terminal device; and
determining, by the network device, a precoding matrix W based on the rank indication, the first precoding matrix indicator, the second precoding matrix indicator, and the third precoding matrix indicator,
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 greater than or equal to R; 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; N t , R, M, and K are all positive integers, M is greater than or equal to 2, N t is an even number, 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 the first precoding matrix indicator corresponds to the first precoding matrix W 1 , the second precoding matrix indicator corresponds to the second precoding matrix W 2 , and the third precoding matrix indicator corresponds to the third precoding matrix W 3 .
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
W
2
=
[
X
2
0
0
X
2
]
is 1, and the remaining elements are 0, wherein p is an integer 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 ], and each element in X 1 is a column vector comprising N t /2 elements.
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
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, the remaining 2K-T column vectors in W 2 are indicated by the T column vectors and the second precoding matrix indicator, T is an integer greater than or equal to 2, and T is less than K.
7. The method according to claim 1 , wherein 2K column vectors in W 2 are indicated by a configuration parameter and the second precoding matrix indicator.
8. A communication device, comprising:
a receiver, the receiver configured to receive a rank indication, a first precoding matrix indicator, a second precoding matrix indicator, and a third precoding matrix indicator from a terminal device; and
a processor, the processor configured to determine a precoding matrix W based on the rank indication, the first precoding matrix indicator, the second precoding matrix indicator, and the third precoding matrix indicator,
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 greater than or equal to R; 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; N t , R, M, and K are all positive integers, M is greater than or equal to 2, N t is an even number, 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 the first precoding matrix indicator corresponds to the first precoding matrix W 1 , the second precoding matrix indicator corresponds to the second precoding matrix W 2 , and the third precoding matrix indicator corresponds to the third precoding matrix W 3 .
9. The communication device 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
W
2
=
[
X
2
0
0
X
2
]
is 1, and the remaining elements are 0, wherein p is an integer from 1 to M.
10. The communication device 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=[v 0 . . . v M−1 ], and each element in X 1 is a column vector comprising N t /2 elements.
11. The communication device according to claim 8 , 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
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 communication device 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 , wherein P 1 is greater than or equal to P 2 , and P 2 is greater than or equal to P 3 .
13. The communication device according to claim 8 , wherein T column vectors in 2K column vectors in W 2 are indicated by the first precoding matrix indicator, the remaining 2K-T column vectors in W 2 are indicated by the T column vectors and the second precoding matrix indicator, T is an integer greater than or equal to 2, and T is less than K.
14. The communication device according to claim 8 , further comprising a transmitter, wherein the transmitter is configured to send a configuration parameter, and wherein 2K column vectors in W 2 are indicated by the configuration parameter and the second precoding matrix indicator.
15. The communication device of claim 8 , wherein the processor includes at least one of a central processing unit (CPU), a digital signal processor (DSP), an application-specific integrated circuit (ASIC) or a field programmable gate array (FPGA).
16. The communication device of claim 15 , wherein the communication device is a base station.