Beamforming with partial channel knowledge
View Patent ↗An apparatus for use in transmit beamforming to a beamformee having N R receive antennas. The apparatus includes a controller configured to i) construct a partial channel matrix that describes a multiple input, multiple output (MIMO) channel between a beamformer and M receive antennas, wherein M is less than N R , and ii) generate L independent vectors using the partial channel matrix, wherein L is a rank of the partial channel matrix. When a number N S of one or more streams is greater than L, the controller is further configured to i) select the L independent vectors as steering vectors to steer L streams of the plurality of streams, and ii) select N S −L orthogonal vectors in a null space of the L independent vectors as steering vectors to steer a remainder of the streams in the plurality of streams.
1. A method, in a transmitter, for selecting steering vectors for transmitting one or more streams between the transmitter and a receiver, wherein the transmitter has a plurality of transmit antennas, the receiver has a plurality of receive antennas, the number of receive antennas in the plurality of receive antennas is N R , and the number of streams in the one or more steams is N S , the method comprising:
constructing a partial channel matrix that describes a multiple input, multiple output (MIMO) channel between the plurality of transmit antennas and a set of one or more of the receive antennas, wherein the number of receive antennas in the set of one or more of the receive antennas is M, and M is less than N R ;
generating one or more independent vectors using the partial channel matrix, wherein the number of independent vectors in the one or more independent vectors is L, and L is a rank of the partial channel matrix; and
when N S is greater than L,
(i) selecting the one or more independent vectors as one or more first steering vectors to steer a first set of one or more streams in the one or more streams, wherein the number of streams in the first set of one or more streams is L;
(ii) selecting one or more orthogonal vectors in a null space of the one or more independent vectors as one or more second steering vectors to steer a second set of one or more streams in the one or more streams, wherein the number of orthogonal vectors in the one or more orthogonal vectors is N S −L, wherein the number of streams in the second set of one or more streams is N S −L, and the N S −L streams in the second set of one or more streams are not in the first set of one or more streams;
(iii) utilizing the one or more first steering vectors for transmitting the first set of one or more streams; and
(iv) utilizing the one or more second steering vectors for transmitting the second set of one or more streams.
2. The method of claim 1 , wherein:
the number of transmit antennas in the plurality of transmit antennas is N T , and
a dimensionality of the null space is N T −L.
3. The method of claim 2 , further comprising selecting, over time, different orthogonal vectors as the one or more second steering vectors when i) N S is greater than L, and ii) N T is greater than or equal to N S .
4. The method of claim 2 , further comprising selecting, over frequency, different orthogonal vectors as the one or more second steering vectors when i) N S is greater than L, and ii) N T is greater than or equal to N S .
5. The method of claim 1 , wherein generating one or more independent vectors using the partial channel matrix includes performing singular value decomposition (SVD) of the partial channel matrix.
6. The method of claim 1 , wherein the number N S of streams to be transmitted to the receiver is less than or equal to a minimum of N R and N T , wherein N T is the number of transmit antennas in the plurality of transmit antennas.
7. The method of claim 1 , wherein constructing the partial channel matrix comprises:
determining an additional partial channel matrix corresponding to a backward channel; and
determining the partial channel matrix from the additional partial channel matrix.
8. The method of claim 1 , wherein when i) N S =2 and ii) M=1:
selecting the one or more independent vectors as the one or more first steering vectors comprises selecting one independent vector to steer a first stream to a single receive antenna of the receiver; and
selecting the one or more orthogonal vectors in the null space of the one or more independent vectors comprises selecting a vector to steer a second stream in a null space of a row vector in the partial channel matrix.
9. The method of claim 1 , further comprising, when N S is less than or equal to L, selecting a set of one or more independent vectors as a third set of one or more steering vectors to steer the one or more streams, wherein the number of independent vectors in the set of independent vectors is N S .
10. The method of claim 9 , wherein when i) N S =1 and ii) M=1:
selecting the set of one or more independent vectors as the third set of one or more steering vectors to steer the one or more streams comprises selecting one independent vector to steer the one stream to a single receive antenna of the receiver.
11. The method of claim 9 , wherein when i) N S =1 and ii) M=2:
generating the one or more independent vectors using the partial channel matrix comprises generating a single independent vector using the partial channel matrix, and
selecting the set of one or more independent vectors as the third set of one or more steering vectors to steer the one or more streams comprises selecting the single independent vector to steer the one stream.
12. An apparatus for use in transmit beamforming to a beamformee, wherein the beamformee has N R a plurality of receive antennas, wherein the number of receive antennas in the plurality of receive antennas is N R , the apparatus comprising:
a controller configured to
construct a partial channel matrix that describes a multiple input, multiple output (MIMO) channel between a beamformer and a set of one or more of the plurality of receive antennas, wherein the number of receive antennas in the set of one or more receive antennas is M, and M less than N R ,
generate one or more independent vectors using the partial channel matrix, wherein the number of independent vectors in the one or more independent vectors is L, and L is a rank of the partial channel matrix, and
when a number N S of one or more streams is greater than L:
(i) select the one or more independent vectors as one or more first steering vectors to steer a first set of one or more streams in the one or more streams, wherein the number of streams in the first set of one or more streams is L;
(ii) select one or more orthogonal vectors in a null space of the one or more independent vectors as one or more second steering vectors to steer a second set of one or more streams in the one or more streams, wherein the number of orthogonal vectors in the one or more orthogonal vectors is N S −L, wherein the number of streams in the second set of one or more streams is N S −L, and the N S −L streams in the second set of one or more streams are not in the first set of one or more streams;
(iii) cause the one or more first steering vectors to be used to transmit the first set of one or more streams; and
(iv) cause the one or more second steering vectors to be used to transmit the second set of one or more streams.
13. The apparatus of claim 12 , wherein
the beamformer has N T transmit antennas, and
a dimensionality of the null space is N T −L.
14. The apparatus of claim 13 , wherein the controller is configured to select, over time, different orthogonal vectors as the one or more second steering vectors when i) N S is greater than L, and ii) N T is greater than or equal to N S .
15. The apparatus of claim 13 , wherein the controller is configured to select, over frequency, different orthogonal vectors as the one or more second steering vectors when i) N S is greater than L, and ii) N T is greater than or equal to N S .
16. The apparatus of claim 12 , further comprising one or more radio interfaces coupled to the controller, wherein the one or more radio interfaces are configured to couple to N T transmit antennas.
17. The apparatus of claim 12 , wherein the controller is configured to generate the one or more independent vectors based on performing a singular value decomposition (SVD) of the partial channel matrix.
18. The apparatus of claim 12 , wherein the number N S of streams to be transmitted to the receiver is less than or equal to a minimum of N R and a number N T of the transmit antennas of a beamformer.
19. The apparatus of claim 12 , wherein the controller is configured to:
determine an additional partial channel matrix corresponding to a backward channel, and
determine the partial channel matrix from the additional partial channel matrix.
20. The apparatus of claim 12 , wherein the controller is configured to, when N S is less than or equal to L, select a set of one or more independent vectors as one or more third steering vectors to steer the one or more streams, wherein the number of independent vectors in set of one or more independent vectors is N S .