Beamforming method and apparatus using a rate splitting scheme in a multi-cell multi-antenna interference channel

1. A target transmitter corresponding to a target receiver, comprising:

a rate splitting encoder configured to encode a first stream and a second stream for transmission by the target transmitter to the target receiver according to a rate splitting scheme; and

a transmission beamformer configured to:

use transmission beamforming vectors to align the first stream and a third stream without aligning the second stream and a fourth stream in a first reception spatial dimension of the target receiver, wherein the first stream and the third stream are aligned by applying a span of a first reception beamforming vector; and

use the transmission beamforming vectors to align the second stream and the fourth stream without aligning the first stream and the third stream in a second reception spatial dimension of the target receiver, wherein the second and fourth stream are aligned by applying a span of a second reception beamforming vector, wherein

the third stream and the fourth stream are transmitted by a neighbor transmitter of the target transmitter.

2. The target transmitter of claim 1 , wherein the transmission beamforming vectors are generated based on:

channel information between the target transmitter and the target receiver; and

channel information between the target transmitter and the neighbor receiver.

3. The target transmitter of claim 1 , wherein the transmission beamforming vectors are generated based on:

reception beamforming vectors of the target receiver; and

reception beamforming vectors of the neighbor receiver.

4. The target transmitter of claim 3 , wherein the reception beamforming vectors of the target receiver are linearly independent from the reception beamforming vectors of the neighbor receiver.

5. The target transmitter of claim 1 , further comprising a transmission beamforming vector generator configured to generate transmission beamforming vectors for the first stream and the second stream.

6. The target transmitter of claim 1 , wherein the rate splitting encoder is further configured to encode the first stream and the second stream to enable the neighbor receiver corresponding to the neighbor transmitter to decode:

a common message of the first stream received in a first reception spatial dimension of the neighbor receiver; and

a common message of the second stream received in a second reception spatial dimension of the neighbor receiver.

7. The target transmitter of claim 1 , wherein the rate splitting scheme allows the target transmitter to separate a message to be transmitted into multiple partial messages.

8. The target transmitter of claim 7 , wherein the multiple partial messages include a common message and a private message.

9. The target transmitter of claim 8 , wherein the target transmitter is further configured to adjust a transmission power of the private message such that the first receiver decodes the private message and the second receiver does not decode the private message.

10. The target transmitter of claim 1 , wherein a span of a product between a channel matrix from the target transmitter to the target receiver and transmission beamforming vectors of the first stream and a product between a channel matrix from the neighbor transmitter to the largest receiver and transmission beamforming vectors of the third stream is the same as a span of the first reception beamforming vector, and

a span of a product between the channel matrix from the target transmitter to the target receiver and transmission beamforming vectors of the second stream and a product between the channel matrix from the neighbor transmitter to the target receiver and transmission beamforming vectors of the fourth stream is the same as a span of the second reception beamforming vector.

11. The target transmitter of claim 1 , wherein the transmission beamforming vectors are designed based on the equations,

span( w 1 )=span[ H 11 v 1 H 12 v 3 ]

span( w 2 )=span[ H 11 v 2 H 12 v 4 ]

span( w 3 )=span[ H 22 v 3 H 21 v 1 ]

span( w 4 )=span[ H 22 v 4 H 21 v 2 ],

wherein w 1 corresponds to the first reception beamforming vector of the target receiver, w 2 corresponds to the second reception beamforming vector of the target receiver, w 3 corresponds to the first reception beamforming vector of the neighbor receiver, w 4 corresponds to the second reception beamforming vector of the neighbor receiver, H 11 corresponds to a channel from the target transmitter to the target receiver, H 12 corresponds to a channel from the neighbor transmitter to the target receiver, H 22 corresponds to a channel from the neighbor transmitter to the neighbor receiver, H 21 corresponds to a channel from the target transmitter to the neighbor receiver, v 1 corresponds to a transmission beamforming vector for the first stream, v 2 corresponds to a transmission beamforming vector for the second stream, v 3 corresponds to a transmission beamforming vector for the third stream, v 4 corresponds to a transmission beamforming vector for the fourth stream.

12. The target transmitter of claim 1 , wherein the target transmitter is configured to establish the rate splitting encoder in response to the aligning of the first stream and the third stream, and the aligning of the second stream and the fourth stream.

13. The target transmitter of claim 1 , wherein the target transmitter is a first multi-antenna transmitter in a first cell, and the neighbor transmitter is a second multi-antenna transmitter in a second cell, the first cell being adjacent to the second cell.

14. A target receiver corresponding to a target transmitter, comprising:

a reception beamformer configured to use reception beamforming vectors to:

remove, in a first reception spatial dimension, components of a second stream and a fourth stream included in a signal received by the target receiver; and

remove, in a second reception spatial dimension, components of a first stream and a third stream included in the signal received by the target receiver, the first stream and the second stream being transmitted by the target transmitter, and the third stream and the fourth stream being transmitted by a neighbor transmitter of the target transmitter, wherein

the first stream and the third stream are aligned without aligning the second stream and the fourth stream by applying a span of a first reception beamforming vector; and

the second stream and the fourth stream are aligned without aligning the first stream and the third stream by applying a span of a second reception beamforming vector; and

a rate splitting decoder configured to

decode the first stream and

the second stream.

15. The target receiver of claim 14 , wherein the reception beamformer uses reception beamforming vectors generated based on channel information between the target transmitter and the target receiver and channel information between the neighbor transmitter and the target receiver to remove, in the first reception spatial dimension, components of the second stream and the fourth stream from the signal received by the target receiver and to remove, in the second reception spatial dimension, components of the first stream and the third stream from the signal received by the target receiver.

16. The target receiver of claim 14 , wherein the reception beamforming vectors are generated based on:

transmission beamforming vectors of the target transmitter; and

transmission beamforming vectors of the neighbor transmitter.

17. The target receiver of claim 14 , wherein the reception beamforming vectors are linearly independent.

18. The target receiver of claim 14 , wherein the rate splitting decoder is further configured to:

decode the decodable common message of the third stream to remove the decodable common message of the third stream; and

decode the decodable common message of the fourth stream to remove the decodable common message of the fourth stream.

19. The target receiver of claim 14 , wherein a span of a product between a channel matrix from the largest transmitter to the target receiver and transmission beamforming vectors of the first stream and a product between a channel matrix from the neighbor transmitter to the target receiver and transmission beamforming vectors of the third stream is the same as a span of the first reception beamforming vector, and a span of a product between the channel matrix from the target transmitter to the target receiver and transmission beamforming vectors for the second stream and a product between the channel matrix from the neighbor transmitter to the target receiver and transmission beamforming vectors of the fourth stream is the same as a span of the second reception beamforming vector.

20. The target receiver of claim 14 , wherein the reception beamforming vectors are designed based on the equations,

span( w 1 )=span[ H 11 v 1 H 12 v 3 ]

span( w 2 )=span[ H 11 v 2 H 12 v 4 ]

span( w 3 )=span[ H 22 v 3 H 21 v 1 ]

span( w 4 )=span[ H 22 v 4 H 21 v 2 ],

wherein w 1 corresponds to the first reception beamforming vector of the target receiver, w 2 corresponds to the second reception beamforming vector of the target receiver, w 3 corresponds to the first reception beamforming vector of the neighbor receiver, w 4 corresponds to the second reception of the neighbor receiver, H 11 corresponds to a channel from the target transmitter to the target receiver, H 12 corresponds to a channel from the neighbor transmitter to the target receiver, H 22 corresponds to a channel from the neighbor transmitter to the neighbor receiver, H 21 corresponds to a channel from the target transmitter to the neighbor receiver, v 1 corresponds to a transmission beamforming vector for the first stream, v 2 corresponds to a transmission beamforming vector for the second stream, v 3 corresponds to a transmission beamforming vector for the third stream, v 4 corresponds to a transmission beamforming vector for the fourth stream.

21. The target receiver of claim 14 , wherein the target transmitter is a first multi-antenna transmitter in a first cell, and the neighbor transmitter is a second multi-antenna transmitter in a second cell, the first cell being adjacent to the second cell.