Hybrid beamforming for uplink transmission

1. An apparatus comprising:

at least one processor; and

at least one memory storing instructions that, when executed by the at least one processor, to cause the apparatus at least to:

determine a transmission beam for downlink transmissions;

provide first beamforming instructions, for forming the transmission beam, to a transmission path comprising a digital to analog converter and an antenna column that comprises at least a first antenna sub-array and a second antenna sub-array and wherein, along the transmission path, the first antenna sub-array is connected to a first phase shifter comprising a first pair of switches connected using delay lines, and the second antenna sub-array is connected to a second phase shifter comprising a second pair of switches connected using delay lines, and wherein the first phase shifter and the second phase shifter are both connected to the digital to analog converter;

determine, for the first antenna sub-array, at least one receiving beam that is a first receiving beam, and for the second antenna sub-array, at least one receiving beam that is a second receiving beam for receiving uplink transmissions, wherein the first antenna sub-array is configured to provide a first plurality of concurrent receiving beams and the second antenna sub-array is configured to provide a second plurality of concurrent receiving beams;

provide second beamforming instructions, for forming at least the first receiving beam and at least the second receiving beams, to a first receiving path and a second receiving path, respectively, wherein the first receiving path comprises the first phase shifter that is connected to the first antenna sub-array and to a first analog to digital converter, and the second receiving path comprises the second phase shifter that is connected to the second antenna sub-array and to a second analog to digital converter, and wherein the first receiver path is connected to the first phase shifter using a first dedicated switch state associated with the first pair of switches, and the second receiver path is connected to the second phase shifter using a second dedicated switch state associated with the second pair of switches; and

transmit the downlink transmissions using the transmission beam and receive the uplink transmissions using the first and the second receiving beams.

2. The apparatus according to claim 1 , wherein the apparatus is further caused to perform beamforming of the first and the second receiving beams in a digital domain.

3. The apparatus according to claim 1 , wherein the first dedicated switch state, associated with the first pair of switches, is a state of the switch, comprised in the first pair of switches, that is closer to the first antenna sub-array, and the second dedicated switch state, associated with the second pair of switches, is a state of the switch, comprised in the second pair of switches, that is closer to the second antenna sub-array.

4. The apparatus according to claim 1 , wherein the antenna column comprises third antenna sub-array that is connected to a third phase shifter that comprises a third pair of switched connected using delay lines, and the third phase shifter is comprised in the transmission path and is further connected the digital to analog converter, and wherein the third phase shifter is comprised in a third receiving path and is further connected to a third analog to digital converter comprised in the third receiving path.

5. The apparatus according to claim 4 , wherein the apparatus is further caused to determine a third receiving beam for receiving the uplink transmission and the second beamforming instructions further comprise instructions for forming the third receiving beam.

6. The apparatus according to claim 1 , wherein the pairs of switches are controlled using their respective control interfaces.

7. The apparatus according to claim 1 , wherein at least one switch comprised in the phase shifters is configured to have four different states.

8. The apparatus according to claim 1 , wherein the apparatus is comprised in an access node.

9. A method comprising:

determining a transmission beam for downlink transmissions;

providing first beamforming instructions, for forming the transmission beam, to a transmission path comprising a digital to analog converter and an antenna column that comprises at least a first antenna sub-array and a second antenna sub-array and wherein, along the transmission path, the first antenna sub-array is connected to a first phase shifter comprising a first pair of switches connected using delay lines, and the second antenna sub-array is connected to a second phase shifter comprising a second pair of switches connected using delay lines, and wherein the first phase shifter and the second phase shifter are both connected to the digital to analog converter;

determining, for the first antenna sub-array, at least one receiving beam that is a first receiving beam, and for the second antenna sub-array, at least one receiving beam that is a second receiving beam for receiving uplink transmissions, wherein the first antenna sub-array is configured to provide a first plurality of concurrent receiving beams and the second antenna sub-array is configured to provide a second plurality of concurrent receiving beams;

providing second beamforming instructions, for forming at least the first receiving beam and at least the second receiving beams, to a first receiving path and a second receiving path, respectively, wherein the first receiving path comprises the first phase shifter that is connected to the first antenna sub-array and to a first analog to digital converter, and the second receiving path comprises the second phase shifter that is connected to the second antenna sub-array and to a second analog to digital converter, and wherein the first receiver path is connected to the first phase shifter using a first dedicated switch state associated with the first pair of switches, and the second receiver path is connected to the second phase shifter using a second dedicated switch state associated with the second pair of switches; and

transmitting the downlink transmissions using the transmission beam and receiving the uplink transmissions using the first and the second receiving beams.

10. The method according to claim 9 , wherein the method further comprises performing beamforming of the first and the second receiving beams in a digital domain.

11. The method according to claim 9 , wherein the first dedicated switch state, associated with the first pair of switches, is a state of the switch, comprised in the first pair of switches, that is closer to the first antenna sub-array, and the second dedicated switch state, associated with the second pair of switches, is a state of the switch, comprised in the second pair of switches, that is closer to the second antenna sub-array.

12. The method according to claim 9 , wherein the antenna column comprises third antenna sub-array that is connected to a third phase shifter that comprises a third pair of switched connected using delay lines, and the third phase shifter is comprised in the transmission path and is further connected the digital to analog converter, and wherein the third phase shifter is comprised in a third receiving path and is further connected to a third analog to digital converter comprised in the third receiving path.

13. The method according to claim 12 , wherein the method further comprises determining a third receiving beam for receiving the uplink transmission and the second beamforming instructions further comprise instructions for forming the third receiving beam.

14. The method according to claim 9 , wherein at least one switch comprised in the phase shifters is configured to have four different states.

15. A non-transitory computer readable medium comprising program instructions stored thereon for performing at least the following:

determining a transmission beam for downlink transmissions;

providing first beamforming instructions, for forming the transmission beam, to a transmission path comprising a digital to analog converter and an antenna column that comprises at least a first antenna sub-array and a second antenna sub-array and wherein, along the transmission path the first antenna sub-array is connected to a first phase shifter comprising a first pair of switches connected using delay lines, and the second antenna sub-array is connected to a second phase shifter comprising a second pair of switches connected using delay lines, and wherein the first phase shifter and the second phase shifter are both connected to the digital to analog converter;

determining, for the first antenna sub-array, at least one receiving beam that is a first receiving beam, and for the second antenna sub-array, at least one receiving beam that is a second receiving beam for receiving uplink transmissions, wherein the first antenna sub-array is configured to provide a first plurality of concurrent receiving beams and the second antenna sub-array is configured to provide a second plurality of concurrent receiving beams;

providing second beamforming instructions, for forming at least the first receiving beam and at least the second receiving beams, to a first receiving path and a second receiving path, respectively, wherein the first receiving path comprises the first phase shifter that is connected to the first antenna sub-array and to a first analog to digital converter, and the second receiving path comprises the second phase shifter that is connected to the second antenna sub-array and to a second analog to digital converter, and wherein the first receiver path is connected to the first phase shifter using a first dedicated switch state associated with the first pair of switches, and the second receiver path is connected to the second phase shifter using a second dedicated switch state associated with the second pair of switches; and

transmitting the downlink transmissions using the transmission beam and receiving the uplink transmissions using the first and the second receiving beams.