Channel state information feedback for enhanced downlink multiple input—multiple output operation

1. A method, comprising:

deriving multiple input-multiple output feedback information using a set of precoding matrices associated with at least one precoding codebook;

signaling, in a first plurality of resource elements, channel state information associated with a first precoding matrix indicator of the set of precoding matrices jointly with a transmission rank; and

signaling separately, in a second plurality of resource elements, channel state information associated with a second precoding matrix indicator of the set of precoding matrices.

2. The method according to claim 1 , where the first precoding matrix indicator and the second precoding matrix indicator of the set of precoding matrices pertain to wideband communication channel properties.

3. The method according to claim 1 , where the transmission rank is signaled implicitly with the first precoding matrix indicator.

4. The method according to claim 1 , where the channel state information associated with the first precoding matrix indicator is signaled in a first subframe of a frame, and where the channel state information associated with the second precoding matrix indicator is signaled in at least one subsequent subframe of the frame following the first subframe of the frame.

5. The method according to claim 1 , where the signaling is performed using a physical uplink control channel.

6. The method according to claim 1 , where the signaling is performed one of periodically or aperiodically using a physical uplink shared channel, and where the signaling the channel state information associated with the first precoding matrix indicator and the transmission rank is performed using at least one set of resource elements of a block of single carrier-frequency division multiple access symbols, where the at least one set of resource elements is one of following a set of resource elements or is before a set of resource elements used to signal the channel state information associated with the second precoding matrix indicator.

7. A non-transitory computer readable memory embodying computer program instructions executable by at least one processor to perform the method according to claim 1 .

8. An apparatus, comprising:

at least one processor; and

at least one memory including computer program code, where the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus to at least:

derive multiple input-multiple output feedback information using a set of precoding matrices associated with at least one precoding codebook;

signal, in a first plurality of resource elements, channel state information associated with a first precoding matrix indicator of the set of precoding matrices jointly with a transmission rank; and

signal separately, in a second plurality of resource elements, channel state information associated with a second precoding matrix indicator of the set of precoding matrices.

9. The apparatus according to claim 8 , where the first precoding matrix indicator and the second precoding matrix indicator of the set of precoding matrices pertain to wideband communication channel properties.

10. The apparatus according to claim 8 , where the transmission rank is signaled implicitly with the first precoding matrix indicator.

11. The apparatus according to claim 8 , where the at least one memory including the computer program code is configured, with the at least one processor, to cause the apparatus to signal the channel state information associated with the first precoding matrix indicator in a first subframe of a frame, and signal the channel state information associated with the second precoding matrix indicator in at least one subsequent subframe of the frame following the first subframe of the frame.

12. The apparatus according to claim 8 , where the at least one memory including the computer program code is configured, with the at least one processor, to cause the apparatus to perform the signaling using a physical uplink control channel.

13. The apparatus according to claim 8 , where the at least one memory including the computer program code is configured, with the at least one processor, to cause the apparatus to perform the signaling one of periodically or aperiodically using a physical uplink shared channel, and to perform the signaling of the channel state information associated with the first precoding matrix indicator and the transmission rank using at least one set of resource elements of a block of single carrier-frequency division multiple access symbols, where the at least one set of resource elements is one of following a set of resource elements or is before a set of resource elements used to signal the channel state information associated with the second precoding matrix indicator.

14. A method, comprising:

receiving signaling in a first plurality of resource elements of channel state information associated with a first precoding matrix indicator of a set of precoding matrices jointly with a transmission rank;

receiving signaling separately in a second plurality of resource elements of channel state information associated with a second precoding matrix indicator of the set of precoding matrices; and

controlling a downlink multiple input-multiple output transmission in accordance with the received signaling.

15. The method according to claim 14 , where the first precoding matrix indicator and the second precoding matrix indicator of the set of precoding matrices pertain to wideband communication channel properties.

16. The method according to claim 14 , where the transmission rank is implicitly determined based on the received signaling.

17. The method according to claim 14 , where the signaling is received via a physical uplink control channel.

18. A non-transitory computer readable memory embodying computer program instructions executable by at least one processor to perform the method according to claim 14 .

19. An apparatus, comprising:

at least one processor; and

at least one memory including computer program code, where the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus to at least:

receive signaling in a first plurality of resource elements of channel state information descriptive associated with a first precoding matrix indicator of a set of precoding matrices jointly with a transmission rank;

receive signaling separately in a second plurality of resource elements of channel state information associated with a second precoding matrix indicator of the set of precoding matrices; and

control a downlink multiple input-multiple output transmission in accordance with the received signaling.

20. The apparatus according to claim 19 , where the first precoding matrix indicator and the second precoding matrix indicator of the set of precoding matrices pertain to wideband communication channel properties.

21. The apparatus according to claim 19 , where the signaling is received via a physical uplink control channel.

22. The apparatus according to claim 19 , comprising the at least one memory including the computer program code is configured, with the at least one processor, to cause the apparatus to determine the transmission rank based on the received signaling.