Channel state information feedback

1. A method of providing channel state information for a wireless communications channel provided between a first network node having at least M transmission antennas and a second network node having at least N reception antennas, the method comprising:

determining characteristics of each of a plurality of taps resolvable in the time domain of at least one sub-channel within the channel from signals received by the at least N reception antennas over the channel from the at least M transmission antennas;

arranging a set of the characteristics of each of the plurality of taps into at least one vector;

quantizing the at least one vector in which a set of the characteristics of each of the plurality of taps are arranged by selecting one of a plurality of codebook vectors at a first level of a hierarchical codebook of vectors; and

providing, to the first network node, an indication of an index to the one of a plurality of codebook vectors,

wherein the determining further comprises:

determining characteristics of L taps resolvable in the time domain of each sub-channel within the channel from signals received by the at least N reception antennas over the channel from the at least M transmission antennas, where L is a positive integer.

2. The method of claim 1 , wherein the quantizing comprises:

quantizing the at least one vector by selecting, for each vector, one of a plurality of codebook vectors at a first level from one of a plurality of hierarchical codebooks of vectors.

3. The method of claim 1 , further comprising:

requantizing the at least one vector by selecting one of a plurality of hierarchically-related codebook vectors from hierarchically-related levels of the hierarchical codebook of vectors; and

providing, to the first network node, an indication of an index to the one of a plurality of hierarchically-related codebook vectors.

4. The method of claim 3 , wherein the one of a plurality of hierarchically-related codebook vectors from hierarchically-related levels of the hierarchical codebook of vectors comprises one of a plurality of child codebook vectors from child levels of the hierarchical codebook.

5. The method of claim 3 , wherein the one of a plurality of hierarchically-related codebook vectors from hierarchically-related levels of the hierarchical codebook of vectors comprises one of a plurality of parent codebook vectors from parent levels of the hierarchical codebook.

6. The method of claim 1 , further comprising:

pre-processing the at least one vector prior to the quantizing.

7. The method of claim 6 , wherein the pre-processing comprises quantizing at least one scalar value produced by the normalizing and providing, to the first network node, an indication of the at least one scalar.

8. The method of claim 1 , wherein the arranging further comprises:

arranging the characteristics of the L taps resolvable in the time domain of each sub-channel within the channel into vectors of characteristics for each of the at least N reception antennas at each tap.

9. The method of claim 1 , wherein the arranging further comprises:

arranging the characteristics of the L taps resolvable in the time domain of each sub-channel within the channel into vectors of characteristics for each of the at least M transmission antennas at each tap.

10. The method of claim 1 , wherein the arranging further comprises:

arranging the characteristics of the L taps resolvable in the time domain of each sub-channel within the channel into a concatenation of vectors of characteristics for each reception antenna at each tap.

11. The method of claim 1 , wherein the arranging further comprises:

arranging the characteristics of the L taps resolvable in the time domain of each sub-channel within the channel into a concatenation of vectors of characteristics for each transmission antenna at each tap.

12. The method of claim 1 , wherein the arranging further comprises:

arranging the characteristics of the L taps resolvable in the time domain of each sub-channel within the channel into vectors of characteristics for each of the at least M transmission antennas and each of the at least N reception antennas, each vector having a dimension of 1×L.

13. A method implemented by a non-transitory computer readable storage medium, in which a program is saved, the program comprising instructions which, when they are executed in a programmable device, cause the provision of channel state information for a wireless communications channel between a first network node having at least M transmission antennas and a second network node having at least N reception antennas, the method, comprising:

determining characteristics of each of a plurality of taps resolvable in the time domain of at least one sub-channel within the channel from signals received by the at least N reception antennas over the channel from the at least M transmission antennas;

arranging a set of the characteristics of each of the plurality of taps into at least one vector;

quantizing the at least one vector in which a set of the characteristics of each of the plurality of taps are arranged by selecting one of a plurality of codebook vectors at a first level of a hierarchical codebook of vectors; and

providing, to the first network node, an indication of an index to the one of a plurality of codebook vectors,

wherein the determining further comprises:

determining characteristics of L taps resolvable in the time domain of each sub-channel within the channel from signals received by the at least N reception antennas over the channel from the at least M transmission antennas, where L is a positive integer.

14. A first network node having at least N reception antennas and operable to provide channel state information for a wireless communications channel provided between second network node having at least M transmission antennas and the first network node, the network node comprising:

determination logic operable to determine characteristics of each of a plurality of taps resolvable in the time domain of at least one sub-channel within the channel from signals received by the at least N reception antennas over the channel from the at least M transmission antennas;

arrangement logic operable to arrange the characteristics of each of the plurality of taps into at least one vector;

quantization logic operable to quantize the at least one vector in which a set of the characteristics of each of the plurality of taps are arranged by selecting one of a plurality of codebook vectors at a first level of a hierarchical codebook of vectors; and

provision logic operable to provide, to the another network node, an indication of an index to the one of a plurality of codebook vectors,

wherein the determining further comprises:

determining characteristics of L taps resolvable in the time domain of each sub-channel within the channel from signals received by the at least N reception antennas over the channel from the at least M transmission antennas, where L is a positive integer.

15. The method of claim 1 , wherein at least one of M and N is an integer value greater than 1.

16. The method of claim 13 , wherein at least one of M and N is an integer value greater than 1.

17. The network node of claim 14 , wherein at least one of M and N is an integer value greater than 1.