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.