Hierarchic beam-forming in a cloud radio access network

A system for reducing the number of control-bits for enabling joint processing between smart remote radio heads (S-RRHs) of a mobile cellular network comprising:

• a smart remote radio head (S-RRH) configured to determine estimates of a communications channel established with end users of the S-RRH, to divide the communications channel into served end user channels and non-served end user channels, to determine a first pre-coding matrix as a projection matrix of a subspace spanned by the served end user channels into a null space of the non-served end user channels, to apply the first pre-coding matrix to a front-end of the S-RRH to create a lower dimension effective channel to the end users, to quantize channel state information (CSI) of the lower dimension effective channel, to deliver the quantized, lower dimension CSI to a computing unit, to receive a joint beam-forming matrix including a second pre-coding matrix from the computing unit, to apply the first and second pre-coding matrices to the front-end of the S-RRH to set a beam-forming channel between the S-RRH and the end users;
• and
• the computing unit, configured to calculate from the lower dimension CSI, together with additional CSI from one or more additional S-RRHs, the joint beam-forming matrix, including the second pre-coding matrix for the S-RRH.