In the case of digital beamforming, each antenna element in a completely connected architecture must have its own radio frequency (RF) series. The analog phase shifter (PSs) applies the analog beamformer; all of its elements have the same amplitude but different phases. The goal is to optimise the overall throughput or sum rate R (A, D) obtained over Gaussian signalling on MMwave channels by designing (A, D)
The related sum rate optimization problem looks like this:
Here, set F consists all possible analog beamformers (size of Nt X NRFt matrices) with constant-magnitude entries.
Now for hybrid architecture we will find singular value decomposition (SVD) of channel matrix to find the stronger eigen values and we will only allocate power accordingly to these paths to achieve low overhead in hybrid architecture (Appendix B). For example we will further divide the eigen value matrix (Σ) into two parts (Eqn 6.5) where Σ1 is a Ns X Ns matrix; where Ns indicates rank of matrix or how many simultaneous data streams are available between BS and MS