Algorithm 1 Angle-based Beam Selection Algorithm

Input: ${\{{\gamma }_k,{\theta }_k,{\alpha }_k,|{\mathcal{N}}_k\left|\right\}}_{\forall k}$, W, B.   1: Initialize:    1-a: $({\vartheta }_k^x,{\vartheta }_k^y)\leftarrow {\theta }_k$, $\forall k\in \mathcal{K}$.    1-b: $({\vartheta }_n^x,{\vartheta }_n^y)\leftarrow {\mathbf{w}}_n$, $\forall n\in \mathcal{N}$.   2: for  $k\in \mathcal{K}$ do   3:      ${\ell }_k\leftarrow arg{min}_{n\in \mathcal{N}}\left({|\Delta {\vartheta }_{k,n}^x|}^2+{|\Delta {\vartheta }_{k,n}^y|}^2\right)$.   4:      Calculate ${\eta }_{k,{\ell }_k}$ as described in (18).   5:      Set ${\mathcal{N}}_k$ with indices ${\ell }_k$ and sequences ${\mathcal{T}}^x,{\mathcal{T}}^y$.   6:      for $n\in {\mathcal{N}}_k$ do   7:          Calculate ${\eta }_{k,n}$ as described in (18).   8:      end for   9:      ${\mathcal{N}}_k^{★}\leftarrow \{n\in {\mathcal{N}}_k\mid {\eta }_{k,n}\ge {\alpha }_k{\eta }_{k,{\ell }_k}\}$. 10: end for 11: ${\mathcal{N}}^{★}\leftarrow {\bigcup }_{k=1}^K{\mathcal{N}}_k^{★}$ 12: if $|{\mathcal{N}}^{★}|>B$ then 13:      for $n\in {\mathcal{N}}^{★}$ do 14:           $s_n\leftarrow {\sum }_{k=1}^K{\eta }_{k,n}$. 15:      end for 16:      ${\mathcal{N}}^{★}\leftarrow {arg\; max}_{\mathcal{S}\subseteq {\mathcal{N}}^{★},\left|\mathcal{S}\right|=B}{\sum }_{n\in \mathcal{S}}{s}_n$. 17: end if 18: Calculate $\mathbf{A}$ as described in (26). Output: $\mathbf{A}$.