Algorithm 1 Recursive algorithm to calculate the impulse response.

1:function h_func($\mathbf{h},\mathbf{tx},\mathbf{rx},\mathbf{s},{\mathbf{s}}_{\mathbf{ant}},\mathbf{P},\mathbf{d},{\mathbf{k}}_{\mathbf{i}},\mathbf{k}$) 2:      if $k==k_i$ then                                              ▹ Source is TX 3:             if $k_i==0$ then                                        ▹ Receiver is RX 4:                    Calculate $[\mathit{\omega }$, $\mathit{\gamma }$, ${\mathbf{d}}_{\mathrm{rs}}]$ from (tx, rx) with (9)–(11) 5:                    Calculate signal strength ${\mathbf{P}}_{\mathbf{rs}}$ with (8) substituting ${\mathbf{P}}_{\mathbf{s}}$ for $\mathbf{P}$ 6:                    Calculate discrete time ${\mathbf{t}}_{\mathbf{rs}}$ from distance $\mathbf{d}+{\mathbf{d}}_{\mathbf{rs}}$, and light velocity 7:                    if $\gamma$ < FoV then 8:                          $\mathbf{h}\left({\mathbf{t}}_{\mathbf{rs}}\right)=\mathbf{h}\left({\mathbf{t}}_{\mathbf{rs}}\right)+{\mathbf{P}}_{\mathbf{rs}}$ 9:                    end if 10:             else                              ▹ Received signal strength at all points from TX 11:                    for $\mathbf{i}$ from $\mathbf{1}$ to $\mathbf{N}$ do 12:                         Calculate $[\mathit{\omega }$, $\mathit{\gamma }$, ${\mathbf{d}}_{\mathrm{rs}}]$ from $\left(\mathbf{tx},\mathbf{i}\right)$ with (9)–(11) substituting $\mathbf{rx}$ for the $\mathbf{i}$ element 13:                         Calculate signal strength ${\mathbf{P}}_{\mathbf{rs}}$ with (8) substituting $\mathbf{rx}$ for the $\mathbf{i}$ element and $\mathbf{Ps}$ for $\mathbf{P}$ 14:                         h_func($\mathbf{h},\mathbf{tx},\mathbf{rx},\mathbf{i},\mathbf{tx},{\mathbf{P}}_{\mathbf{rs}},\mathbf{d}+{\mathbf{d}}_{\mathbf{rs}},{\mathbf{k}}_{\mathbf{i}}-\mathbf{1},\mathbf{k}$) 15:                    end for 16:             end if 17:      else                                              ▹ Source is not TX 18:             if $k_i==0$ then                                     ▹ Receiver is RX 19:                    Calculate $[\mathit{\alpha },$ ${\mathbf{d}}_{\mathbf{nm}},$ $\mathit{\gamma },\mathit{\theta },\mathit{\varphi }]$ from $({\mathbf{s}}_{\mathbf{ant}},\mathbf{s},\mathbf{rx})$ with (17)–(20), (23) substituting $\mathbf{n}=\mathbf{rx}$, $\mathbf{m}=\mathbf{s}$ and $\mathbf{l}={\mathbf{s}}_{\mathbf{ant}}$ 20:                    Calculate signal strength ${\mathbf{P}}_{\mathbf{nml}}$ with (14) substituting ${\mathbf{P}}_{\mathbf{ml}}$ for $\mathbf{P}$ 21:                    Calculate discrete time ${\mathbf{t}}_{\mathbf{nm}}$ from distance $\mathbf{d}+{\mathbf{d}}_{\mathbf{nm}}$, and light velocity 22:                    if $\alpha$ < FoV then 23:                         $\mathbf{h}\left({\mathbf{t}}_{\mathbf{nm}}\right)=\mathbf{h}\left({\mathbf{t}}_{\mathbf{nm}}\right)+{\mathbf{P}}_{\mathbf{nml}}$ 24:                    end if 25:             else                             ▹ Received signal strength at all points from TX 26:                    for $\mathbf{i}$ from $\mathbf{1}$ to $\mathbf{N}$ do 27:                         Calculate $[\mathit{\alpha },$${\mathbf{d}}_{\mathbf{nm}},$$\mathit{\gamma },\mathit{\theta },\mathit{\varphi }]$ from $\left({\mathbf{s}}_{\mathbf{ant}},\mathbf{s},\mathbf{i}\right)$ with (17)–(20), (23) substituting $\mathbf{n}=\mathbf{i}$, $\mathbf{m}=\mathbf{s}$ and $\mathbf{l}={\mathbf{s}}_{\mathbf{ant}}$ 28:                         Calculate signal strength ${\mathbf{P}}_{\mathbf{nml}}$ with (14) substituting ${\mathbf{P}}_{\mathbf{ml}}$ for $\mathbf{P}$ 29:                         h_func($\mathbf{h},\mathbf{tx},\mathbf{rx},\mathbf{i},\mathbf{s},{\mathbf{P}}_{\mathbf{nml}},\mathbf{d}+{\mathbf{d}}_{\mathbf{nm}},{\mathbf{k}}_{\mathbf{i}}-\mathbf{1},\mathbf{k}$) 30:                    end for 31:             end if 32:      end if 33:end function