Algorithm 2: PBS Density Optimization (PDO) Algorithm.

1. Initialization: (1) Initialize the network scenario and the values ${\lambda }_u$, ${\lambda }_m$ and $B_p$, where $B_p\in \left(0,25\right]$. (2) Set the initial value of ${\rho }_{p,m}=0.03$. (3) Denote $\sigma$ as the variable step length of ${\rho }_{p,m}$. Denote $E{E}^{*}$ as the optimal value of the network EE. Denote ${\rho }_{p,m}^{*}$ as the optimized ratio between PBS density MBS density. Let ${\rho }_{p,m}^{*}={\rho }_{p,m}$, $E{E}^{*}=EE\left({\rho }_{p,m}\right)\left|{}_{{\lambda }_u,B_p}\right.$ and $\sigma =0.03$. 2. Calculate the optimal ratio of PBS density to MBS density while ${\rho }_{p,m}\le 30$ do  ${\rho }_{p,m}={\rho }_{p,m}+\sigma$  $E{E}^{\prime }=EE\left({\rho }_{p,m}\right)\left|{}_{{\lambda }_u,B_p}\right.$ according to Equation (14)  if $E{E}^{\prime }>E{E}^{*}$ then   ${\rho }_{p,m}^{*}={\rho }_{p,m}$, $E{E}^{*}=E{E}^{\prime }$  end if end while 3. Obtain the optimal PBS density ${\lambda }_p^{*}={\lambda }_m{\rho }_{p,m}^{*}$