Algorithm 1 Selection of core helper node

1: Obtain the set of candidate core helpers ${\mathcal{U}}_{i,j}$ for link ${\mathcal{P}}_{i,j}$ according to Equation (11).  2: Traverse $u\in {\mathcal{U}}_{i,j}$, and calculate the related two-stage link cost ${\mathcal{C}}_{i,u,j}$ by Equations (14–16).  3: Determine the core helper with the optimized two-stage link cost ${\mathcal{C}}_{i,j}^{\mathrm{TSC}}$ by Equation (19).  4: The link ${\mathcal{P}}_{i,j}$ owns a core helper $u_{i,j}^{*}\Leftarrow {\displaystyle \underset{u\in {\mathcal{U}}_{i,j}}{argmin}}\left\{{\mathcal{C}}_{i,u,j}\right\}$.