Algorithm 1 Multi Shortest Path Data Forwarding Strategy (MSPDFS).

Initialization: Assume that the UAV chose a K-element combination from M CH robots, $S_a^K$, to look for a trajectory to visit all CH robots in that combination. $|S_a^K|$ is cardinality of the set $S_a^K$. Given the combination $S_a^K$, data forwarding strategy is formed as follows. Algorithm: for$i=1:M$do       # Comment: If CH robot i is on the trajectory of the UAV   if $i\in S_a^K$ then            # Comment: No need to forward data to another CH robot            $u_i=\varnothing$ and ${\gamma }_i^{\pi }=0$   else            # Comment: Calculate shortest paths for all CH robot on the trajectory of the UAV.     for $j=1:|S_a^K|$ do            find shortest path (minimum energy path strategy for data forwarding) from the position of CH robot i to the position of CH robot $S_a^K\left(j\right)$.     end for            Compare it with the shortest path to origin (initial position of the UAV) and choose the shorter one. find the optimal strategy ${\displaystyle u_i^{*}=arg\underset{u_i}{min}{E}_i^{\pi }\left(u_i\right)}$ by comparing the energy cost of the best strategy for each destination, $S_a^K\left(j\right)$.   end if end for Output: The optimal data forwarding strategy $u_i^{*}$ for each CH robot i given $S_a^K$