Algorithm 1: Two-Round Relay Selection (2-RRS) Scheme Algorithm.

Input: Define N number of relay, ${\gamma }_{th}$;

while S transmit to N Relays

Update ${\gamma }_{S{R}_i}$;

First Round Selection

for $i=1:N$

Initialize ${\Omega }^M=0$;

while ${\gamma }_{S{R}_i}>={\gamma }_{th}$

update the group ${\Omega }^M$;

There are M relay successfully decode S information, $0<M<N$;

end while

end for

Second Round Selection:

if $M>0$ then

Find the best relay $R_s$ maximizing ${\gamma }_{R_{j}D}$;

$R_s=arg{\max }_{j\in M}\left({\gamma }_{R_{j}D}\right)$

end if

end while