Algorithm 1 Preamble generation scheme

Require:       The sets of available sub-preambles $S_s,S_d$; location index for the dedicated sub-preamble $\mu$; Ensure:       A preamble sequence for an RA-attempting device $x_{u_1,v_s}^{u_2,v_d}\left(n\right)$;   1:  Randomly select a sub-preamble sequence from $S_s$ as a shared sub-preamble, $x_{u_s,v_s}\left(n_s\right)$;   2:  Randomly select a sub-preamble sequence from $S_d$ as a dedicated sub-preamble, $x_{u_d,v_d}\left(n_d\right)$;   3:  Randomly select a location index for the dedicated sub-preamble, $\mu$;   4:  if  $\mu =1$  then   5:    Generating a preamble according to Equation (7);   6:else   7:    Generating a preamble according to Equation (8);   8:end if