Algorithm 1 Concatenated Encoder

Input:  Read $Ps={(P{s}_1,P{s}_2,\cdots ,P{s}_g)}^T$ from the queue, ${\mathrm{\Omega }}_d=({\mathrm{\Omega }}_1,{\mathrm{\Omega }}_2,\cdots ,{\mathrm{\Omega }}_{max})$, the PDU sessions number $N_L$;  Output:  $\overline{P}c$ 1:$P{c}_{g\gamma \times 1}\leftarrow 0_{g\gamma }$;                              ▹ Raptor code encoding procedure 2:$G_{g\gamma \times m}^{Raptor}=G_{g\gamma \times m}^{LT}{G}_{m\times g}^{pre}$; 3:$P{c}_{g\gamma \times 1}=G_{g\gamma \times g}^{Raptor}P{s}_{g\times 1}$; 4:$\overline{\mathit{RP}}\mathit{c}\leftarrow P{c}_{g\gamma \times 1}$;           ▹ Packet-level Raptor code encoder output $\overline{\mathit{RP}}\mathit{c}$ 5:Generate uniform random matrix $\mathit{X}=\{X_1,X_2,\cdots ,X_M\}$; 6:Split $\overline{\mathit{RP}}\mathit{c}$ into K groups($RP{c}_1,RP{c}_2,\cdots ,RP{c}_K$);     ▹ Lagrange encoding procedure 7:for  $i=1,2,\cdots ,N$  do 8:   $LP{c}_i\leftarrow$${\sum }_{j\in \left[K\right]}RP{c}_j·{\prod }_{k\in [K+M]\setminus \left\{j\right\}}\frac{{\alpha }_i-{\beta }_k}{{\beta }_j-{\beta }_k}+{\sum }_{j=K+1}^{K+M}{X}_j·{\prod }_{k\in [K+M]\setminus \left\{j\right\}}\frac{{\alpha }_i-{\beta }_k}{{\beta }_j-{\beta }_k}$; ${\left\{{\alpha }_i\right\}}_{i=1}^{K+M}\cap {\left\{{\beta }_j\right\}}_{j=1}^K=\varnothing$ 9:   $\overline{P}c\leftarrow append[\overline{P}c,LP{c}_i]$ 10:end for               ▹ Fast Polynomial interpolation 11:return $\overline{P}c$;