## 3 Proposed Scheme
### Metaheuristic-tabu Search Algorithm
Other simulation parameters are selected based on the 3 rd generation partnership project evolved universal terrestrial radio access (3 GPP E-UTRA) regulation [34]. ### Simulation Results

In this subsection, we compare our proposed spectrum reuse-based throughput optimization for M-D2D communications against the random resource allocation scheme discussed in [20]. The study analyzed a cluster formation based resource allocation method, which allocates the resources randomly. For performance comparison, we level our proposed scheme as RA w/ MH-TS. Specifically, we denote our proposed resource allocation scheme before introducing the metaheuristic-tabu search algorithm as RA w/o M-TS. We denote the reference scheme [20] as RRA w/ MH-TS and RRA w/o MH-TS. The variation of coverage probability of M-D2D users with respect to the threshold SINR is shown in Figure 3a. From Figure 3a, we can see that our proposed scheme attains the highest coverage probability as compared with other schemes. Moreover, we observe that as the threshold SINR increases the coverage probability decreases. Specifically, for all the methods, M-D2D users achieved 63.54% to 87.76% of the coverage probability at the threshold SINR of 5 dB. Figure 3b depicts the variation of the coverage probability of cellular users with respect to the threshold SINR. It can be seen from Figure 3b that for all the methods, the cellular user with the metaheuristic-tabu search algorithm attained 65% to 86.84% of the coverage probability at the threshold SINR of -5 dB. As shown in Figure 3a,b, the coverage probability becomes worse for both M-D2D and cellular users with the increase in the threshold SINR of the network. Finally, we observe that for the given threshold SINR, the coverage probabilities of M-D2D communications are greater than those for cellular communications. This is due to the fact that the communication distances in M-D2D communications are less. \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameters** & **Values** \\ \hline Noise power & \(-174\) dBm/Hz \\ D2D grouping radius & 1-50 m \\ Total number resource blocks & 50 [34] \\ Link bandwidth & 180 kHz \\ The maximum transmission power of D2D user & 15 dBm \\ The maximum transmission power of cellular user & 25 dBm \\ Number of D2D groups & 20 \\ Number of D2D receivers in a group & 2\(\sim\)5 \\ User distribution & Uniform \\ Channel bandwidth & 10 MHz [34] \\ Path loss exponent & 4 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Main simulation parameters and values. The variation of the average throughput of M-D2D users as a function of the number of M-D2D groups in a cell is shown in Figure 4a. We observe that the throughput increases as the number of M-D2D groups in a cell increases. Moreover, it is seen that the throughput of our proposed resource allocation scheme shows a trend of a continuous increase. Therefore, we can conclude from our observation that the FFR technique was significantly employed for designing a high throughput cellular network. In Figure 4b, we plot the average throughput achieved by the cellular user as a function of the number of M-D2D groups in a cell. With the increase in the number of M-D2D groups in a cell, the cellular user throughput decreases. This is due to the fact that the M-D2D transmitter generates uplink interference to the eNB, which directly impacts on the performance of cellular users. Figure 5a shows the received SINR of the M-D2D user with respect to the variable distance between M-D2D receivers and the cellular user. As shown in Figure 5a, the received SINR of M-D2D increases with the increase of the distance between M-D2D receivers and cellular users. This is due to

Figure 4: (**a**) Average throughput of M-D2D users as a function of the number of M-D2D groups in a cell; (**b**) average throughput of cellular users as a function of the number of M-D2D groups in a cell. Figure 3: (**a**) Coverage probability of M-D2D user with varying threshold SINR, and (**b**) coverage probability of cellular users with varying threshold SINR.