# Energy-Efficient Resource and Power Allocation for Underlay Multicast Device-to-Device Transmission
## 5 Simulation Results
UE: user equipment; RB: resource blocks; SINR: signal-to-interference-and-noise ratio; CU: cellular users; D2D: Device-to-Device. Figure 2: Cluster Energy Efficiency versus D2D cluster radius. QoS: quality of service. scheme is initially inferior to that of [7] and gradually outperforms other schemes with the increase of D2D cluster radius. The reason is twofold. Firstly, our proposed scheme aims at maximizing the EE performance of the D2D clusters, which adopts a smaller transmit power when the radius of the D2D multicast group is small. This explains why the total throughput of our proposed scheme is smaller than that of the scheme in [7], which always adopts the maximum transmit power. However, with the increase of D2D cluster radius, our proposed scheme will gradually increase the transmit power of D2D users while decrease the transmit power of co-channel CUs in order to ensure reliable D2D multicast transmission, which leads to increased total throughput. Secondly, compared with schemes in [14; 18], the resource relationship of our proposed scheme is based on minimizing the interference of D2D links. As a result, the CU who brings the least interference will be paired up with the D2D multicast cluster accordingly. This explains why our proposed scheme has better performance. Similarly, it is shown that the sum throughput of all four algorithms increases with the increase of user numbers. The impact of energy efficiency on total throughput of D2D multicast groups is shown in Figure 4. It can be observed that the energy efficiency performance of our proposed scheme and the scheme in [14] both decrease with the increase of total throughput. This is explained as when the total throughput increases, according to our proposed power control scheme, the transmit power also increases, which contributes to decreased energy efficiency. Moreover, based on minimizing the interference of D2D clusters, our proposed heuristic algorithm allocates better cellular resource to D2D clusters. Meanwhile, it also decreases the transmit power of co-channel CUs, which contributes to improved EE performance of D2D multicast clusters. Figure 5 plots the average SINR of D2D multicast clusters with different D2D cluster radius. We assume that there are totally 500 UEs randomly distributed in the simulation area. From the figure, we can infer that for the schemes which include power control scheme, such as our proposed algorithm and the scheme in [14], the SINR distribution does not obviously decrease with the increase of D2D group radius. This is because according to the changing channel conditions and resource reuse relationships, the power control method jointly adjusts the transmission power of both D2D clusters and CUs, which ensures reliable D2D multicast transmission [19]. On the contrary, for the algorithms which do not incorporate power control schemes, such as [7; 18], the QoS requirement of D2D multicast clusters in terms of minimum SINR constraint cannot be guaranteed when the channel quality becomes worse. Figure 3: Total Throughput of D2D multicast clusters versus D2D cluster radius. Figure 6 plots the Cumulative Distribution Function (CDF) curve of cellular users' SINR concerning with different schemes. It can be obviously seen that with the introduction of power control scheme, the SINR curves of both [14] and our proposed scheme decrease, while the SINR curves of [7; 18] are not severely impacted. This is because our proposed strategy decreases the transmit power of CUs in order to maximize the total energy-efficiency of D2D multicast clusters, which results in deterioration of CU's SINR. However, compared with [14], our resource allocation strategy will pick up a CU who brings the least interference for the D2D multicast cluster. Hence, the co-channel interference caused by underlay D2D transmission will be effectively controlled, which contributes to improved SINR of C-links. From Figure 6, we can also infer that although the link quality of CUs has been affected a little for the proposed scheme.