# Joint Power and Time Allocation in Hybrid NoMA/OMA IoT Networks for Two-Way Communications
## 4 Simulation Analysis
For the power allocation with fixed time allocation proportion, the overall transmission time is firstly divided equally on the DL and UL, and then the allocated DL transmission time is further equally divided into \(K\) intervals to support the DL TDMA. Thus qualitatively, \(\tau=\frac{1}{2}\), \(\tau_{\rm k}=\frac{1}{2K}\), \(\forall k\). Figure 4 presents the system power performance for the two resource allocation methods under symmetric traffic levels on the DL and UL, i.e., \(\bar{R}\stackrel{{\Delta}}{{=}}\bar{R}_{\rm D}=\bar{R}_{\rm U}\). Simulations from Figure 4 show that the joint method greatly reduces the system's power consumption as compared with the power allocation method under fixed time allocation. Obviously, the additional freedom of transmission time in the joint method allows for further reduction in the system's power. Finally, we compare our proposed hybrid NoMA/OMA scheme with the pure OMA scheme and the pure NoMA scheme. In the pure OMA scheme, TDMA was applied on both the DL and UL, and the joint power and time allocation for each user were still adopted for the system design, as in the hybrid NoMA/OMA scheme. In the pure NoMA scheme, NoMA was applied on both the UL and DL, and the joint power and time allocation were adopted as well. Figure 5 illustrates the system's power consumption for the three schemes under three distinct DL and UL rate combinations. For the convenience of illustration, the hybrid NoMA/OMA scheme, the NoMA scheme, and the OMA scheme are labeled with 'hybrid', 'NoMA', and 'OMA', respectively, in the figure. Admittedly, when the system can afford the NoMA MUD on both the UL and DL, the hybrid scheme is inferior to the pure NoMA scheme. When the NoMA MUD cannot be affordable for the IoDs, the proposed scheme performs better than the OMA scheme. Quantitatively, for the transmission rate combinations \((\bar{R}_{\rm D},\bar{R}_{\rm U})=(1,3)\), \((\bar{R}_{\rm D},\bar{R}_{\rm U})=(2,2)\), and \((\bar{R}_{\rm D},\bar{R}_{\rm U})=(3,1)\), the system power of the OMA scheme is almost 3 times, 2 times, or 1.4 times that of the hybrid scheme, respectively; or equivalently, the proposed scheme saves nearly 67%, 50%, and 30% power as compared with the OMA scheme, respectively, implying that the more demanding the UL rate requirement, the greater the advantage of the hybrid scheme over the OMA scheme. Fortunately, in most low-cost IoT applications, such as wireless sensor networks, the UL  
Figure 4: Performance comparison between the joint resource allocation and the power allocation under fixed time allocation. traffic is dominating on the two-way transmissions, and thus a power efficient system can be reached in these IoT application scenarios. This result is not difficult to understand in that on the UL, NoMA and OMA are respectively applied in the hybrid scheme and the OMA scheme, and the superiority of the hybrid scheme over the OMA scheme is actually the superiority of NoMA over OMA. As a compromise, the hybrid scheme not only achieves NoMA gains by exploiting the rich computational resources at the AP, but also makes the IoD receivers realizable by using low-complexity OMA.