## 4 Evaluation
### Evaluation and Comparison Framework  
To evaluate the proposed optimization framework in diverse dynamic vehicular networks, we compared its performance with four baseline methods, R&R/opt, Util&LB/opt, SSF/opt, and RND/opt, each of which is summarized as below. * Proposed: The proposed optimal solution that consists of the optimal association, channel assignment and NOMA-OMA switching (see Section 3.2.1), which is followed by the optimal power allocation (see Section 3.2.2). * R&R/opt: The optimization problem with relaxation and rounding (see Section 3.3.1). It first solves the optimal association, channel assignment and NOMA-OMA switching with relaxed binary variables. Then, to recover the binary solution simple rounding technique is applied while checking the validity of the recovered solution. The following power allocation is carried out in an optimal manner as the proposed approach does. * Util&LB/opt: The RSU-VU association is carried out first. Then, per-RSU channel assignment and NOMA-OMA switching problem is invoked in a distributed manner, where all the mentioned problems use binary variables. The following power allocation is carried out as Proposed does. For the weight parameter, \(\alpha=0.8\) is assumed to put more weight to power minimization which is the main focus of this study. The unit-scaling term, \(m_{1}\) and \(m_{2}\) is set to the maximum possible value of the corresponding term, respectively. * SSF/opt: The Signal Strength First (SSF) approach is taken to make the association between VUs and RSUs, which assigns VUs to RSUs based on signal strength, ignoring load balancing and interference, followed by optimal channel and power allocation. The remaining steps including per-RSU channel assignment, NOMA/OMA switching and power allocation are carried out in the same manner as Util&LB/opt does. * RND/opt: A random algorithm that uniformly randomizes and makes the RSU-VU association, channel assignment, and NOMA-OMA switching decisions, while optimal power allocation is still carried out as above. Although random, RND/opt verifies the validity of the decision, which means that the association is made only if there is an accessibility relation between VU and RSU, and the channel assignment is made only when there is an availability. For performance comparison, the performance metrics of total power consumption, fairness, NOMA utilization ratio, and CPU time have been utilized. Each metric is formulated as described below:  
* Total power consumption (dBm or watt): Total power consumption represents the sum of the transmit power consumed by all RSUs considered in each scenario, i.e., \(p_{\sum}=\sum_{b}\sum_{c}\sum_{u}p_{bcu}^{h}+p_{bcu}^{l}\). The resulting values are computed in watts, and conversion to dBm is performed using the following calculation: \(10\times log_{10}(p_{\sum}/1 mW)\). * Fairness ([PERSON]'s fairness index [34]): The [PERSON]'s fairness index is widely used to measure the equitable distribution of resources [35]. Using this index, the fairness score \(\mathcal{J}\) for the fair distribution of VUs among RSUs is calculated as follows: \[\mathcal{J}(y_{1},y_{2},\cdots,y_{N_{RSU}})=\frac{(\sum_{b=1}^{N_{RSU}}y_{b})^{ 2}}{N_{RSU}\times\sum_{i=b}^{N_{RSU}}y_{b}^{2}},\] where \(y_{b}=\sum_{vb}y_{bu}\) in Util&LB/opt and SSF/opt, and \(y_{b}=\sum_{vc}\sum_{vu}x_{bcu}^{hl}+x_{bcu}^{l}\) in Proposed, R&R/opt and RND/opt. Here, \(y_{b}\) represents the number of VUs associated with RSU \(b\). * NOMA utilization ratio: The NOMA utilization ratio reflects the fraction of channels configured for NOMA communication relative to the total number of available channels across all RSUs. Using the mathematical notations from Section 3, the ratio is calculated as follows: Let the set \(S\) be defined as \(\{(b,c)|\sum_{u}x_{bcu}^{h}+x_{bcu}^{l}=2,\forall b,c\}\), where each element \((b,c)\) is a tuple that satisfies the condition that channel \(c\) in RSU \(b\) is used for NOMA communication by assigning the channel to two users.