## 3 System-Level Configuration
### System-Level Simulations
For numerology 0 of 5G NR, \(\Delta\)f = 15 KHz and 168 subcarriers are being transmitted in every PRB during 1 ms. The minimum throughput of each IoT device is 2 Kbps, assuming transmission in one carrier with QPSK symbols, and the minimum spectral efficiency per IoT device is \(\varepsilon_{\text{u}}\) = 2/15 bps/Hz. There is a theoretical equation for the maximum throughput, assuming perfect power control and a single cell with no inter-cell interference [9], which is  
\[Th_{max}=0.5\times B\times\left(1-\tau_{p}\right)\times\log_{2}(1+SINR) \tag{5}\]  
where \(\tau_{p}\) is fraction of time for pilot symbols' transmission and \(B\) is the total bandwidth. SINR is the signal to interference plus noise ratio. \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value** \\ \hline Coherence time Tc & 50 ms \\ Coherence band Bc & 1.697 MHz \\ Maximum time Tp & 12.5 ms \\ Maximum \(N_{\text{sc}}\) & 79,200 \\ Max. active IoT devices \(N_{\text{sc}}\)/4 & 19,800 \\ Number of sectors & 12 \\ Number of IoT devices/sector & 1650 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Additional simulation parameters for the smart city scenario. In Figure 7, the throughput performance versus number of users is shown for different number of antennas at BS in each sector of the scenario, and for different frequency carriers. The throughput curves in Figure 7 were obtained with a maximum transmitted power of 10 mW. The settings are described in Table 1. In this scenario, we used \(N_{s}=1\), \(N_{c}=1\), \(N_{lx}=1\), and \(N_{rx}=144\), 256 or 576 antennas. As expected, the frequency carrier of 3.6 GHz provides the highest throughput compared to 28 GHz due to its lower path attenuation. Increasing \(N_{rx}\) provides higher throughput independently of the frequency carrier. Increasing the number of UPA antennas allows us to more efficiently serve more IoT devices at the same time. For almost all curves, as \(N_{rx}\) increases, the throughput increases up to a certain point, and then it decreases. The decrease in throughput after a certain \(N_{u}\) depends on \(N_{rx}\). Increasing \(N_{u}\) above \(N_{rx}\), at sector level, increases intra-cell and inter-cell interferences, thus decreasing the throughput. In addition, there are higher number of IoT devices at the border of the cells with SINR below the reference to avoid errors in packet. Due to the C-RAN operation mode, almost no reference pilot symbol contamination occurs. For 3.6 GHz, the maximum simulated spectral efficiency occurs for \(N_{u}=19\),800 and \(N_{rx}=576\), corresponding to \(\varepsilon=508/24.75=20.53\) bps/Hz, where 508 Mbps is the aggregate throughput of 19,800 IoT devices and B = 24.75 MHz is the occupied bandwidth. The theoretical maximum spectral efficiency is \(\varepsilon_{\max}=554/24.75=22.40\) bps/Hz. In Figure 8, the throughput performance versus \(N_{u}\) is shown for a different number of antennas at BS in each sector and a carrier frequency of 28 GHz, both without and with RIS panels (\(N_{ris}=576\)). We compare four standard communication curves without any RIS, only with BSs and IoT devices, with three curves with RISs panels spread around the scenario. The former curves consist only of direct links between the IoT devices and the receivers. The other cases consist of a combination of direct link connections and RIS-aided connections. They are represented as a percentage of IoT devices that are transmitting signals to BS plus the percentage of IoT devices also with RIS connections, namely %BS + %RIS. For example, 100%BS + 0%RIS means that all IoT devices are attached to the BSs,  
Figure 7: Throughput vs. number of IoT devices for a smart city scenario with \(N_{lx}=1\) and \(P_{lx}=10\) dBm, for carrier frequencies of 3.6 GHz and 28 GHz. whereas 89%BS + 11%/RIS represents 89% of spread-out IoT devices linked to nearest BS, and the 11% remaining IoT devices are linked to nearest RISs. C-RAN processes data received from the two best links involving each IoT device.