## 3 System-Level Configuration
### System-Level Simulations
For example, as shown in Figure 7, depending on \(N_{rx}\), the throughput increases up to a certain point, and then it decreases. The decrease in throughput after a certain \(N_{u}\) depends on \(N_{rx}\). At sector level, increasing \(N_{u}\) above \(N_{rx}\) increases intra-cell and inter-cell interferences, thus decreasing the throughput. As expected, the introduction of RIS panels at cell borders provides higher throughput compared to BS-only connections. As expected, increasing the number of receiving UPA antennas results in higher throughput due to their higher multiple-access capability. The throughput gain introduced by RIS panels with \(N_{ris}=576\) increases with the decreasing number of UPA antennas \(N_{rx}=576\), 256 and 144. The gain is more noticeable for increasing \(N_{u}\), because more users become close to where RIS panels are localized at the cell borders. Only for 28 GHz have we considered a UPA with \(N_{rx}=1024\) antennas because of its size. As expected, the maximum throughput is achieved for \(N_{rx}=1024\) due to its higher multiple-access capability. Figure 9 presents the coverage versus transmitted power for \(N_{u}=19\),800 with the same conditions as Figure 8. The comparison between Figures 8 and 9 shows that there is a direct correspondence between the throughput performance and the associated coverage. For the maximum transmitted power of 10 mW, the smallest coverage of 44% is achieved by the curve 100%BS + 0%RIS, \(N_{rx}=144\), whereas the highest coverage is 93% which is obtained by the curve 100%BS + 0%RIS, \(N_{rx}=1024\). Thus, the maximum coverage gain is 111%. The next highest coverage of 90% corresponds to the curve 89%BS + 11%RIS, \(N_{rx}=576\) and represents a coverage gain of 104% that includes a reduction in the number of antennas but the introduction of RIS. Still, the main contribution to the coverage gain is due to the number of antennas, which is 97%. Figure 8: Throughput vs. number of IoT devices for the smart city scenario with \(N_{tx}=1\) and \(P_{tx}=10\) dBm, for a carrier frequency of 28 GHz, \(N_{ris}=576\). Next, we tested the stadium with pitch scenario with different parameters. For this purpose, we adopted a higher number of subcarriers \(N_{c}\) combined with more spatial streams and larger transmit powers. The numerology of 5G NR is 3, with \(\Delta f=120\) KHz; the bandwidth is 400 MHz, and 112 symbols are transmitted every millisecond. The maximum number of subcarriers is 3300. In this scenario, the main KPI is throughput associated with the number of connections per unit of area. In all simulations in the stadium, the transmitter-side BS has \(N_{tx}=64\), whereas the receiver-side user has the same number of antennas, namely, \(N_{rx}=16\). Different numbers of transmitted symbols per subcarrier were considered in the simulations: \(N_{s}=2\) and \(N_{s}=3\). The number of OFDM subcarriers (\(N_{c}\)) used in the evaluations is variable, namely, \(N_{c}=12\), 60, 120, 132, 216 or 240. All these numbers are multiples of 12, which correspond to the number of subcarriers of a PRB in 5G NR. Users are placed uniformly around TRPs localized close to the four corners of the stadium turf. Some 46% of users are on turf, while the remaining 54% are sitting in the stadium stands (see Figure 4 and Table 2). The configuration with 100%BS + 0%RIS has 4 BSs and 12 sectors and matches a typical cellular system. In this case, users are uniformly distributed within a radius of 57 m (see Table 2). On the other hand, when simulating cases with BSs and RISs operating simultaneously, users that are connected to BSs will be uniformly distributed within a circle with a radius of 34 m. RIS panels are uniformly distributed inside the scenario, and users served by RISs are distributed uniformly within a radius of 17 m.  
In Figure 10, the throughput performance versus the number of users in the stadium scenario is shown. The throughput curves of Figure 10 were obtained with a maximum transmitted power of 250 mW.