## 3 System-Level Configuration
### System-Level Simulations  
The signal-to-noise ratio (SNR) in dB considered in the system-level simulations is obtained from \(SNR=(E_{s}/N_{0})+10\ log(Rs/B)\) dB, where \(Rs\) is the total transmitted symbol rate per antenna and user, \(B\) is the total bandwidth (we considered 50 MHz at 3.6 GHz and 28 GHz for the smart city with numerology 0, and 400 MHz at 28 GHz and 100 GHz for the other scenarios with numerology 3), and \(E_{s}/N_{0}\) is the ratio of symbol energy to noise spectral density in dB. Values of \(E_{s}/N_{0}\) are obtained from the link-level BER results. In this work, we only considered QPSK modulated symbols. The frame structure of 5G NR has both a frequency division duplex (FDD), used in the paired spectrum, and a time division duplex (TDD), used for the unpaired spectrum. We chose TDD in this work for all scenarios. The subcarrier spacing, transmission time interval, cyclic prefix (CP), and the number of symbols per slot are all defined by the proposed 5G NR scalable OFDM numerology [15]. Figure 6: BER versus distance for a scenario with fc = 28 GHz, \(N_{tx}=64\), \(N_{s}=3\), \(N_{rx}=16\), \(N_{ris}=144\) or \(576\) elements with \(N_{c}=1\). Our scenarios were simulated considering numerologies 0 and 3. Numerology 0 (4G) was chosen for smart city scenario because the most important key performance indicator (KPI) is the coverage of IoT devices, not their throughput, and numerology 3 for the stadium with pitch and indoor factory scenarios, in mmWave and THz bands, respectively. For the smart city scenario, we considered different UPA antenna arrays with \(N_{rx}\) = 144, 256, and up to 576 elements on the receiver side (BS). For the IoT device (on the transmitter side), \(N_{tx}\) = 1, \(N_{s}\) = 1 and \(N_{c}\) = 1. For numerology 0, \(\Delta\)f = 15 KHz, and every PRB has 12 carriers (B\({}_{\text{prb}}\) = 180 KHz) with 14 symbols per subframe duration Ts = 1 ms, with 168 (12 \(\times\) 14) subcarriers. In real cellular networks with massive MIMO, there is a coherence interval where channel information does not change much, and pilot reference symbols must be retransmitted. The coherence interval is  
\[\tau_{c}=T_{c}\times B_{c} \tag{4}\]  
where coherence time \(T_{c}\) = 50 ms is well fitted for nomadic and static low-power IoT devices [34], and \(B_{c}\) = 1.697 MHz (9.42857 \(\times\) 180 KHz) is adequate for an urban city scenario such as a smart city. In \(\tau_{c}\), the maximum number of subcarriers is \(N_{\text{sc}}\) = 79,200 (168 \(\times\) 50 \(\times\) 9.42857). Half of the coherence interval can be used for uplink data transmission, and the remaining half of the coherence interval can be used for downlink transmission. We need orthogonal reference pilots in uplink that must be subtracted from uplink data symbols. For uplink data and reference pilots, we must have \(N_{\text{sc}}\)/4 = 79,200/4 = 19,800 subcarriers. Assuming that we divide 19,800 into twelve groups (scenario has 4 BS \(\times\) 3 sectors), then we obtain 19,800/12 = 1650 subcarriers, one for each IoT device transmitting in each sector at the same time without any intra-cell interference. Table 4 presents the additional simulation parameters of the smart city scenario. In real situations, the number of active IoT devices per sector can be much higher because of the sleeping time of IoT devices. Sensors do not need to transmit packets every 1 ms.  
For the smart city scenario, we consider only the uplink, wherein IoT devices are transmitting to BS and RIS at the same time. Uplink power control is appropriately applied so that the received powers are the same for almost all IoT devices. However, data sent from IoT devices that are too far from the receivers, i.e., BSs and/or RISs, might not be well received. There is a minimum received power that must be above the receiver sensitivity so that packets are correctly received. We take as a reference the BER \(\leq\) 5 \(\times\) 10\({}^{-4}\) to decide which packets are received without bit error.