## 3 Numerical Results
### System-Level Simulations  
Bit and block error rate (BER/BLER) results obtained from link-level simulations are used as input for the system-level evaluation. As presented in the system model section, we consider an indoor office virtualized C-RAN, where the network determines which APs are to be associated with each UE. The total number of sites with APs is 12, which are equally spaced. Each site with APs consists of three transmission and reception points (TRPs), each one equipped with UPAs with \(N_{tx}\) antennas, while UEs also have one UPA with \(N_{rx}\) antennas. The number of antennas \(N_{tx}\) of each array is 100 or 256 antennas whereas the separation between antennas of the array is a half wavelength. The signal-to-noise ratio (SNR) in dB considered in the system-level simulations is obtained from \(\text{SNR}\ =\ (E_{s}/N_{0})+10\ log(R_{s}/B)\ \text{dB}\), where \(R_{s}\) is the total transmitted symbol rate per  
Figure 6: BER performance versus SNR achieved by the proposed precoder with \(N_{tx}\) = 256, \(N_{rx}\) = 4, \(N_{u}\) = 4, \(N_{RF}^{rx}=14\), \(F\) = 828 and \(N_{s}\) = 2, considering several versions of the algorithm (only NLOS component). antenna and user, B is the total bandwidth, and \(E_{s}/N_{0}\) is the ratio of symbol energy to noise spectral density in dB. Values \(E_{s}/N_{0}\) are obtained from the link-level BLER results. The BLER can be expressed using the BER, according to the following expression  
\[\text{BLER}\ =\ 1\ -\ (1\ -\ \text{BER})^{L} \tag{9}\]  
where \(L\) is the length of the block in bits. \(L\) can be calculated as \(L=2\times F\), since the selected modulation is quadrature phase shift keying (QPSK) and each subcarrier transports a symbol with 2 bits. By maintaining the reference \(\text{BLER}\ (\text{BLER}_{ref})\) equal to 0.1 as the \(F\) increases, we must decrease the respective reference \(\text{BER}\ (\text{BER}_{ref})\). We considered the fifth numerology of 5G NR with spacing between the subcarriers of 480 KHz. The transmission time interval (\(TTI\)) of this numerology is 31.25 us and the total bandwidth is \(B_{t}\) = 400 MHz. Up to 16 carriers can be aggregated if more bandwidth and higher binary rates, according to the 5G NR specifications, are to be achieved. We used the 3D InD-MO channel model specified by 3 GPP [25] which has a LOS probability (\(P_{LOS}\)) equal to 1 for a distance lower than 1.2 m between the AP and terminals. The probability of NLOS components is \(P_{NLOS}=1-P_{LOS}\) and depends on the distance between the AP and the terminals. Previously, we started our study by comparing several solutions available in the literature concerning hybrid precoding algorithms in terms of BER versus SNR. Based on those results, we decided to analyze the performance of a system, where the APs operate in the mmWave/THz bands with massive/ultra-massive antenna arrays combined with those different hybrid precoding architectures. For this evaluation, first, we start by considering that the cluster size is equal to one. When the RAN cluster size is one (1C), we have the traditional cellular network where each AP generates inter-site interference. When the RAN cluster size is three, the network is partitioned into three adjacent site sets and each user is served at the same time by three TRPs generating much less inner interference. It is important to note that the throughput presented in the following figures concerns the average throughput value of the various UEs moving randomly throughout the 200 s of simulation. Initially, the terminals are placed uniformly distributed inside each sector served by an UPA antenna. The movement of the terminals is \"Random waypoint around AP\". At every 0.5 ms of simulation, the SNR at all terminals is calculated. Those blocks which are received with SNR \(>\) SNR\({}_{\text{target}}\) are considered in the throughput calculation. The blocks that are received with SNR \(<\) SNR\({}_{\text{target}}\) are not counted in the throughput due to the throughput definition itself.