## 1 Introduction
This phenomenon tends to worsen, especially in systems designed for outdoor environments. Another particular characteristic that is verified at mmWave and THz bands is that the propagation channel tends to be spatially sparse, which results in a lower number of propagation paths. Such challenges can be attenuated with the aid of RISs, since these IoT devices can operate as a centralized beamformer that can increase the channel gains. Moreover, RIS can also create additional propagation paths around major obstacles and enable line-of-sight (LOS) links to distant receivers [22]. In [23], the authors studied a system operating at the THz band using an RIS for an indoor and outdoor scenario that optimizes the phase shifts of the individual elements in order to assist an ultra-massive MIMO (um-MIMO) communication link. Performance results showed that the approach was capable of effectively extending the communication range. The authors in [24], developed an algorithm to calculate the ideal phases for each RIS element in order to maximize the capacity of the transmission. In their study, a multiple-input-multiple-output-OFDM (MIMO-OFDM) link with a frequency-selective fading channel and perfect channel state information was considered. According to the literature, due to their EE, RISs can be a viable alternative to traditional amplifiers and relays when considering multi-user communication scenarios, as demonstrated by the authors in [25]. The authors in [26] described a system with a single AP that distributes packets to several users. The system is able to improve the performance of both orthogonal multiple access (OMA) and NOMA with the aid of RIS. Although they considered only a single antenna for both transmitter and receiver, it was proved that RIS can enhance both the capacity and rate of the system. Nevertheless, point-to-point communications in MIMO systems aided by RIS are still a challenge. Although some results obtained with system-level evaluations of wireless cellular networks and test bench prototypes exist in the literature [27; 28; 29; 30], they all comprise small-scale configurations. Furthermore, the use of RIS-assisted systems combined with MIMO configurations in C-RANrequires more in-depth research into the optimization process and overall impact. In [31], an RIS-aided cellular network was considered, and an algorithm for joint optimization of active beamforming at the BS and passive beamforming of the RIS was also presented. Their simulation results showed some performance improvements against other existing algorithms. In [32], the authors presented one of the first system-level studies of RIS-aided network deployment, using two frequencies of fifth-generation new radio (5G NR), namely, 3.5 GHz and 28 GHz. While assuming a simplified operation in the far-field region with the RISs configured as anomalous reflectors, they demonstrated through a three-dimensional simulator how RISs can benefit a typical 5G urban network. Additionally, in [33], the authors studied a system-level design with an improved antenna model that analyses the path loss, power, and overall coverage between the transmitter and receiver with the aid of relayed RIS. Their results showed that the impact of the placement of RIS can affect the performance of the system, especially at the edges of the sector cell. Despite the promising results of these initial studies, more research on the integration of RIS in future wireless networks is required before large-scale experimental deployments can become a reality. In fact, at mm-Wave or THz frequencies, the distances between BSs will tend to be short, enabling users to be connected to more than one BS simultaneously. We adopt the same optimization approach from [12], namely, the joint AM-SVD-APG iterative algorithm applied to the uplink and downlink to effectively enable the implementation of smart radio environments.