## 1 Introduction  
In recent years we have been witnessing the increasing deployment of the fifth generation of wireless communications (5G). This generation represents a significant mark in the way we communicate, enabling new applications that would be otherwise infeasible with the technology of previous generations. Therefore, several new technologies were incorporated into 5G which were crucial to achieving all the requirements that are needed for the operation of these systems. However, the telecommunications field is experiencingfast growth over the last few decades, which has been motivating the academy and the industry to invest in the design, testing and deployment of the next generation of wireless communications (6G). Within this context, terahertz (THz) communications have been attracting more and more attention, being referred to by the research community as one of the most promising research fields on the topic, not only for the availability of spectrum but also because of the achievable rates that can be offered to the users [1; 2]. THz systems are becoming feasible due to the recent advances in the field of THz devices, and they are expected to ease the spectrum limitations of today's systems [3]. However, there are several issues that can affect the system performance, such as the reflection and scattering losses through the transmission path, the high dependency between range and frequency of channels in the THz band and also the need for controllable time-delay phase shifters. Such limitations require not only the proper system design but also the definition of a set of strategies to enable communications [4; 5]. According to the literature, some of the challenges for beyond 5G networks (B5G) are the fabrication of plasmonic nano array antennas, channel estimation, precoding, signal detection, beamforming, and beamsteering [6]. To overcome the distance limitation in THz communications, one can take advantage of the very large antenna arrays that can be implemented at these bands while minimizing interference between multiple users. However, when working with massive/ultra-massive arrays of antennas, a fully digital precoder is often not feasible and hybrid designs must be used instead. Regarding the hybrid precoder, it is necessary to adopt the most adequate architecture in order to maintain the intended trade-off between performance and complexity. Fully-connected (FC) structures based on phase shifters, arrays of subarrays (AoSAs) and dynamic arrays of subarrays (DAoSAs) represent some of the most referred to architectures in the literature [7; 8; 9; 10; 11]. From the energy efficiency (EE) and power consumption perspective, which are particularly relevant, and the mmWave/THz bands, the use of partially connected (PC) structures, such as AoSAs and DAoSAs, can be more efficient than fully connected structures. In particular, DAoSAs represent a much more appealing solution since they can offer a good compromise (in terms of performance) between fully connected structures, which have a higher implementation complexity (especially with a massive number of antennas), and AoSAs, which are lighter but can suffer significant degradation in performance. Concerning this topic, one can find in the literature a wide range of schemes for multiple-input multiple-output (MIMO) systems considering both uplink and downlink scenarios [7; 8; 9; 10; 11], but there is a significant imbalance between the number of approaches aimed at those scenarios for hybrid precoding at higher frequencies. The authors of [12] proposed two algorithms for low-complexity hybrid precoding and beamforming for multi-user (MU) mmWave systems. Even though they assume only one stream per user, i.e., the number of data streams (\(N_{s}\)) is equal to the number of users (\(N_{u}\)), it is shown that the algorithms achieve interesting results when compared to the fully-digital solution. The concept of precoding based on adaptive RF-chain-to-antenna was only introduced in [13] for single user (SU) scenarios but showed promising results.