## 1 Introduction
IRS is an array of smart reflecting surfaces that are separated by a distance equal to half of the wavelength [12]. IRS technology was first proposed in [13] as a promising technology for the future sixth generation (6G) wireless communications and beyond systems. One crucial aspect to highlight is that the IRS enables the gNodeB to support the UE by establishing a virtual line-of-sight (LOS) path when the physical LOS path is obstructed [14]. This capability of the IRS is of utmost significance. The deployment of this technology is versatile, as it can be implemented on various structures such as buildings, walls, ceilings, and even underground tunnels [15]. IRS elements may be active or passive. Passive IRS has the ability to independently modify the incident signal in various ways. These modifications can involve changes in phase, amplitude, frequency, or even polarization [16]. IRS enables efficient signal reflection, beamforming, extending signal coverage, and interference mitigation [17]. However, unlike passive IRS, active IRS can also amplify the reflected signal. This is achieved through the integration of active reflection amplifiers within each active IRS element [18]. Sophisticated beamforming and precoding were studied in [19]. IRS is versatile and compatible with various communication technologies, such as millimeter-wave and terahertz communications, Simultaneous Wireless Information, and Power Transfer (SWIPT), Unmanned Aerial Vehicle Networks (UAV), MIMO systems, cell edge communication, physical layer security, and Non-Orthogonal Multiple Access (NOMA) [20]. The implementation of the Smart electromagnetic environment, by introducing several active and passive devices that are able to reach blind spots or to cover desired areas without increasing the number of base stations, is very challenging [21]. Among them, Smart Electromagnetic Skins (SESs), are very thin passive surfaces capable of enabling non-specular reflection to reach blind spots or cover target areas [22]. In contrast to traditional Access Points (APs) or relays, IRS operates solely through passive reflection and does not necessitate high energy consumption or costly hardware [23]. This characteristic enables IRS to be deployed in a dense manner, offering substantial enhancements to the network performance [24]. In the next-generation wireless communication system, the utilization of IRS technology plays a crucial role in enhancing the performance of the physical layer. In [25], the authors proposed an IRS-assisted millimeter-wave massive MIMO system with transmit antenna selection using the Alamouti scheme and hybrid analog-digital beamforming to achieve better beamforming gain. Moreover, the use of IRS also leads to significant BER improvements. The Alamouti technique is used in the transmitting side where only two antennas are used. The authors in [26] proposed the usage of IRS to improve the BER of the system to eliminate the effect of electromagnetic interference. In addition, they used STBC using three transmitting antennas to compensate the bad performance of the system. In [27], the authors introduced two MIMO systems assisted by IRS to improve the spectral efficiency by redesigning the classical Alamouti scheme and vertical Bell Labs Layered Space-Time (V-BLAST) for the IRS-aided communication scenario. Hence, the proposed methodology of [27] demonstrated that these redesigned systems achieved significantly enhanced end-to-end performance, highlighting the potential of IRS in boosting the spectral efficiency. In [28], the authors introduced the design of the IRS-aided QO-STBC scheme, where Quasi-Orthogonal STBC (QOSTBC) is applied on IRS elements instead of transmitting antennas. The proposed approach in [29] utilizes a phase-programmable meta-surface, which is fabricated and evaluated through a prototype system. The prototype system successfully achieves real-time RIS-based Alamouti space-time transmission over the air, demonstrating the effectiveness of the proposed approach.