# Intelligent Reflecting Surface-Assisted Wireless Communication Using RNNs: Comprehensive Insights
## 3 System Model  
### IRS Architecture and Working  
When an electromagnetic (EM) wave encounters the boundary between two isotropic mediums, the relationship between the angles of incidence, reflection, and refraction is described by [PERSON]'s law. In standard cases, the angle of incidence equals the angle of reflection for smooth surfaces, as shown in Figure 2a. However, recent developments in metasurfaces allow modifying surface impedance to induce specific phase shifts between incident and scattered waves. By dividing the surface into many small elements, each programmed with a particular phase shift, the reflected EM wave can be steered to a different angle than predicted by [PERSON]'s law. As shown in Figure 2b, a fully configurable phase shift for each metasurface element can direct the reflected beam to any desired angle. In practice, achieving precise or continuous phase shifts is challenging due to control complexities, making signal processing and machine learning techniques useful for designing IRSs [22]. Figure 2: (**a**) The regular reflector; (**b**) IRS reflector. IRSs are made up of a wide range of inexpensive passive reflecting components that are capable of adjusting the incident electromagnetic wave phase, amplitude, and even polarization. The propagation environment of wireless signals may be dynamically adjusted using these programmable surfaces. For a variety of purposes, including boosting signal strength, lowering interference, or covering regions with poor signals, IRSs in wireless communication systems work by reflecting and redirecting signals. An example of an IRS-aided wireless system in action is shown in Figure 3.  
Here is how IRSs work in a typical wireless communication setup:  
_Signal Transmission:_ A signal is transmitted from a BS or user toward the IRS. _Surface Reflection:_ The IRS components are adjusted to modify the incoming signal's phase and/or amplitude in order to direct it toward the intended target, which might be a BS or another user. _Signal Reception:_ The modified signal reaches the receiver with enhanced quality, having avoided obstacles, reduced interference, and optimized the transmission path for improved signal strength and reliability. In order to provide a smart propagation environment where wireless communication is boosted without the need for active, power-hungry components like amplifiers, IRSs may be managed in real-time to react to changing environmental circumstances, such as user movement or barriers. Key motivations behind using IRSs in wireless communication are listed as follows:  
* _Improved signal coverage:_ IRSs may greatly increase the coverage area, especially in areas with many impediments, by reflecting signals around objects like walls or buildings that often impede wireless signals. * _Energy efficiency:_ IRSs may reflect signals with low energy usage as it is made up of passive components that do not require active, power-hungry transmitters. This lowers the total energy consumption of wireless networks. * _Reduced interference:_ IRSs may reduce interference by carefully rerouting communications away from places or devices that cause interference. This is especially helpful when there are lots of devices interacting at once in congested areas. * _Enhanced spectral efficiency:_ IRSs aid in the effective use of the available spectrum by modifying the wireless environment and boosting the data rates and overall capacity of wireless networks. * _Cost-effective deployment:_ As an IRS is passive, it is less expensive to install and operate than power-hungry relays or new base stations. This makes it a more cost-effective option overall. * _Support for 5G and beyond:_ By improving communication at high-frequency bands like millimeter waves (mmWave), which are vulnerable to high route loss and limited penetration, IRSs can supplement 5G technology. Figure 3: IRS working principle in wireless mobile communication system. The common perception of relays is that they are active components that require a separate power supply to function.