## 1 Introduction  
Intelligent reflecting surface (IRS) recently sparked considerable interest as a potential method for improving the efficiency of wireless communication systems [1]. An IRS is a 2D planar meta-surface with the flexibility to embed numerous inexpensive and passive reflecting elements on a single meta-surface, giving it a direct line of sight (LoS) to the access points (AP) or base station (BS), making it easy to deploy on structures such as walls, ceilings, and tunnels. The Figure 1 shows a typical arrangement of IRS aided wireless communication system. IRS can be used to boost radio systems' capacity by lowering interference and raising the signal-to-noise ratio (SNR). IRS may efficiently cancel out interference and enhance the signal's overall quality by adjusting the signal's reflection angle and phase. Overall, the incorporation of IRS into the 6G standard has tremendous promise for enhancingthe efficiency of radio networks, expanding their reach, and cutting costs for wireless providers [2]. The deployment and design of IRSs have been the subject of numerous studies aimed at improving wireless network performance in terms of capacity, signal quality, coverage and security [3]. In order to increase the SNR of an IRS-enabled wireless communication system, a joint optimisation framework for IRS placement and phase management is proposed in [4]. The SNR in turn will increase the achievable rate of the system. It demonstrates that the SNR of the system can be significantly improved by intelligently deciding the placement and phase shift of the IRS. In a similar approach in [5], the authors proposed an ideal design and deployment method for IRS in a wireless communication system which will ensure that the achievable rate of the system is maximised. In the proposed method, both the amount of phase shift and the IRS's geometry are optimised using a genetic algorithm. IRSs have emerged as a promising solution for minimising transmit power in wireless communication systems. Unlike conventional relay systems, IRS utilises passive signal reflection to direct energy efficiently toward receivers. In multi-user downlink scenarios, integrating IRS has been shown to significantly lower the transmit power required to meet specific signal-to-interference-plus-noise ration (SINR) targets, particularly as the number of reflecting elements increases [4]. For instance, [PERSON]. [6] examined an IRS-assisted cognitive radio network and found that configurations with 8 to 32 IRS elements provided 20-32 dB performance improvements compared to systems without IRS. These findings highlight IRS's potential to enhance energy efficiency without compromising system throughput. IRS also contributes to improved bandwidth utilisation and spectral efficiency by reinforcing signal strength and coverage, thus supporting more effective frequency reuse. Research in mmWave communications reveals that enlarging the IRS array or increasing transmit power can dramatically enhance spectral efficiency--achieving up to a 3\(\times\) gain at 5 MHz and up to 14\(\times\) at 25 MHz bandwidths [7]. These benefits stem from IRS's ability to mitigate signal degradation due to multipath and interference, resulting in higher data rates over existing spectrum resources. Therefore, IRS technology plays a critical role in  
Figure 1: Intelligent reflecting surface-aided wireless communication. optimising spectrum efficiency, which is vital for supporting the massive capacity demands of 6G networks [8]. From the viewpoint of network providers, quality of service (QoS) reflects the capability of the communication system to deliver consistent performance tailored to various user applications. Key QoS indicators include data throughput, latency, jitter, reliability, and outage probability, all of which are essential for fulfilling service-level agreements (SLAs) and ensuring user satisfaction. In wireless networks enhanced by IRS, delivering QoS becomes both more challenging and more promising.