###### Abstract  
In this paper, passive Intelligent Reflecting Surface (IRS) is used to enhance the performance of a Full Duplex (FD) bidirectional Machine Type Communication (MTC) system with two source nodes. Each node is equipped with two antennas to operate in FD mode. In reality, self-interference and discrete phase shifting are two major impairments in FD and IRS-assisted communication, respectively. The self-interference at source nodes operating in FD mode is mitigated by increasing the number of meta-surface elements at the IRS. Bit Error Rate (BER) and outage performances are analyzed with continuous phase shifting and discrete phase shifting in IRS. Closed-form analytical expressions are derived for the outage probability and BER performances of the IRS-assisted bidirectional FD-MTC system with a continuous phase shifter. The outage and BER performances of the IRS-assisted bidirectional MTC system in the FD mode have Signal-to-Noise Ratio (SNR) improvement compared with the IRS-assisted bidirectional MTC system in Half Duplex (HD) mode, as the number of reflecting elements in IRS is doubled in the FD mode. The outage and BER performances are degraded by a discrete phase shifter. Hence, performance degradation of the proposed IRS-assisted bidirectional FD-MTC is examined for 1-bit shifter (0, \(\pi\)), 2-bit shifter (0, \(\pi\)/2, \(\pi\), \(3\pi\)/2), and for 3-bit shifter (0, \(\pi\)/4, \(\pi\)/2, \(3\pi\)/4, \(\pi\)/5\(\pi\)/4, \(3\pi\)/2, \(7\pi\)/4). The performance degradation when a discrete phase shifter is employed in IRS is compared with the ideal continuous phase shifter in IRS. Further, achievable rate analysis is carried out for finding the best location of the IRS in a bidirectional FD-MTC system. Intelligent Reflecting Surface; bidirectional; bit error rate; outage probability; discrete phase shifter; machine type communication +
Footnote †: journal: Applied
IRS is enabled by a metamaterial surface that can be electronically reconfigured to alter the propagation of radio waves. This reconfigurability of the radio environment in IRS overcomes many of the restrictions of conventional wireless communication, such as interference, shadowing, and multi-path propagation. IRS can be used in both indoor and outdoor environments of wireless communication systems, such as 5G and beyond 5G (B5G), to achieve better signal quality and coverage, and it can also be integrated with other wireless technologies, such as beamforming to achieve a more efficient wireless communication system. Machine Type Communication (MTC) is specially designed with low power consumption, low data rate, and high reliability for Machine-to-Machine (M2M) and Internet of Things (IoT) applications [4]. MTC devices are typically embedded in everyday objects and communicate with other devices to perform specific tasks. Examples include smart meters, industrial automation systems, and connected vehicles. It involves the exchange of information between two or more machines, without the need for human intervention. On the other hand, MTC devices are designed to operate in harsh environments and must be able to function reliably in the presence of interference and noise. MTC connects machines wirelessly to form an interconnection of machine-type devices known as IoT. Even in large path loss, it can establish communication with unidirectional relaying or bidirectional relaying, which operates in Decode and Forward (DF) or Amplify and Forward (AF) mode [5]. In the proposed system, IRS is used in place of DF relaying to improve the channel gain between two machines. More meta surface elements are required in IRS to improve channel gain [6]. MTC operates in bidirectional FD mode for simultaneous transmission and reception of data over the same frequency band is considered in the proposed system model. Combining the benefits of IRS with MTC will improve the spectral efficiency and reliability of the bidirectional MTC communication system.