Power Optimization of Dual-Polarized IRS-assisted Wireless Networks under Spectral Efficiency Constraints

This research investigates a multi-user wireless communication system that is assisted by a dual-polarized intelligent reflecting surface (DP-IRS). The DP-IRS system includes DP antennas equipped with separate phase shifters for each polarization at both the transmitter and receivers. Our objective is to minimize the total transmit power at the access point (AP) by optimizing the precoder at the AP, operations of the reflecting elements at the DP-IRS, and vertical/horizontal passive phase shifters at the transmit/receive DP antennas while taking into consideration the individual spectral efficiency (SE) constraints of the users. In tackling this problem, we introduce a four-step alternating optimization (AO) algorithm that utilizes the semi-definite relaxation approach. Furthermore, we propose a computationally low-complexity algorithm based on closed-form solutions for a single-user case. The numerical results demonstrate that the proposed algorithms achieve a reduction in transmit power by 74.6% for multi-user scenarios and 99.0% for single-user scenarios when compared to random operations. We also assess the minimized transmit power of the DP-IRS in comparison to that of the Simple IRS (S-IRS). For instance, when targeting a SE of 5.6 bps/Hz for each user, DP-IRS requires 70% lower transmit power than S-IRS for 50 reflecting elements and eight users.