Joint Optimization of IRS Location and Passive Beamforming for Enhanced Received Power

Abstract

Intelligent reflecting surface (IRS) has recently emerged as a promising technology for beyond fifth-generation (B5G) networks conceived from metamaterials that smartly tunes the signal reflections via a large number of low-cost passive reflecting elements. However, the IRS-assisted communication model and the optimization of available resources needs to be improved further for more efficient communications. This paper investigates the enhancement of received power in an IRS-assisted wireless communication by jointly optimizing the phase shifts at the IRS elements and its location. Employing the conventional Friss transmission model, the relationship between the transmitted power and reflected power is established. The expression of the received power incorporates the free space loss, reflection loss factor, physical dimension of the IRS panel, and radiation pattern of the transmit signal. Also, the expression of reflection coefficient of IRS panel is obtained by exploiting the existing data of radar communications. Initially exploring a single IRS element within a two-ray reflection model, we extend it to a more complex multi-ray reflection model with multiple IRS elements in 3D Cartesian space. The expression of the received power in both the cases is derived in a more tractable form, and then, it is maximized by jointly optimizing the underlying variables, i.e., the IRS location and the phase shifts. Further, the optimization of resources are investigated in active IRS, multiple access, and joint active and passive beamforming. Numerical insights and performance comparison reveal that joint optimization leads to a substantial 37% enhancement in received power compared to the closest competitive benchmark.