Resource Allocation for Active IRS-Assisted Multiuser Communication Systems

Abstract

Intelligent reflecting surfaces (IRSs) are envisioned as a low-cost solution to achieve high spectral and energy efficiency in future communication systems due to their ability to customize wireless propagation environments. Although resource allocation design for IRS-assisted multiuser wireless communication systems has been exhaustively investigated in the literature, the optimal design and performance of such systems are still not well understood. To fill this gap, in this paper, we study optimal resource allocation for IRS-assisted multiuser multiple-input single-output (MISO) systems. In particular, we jointly optimize the beamforming at the base station (BS) and the discrete IRS phase shifts to minimize the total transmit power. For attaining the globally optimal solution of the formulated non-convex combinatorial optimization problem, we develop a resource allocation algorithm with guaranteed convergence based on Schur's complement and the generalized Bender's decomposition. Our numerical results reveal that the proposed algorithm can significantly reduce the BS transmit power compared to the state-of-the-art suboptimal alternating optimization-based approach, especially for moderateto-large numbers of IRS elements. I. INTRODUCTIONRecently, intelligent reflecting surfaces (IRSs) have attracted considerable research interest from both academia and industry due to their unique and attractive characteristics. In particular, given their adaptive reflecting elements, IRSs can be flexibly programmed to control the reflections of the propagating wireless signals. Moreover, commonly deployed as thin rectangular planes, IRSs can be attached to building facades, indoor ceilings, and vehicles, hence introducing extra design degrees of freedom (DoFs) for improving the performance of wireless communication systems, e.g., expanding the service coverage, enhancing the security of communications, etc. As a result, IRSs have been envisioned as a promising enabler for establishing future ubiquitous high-data-rate communication networks. Motivated by the aforementioned appealing properties, numerous works have studied the integration of IRSs with other advanced communication techniques, e.g., multiple-input multiple-output (MIMO) transmission, simultaneous wireless information and power transfer (SWIPT) [1], and physical layer security [2].To unleash the potential of IRS-aided wireless communications, several works have focused on the joint design of the transmit beamforming at the base station (BS) and the IRS phase shifters. For instance, in [3], an iterative algorithm based on the branch-and-bound (BnB) method was developed to obtain the globally optimal solution for a single-user IRSassisted multiple-input single-output (MISO) system. Also, the authors in [2] adopted the majorization-minimization (MM) and block coordinate descent (BCD) techniques for the design of a

Active Intelligent Reflecting Surface Assisted Secure Air-to-Ground Communication with UAV Jittering

“…Compared with passive IRS, the active IRS directly reflects the incident signal with the power amplification in the electromagnetic (EM) level, and it still takes the advantage of IRS that no complex and powerhungry radio frequency (RF) chain components are needed. Specifically, in [20]- [22], an active IRS assisted single-input multiple-output uplink system and downlink multiple-input single-output multi-user system were studied respectively, and numerical algorithms were developed to optimize the phase shift and amplification factor of active IRS. Based on the numerical examples, this active IRS design can realize a significantly higher transmission rate compared with those via passive IRS, thus overcoming the fundamental limit of "double fading" effect.…”

Pervasive Machine Learning for Smart Radio Environments Enabled by Reconfigurable Intelligent Surfaces

“…The authors in [89] considered the application of RISs to assist the uplink transmission from multiple UEs to a multi-antenna BS, and devised an optimization framework for jointly designing the transmit covariance matrices and the RIS phase profile with partial Channel State Information (CSI). In [90], [91], active RISs were considered, which can adapt the phase and amplify the magnitude of the reflected incident signal simultaneously with the support of an additional power source. A joint optimization of the RIS phase profile and the BS beamforming vector was presented in [90] with the objective to minimize the BS transmit power.…”

“…In [90], [91], active RISs were considered, which can adapt the phase and amplify the magnitude of the reflected incident signal simultaneously with the support of an additional power source. A joint optimization of the RIS phase profile and the BS beamforming vector was presented in [90] with the objective to minimize the BS transmit power. In [92], the problem of energy efficiency optimization for a wireless communication system with distributed RISs was investigated.…”

Multiuser MISO PS-SWIPT Systems: Active or Passive RIS?

“…The benefits of active RISs have already been investigated [4], [5]. Reference [4] compares the active and passive RIS in a single-input multi-output (MISO) network and formulates the signal-to-noise ratios (SNRs).…”

“…The spectral efficiency of the uplink is investigated in [7], where asymptotic and theoretical performance bounds are derived. [5] develops resource allocations for a multiuser network by minimizing the BS transmit power. Indoor and outdoor applications can deploy active S. Zargari, A. Hakimi, and C. Tellambura with the Department of Electrical and Computer Engineering, University of Alberta, Edmonton, AB, T6G 1H9, Canada (e-mail: zargari,hakimina,ct4@ualberta.ca).…”