Rate Optimization for Reconfigurable Intelligent Surfaces RIS Presenter

Rate Optimization for Reconfigurable Intelligent Surfaces (RIS) Presenter: Pooja Nuti (pnuti@utexas. edu) In collaboration with WNCG alumnus Dr. Javier Rodriguez-Fernandez and Prof. Brian L. Evans Nov. 17 th, 2020 The University of Texas at Austin Wireless Networking & Communications Group (WNCG) Embedded Signal Processing Laboratory (ESPL) 1

Problem Formulation Sub-6 GHz single-user Multiple-Input Single-Output (MISO) rate optimization Nonconvex unit-modular constraint P. Nuti and B. L. Evans, ``Spectral Efficiency vs Complexity in Downlink Algorithms for Reconfigurable Intelligent Surfaces'', Proc. IEEE Int. Conf. on Communications, Jun. 14 -18, 2021, Montreal, Quebec, Canada, submitted. https: //arxiv. org/abs/2011. 04859 CONTRIBUTION: RATE OPTIMIZATION FOR RECONFIGURABLE INTELLIGENT SURFACES 2

Proposed Approach • Prior work suboptimal in handling unit modulus constraints • Semidefinite relaxation to deal with unit modulus constraints • Fixed point iteration and manifold optimization • Suboptimal solutions without guarantee of optimality • Propose four algorithms to optimize equivalent channel power or spectral efficiency [14] X. Yu, D. Xu, and R. Schober, “MISO wireless communication systems via intelligent reflecting surfaces : (invited paper), ” in 2019 IEEE/CIC Intl. Conf. on Commun. China, 2019, pp. 735– 740. [15] Q. Wu and R. Zhang, “Intelligent reflecting surface enhanced wireless network: Joint active and passive beamforming design, ” in 2018 IEEE Global Commun. Conf. , 2018, pp. 1– 6. CONTRIBUTION: RATE OPTIMIZATION FOR RECONFIGURABLE INTELLIGENT SURFACES 3

Simulation Results: Spectral Efficiency and Run-Time Complexity CONTRIBUTION: RATE OPTIMIZATION FOR RECONFIGURABLE INTELLIGENT SURFACES 4

Next Steps • Improve performance of Project Gradient Ascent algorithm • Multiple-input multiple-output (MIMO) wideband scenario • Consider more complete scenarios and implications • Consider lower degree of channel state information • Channel estimation for RIS • Consider practical impairments in RIS-assisted network CONTRIBUTION: RATE OPTIMIZATION FOR RECONFIGURABLE INTELLIGENT SURFACES 5