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Joint IRS Location and Size Optimization in Multi-IRS Aided Two-Way Full-Duplex Communication Systems

IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS 2023年第10期22卷 6518-6533页

作者： Efrem, Christos N. Krikidis, Ioannis Univ Cyprus Dept Elect & Comp Engn CY-1678 Nicosia Cyprus

Intelligent reflecting surfaces (IRSs) have emerged as a promising wireless technology for the dynamic configuration and control of electromagnetic waves, thus creating a smart (programmable) radio environment. In this context, we study a multi-IRS assisted two-way communication system consisting of two users that employ full-duplex (FD) technology. More specifically, we deal with the joint IRS location and size (i.e., the number of reflecting elements) optimization in order to minimize an upper bound of system outage probability under various constraints: minimum and maximum number of reflecting elements per IRS, maximum number of installed IRSs, maximum total number of reflecting elements (implicit bound on the signaling overhead) as well as maximum total IRS installation cost. First, the problem is formulated as a discrete optimization problem and, then, a theoretical proof of its NP-hardness is given. Moreover, we provide a lower bound on the optimum value by solving a linear-programming relaxation (LPR) problem. Subsequently, we design two polynomial-time algorithms, a deterministic greedy algorithm and a randomized approximation algorithm, based on the LPR solution. The former is a heuristic method that always computes a feasible solution for which (a posteriori) performance guarantee can be provided. The latter achieves an approximate solution, using randomized rounding, with provable (a priori) probabilistic guarantees on the performance. Furthermore, extensive numerical simulations demonstrate the superiority of the proposed algorithms compared to the baseline schemes. Finally, useful conclusions regarding the comparison between FD and conventional half-duplex (HD) systems are also drawn.

关键词： Intelligent reflecting surface IRS deployment full-duplex communication discrete optimization NP-hardness linear-programming relaxation randomized rounding approximation algorithm

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Globally Optimal Selection of Ground Stations in Satellite Systems With Site Diversity

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IEEE WIRELESS COMMUNICATIONS LETTERS 2020年第7期9卷 1101-1104页

作者： Efrem, Christos N. Panagopoulos, Athanasios D. Natl Tech Univ Athens Sch Elect & Comp Engn Athens 15780 Greece

The availability of satellite communication systems is extremely limited by atmospheric impairments, such as rain (for radio frequencies) and cloud coverage (for optical frequencies). A solution to this problem is the site diversity technique, where a network of geographically distributed ground stations (GSs) can ensure, with high probability, that at least one GS is available for connection to the satellite at each time period. However, the installation of redundant GSs induces unnecessary additional costs for the network operator. In this context, we study an optimization problem that minimizes the number of required GSs, subject to availability constraints. First, the problem is transformed into a binary-integer-linear-programming (BILP) problem, which is proven to be NP-hard. Subsequently, we design a branch-and-bound (B&B) algorithm, with global-optimization guarantee, based on the linear-programming (LP) relaxation and a greedy method as well. Finally, numerical results show that the proposed algorithm significantly outperforms state-of-the-art methods, and has low complexity in the average case.

关键词： Complexity theory Satellite broadcasting Optical fiber networks Optimized production technology Probability Satellites Satellite communications site diversity ground stations selection cardinality minimization combinatorial optimization binary integer linear programming NP-hardness linear-programming relaxation branch-and-bound method

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IRS Deployment Optimization in Multi-IRS Assisted Two-Way Full-Duplex Communication Systems

IRS Deployment Optimization in Multi-IRS Assisted Two-Way Fu...

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IEEE International Conference on Communications (ICC)

作者： Efrem, Christos N. Krikidis, Ioannis Univ Cyprus Dept Elect & Comp Engn Nicosia Cyprus

ISBN: (数字)9781538683477

ISBN: (纸本)9781538683477

Intelligent reflecting surfaces (IRSs) have emerged as a promising wireless technology for the dynamic configuration of electromagnetic waves. In this context, we study a multi-IRS assisted two-way communication system consisting of two users that employ full-duplex (FD) technology. More specifically, we deal with the joint IRS location and size (i.e., the number of reflecting elements) optimization in order to minimize an upper bound of system outage probability under various constraints. First, the problem is formulated as a discrete optimization problem and, then, a lower bound on the optimum value is computed by solving a linear-programming relaxation (LPR) problem. Subsequently, we design a polynomial-time greedy algorithm based on the LPR solution. The proposed algorithm always computes a feasible solution for which (a posteriori) performance guarantee can be provided. Finally, numerical simulations demonstrate the superiority of the greedy algorithm compared to a baseline scheme and provide useful comparisons between FD and conventional half-duplex (HD) systems.

关键词： Intelligent reflecting surface (IRS) IRS deployment full-duplex (FD) communication discrete optimization linear-programming relaxation greedy algorithm

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