Browsing by Author "Sadi, Y."

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Citation - Scopus: 1
The Effect of Codebook Design on the Conventional SCMA System Performance
(Institute of Electrical and Electronics Engineers Inc., 2020) Şadi, Yalçın; Bardakci, E.; Sadi, Y.; Erkucuk, S.
In 4G systems, Orthogonal Frequency-Division Multiple Access (OFDMA) has been used conventionally for multiple access purposes. This technique has low spectral efficiency since it allocates the resources orthogonally to each user. As an alternative to this technique, Non-orthogonal Multiple Access (NOMA) has been proposed for new generation systems as it allows different users to use the same resources and therefore, increases spectral efficiency. Sparse Code Multiple Access (SCMA) is a code-based NOMA technique and its performance depends on codebook design. In this study, a conventionally used codebook design in the literature has been considered and the system performance has been improved by increasing the distance between the signal constellation points. Considering two different design approaches, the conventional codebook has been modified and about 1dB gain has been achieved in the high signal-to-noiseratio (SNR) region. © 2020 IEEE.
Citation - WoS: 0
Citation - Scopus: 0
Resource Allocation for Discrete Rate Multi-Cell Energy Constrained Communication Networks
(Springer, 2025) Şadi, Yalçın; Iqbal, M.S.; Salik, E.D.; Sadi, Y.; Coleri, S.
Radio frequency energy harvesting is a promising technique to extend the lifetime of wireless powered communication networks (WPCNs) due to its controllability. In this paper, we consider a novel discrete rate based multi-cell WPCN, where multiple hybrid access points (HAPs) transmit energy to the users and users harvest this energy for the information transmission by using a transmission rate selected from a finite set of discrete rate levels. We formulate an optimization problem to minimize the schedule length through optimal rate allocation and scheduling of the users while considering the traffic demand, energy causality and interference constraints. The problem is mixed integer non-linear programming problem. Initially, we investigate the problem for non-simultaneous and simultaneous transmission considering both predetermined and variable transmission rates. We propose optimal and heuristic algorithms for all these categories by using optimality analysis, Perron-Frobenius conditions and iterative improvement of the total schedule length. Then, for the general problem, we propose heuristic algorithm based on the maximization of the number of concurrently transmitting users within each time slot by considering the maximum allowed interference level of the users. Via extensive simulations, we demonstrate significant improvement in schedule length through rate selection and proper scheduling of concurrently transmitting users. © The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature 2024.