Browsing by Subject "NOMA"
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Item Open Access Fair user scheduling for downlink power domain NOMA(Bilkent University, 2019-06) Topçuoğlu, ZaferNon-Orthogonal Multiple Access (NOMA) has been proposed as a new radio access technique in which multiple users (the case of user pairs or triples are covered in this thesis) are allowed to use the wireless channel simultaneously in a way to improve the overall system capacity. A bucket-based Temporal Fair Scheduling algorithm (TFS) has been proposed in the literature for Orthogonal Multiple Access (OMA) systems. In this thesis, we extend this existing work to downlink power domain NOMA by which user pairs or triples are to be scheduled with the goal of maximizing system capacity under temporal fairness constraints. The effectiveness of the proposed fair user scheduling algorithm for NOMA is validated with simulations in which the effects of transmit power and coverage radius of the base station, as well as the number of users are thoroughly studied.Item Open Access An overview of physical layer security with finite-alphabet signaling(Institute of Electrical and Electronics Engineers Inc., 2019) Aghdam, Sina Rezaei; Nooraiepour, A.; Duman, Tolga M.Providing secure communications over the physical layer with the objective of achieving secrecy without requiring a secret key has been receiving growing attention within the past decade. The vast majority of the existing studies in the area of physical layer security focus exclusively on the scenarios where the channel inputs are Gaussian distributed. However, in practice, the signals employed for transmission are drawn from discrete signal constellations such as phase shift keying and quadrature amplitude modulation. Hence, understanding the impact of the finite-alphabet input constraints and designing secure transmission schemes under this assumption is a mandatory step toward a practical implementation of physical layer security. With this motivation, this paper reviews recent developments on physical layer security with finite-alphabet inputs. We explore transmit signal design algorithms for single-antenna as well as multi-antenna wiretap channels under different assumptions on the channel state information at the transmitter. Moreover, we present a review of the recent results on secure transmission with discrete signaling for various scenarios including multi-carrier transmission systems, broadcast channels with confidential messages, cognitive multiple access and relay networks. Throughout the article, we stress the important behavioral differences of discrete versus Gaussian inputs in the context of the physical layer security. We also present an overview of practical code construction over Gaussian and fading wiretap channels, and discuss some open problems and directions for future research.Item Open Access Power allocation and temporal fair user group scheduling for downlink NOMA(Springer, 2021-08) Erturk, E.; Yildiz, O.; Shahsavari, S.; Akar, NailNon-Orthogonal Multiple Access (NOMA) has been proposed as a new radio access technique for cellular networks as an alternative to OMA (Orthogonal Multiple Access) in which the users of a group (pairs or triples of users in a group are considered in this paper) are allowed to use the wireless channel simultaneously. In this paper, for downlink single-input single-output SISO-NOMA, a heuristic power allocation algorithm within a group is first proposed which attempts to ensure that the users of a group benefit from simultaneous transmission equally in terms of achievable throughput. Moreover, a user group scheduling algorithm is proposed for downlink NOMA systems by which a user group is to be dynamically selected for transmission while satisfying long term temporal fairness among the individual contending users. The effectiveness of the proposed power allocation method along with the temporal fair scheduling algorithm for downlink NOMA is validated with simulations and the performance impact of the transmit power and the coverage radius of the base station as well as the number of users are thoroughly studied.