Browsing by Author "Sadi, Yalcin"

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Citation - WoS: 0
Citation - Scopus: 0
A Comparative Analysis of Diversity Combining Techniques for Repetitive Transmissions in Time Spreading Scma Systems
(John Wiley & Sons Ltd, 2024) Ulgen, Oguz; Şadi, Yalçın; Tufekci, Tolga Kagan; Erküçük, Serhat; Sadi, Yalcin; Baykaş, Tunçer; Erkucuk, Serhat; Anpalagan, Alagan; Baykas, Tuncer
Sparse Code Multiple Access (SCMA) is a recently introduced wireless communication network technology. There are various techniques in SCMA systems to increase the system's efficiency, and one of these techniques is time spreading. By adding repetitive transmission and time spreading into SCMA, it is shown in previous works that the Bit-Error-Rate (BER) results are improved convincingly. However, in the previous works, other diversity combining techniques have not been considered. This paper introduces a new approach to further improve the performance of repetitive transmission in SCMA systems with time spreading by adding imperialist competitive algorithm in diversity combining. Alongside, four different combining techniques; equal gain combining, maximal ratio combining, selection combining, and genetic algorithm are considered to bring comparative analysis to show the significance of the new technique. Results show that the proposed method offers up to 2.3 dB gain in terms of BER, under certain conditions.
Citation - WoS: 9
Citation - Scopus: 10
Minimum Length Scheduling for Discrete-Rate Full-Duplex Wireless Powered Communication Networks
(IEEE-Inst Electrical Electronics Engineers Inc, 2022) Şadi, Yalçın; Sadi, Yalcin; Coleri, Sinem
Wireless powered communication networks (WPCNs) will act as a major enabler of massive machine type communications (MTCs), which is a major service domain for 5G and beyond systems. The MTC networks will be deployed by using low-power transceivers with finite discrete configurations. This paper considers minimum length scheduling problem for full-duplex WPCNs, where users transmit information to a hybrid access point at a rate chosen from a finite set of discrete-rate levels. The optimization problem considers energy causality, data and maximum transmit power constraints, and is proven to be NP-hard. As a solution strategy, we define the minimum length scheduling (MLS) slot, which is slot of minimum transmission completion time while starting transmission at anytime after the decision time. We solve the problem optimally for a given transmission order based on the optimality analysis of MLS slot. For the general problem, we categorize the problem based on whether the MLS slots of users overlap over time. We propose optimal algorithm for non-overlapping scenario by allocating the MLS slots, and a polynomial-time heuristic algorithm for overlapping scenario by allocating the transmission slot to the user with earliest MLS slot. Through simulations, we demonstrate significant gains of scheduling and discrete rate allocation.
Citation - WoS: 4
Citation - Scopus: 4
Minimum Length Scheduling for Multi-Cell Full Duplex Wireless Powered Communication Networks
(Mdpi, 2021) Iqbal, Muhammad Shahid; Şadi, Yalçın; Sadi, Yalcin; Coleri, Sinem
Wireless powered communication networks (WPCNs) will be a major enabler of massive machine type communications (MTCs), which is a major service domain for 5G and beyond systems. These MTC networks will be deployed by using low-power transceivers and a very limited set of transmission configurations. We investigate a novel minimum length scheduling problem for multi-cell full-duplex wireless powered communication networks to determine the optimal power control and scheduling for constant rate transmission model. The formulated optimization problem is combinatorial in nature and, thus, difficult to solve for the global optimum. As a solution strategy, first, we decompose the problem into the power control problem (PCP) and scheduling problem. For the PCP, we propose the optimal polynomial time algorithm based on the evaluation of Perron-Frobenius conditions. For the scheduling problem, we propose a heuristic algorithm that aims to maximize the number of concurrently transmitting users by maximizing the allowable interference on each user without violating the signal-to-noise-ratio (SNR) requirements. Through extensive simulations, we demonstrate a 50% reduction in the schedule length by using the proposed algorithm in comparison to unscheduled concurrent transmissions.
Citation - WoS: 1
Citation - Scopus: 3
Noma-Based Radio Resource Allocation for Machine Type Communications in 5g and Beyond Cellular Networks
(IEEE, 2021) Aldemir, Sumeyra; Şadi, Yalçın; Sadi, Yalcin; Erküçük, Serhat; Erkucuk, Serhat; Okumus, F. Batuhan
In this paper, the minimum bandwidth resource allocation problem for non-orthogonal multiple access (NOMA) based machine to machine (M2M) communications in 5G and beyond cellular networks is investigated. In order to solve the problem fast and efficiently, a persistent resource allocation based polynomial-time algorithm considering NOMA and the periodicity of the machine type communication traffic is proposed. The algorithm consists of two phases. In first phase, M2M clusters are divided into NOMA sub-clusters using a technique that minimizes the number of NOMA sub-clusters for a set of devices. In second phase, NOMA sub-clusters are allocated to resource blocks (RB) considering their quality of service (QoS) requirements while achieving minimum bandwidth reservation. Through simulations, the performance of the proposed algorithm is presented in comparison to the previously proposed access grant time interval (AGTI) based radio resource allocation algorithms. It is illustrated that the proposed algorithm improves the spectrum-efficiency significantly.
Citation - WoS: 0
Citation - Scopus: 0
Resource Allocation for Multi-Cell Full-Duplex Wireless Powered Communication Networks
(Springer, 2024) Şadi, Yalçın; Sadi, Yalcin; Kazmi, Syed Adil Abbas; Coleri, Sinem
Wireless powered communication networks (WPCNs) are crucial in achieving perpetual lifetime for the machine-type communication (MTC) and Internet of things (IoT) in fifth-generation (5G) communication and beyond networks. Practical WPCNs cover a broad region and have a significant number of sensors, requiring multi-cell deployment. We investigate the minimum length scheduling problem for a multi-cell full-duplex WPCNs to find the optimal power and schedule by considering the simultaneous transmission, maximum transmit power and energy causality constraints for the users. The optimization problem to minimize the schedule length is combinatorial, thus, difficult to find the global optimum solution. To overcome this, we divide the problem into two subproblems, i.e., power control problem (PCP) and the scheduling problem. Then, we present the optimal polynomial time algorithm for the PCP based on the use of the bisection method and evaluation of the Perron-Frobenius criteria. Then, by using the PCP solution, we calculate the optimal transmission time for the users that are scheduled by the scheduling algorithm. For the scheduling problem, we define a penalty function that represents the gain of simultaneous transmission over the individual transmission of the users and we show that the minimization of schedule length is similar to the minimization of sum of penalties. Following the optimum analysis of the proposed penalty metric, we present a heuristic algorithm that tries to minimize the sum penalties of the simultaneously transmitting users over the schedule. Through extensive simulations, we show significant gains of scheduling for concurrent transmissions over individual transmissions.
Citation - WoS: 0
Citation - Scopus: 0
Sparse Code Multiple Access With Time Spreading and Repetitive Transmissions
(Wiley, 2025) Ulgen, Oguz; Tufekci, Tolga Kagan; Sadi, Yalcin; Erkucuk, Serhat; Anpalagan, Alagan; Baykas, Tuncer
For the next-generation communication systems, to improve spectral efficiency and increase the data rate, new multiple access techniques have been investigated. Orthogonal multiple access techniques are widely used in traditional communication systems while nonorthogonal multiple access (NOMA), proposed in 5G, has been a promising technology for satisfying the demand for future wireless communication networks. Sparse code multiple access (SCMA) is a code-domain NOMA method that provides diversity gain with signal constellation coding. However, to increase the performance of SCMA, there are only limited works provided in the literature in terms of codebook design and receiver design. In this paper, a new multiple-access model is proposed by applying various diversity techniques for downlink SCMA. The performance of the proposed model is evaluated with both computer simulations and theoretical analysis. Results show that the proposed model provides a 1.6 dB gain in terms of the bit error rate (BER) under the Rayleigh fading channel.