Browsing by Author "Erkucuk, Serhat"

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A Comparative Analysis of Diversity Combining Techniques for Repetitive Transmissions in Time Spreading Scma Systems
(John Wiley & Sons Ltd, 2024) Ulgen, Oguz; Tufekci, Tolga Kagan; Sadi, Yalcin; 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.
Evaluation of Noise Distributions for Additive and Multiplicative Smart Meter Data Obfuscation
(IEEE-Inst Electrical Electronics Engineers Inc, 2022) Khwaja, Ahmed S.; Erkucuk, Serhat; Anpalagan, Alagan; Venkatesh, Bala
In this paper, we compare and analyze light-weight approaches for instantaneous smart meter (SM) data obfuscation from a group of consumers. In the literature, the common approach is to use additive Gaussian noise based SM data obfuscation. In order to investigate the effects of different approaches, we consider Gaussian, Rayleigh, generalized Gaussian and chi-square distributions to achieve either additive or multiplicative data obfuscation. For each type of obfuscation approach, we calculate the required parameters to achieve obfuscation such that 50% of the obfuscated data fall outside an interval equalling twice the mean of the instantaneous SM measurements. We also calculate the minimum number of SMs required to estimate the mean of the actual SM measurements, such that the estimate varies within only 0.5% of the actual mean with a 99.5% probability. Simulation results are used to verify the calculations, and it is shown that multiplicative Rayleigh and generalized Gaussian noise require the least number of SMs, which is 90% less than the traditional approach of additive Gaussian noise-based SM data obfuscation.
Noma-Based Radio Resource Allocation for Machine Type Communications in 5g and Beyond Cellular Networks
(IEEE, 2021) Aldemir, Sumeyra; Sadi, Yalcin; 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.
Orbital Angular Momentum Based Communication Systems Under Atmospheric Turbulence
(IEEE, 2020) Sheikh, Abdul Ahad Ashfaq; Basaran, Mehmet; Erkucuk, Serhat
Orbital Angular Momentum (OAM) may be a candidate for future communication systems due to its advantages in terms of high data rates and effective frequency utilization. OAM can provide a solution where a beam is transformed into multiple beams within itself and becomes independent streams of data (pertaining to the principle of orthogonality) to be transferred when properly utilized. However, the free space contains atmospheric turbulence which interferes with the beam propagation of OAM and as a result the photons in the light beam are affected as well as the independence of each OAM mode. Therefore, the data stream suffers crosstalk. In this study, weak and strong atmospheric turbulences and how they affect a variety of OAM modes as they propagate through free space are investigated, and important OAM implementation issues are discussed.
Performance of Scma Systems in Fast-Fading Channels
(Ieee, 2022) Tufekci, Tolga; Ulgen, Oguz; Erkucuk, Serhat; Baykas, Tuncer
In order to satisfy the need for high data rate and high number of users, new generation communication techniques are developed. One of the techniques that may be used in future generation communication networks is Sparse Code Multiple Access (SCMA). With this new technique, the aim is to allocate users frequency resources in a non-orthogonal way by using code books. For this new technique, which is has a potential to be used in 5G and beyond communication networks, most researches have focused on flat fading channels and related results have been provided. In this work, different from earlier studies, fast fading channels have been considered for channels varying at different rates, and bit-error performance results have been provided with computer simulations.
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.