Elektrik - Elektronik Mühendisliği Bölümü Koleksiyonu

Permanent URI for this collectionhttps://gcris.khas.edu.tr/handle/20.500.12469/47

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Citation Count: 0
Fuzzy logic for decision extraction from product reviews
(Institute of Electrical and Electronics Engineers Inc., 2018) Altabbaa, Mhd Tahssin; Ayabakan, Tarik; Öğrenci, Arif Selçuk
Most of manufacturers and merchants sell their products via internet websites where customers buy them and write their reviews regarding the purchased product. These reviews carry a lot of information. Prospective customers are heavily interested in the experience of the predecessor customers where enormous number of reviews are offered by the website per product. In this study given a dataset of reviews we give a solution to estimate a total score of sentiment for the product reviewed. For this purpose fuzzy logic is used to process the subjective comments and to obtain a reliable average estimation for the decision from those individual reviews. The method is executed over different models to search the effects of the frequency of features on the outcome. © 2017 IEEE.
Citation Count: 2
Power Control and Resource Allocation in TDD-OFDM Based Femtocell Networks with Interference
(IEEE, 2017) Arsan, Taner; Arsan, Taner; Panayırcı, Erdal
Femtocell technology is a promising solution for different dilemmas in cellular networks. In femtocell power control the interference experienced by the network is divided into two main tiers according to the type of network whose signal is interfering with another network. In utilizing the functionality of a two-tier network where femtocell technology is deployed a major challenge is in sharing the frequency resource of a macrocell. This paper proposes an enhanced dynamic algorithm bounded by two constraints to optimize the transmission powers of femtocell users in TDD-OFDM based femtocell networks taking into consideration rate enhancement of femtocell mobile stations. We compare our algorithm with the macrocell guard system which allows femtocells to occupy only the subchannels unoccupied by the macrocell.
Citation Count: 43
Sparse Channel Estimation for OFDM-Based Underwater Acoustic Systems in Rician Fading With a New OMP-MAP Algorithm
(IEEE, 2019) Panayırcı, Erdal; Altabbaa, Mhd Tahssin; Uysal, Murat; Poor, H. Vincent
In this paper a new channel estimation algorithm is proposed that exploits channel sparsity in the time domain for an orthogonal frequency division multiplexing (OFDM)-based underwater acoustical (UWA) communications systems in the presence of Rician fading. A path-based channel model is used in which the channel is described by a limited number of paths each characterized by a delay Doppler scale and attenuation factor. The resulting algorithm initially estimates the overall sparse channel tap delays and Doppler shifts using a compressed sensing approach in the form of the orthogonal matching pursuit (OMP) algorithm. Then a computationally efficient and novel channel estimation algorithm is developed by combining the OMP and maximum a posteriori probability (MAP) techniques for estimating the sparse complex channel path gains whose prior densities have complex Gaussian distributions with unknown mean and variance vectors where a computationally efficient maximum likelihood algorithm is proposed for their estimation. Monte Carlo simulation results show that the mean square error and symbol error rate performances of the OMP-MAP algorithm uniformly outperforms the conventional OMP-based channel estimation algorithm in case of uncoded OFDM-based UWA communications systems.
Citation Count: 2
Sparse Channel Estimation for Space-Time Block Coded OFDM-Based Underwater Acoustic Channels
(Institute of Electrical and Electronics Engineers Inc., 2018) Altabbaa, Mhd Tahssin; Öğrenci, Arif Selçuk; Panayırcı, Erdal; Poor, H. Vincent
Communication over acoustic signals underwater results in multi-scale multi-lag channels due to multipath propagation. Hence a robust channel estimation technique has to be present at the receiver. In this paper assuming underwater channels undergoing Rayleigh fading a path-based channel model that characterizes each path of the time-varying sparse channel by a delay a Doppler scale and an attenuation factor is considered. Alamouti's space-time block transmit diversity scheme is used in the form of two transmit antennas and one receiver and the proposed OFDM-based non-data-aided algorithm iteratively estimates the complex channel parameters of each subcarrier using the expectation maximization (EM) method which in turn converges to a true maximum a posteriori probability (MAP) estimate of the unknown channel where the Karhunen-Lo'eve expansion is performed for complexity reduction. Finally the novel channel estimation algorithm combines the aforementioned MAP-EM technique with ESPRIT for delay estimation by exploiting the sparseness of the underwater acoustic channels. The performance of the proposed algorithm is then presented in terms of average mean square error and symbol error rate for QPSK signaling with extreme Doppler spreads and different pilot spacings. It is shown that excellent mean-square error and symbol error rate performance is achieved even in the presence of extreme Doppler shifts. © 2018 IEEE.
Citation Count: 2
Subchannel Allocation and Power Control for Uplink Femtocell Radio Networks with Imperfect Channel State Information
(Springer, 2019) Arsan, Taner; Arsan, Taner; Panayırcı, Erdal
Femtocell technology is emerging as a key solution for mobile operators for its advantage in coverage and capacity enhancement along with its cost effectiveness. However, densely and randomly deployed femtocells while sharing the frequency spectrum of the macrocell arises a severe interference environment. In femtocells deployment, interference coming from a femtocell user affect other femtocell users and the macrocell users, where maintaining the communication of the users in both tiers is a mandatory. In this paper, a novel power control algorithm is proposed for optimizing the uplink transmission powers of femtocell users in a TDD-OFDM communication model in the presence of a channel estimation error and intra-tier interference. We consider signal to interference and noise ratio as the objective function where the proposed constraints deal with: (1) the aggregated interference coming from femtocell tier and received at the active subchannels by the macrocell tier, and (2) the maximum uplink power a femtocell user equipment is allowed to occupy per admissible subchannel. Based on Lagrangian multipliers, the proposed power control approach grants the priority in subchannel usage for macrocell user, then it allows or prohibits frequency reuse of a subchannel with the femtocell tier. A comparison is then made with a pure isolation method that does not allow femtocell user equipments to occupy the active subchannels at the macrocell tier. The numerical results of the proposed approach show a high total rate of femtocell user equipments and the average uplink power is below the maximum allowable transmission power.

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