WoS İndeksli Yayınlar Koleksiyonu / WoS Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7150
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Article Citation - WoS: 2Citation - Scopus: 2Deep Learning Based Adaptive Bit Allocation for Heterogeneous Interference Channels(Elsevier, 2021) Aycan, Esra; Özbek, Berna; Le Ruyet, DidierThis paper proposes an adaptive bit allocation scheme by using a fully connected (FC) deep neural network (DNN) considering imperfect channel state information (CSI) for heterogeneous networks. Achieving an accurate CSI has a crucial role on the system performance of the heterogeneous networks. Different quantization techniques have been employed to reduce the feedback overhead. However, the system performance cannot increase linearly with the number of bits increasing exponentially. Since optimizing the total number of bits is too complex for the entire network, an initial step is performed to distribute the bits to each cell in the conventional method. Then, the distributed bits are further allocated to each channel optimally. In order to enable direct allocation for the entire network, a FC-DNN based method is presented in this study. The optimized number of bits can be directly obtained for a different number of bits and scenarios by the proposed approach. The simulations are performed by using various scenarios with different allocation schemes. The performance results show that the DNN based method achieves a closer performance to the conventional approach. (C) 2021 Elsevier B.V. All rights reserved.Article Citation - WoS: 1Citation - Scopus: 1Spatial Signature for Secure Miso-Ofdm Systems(Institution of Engineering and Technology, 2018) Özbek, Berna; Karabulut Kurt, GüneşPhysical layer security is a promising approach to establish secure communications based on the characteristics of wireless channels. A spatial signature based secure multiple-input single-output (MISO) orthogonal frequency division multiplexing (OFDM) system is proposed to disrupt the reception of a passive eavesdropper by holding two practically relevant assumptions: a limited feedback link for legitimate node and the unavailability of channel state information of eavesdropper. The proposed algorithm achieves a higher average secrecy rate than the conventional secure MISO-OFDM systems in presence of a limited feedback link.Conference Object Citation - Scopus: 3Improved Successive Stream Selection With Quantized Channel in Heterogeneous Networks(Institute of Electrical and Electronics Engineers Inc., 2015) Aycan, Esra; Özbek, Berna; Le Ruyet, DidierThis paper focuses on different distortion metrics in order to analyze the influence of the imperfect channel state information (CSI) on the improved successive stream selection algorithm that manages the interference in a heterogeneous network. The presented approach initially selects the streams from the user of the pico cell, continuing with the strongest streams among the remaining streams that increase the sum rate and satisfy the constraint that at least one stream is selected from each user. In order to reduce the interference, the channel matrices of the remaining streams are projected orthogonally to the virtual transmit and receive channels of the selected stream. The impact of the quantization distortion on the precoding and postcoding design is examined. The performance of two distortion metrics which are the Chordal distance and the Euclidean distance are compared for different number of quantization bits. The performance evaluations are obtained by considering different locations of small cells with respect to the macro cell.Article Citation - Scopus: 1On Stream Selection for Interference Alignment With Limited Feedback in Heterogeneous Networks(John Wiley and Sons Inc., 2016) Aycan, Esra; Özbek, Berna; Le Ruyet, DidierThis paper presents a stream selection based interference alignment approach with imperfect channel state information for heterogeneous networks. The proposed solution constructs stream sequences by selecting only the strongest stream of each user where the first stream of the constructed stream sequences is associated to a pico user. While selecting the streams, the channel matrices of the unselected streams are projected orthogonally to the virtual transmit and receive channels of the selected stream in order to align the interference in the null space of these virtual channels. In addition, the influence of imperfect channel state information on the proposed algorithm is analysed. A bit allocation scheme is given by deriving an upper bound on the rate loss because of quantisation. The simulation results are carried out by considering various scenarios with different locations of pico cells at the cell edge regions of the macro cell. The performance results show that the proposed algorithm with the imperfect channel state information achieves higher performance than the existing algorithms.Conference Object Citation - Scopus: 1Secure Multiuser Miso Communication Systems With Quantized Feedback(Institute of Electrical and Electronics Engineers Inc., 2016) Özbek, Berna; Özdoğan, Özgecan; Karabulut Kurt, GüneşPhysical layer security is a promising approach to provide secure communications by considering the characteristics of wireless channels. In this work, we propose a secure multiple input single output (MISO) multiuser system with a quantized feedback link. We assume that eavesdropper is passive and its channel state information (CSI) is not available at transmitter. In order to disrupt reception of a passive eavesdropper, we schedule more than one legitimate user. For the sake of ensuring secure communication, the CSI of legitimate users has great impact on overall performance of secrecy sum capacity. The proposed solution applies a semi-orthogonal selection with a specific codebook to reduce the quantization errors for legitimate user side while disrupting the reception of the eavesdropper. The proposed solution improved secrecy sum capacity while reducing the feedback overhead for secure MISO multiser system.Article Citation - WoS: 6Citation - Scopus: 9Adaptive Limited Feedback Links for Cooperative Multi-Antenna Multicell Networks(Springer Verlag, 2014) Özbek, Berna; Ruyet, Didier LeThe overall performance of cooperative networks is quite sensitive to channel state information (CSI) of serving and interfering base stations (BSs) and affected strongly by quality of limited feedback links. In this paper, we propose two adaptive limited feedback strategies for intercell interference cancelation in multi-antenna multicell networks. The first proposed strategy is developed to improve average multicell capacity assuming a fixed rate feedback link. This algorithm is based on adaptation of the number of bits to quantize CSI of serving and interfering BSs according to transmitter power and location of the user in its own cell. The second proposed strategy is designed in a way to increase average capacity of cell-edge users assuming an adaptive rate feedback link. This algorithm is based on the idea of allocating more bits to quantize CSI of users at cell-edge regions while allocating less bits for users near the serving BS. We illustrate performance of the proposed feedback links for downlink cooperative multi-antenna multicell networks in wireless channels.Conference Object Citation - WoS: 5Citation - Scopus: 5On Precoding Mimo-Fbmc With Imperfect Channel State Information at the Transmitter(Institute of Electrical and Electronics Engineers Inc., 2014) Le Ruyet, Didier; Zakaria, Rostom; Özbek, BernaThis paper studies the impact of imperfect channel state information (CSI) due to limited feedback link on the performance of multi-user MIMO system using filter bank based multicarrier (FBMC) modulation. The system is composed of a transmitter performing Zero Forcing (ZF) precoding and single antenna receivers applying decoding techniques. Simulation-based results show that except when the number of users is less than the number of transmit antennas, the BER performance and capacity of FBMC and OFDM modulation are the same. These results are theoretically justified due to the distribution of the interfering terms. As in OFDM, depending on the number of interferers, for a given BER performance target, the required number of feedback bits per channel vector can be rather high. FBMC becomes attractive not only because it relaxes the synchronization with respect to OFDM, but also because it achieves the same performance results as OFDM for multiuser MIMO precoding even in the case of imperfect CSI at the transmitter. © 2014 IEEE.