Browsing by Author "Duman, Tolga M."

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Open Access
Analysis of DF relay selection in massive MIMO systems with hardware ımpairments
(IEEE, 2020) Kazemi, M.; Mohammadi, A.; Duman, Tolga M.
We consider a massive multiple-input multiple-output (m-MIMO) system in which a source communicates with a destination with the help of multiple single-antenna decode-and-forward (DF) relays. Employing optimal relay selection, we analyze the system performance in presence of hardware impairments (HWI) for two m-MIMO scenarios: massive-antenna source and single-antenna destination (m-MIMO I), and massive-antenna source and destination (m-MIMO II). We obtain lower bounds on the average signal-to-noise plus distortion ratio (SNDR) of the system and show that in the m-MIMO II regime, the HWI levels at the relays become the only limiting factors. Employing extreme value theory, we demonstrate that as the number of relays increases the end-to-end SNDR of the system tends to Gumbel and Weibull distributions for the m-MIMO I and m-MIMO II systems, respectively. In addition, for both arbitrary numbers of source and destination antennas and m-MIMO scenarios, we provide closed form expressions for optimal power allocation between the source and the selected relay, and the effects of HWI level distributions between the receiving and the transmitting parts of the relay (which can be exploited for optimal system design under cost constraints).
Open Access
Approximate weight distribution of polarization-adjusted convolutional (PAC) codes
(IEEE, 2022) Seyedmasoumian, Sadra; Duman, Tolga M.
Polarization-adjusted convolutional (PAC) codes combine polar and convolutional transformations to enhance the distance properties of polar codes. They offer a performance very close to the finite-length information-theoretic bounds for short blocklengths. In this paper, we develop a method of computing the weight distribution of PAC codes in an approximate form by employing a probabilistic technique. We demonstrate that the results well match the exact weight distributions for small codes that can be computed using a brute-force algorithm. We also present a way of employing the results (along with a union bound on the code performance) to design specific PAC codes or, more precisely, to determine suitable rate profiles via simulated annealing. Numerical examples illustrate that the PAC codes with the designed rate profiles offer superior performance.
Open Access
Artificial-noise-aided secure transmission over finite-ınput ıntersymbol ınterference channels
(IEEE, 2018-06) Hanoğlu, Serdar; Aghdam, Sina Rezaei; Duman, Tolga M.
We propose an artificial noise (AN) injection strategy for securing communication over finite-input intersymbol interference (lSI) channels. The technique relies on injection of colored noise whose power spectral density has the least match with the spectrum of the main channel in a certain sense. By evaluation of an achievable secrecy rate, we demonstrate that the proposed AN injection based solution results in a considerable improvement over the existing approaches, especially when the eavesdropper works at high signal-to-noise ratios (SNRs).
Open Access
Asymptotic analysis of contention resolution ALOHA with replica concatenation
(Institute of Electrical and Electronics Engineers Inc., 2019) Akyıldız, Talha; Demirhan, U.; Duman, Tolga M.
In this paper, we present an asymptotic performance analysis of contention resolution ALOHA (CRA) on the collision channel for both regular and irregular repetition rates. In addition, we consider an improvement to CRA by merging the clean parts of replicas in partial collisions and extend our analysis to this scenario. Specific designs of repetition distributions based on the new analysis show that the optimized solutions for irregular repetition slotted ALOHA (IRSA) perform well in both CRA and the enhanced scheme.
Open Access
An asynchronous two-way relay system with full delay diversity in time-varying multipath environments
(IEEE, 2015-02) Salim, A.; Duman, Tolga M.
We consider design of asynchronous OFDM-based diamond two-way-relay (DTWR) systems in time-varying frequency-selective (doubly-selective) fading channels such as underwater acoustic (UWA) channels. In a DTWR channel, two users exchange their messages with the help of two relays. Most of the existing work on asynchronous DTWR systems assume only small relative propagation delays between the received signals at each node. However, in practical systems, significant delays may take place. Our proposed system is able to tolerate the delay even if it exceeds the length of the OFDM block which is almost inevitable in UWA channels. We provide analytical and numerical results to verify the advantages of the proposed scheme in mitigating large delays in different fading conditions.
Open Access
Blind federated edge learning
(IEEE, 2021-03-19) Amiri, M. M.; Duman, Tolga M.; Gündüz, D.; Kulkarni, S. R.; Poor, H. V.
We study federated edge learning (FEEL), where wireless edge devices, each with its own dataset, learn a global model collaboratively with the help of a wireless access point acting as the parameter server (PS). At each iteration, wireless devices perform local updates using their local data and the most recent global model received from the PS, and send their local updates to the PS over a wireless fading multiple access channel (MAC). The PS then updates the global model according to the signal received over the wireless MAC, and shares it with the devices. Motivated by the additive nature of the wireless MAC, we propose an analog `over-the-air' aggregation scheme, in which the devices transmit their local updates in an uncoded fashion. However, unlike recent literature on over-the-air FEEL, here we assume that the devices do not have channel state information (CSI), while the PS has imperfect CSI. On the other hand, the PS is equipped with multiple antennas to alleviate the destructive effect of the channel, exacerbated due to the lack of perfect CSI. We design a receive beamforming scheme at the PS, and show that it can compensate for the lack of perfect CSI when the PS has a sufficient number of antennas. We also derive the convergence rate of the proposed algorithm highlighting the impact of the lack of perfect CSI, as well as the number of PS antennas. Both the experimental results and the convergence analysis illustrate the performance improvement of the proposed algorithm with the number of PS antennas, where the wireless fading MAC becomes deterministic despite the lack of perfect CSI when the PS has a sufficiently large number of antennas.
Open Access
Capacity bounds for the poisson-repeat channel
(Institute of Electrical and Electronics Engineers, 2023-08-22) Kazemi, Mohammad; Duman, Tolga M.
We develop bounds on the capacity of Poisson-repeat channels (PRCs) for which each input bit is independently repeated according to a Poisson distribution. The upper bounds are obtained by considering an auxiliary channel where the output lengths corresponding to input blocks of a given length are provided as side information at the receiver. Numerical results show that the resulting upper bounds are significantly tighter than the best known one for a large range of the PRC parameter ? (specifically, for ? =0.35). We also describe a way of obtaining capacity lower bounds using information rates of the auxiliary channel and the entropy rate of the provided side information.
Open Access
Channel reconstruction based multiuser precoding with limited feedback
(IEEE, 2021-09-06) Özateş, Mert; Kazemi, Mohammad; Göken, Çağrı; Duman, Tolga M.
We consider the downlink of a multiuser multiple-input multiple-output (MU-MIMO) system, where each user feeds back a partial channel state information (CSI), namely, the quantized version of the dominant eigenvector of its channel covariance matrix, to the base station (BS) for precoding. Specifically, we propose a downlink multiuser precoding scheme by first reconstructing the equivalent channel matrix of each user via a limited feedback, and then by employing a precoder to suppress the multiuser interference at the receivers. For the single stream case, a signal-to-leakage-and-noise ratio (SLNR) based precoding is employed, while for the full stream case with limited feedback, we employ a lattice reduction aided block diagonalization type precoding with suitable modifications at the receiver side. Extensive numerical examples which are provided using the 5G new radio (5G-NR) channel models demonstrate that the proposed schemes outperform the existing eigenvector based algorithms, and they are more robust against the downlink channel estimation errors.
Open Access
Code design for binary energy harvesting channel
(IEEE, 2017) Dabirnia, Mehdi; Duman, Tolga M.
We consider a binary energy harvesting communication system with a finite battery transmitter over a noisy channel, and design explicit and implementable codes based on concatenation of a nonlinear trellis code (NLTC) with an outer low density parity check (LDPC) code. We propose two different decoding methods where the simplified one ignores the memory in the battery state while the more sophisticated one utilizes the memory. Numerical results demonstrate that the designed codes outperform other reference schemes. The results also show the superiority of the improved decoding approach over the naive solution.
Open Access
Code design for discrete memoryless interference channels
(Institute of Electrical and Electronics Engineers, 2018) Dabirnia, Mehdi; Tanc, A. K.; Sharifi S.; Duman, Tolga M.
We study the design of explicit and implementable codes for the two-user discrete memoryless interference channels (DMICs). We consider Han-Kobayashi (HK) type encoding where both public and private messages are used and propose coding techniques utilizing a serial concatenation of a nonlinear trellis code (NLTC) with an outer low-density parity-check (LDPC) code. Since exact analytical treatment of the BCJR decoder for the inner trellis-based code appears infeasible, we analytically investigate the iterative decoding process in the asymptotic regime where the probability of decoding error tends to zero. Based on this approximate analysis, we derive a stability condition for this type of a concatenated coding scheme for the first time in the literature. Furthermore, we use an extrinsic information transfer analysis to design the outer LDPC code while fixing the inner NLTC, and utilize the derived stability condition to accelerate the design process and to avoid code ensembles that potentially produce high error floors. Via numerical examples, we demonstrate that our designed codes achieve rate pairs close the optimal boundary of the HK subregion, which cannot be obtained without the use of nonlinear codes. Also, we verify that the estimated thresholds of the designed codes via finite block length simulations and show that our designs significantly outperform the point-to-point optimal codes, hence demonstrating the need for designs specifically tailored for DMICs.
Open Access
Coded caching with user grouping over wireless channels
(IEEE, 2020) Büşra, Tegin; Duman, Tolga M.
We study coded caching over non-ergodic fading channels. As the multicast capacity of a broadcast channel is restricted by the user experiencing the worst channel conditions, we formulate an optimization problem to minimize the transmission time by grouping users based on their channel conditions, and transmit coded messages according to the worst channel conditions in the group, as opposed to the worst among all. We develop two algorithms to determine the user groups: a locally optimal iterative algorithm and a numerically more efficient solution through a shortest path problem, and we illustrate the effectiveness of developed solutions via numerical examples.
Open Access
Coding for two-user energy harvesting interference channel
(IEEE, 2020) Dabirnia, Mehdi; Duman, Tolga M.
A two-user interference channel with energy harvesting transmitters, each equipped with a finite battery, is considered. Achievable rate regions (ARRs) considering independent and identically distributed Shannon strategies at both users and ignoring the memory in the battery state are obtained for both single-user decoding and joint decoding at the receivers. Explicit and implementable codes based on concatenation of a nonlinear trellis code (NLTC) with an outer low-density parity-check code are designed, and it is demonstrated that rate pairs close to the boundary of ARR can be obtained with this approach. Furthermore, an improved alternative decoding scheme which exploits the memory in the battery state is developed, and it is shown to be highly superior to the simple decoding approach via numerical examples. Superiority of the newly developed practical channel coding solutions over the previously known alternative approaches are illustrated via extensive set of examples as well.
Open Access
Collision resolution for random access
(IEEE, 2021-10-28) Kazemi, Muhammad; Duman, Tolga M.
As a building block toward a simple and scalable solution for massive random access, we introduce collision-resolution algorithms using successive interference cancellation (SIC) based on the received signals, with no need for any coordination or codebook differentiation. We first consider two-user multiple access with the ZigZag algorithm. We prove that the original ZigZag and a modified version of it, called double-zipper ZigZag, attain the same performance as the optimal coordinated time-sharing in the high signal to noise ratio (SNR) regime, even in the presence of channel state information (CSI) errors. We then extend the results to the case of arbitrary number of users employing delay-domain processing. Specifically, we introduce delay-domain zero forcing and its regularized version, which are able to cancel and suppress the interference among users, respectively. By obtaining a post-processing system model and characterizing the accumulated noise during the decoupling process, we also derive bounds on the achievable sum-rates of the proposed algorithm for both cases of perfect and imperfect CSI. Simulation results show that the newly proposed approach have comparable performance with coordinated time-sharing at high SNRs.
Open Access
Connectivity analysis of an AUV network with OFDM based communications
(IEEE, 2017) Bereketli, A.; Tümçakır, M.; Yazgı, İ.; Yeni, B.; Köseoğlu, M.; Duman, Tolga M.
Autonomous underwater vehicle (AUV) networks play a crucial role in tactical, commercial, and scientific applications, where reliable and robust communication protocols are needed due to the challenging characteristics of the channel. With this motivation, connectivity of AUV networks in different regions with varying transducer characteristics are analyzed through simulations based on real-life orthogonal frequency division multiplexing (OFDM) based communication experiments over noisy and Doppler-distorted channels. Doppler compensation is performed according to the autocorrelation using the cyclic prefix. Using binary and quadrature phase shift keying (BPSK and QPSK) modulation schemes in conjunction with low density parity check (LDPC) coding, error rate levels are investigated through shallow water pond and at-sea experiments. It is shown that, the utilized transmission scheme is capable of correcting all bit errors among nearly one million bits transmitted up to a distance of 1 km, yielding a payload rate of 15.6 kbps with 4096 subcarriers and QPSK modulation. The simulations provide key parameters that must be taken into account in the design of scalable and connected AUV networks.
Open Access
Deep neural network based precoding for wiretap channels with finite alphabet inputs
(IEEE, 2021-04-28) Gümüş, Mücahit; Duman, Tolga M.
We consider secure transmission over multi-input multi-output multi-antenna eavesdropper (MIMOME) wiretap channels with finite alphabet inputs. We use a linear precoder to maximize the secrecy rate, which benefits from the generalized singular value decomposition to obtain independent streams and exploits the function approximation abilities of deep neural networks (DNNs) for solving the required power allocation problem. It is demonstrated that the DNN learns the optimal power allocation without any performance degradation compared to the conventional technique with a significant reduction in complexity.
Open Access
Double-zipper: multiple access with zigzag decoding
(IEEE, 2020) Kazemi, Mohammad; Duman, Tolga M.; Medard, M.
As a building block toward a simple and scalable solution to massive random access, we consider two-user multiple access with ZigZag decoding, with no need for any coordination or codebook differentiation. We derive closed-form bounds on the achievable sum-rates of the original ZigZag and a modified version of it, called double-zipper ZigZag, for both cases of perfect and imperfect channel state information (CSI). We also show that performances of both versions of ZigZag approach that of optimal coordinated time-sharing in the high signal to noise ratio regime, even in the presence of CSI errors.
Open Access
Editorial a message from the editor-in-chief
(IEEE, 2020) Duman, Tolga M.
Open Access
Energy harvesting and wireless power transfer enabled wireless networks
(Elsevier, 2020) Duman, Tolga M.; Zhao, N.; Nallanathan, A.; Chen, Y.; Pan, M.
Development of wireless communication networks, connected devices, and improvement of Internet of Things (IoT) will deeply impact in every aspect of human life. In future mobile systems, a tremendous number of low-power wireless devices will exist within the densely deployed heterogeneous networks. One key challenge from the growing demand in wireless applications is a sufficient and flexible energy supply. Hence, a natural spin from the traditional and limited energy sources to alternative energy sources is a natural step to supply the exponential growth of energy demand of the mankind. Recently, energy harvesting (EH) has emerged as an important method to provide a power supply for green self-sufficient wireless nodes, in which the energy captured from intentional or ambient sources can be collected to replenish the batteries. Besides, EH has been investigated as a promising technology to overcome the energy scarcity problem in energy constrained wireless communication systems, especially for wireless networks with fixed energy supplies. Compared with conventional EH sources such as solar, wind, vibration, thermoelectric effects or other physical phenomena, which rely on external energy sources that are not components of communication networks, a new operation of EH which collects energy from ambient radio-frequency (RF) signals has been proposed. As RF signals are commonly used as a vehicle for transmitting information in wireless networks, simultaneous wireless information and power transfer (SWIPT) has become an emerging technique attracting great attention from both academia and industry. Towards this end, this special issue includes a collection of 24 papers, and we aim to disseminate the latest research and innovations on energy harvesting and wireless power transfer enabled wireless networks.
Open Access
Energy harvesting irregular repetition ALOHA with replica concatenation
(IEEE, 2021) Akyıldız, Talha; Demirhan, U.; Duman, Tolga M.
In this paper, we consider an asynchronous random access scheme called irregular repetition ALOHA (IRA) as a generalization of contention resolution ALOHA (CRA) with varying repetitions. We present an asymptotic performance analysis of CRA and IRA on the collision channel for regular and irregular repetition rates. We also propose an improvement by merging the clean parts of packet replicas in partial collisions, and extend our analysis to this scenario as well. Specific designs of repetition distributions based on the new analysis show that the optimized solutions of irregular repetition slotted ALOHA (IRSA) perform well in both IRA and the enhanced scheme, and they considerably outperform the regular repetition distributions. We also introduce energy harvesting (EH) to both schemes as a practical and sustainable adaptation, where users are able to harvest energy and store it in their finite-capacity batteries. We model the battery state by a discrete-time Markov chain and derive an optimal transmission policy to maximize the asymptotic performance of the system. We provide comprehensive numerical results for both practical and asymptotic scenarios to verify the validity of the proposed analyses, and illustrate the benefits of the proposed systems.
Open Access
Energy-harvesting irregular repetition slotted ALOHA with unit-sized battery
(IEEE, 2018-05) Demirhan, U.; Duman, Tolga M.
We propose an irregular repetition slotted ALOHA (IRSA) based uncoordinated random access scheme for energy harvesting (EH) nodes. Specifically, we consider the case in which each user has a unit- sized battery that is recharged with energy harvested from the environment in a probabilistic manner. We analyze this scheme by deriving asymptotic throughput expressions, and obtain optimized probability distributions for the number of packet replicas for each user. We demonstrate that for the case of IRSA with EH nodes, these optimized distributions perform considerably better than those of slotted ALOHA (SA), contention resolution diversity slotted ALOHA (CRDSA) and IRSA, which do not take into account the EH process, for both asymptotic and finite frame length scenarios.