19 results on '"Akin, Sami"'
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2. Cognitive radio transmission under QoS constraints and interference limitations
- Author
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Akin, Sami and Gursoy, Mustafa Cenk
- Published
- 2012
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3. On the Energy and Data Storage Management in Energy Harvesting Wireless Communications.
- Author
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Akin, Sami and Gursoy, M. Cenk
- Subjects
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ENERGY harvesting , *LARGE deviation theory , *WIRELESS communications , *ENERGY storage , *CLOUD storage , *WIRELESS channels , *ERROR probability - Abstract
Energy harvesting (EH) in wireless communications has become the focus of recent transmission technology studies. Herein, energy storage modeling is one of the crucial design benchmarks that must be treated carefully. Understanding the energy storage dynamics and the throughput levels is essential especially for communication systems in which the performance depends solely on harvested energy. While energy outages should be avoided, energy overflows should also be prevented in order to utilize all harvested energy. Hence, a simple, yet comprehensive, analytical model that can represent the characteristics of a general class of EH wireless communication systems needs to be established. In this paper, invoking tools from large deviation theory along with Markov processes, a firm connection between the energy state of the battery and the data transmission process over a wireless channel is established for an EH transmitter. In particular, a simple exponential approximation for the energy overflow probability is formulated, with which the energy decay rate in the battery as a measure of energy usage is characterized. Then, projecting the energy outages and supplies on a Markov process, a discrete state model is established and an expression for the energy outage probability for given energy arrival and demand processes is provided. Finally, under energy overflow and outage constraints, the average data service (transmission) rate over the wireless channel is obtained and the effective capacity of the system, which characterizes the maximum data arrival rate at the transmitter buffer under quality-of-service (QoS) constraints imposed on the data buffer overflow probability, is derived. [ABSTRACT FROM AUTHOR] more...
- Published
- 2019
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4. Effective Capacity in MIMO Channels With Arbitrary Inputs.
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Hammouda, Marwan, Akin, Sami, Gursoy, M. Cenk, and Peissig, Jurgen
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TELECOMMUNICATION systems -- Design & construction , *QUALITY of service , *SIGNAL-to-noise ratio , *ANTENNAS (Electronics) , *ASYMPTOTIC efficiencies - Abstract
Recently, communication systems that are both spectrum and energy efficient have attracted significant attention. Different from the existing research, we investigate the throughput and energy efficiency of a general class of multiple-input and multiple-output systems with arbitrary inputs when they are subject to statistical quality-of-service (QoS) constraints, which are imposed as limits on the delay violation and buffer overflow probabilities. We employ the effective capacity as the performance metric, which is the maximum constant data arrival rate at a buffer that can be sustained by the channel service process under specified QoS constraints. We obtain the optimal input covariance matrix that maximizes the effective capacity under a short-term average power constraint. Following that, we perform an asymptotic analysis of the effective capacity in the low signal-to-noise ratio and large-scale antenna regimes. In the low signal-to-noise ratio regime analysis, in order to determine the minimum energy-per-bit and also the slope of the effective capacity versus energy-per-bit curve at the minimum energy-per-bit, we utilize the first and second derivatives of the effective capacity when the signal-to-noise ratio approaches zero. We observe that the minimum energy-per-bit is independent of the input distribution, whereas the slope depends on the input distribution. In the large-scale antenna analysis, we show that the effective capacity approaches the average transmission rate in the channel with the increasing number of transmit and/or receive antennas. Particularly, the gap between the effective capacity and the average transmission rate in the channel, which is caused by the QoS constraints, is minimized with the number of antennas. In addition, we put forward the nonasymptotic backlog and delay violation bounds by utilizing the effective capacity. Finally, we substantiate our analytical results through numerical illustrations. [ABSTRACT FROM PUBLISHER] more...
- Published
- 2018
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5. Link Selection in Hybrid RF/VLC Systems Under Statistical Queueing Constraints.
- Author
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Hammouda, Marwan, Akin, Sami, Vegni, Anna Maria, Haas, Harald, and Peissig, Jurgen
- Abstract
The co-deployment of radio frequency (RF) and visible light communication (VLC) technologies has been investigated in indoor environments to enhance network performances and to address specific quality-of-service (QoS) constraints. In this paper, we explore the benefits of employing both technologies when the QoS requirements are imposed as limits on the buffer overflow and delay violation probabilities, which are important metrics in designing low latency wireless networks. Particularly, we consider a multi-mechanism scenario that utilizes RF and VLC links for data transmission in an indoor environment, and then propose a link selection process through which the transmitter sends data over the link that sustains the desired QoS guarantees the most. Considering an ON–OFF data source, we employ the maximum average data arrival rate at the transmitter buffer and the non-asymptotic bounds on data buffering delay as the main performance measures. We formulate the performance measures under the assumption that both links are subject to average and peak power constraints. Furthermore, we investigate the performance levels when either one of the two links is used for data transmission, or when both are used simultaneously. Finally, we show the impacts of different physical layer parameters on the system performance through numerical analysis. [ABSTRACT FROM PUBLISHER] more...
- Published
- 2018
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6. A Method for Cross-Layer Analysis of Transmit Buffer Delays in Message Index Domain.
- Author
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Akin, Sami and Fidler, Markus
- Subjects
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TRANSMITTERS (Communication) , *RADIO transmitters & transmission , *WIRELESS communications , *BLUETOOTH technology , *MIMO systems - Abstract
In data transmission systems, quality-of-service constraints are commonly defined in the form of buffer overflow probability or delay violation probability at a transmitter buffer. Some of the studies that employ the large-deviation principle have taken the buffer overflow probability as the quality-of-service constraint and performed the associated analyses in the time domain. The delay violation probability has been investigated through the buffer overflow probability given that there exists a constant service rate from or a constant data arrival rate at a buffer. These studies cultivated the concepts of effective bandwidth and effective capacity, respectively. Different from the existing studies, we investigate the performance of a transmitter buffer in the message index domain rather than the time domain by taking the waiting time (buffering delay) as the primary quality-of-service constraint. We characterize the waiting time violation probability when both the data arrival and service processes are stochastic, and provide two new concepts: effective interarrival time and effective service time, which are the duals of effective bandwidth and effective capacity, respectively, in the message index domain. The effective interarrival time of a data arrival process determines the maximum constant service time for a message that can sustain the arrival process under a stochastic waiting time constraint, and the effective service time of a data service process determines the minimum constant interarrival time between successive messages arriving at a buffer that the service process can sustain. We show that we can obtain the effective capacity of a service process or the effective bandwidth of an arrival process through the effective service time or the effective interarrival time of the corresponding process, respectively, in cases where it is difficult to formulate the effective capacity and the effective bandwidth without numerical techniques or particular assumptions. Noting that our proposed techniques can be applied in vehicular communication scenarios, e.g., highways, urban areas, and rural areas, we finally analyze a typical data dissemination and collection task in vehicular networks using a broadcast downlink and a slotted Aloha uplink transmission. [ABSTRACT FROM AUTHOR] more...
- Published
- 2018
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7. Energy Harvesting Communications Under Energy Underflow Constraints.
- Author
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Akin, Sami
- Abstract
We focus on energy management in a transmission system that harvests energy from the environment and stores the harvested energy in a battery. Because of the constraint in certain batteries that we cannot drain the stored energy completely, we study energy underflow, which is a result of the case the energy in the battery falls below a certain level. We formulate the available space to store more energy in the battery. Then, using the stochastic steady-state relation between the energy arrival and demand processes, we provide a closed-form expression for the energy underflow probability in the battery. Finally, we employ different energy demand processes from the battery, and then compare the average data service rates in the wireless channel under different energy underflow constraints. [ABSTRACT FROM PUBLISHER] more...
- Published
- 2017
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8. On the Transmission Rate Strategies in Cognitive Radios.
- Author
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Akin, Sami and Fidler, Markus
- Abstract
We investigate instantaneous transmission rate strategies for secondary users in cognitive radio networks by analyzing their effective capacity performance in different signal-to-noise ratio regimes with different quality-of-service constraints and transmission block sizes. Describing a channel model with one secondary transmitter and one secondary receiver with the potential presence of primary users, we present an interference power constraint that limits the transmission power of secondary users not only when a channel is sensed as busy but also when a channel is sensed as idle. Calling the existing transmission rate strategy Optimistic Policy, we introduce two other strategies, particularly Conservative Policy and Greedy Policy. Secondary users in Optimistic Policy set the instantaneous transmission rate to the instantaneous mutual information assuming the correctness of channel sensing results, whereas they set the instantaneous transmission rate to the instantaneous mutual information regarding possible transmission outages in Conservative Policy and disregarding possible transmission outages in Greedy Policy. We construct a state transition diagram and formulate the effective capacity employing these policies. We calculate the minimum energy-per-bit requirements and the high signal-to-noise ratio slope in order to explore performance variations in low and high signal-to-noise ratio regimes, respectively. Correspondingly, we show that Optimistic Policy is, in general, more favorable in secondary users when the quality-of-service constraints are loose, the transmission blocks are shorter, and the signal-to-noise ratio is low. On the other hand, Conservative Policy is better when the quality-of-service constraints are strict, the transmission blocks are longer, and the signal-to-noise ratio is high. [ABSTRACT FROM PUBLISHER] more...
- Published
- 2016
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9. Performance analysis of energy-detection-based massive SIMO.
- Author
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Hammouda, Marwan, Akin, Sami, and Peissig, Jurgen
- Published
- 2015
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10. Effective capacity in multiple access channels with arbitrary inputs.
- Author
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Hammouda, Marwan, Akin, Sami, and Peissig, Jurgen
- Published
- 2015
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11. Backlog and Delay Reasoning in HARQ System.
- Author
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Akin, Sami and Fidler, Markus
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- 2015
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12. The Interplay Between Data Transmission Power and Transmission Link Utilization.
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Akin, Sami
- Abstract
We consider a single-input single-output communications link in which a transmitter and a receiver, both having data buffers with their own unique quality-of-service (QoS) constraints, perform data transmission over a time-selective flat fading wireless channel. Regarding the stochastic nature of the wireless channel in the physical layer, we first provide the effective capacity at the transmitter buffer. Then, we assume a data arrival process with a constant rate to the transmitter buffer and identify the departure process from the transmitter to the receiver. Noting that the departure process is the arrival process at the receiver buffer, we find the effective bandwidth at the receiver buffer. Establishing the maximum transmission link utilization as the ratio between the effective capacity at the transmitter and the effective bandwidth at the receiver, we investigate the relationship between the transmission power in the channel and the maximum transmission link utilization under QoS requirements by employing different symbol modulation techniques in a Rayleigh fading environment. [ABSTRACT FROM PUBLISHER] more...
- Published
- 2015
- Full Text
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13. Performance Analysis of Cognitive Radio Systems With Imperfect Channel Sensing and Estimation.
- Author
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Akin, Sami and Gursoy, M. Cenk
- Subjects
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COGNITIVE radio , *CHANNEL estimation , *FALSE alarms , *GAUSSIAN distribution , *INTERFERENCE (Telecommunication) , *TIME-varying channels - Abstract
In cognitive radio systems, employing sensing-based spectrum access strategies, secondary users are required to perform channel sensing to detect the activities of licensed primary users in a channel, and in realistic scenarios, channel sensing occurs with possible errors due to miss-detections and false alarms. As another challenge, time-varying fading conditions in the channel between the secondary transmitter and the secondary receiver have to be learned via channel estimation. In this paper, performance of causal channel estimation methods in correlated cognitive radio channels under imperfect channel sensing results is analyzed, and achievable rates for reliable communication under both channel and sensing uncertainty are investigated by considering the input-output mutual information. Initially, cognitive radio channel model with channel sensing error and channel estimation is described. Then, using pilot symbols, minimum mean square error (MMSE) and linear-MMSE (L-MMSE) estimation methods are employed at the secondary receiver to learn the channel fading coefficients. Expressions for the channel estimates and mean-squared errors (MSE) are determined, and their dependencies on channel sensing results, and pilot symbol period and energy are investigated. Since sensing uncertainty leads to uncertainty in the variance of the additive disturbance, channel estimation strategies and performance are interestingly shown to depend on the sensing reliability. It is further shown that the L-MMSE estimation method, which is in general suboptimal, performs very close to MMSE estimation. Furthermore, assuming the channel estimation errors and the interference introduced by the primary users as zero-mean and Gaussian distributed, achievable rate expressions of linear modulation schemes and Gaussian signaling are determined. Subsequently, the training period, and data and pilot symbol energy allocations are jointly optimized to maximize the achievable rates for both signaling schemes. [ABSTRACT FROM PUBLISHER] more...
- Published
- 2015
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14. Effective capacity in cognitive radio broadcast channels.
- Author
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Hammouda, Marwan, Akin, Sami, and Peissig, Jurgen
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- 2014
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15. Security in cognitive radio networks.
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Akin, Sami
- Published
- 2014
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16. Achievable rates and energy efficiency in cognitive radio channels with sensing errors.
- Author
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Gursoy, M. Cenk, Ozcan, Gozde, and Akin, Sami
- Abstract
In this paper, achievable rates and energy efficiency in cognitive radio channels are analyzed in the presence of sensing errors. The cognitive secondary users are initially assumed to perform channel sensing and then enter into data transmission phase. Under sensing uncertainty and Gaussian primary user interference assumptions, additive disturbance experienced at the secondary receiver is seen to have a Gaussian mixture density. Achievable rates under such assumptions are examined and a closed-form rate expression is determined. An outage capacity formulation is also derived. Finally, energy efficiency is analyzed by investigating the minimum energy per bit and wideband slope expressions in the low-SNR regime. Through this analysis, tradeoffs and interactions between sensing parameters, sensing performance, throughput, transmission energy, and energy efficiency are identified. [ABSTRACT FROM PUBLISHER] more...
- Published
- 2012
- Full Text
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17. On the Throughput and Energy Efficiency of Cognitive MIMO Transmissions.
- Author
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Akin, Sami and Gursoy, Mustafa Cenk
- Subjects
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ENERGY consumption , *MIMO systems , *QUALITY of service , *COGNITIVE radio , *DETECTOR circuits , *ELECTRIC interference - Abstract
In this paper, throughput and energy efficiency of cognitive multiple-input–multiple-output (MIMO) systems operating under quality-of-service (QoS) constraints, interference limitations, and imperfect channel sensing are studied. It is assumed that transmission power and covariance of the input signal vectors are varied, depending on the sensed activities of primary users (PUs) in the system. Interference constraints are applied on the transmission power levels of cognitive radios (CRs) to provide protection for the PUs, whose activities are modeled as a Markov chain. Considering the reliability of the transmissions and channel sensing results, a state transition model is provided. Throughput is determined by formulating the effective capacity. The first derivative of the effective capacity is derived in the low-power regime, and the minimum bit energy requirements in the presence of QoS limitations and imperfect sensing results are identified. Minimum energy per bit is shown to be achieved by beamforming in the maximal-eigenvalue eigenspace of certain matrices related to the channel matrix. In a special case, wideband slope is determined for a more refined analysis of energy efficiency. Numerical results are provided for the throughput for various levels of buffer constraints and different number of transmit and receive antennas. The impact of interference constraints and benefits of multiple-antenna transmissions are determined. It is shown that increasing the number of antennas when the interference power constraint is stringent is generally beneficial. On the other hand, it is shown that, under relatively loose interference constraints, increasing the number of antennas beyond a certain level does not lead to much increase in throughput. [ABSTRACT FROM AUTHOR] more...
- Published
- 2013
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18. Performance Analysis of Cognitive Radio Systems under QoS Constraints and Channel Uncertainty.
- Author
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Akin, Sami and Gursoy, Mustafa Cenk
- Abstract
In this paper, performance of cognitive transmission over time-selective flat fading channels is studied under quality of service (QoS) constraints and channel uncertainty. Cognitive secondary users (SUs) are assumed to initially perform channel sensing to detect the activities of the primary users, and then attempt to estimate the channel fading coefficients through training. Energy detection is employed for channel sensing, and different minimum mean-square-error (MMSE) estimation methods are considered for channel estimation. In both channel sensing and estimation, erroneous decisions can be made, and hence, channel uncertainty is not completely eliminated. In this setting, performance is studied and interactions between channel sensing and estimation are investigated. Following the channel sensing and estimation tasks, SUs engage in data transmission. Transmitter, being unaware of the channel fading coefficients, is assumed to send the data at fixed power and rate levels that depend on the channel sensing results. Under these assumptions, a state-transition model is constructed by considering the reliability of the transmissions, channel sensing decisions and their correctness, and the evolution of primary user activity which is modeled as a two-state Markov process. In the data transmission phase, an average power constraint on the secondary users is considered to limit the interference to the primary users, and statistical limitations on the buffer lengths are imposed to take into account the QoS constraints of the secondary traffic. The maximum throughput under these statistical QoS constraints is identified by finding the effective capacity of the cognitive radio channel. Numerical results are provided for the power and rate policies. [ABSTRACT FROM PUBLISHER] more...
- Published
- 2011
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19. Effective Capacity Analysis of Cognitive Radio Channels for Quality of Service Provisioning.
- Author
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Akin, Sami and Gursoy, Mustafa Cenk
- Abstract
In this paper, the performance of cognitive radio systems is studied when the secondary users operate under statistical quality of service (QoS) constraints. In the cognitive radio channel model, secondary users initially perform channel sensing, and then engage in data transmission at two different average power levels depending on the channel sensing results. A state transition model is constructed to model this cognitive transmission channel. Statistical QoS constraints are imposed as limitations on buffer violation probabilities. Effective capacity of the cognitive radio channel, which provides the maximum throughput under such QoS constraints, is determined. This analysis is conducted for fixed-power/fixed-rate, fixed-power/variable-rate, and variable-power/variable-rate transmission schemes under different assumptions on the availability of channel side information (CSI) at the transmitter. The interactions and tradeoffs between the throughput, QoS constraints, and channel sensing parameters (e.g., sensing duration and threshold, and detection and false alarm probabilities) are investigated. The performances of fixed-rate and variable-rate transmission methods are compared in the presence of QoS limitations. It is shown that variable schemes outperform fixed-rate transmission techniques if the detection probabilities are high. Performance gains through adapting the power and rate are quantified and it is shown that these gains diminish as the QoS limitations become more stringent. [ABSTRACT FROM PUBLISHER] more...
- Published
- 2010
- Full Text
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