Browsing by Subject "Power allocation"

Now showing 1 - 17 of 17

Open Access
Convexity properties of detection probability for noncoherent detection of a modulated sinusoidal carrier
(Institute of Electrical and Electronics Engineers, 2018) Öztürk, Cüneyd; Dülek, B.; Gezici, Sinan
In this correspondence paper, the problem of noncoherent detection of a sinusoidal carrier is considered in the presence of Gaussian noise. The convexity properties of the detection probability are characterized with respect to the signal-To-noise ratio (SNR). It is proved that the detection probability is a strictly concave function of SNR when the false alarm probability α satisfies α > e-2, and it is first a strictly convex function and then a strictly concave function of SNR for α < e-2. In addition, optimal power allocation strategies are derived under average and peak power constraints. It is shown that on-off signaling can be optimal for α < e-2 depending on the power constraints, whereas transmission at a constant power level that is equal to the average power limit is optimal in all other cases.
Open Access
A game theoretic approach to channel switching in the presence of jamming
(IEEE, 2021-10-14) Bozkurt, Berk; Sezer, A. D.; Gezici, Sinan; Girici, T.
In this letter, a channel switching problem is investigated in the presence of jamming based on a game theoretic approach. First, a convex formulation of the optimal channel switching problem is proposed for a given jamming strategy. Then, considering a fixed channel switching strategy, an explicit solution of the optimal jammer power allocation problem is obtained. Consequently, a game theoretic formulation is proposed and the existence of a pure-strategy Nash equilibrium is shown for the proposed channel switching game between the transmitter and the jammer.
Open Access
Jamming of Wireless Localization Systems
(Institute of Electrical and Electronics Engineers Inc., 2016) Gezici, Sinan; Gholami, M. R.; Bayram, S.; Jansson M.
In this paper, the optimal jamming of wireless localization systems is investigated. Two optimal power allocation schemes are proposed for jammer nodes in the presence of total and peak power constraints. In the first scheme, power is allocated to jammer nodes in order to maximize the average Cramér-Rao lower bound (CRLB) of target nodes, whereas in the second scheme, the power allocation is performed for the aim of maximizing the minimum CRLB of target nodes. Both the schemes are formulated as linear programs, and a closed-form solution is obtained for the first scheme. For the second scheme, under certain conditions, the property of full total power utilization is specified, and a closed-form solution is obtained when the total power is lower than a specific threshold. In addition, it is shown that non-zero power is allocated to at most NT jammer nodes according to the second scheme in the absence of peak power constraints, where NT is the number of target nodes. In the presence of parameter uncertainty, robust versions of the power allocation schemes are proposed. Simulation results are presented to investigate the performance of the proposed schemes and to illustrate the theoretical results. © 2016 IEEE.
Open Access
Jamming strategies in wireless source localization systems
(IEEE, 2019-08) Keskin, Musa Furkan; Öztürk, Cüneyd; Bayram, Suat; Gezici, Sinan
We consider optimal jamming strategies in wireless source localization systems, where anchor nodes estimate positions of target nodes in the presence of jammers that emit zero-mean Gaussian noise. The Cramér-Rao lower bound (CRLB) for target location estimation is derived and the problem of optimal power allocation for jammer nodes is formulated to maximize the average CRLB for target nodes under total and peak power constraints. Exploiting the special problem structure and successive convex approximation techniques, we develop an iterative algorithm that transforms the original non-convex problem into a sequence of convex geometric programs. In addition, we present a closed-form solution that is asymptotically optimal. Numerical results demonstrate the improved jamming performance of the proposed solutions over the uniform power allocation strategy.
Open Access
Localization via visible light systems
(Institute of Electrical and Electronics Engineers, 2018) Keskin, M. F.; Sezer, A. D.; Gezici, Sinan
Visible light communication (VLC) is an emerging paradigm that enables multiple functionalities to be accomplished concurrently, including illumination, high-speed data communications, and localization. Based on the VLC technology, visible light positioning (VLP) systems aim to estimate locations of VLC receivers by utilizing light-emitting diode (LED) transmitters at known locations. VLP presents a viable alternative to radio frequency (RF)-based positioning systems by providing inexpensive and accurate localization services. In this paper, we consider the problem of localization in visible light systems and provide an extensive survey of various location estimation techniques, accompanied by discussions of their relative merits and demerits within the context of accuracy and computational complexity. In addition, we investigate a cooperative VLP system architecture in which VLC receiver units are able to communicate with each other for the purpose of cooperation, and present a low-complexity, iterative localization algorithm to demonstrate the benefits of cooperation in VLP systems. Finally, we investigate optimal strategies for power allocation among LED transmitters to maximize the localization accuracy subject to power and illumination constraints.
Open Access
Optimal and robust power allocation for visible light positioning systems under illumination constraints
(IEEE, 2019-01) Keskin, Musa Furkan; Sezer, Ahmet Dündar; Gezici, Sinan
The problem of optimal power allocation among light emitting diode (LED) transmitters in a visible light positioning system is considered for the purpose of improving localization performance of visible light communication (VLC) receivers. Specifically, the aim is to minimize the Cramér-Rao lower bound (CRLB) on the localization error of a VLC receiver by optimizing LED transmission powers in the presence of practical constraints, such as individual and total power limitations and illuminance constraints. The formulated optimization problem is shown to be convex and thus can efficiently be solved via standard tools. We also investigate the case of imperfect knowledge of localization parameters and develop robust power allocation algorithms by taking into account both overall system uncertainty and individual parameter uncertainties related to the location and orientation of the VLC receiver. In addition, we address the total power minimization problem under predefined accuracy requirements to obtain the most energy-efficient power allocation vector for a given CRLB level. Numerical results illustrate the improvements in localization performance achieved by employing the proposed optimal and robust power allocation strategies over the conventional uniform and non-robust approaches.
Open Access
Optimal channel switching and randomization over flat-fading channels for outage capacity maximization
(Institute of Electrical and Electronics Engineers, 2022-11-16) Masrur, Saad; Gezici, Sinan
In this letter, the optimal channel switching and randomization problem is formulated and its solution is characterized for flat-fading Gaussian noise channels with the aim of outage capacity maximization under average power and outage probability constraints. For the single user scenario, it is proved that the optimal solution can always be realized by performing one of the following strategies: (1) Transmission over a single channel with no randomization. (2) Channel switching between two channels with no randomization. (3) Randomization between two parameter sets over a single channel. Hence, the solution can easily be obtained by considering only these three strategies. However, for the multiuser scenario, obtaining the optimal solution can have very high computational complexity. Therefore, an algorithm is proposed to calculate an approximately optimal channel switching and randomization solution (with adjustable approximation accuracy) based on the solution of a linearly constrained linear optimization problem.
Open Access
Optimal channel switching in multiuser systems under average capacity constraints
(Elsevier, 2017) Sezer, A. D.; Gezici, Sinan
In this paper, the optimal channel switching problem is studied for average capacity maximization in the presence of multiple receivers in the communication system. First, the optimal channel switching problem is proposed for average capacity maximization of the communication between the transmitter and the secondary receiver while fulfilling the minimum average capacity requirement of the primary receiver and considering the average and peak power constraints. Then, an alternative equivalent optimization problem is provided and it is shown that the solution of this optimization problem satisfies the constraints with equality. Based on the alternative optimization problem, it is obtained that the optimal channel switching strategy employs at most three communication links in the presence of multiple available channels in the system. In addition, the optimal strategies are specified in terms of the number of channels employed by the transmitter to communicate with the primary and secondary receivers. Finally, numerical examples are provided in order to verify the theoretical investigations.
Open Access
Optimal jamming of wireless localization systems
(IEEE, 2015-06) Gezici, Sinan; Gholami, M.R.; Bayram, S.; Jansson, M.
In this study, optimal jamming of wireless localization systems is investigated. Two optimal power allocation schemes are proposed for jammer nodes in the presence of total and peak power constraints. In the first scheme, power is allocated to jammer nodes in order to maximize the average Cramér-Rao lower bound (CRLB) of target nodes whereas in the second scheme the power allocation is performed for the aim of maximizing the minimum CRLB of target nodes. Both schemes are formulated as linear programs, and a closed-form expression is obtained for the first scheme. Also, the full total power utilization property is specified for the second scheme. Simulation results are presented to investigate performance of the proposed schemes. © 2015 IEEE.
Open Access
Optimal power allocation and optimal linear encoding for parameter estimation in the presence of a smart eavesdropper
(IEEE, 2022-08-11) Abadi, Erfan Mehdipour; Göken, Çağrı; Öztürk, Cüneyd; Gezici, Sinan
In this article, we consider secure transmission of a deterministic vector parameter from a transmitter to an intended receiver in the presence of a smart eavesdropper. The aim is to determine the optimal power allocation and optimal linear encoding strategies at the transmitter to maximize the estimation performance at the intended receiver under constraints on the estimation performance at the eavesdropper and on the transmit power. First, the A-optimality criterion is adopted by utilizing the Cramér-Rao lower bound as the estimation performance metric, and the optimal power allocation and optimal linear encoding strategies are characterized theoretically. Then, corresponding to the D-optimality criterion, the determinant of the Fisher information matrix is considered as the estimation performance metric. It is shown that the optimal linear encoding and optimal power allocation strategies lead to the same solution for this criterion. In addition, extensions of the theoretical results are provided to cases with statistical knowledge of systems parameters. Numerical examples are provided to investigate the optimal power allocation and optimal linear encoding strategies in different scenarios.
Open Access
Optimal power allocation for average detection probability criterion over flat fading channels
(Institute of Electrical and Electronics Engineers Inc., 2017) Sarıtaş, S.; Dulek, B.; Sezer, A. D.; Gezici, Sinan; Yüksel S.
In this paper, the problem of optimal power allocation over flat fading additive white Gaussian noise channels is considered for maximizing the average detection probability of a signal emitted from a power constrained transmitter in the Neyman-Pearson framework. It is assumed that the transmitter can perform power adaptation under peak and average power constraints based on the channel state information fed back by the receiver. Using results from measure theory and convex analysis, it is shown that this optimization problem, which is in general nonconvex, has an equivalent Lagrangian dual that admits no duality gap and can be solved using dual decomposition. Efficient numerical algorithms are proposed to determine the optimal power allocation scheme under peak and average power constraints. Furthermore, the continuity and monotonicity properties of the corresponding optimal power allocation scheme are characterized with respect to the signal-to-noise ratio for any given value of the false alarm probability. Simulation examples are presented to corroborate the theoretical results and illustrate the performance improvements due to the proposed optimal power allocation strategy.
Open Access
Optimal power allocation for jammer nodes in wireless localization systems
(Institute of Electrical and Electronics Engineers Inc., 2017) Bayram, S.; Keskin, M. F.; Gezici, Sinan; Arıkan, Orhan
In this paper, optimal power allocation strategies are investigated for jammer nodes in a wireless localization system. Building upon the concept of the restricted Bayesian approach, a generalized optimization strategy, called the restricted scheme, is proposed for power allocation of jammer nodes, and its theoretical properties are characterized. In the restricted scheme, the aim is to maximize the average Cramér-Rao lower bound (CRLB) of target nodes while keeping their minimum CRLB above a predefined level in the presence of average (total) and peak power constraints. It is proved that the average CRLB achieved by the restricted scheme is a strictly decreasing and concave function of the constraint on the minimum CRLB level. A closed-form solution is obtained for the restricted scheme when the tradeoff parameter and the total power limit are below certain thresholds. In addition, it is shown that the optimal solution of the restricted scheme corresponds to the use of at most NT jammer nodes, where NT is the number of target nodes, and that the optimal solution of the minimum CRLB maximization scheme is determined by at most NJ target nodes, where NJ is the number of jammer nodes. Extensions of the restricted scheme and an alternative scheme that aims to maximize the number of disabled target nodes (whose CRLBs are above a preset level) are considered, and the corresponding optimal strategies for jammer power allocation are identified. Numerical examples are provided to verify the theoretical derivations for various network configurations.
Open Access
Outage capacity and throughput maximization using theoretical and learning-based approaches
(2023-07) Masrur, Saad
This thesis explores two research problems in wireless communications: the optimal channel switching and randomization problem in flat-fading Gaussian noise channels, and channel selection and switching approaches based on the upper confidence bound (UCB) bandit algorithm. In the first part of the thesis, the optimal channel switching and randomization problem is formulated and its solution is characterized for flat-fading Gaussian noise channels with the aim of outage capacity maximization under average power and outage probability constraints. For the single user scenario, it is proved that the optimal solution can always be realized by performing one of the following strategies: (1) Transmission over a single channel with no randomization. (2) Channel switching between two channels with no randomization. (3) Randomization between two parameter sets over a single channel. Hence, the solution can easily be obtained by considering only these three strategies. However, for the multiuser scenario, obtaining the optimal solution can have very high computational complexity. Therefore, an algorithm is proposed to calculate an approximately optimal channel switching and randomization solution (with adjustable approximation accuracy) based on the solution of a linearly constrained linear optimization problem. In the second part of the thesis, we consider the case of unknown channel statistics at the transmitter, and propose channel selection and channel switching approaches based on the UCB bandit algorithm for communications between a transmitter and a receiver over a block fading channel. In the absence of channel switching in a block, we propose a UCB bandit algorithm for selecting the best channel among the possible set of channels for maximizing the number of correctly received symbols per unit of time. In the presence of channel switching, we first define a set of virtual channels by considering all possible channel pairs with various power levels and timesharing factors. Then, a UCB bandit algorithm is utilized to determine the best virtual channel; hence, to find the optimal channel switching strategy. Also, a low complexity version of this algorithm is proposed for efficient convergence to the optimal solution when a high number of virtual channels exists. In addition, for comparison purposes, theoretical limits are presented when the channel statistics are available at the transmitter. Simulation results indicate that the proposed UCB bandit algorithms can achieve very close performance to theoretical limits over a sufficiently large number of blocks, and make benefits of channel switching be realized.
Open Access
Physical layer security over frequency selective fading channels
(2016-01) Ayhan, Kadir
The inherent open nature of the transmission medium makes security a challenging issue in wireless networks. Physical layer security, which is an alternative or a complement to the cryptographic approaches, exploits the differences between the physical properties of different channels in order to provide secrecy. The idea is to ensure that the received signal at an eavesdropper is degraded compared to that of the legitimate receiver in some sense which guarantees that the confidential messages cannot be recovered by an unintended receiver. Over the last decade, various researchers have studied fundamental limits of physical layer security under different wiretap channel models, including Gaussian and fading channels, and with different assumptions on the transmitter’s knowledge on the channel state information. In this thesis, we study physical layer security over frequency selective fading channels modelling certain wireless links. Specifically, we investigate optimal and suboptimal power allocation schemes across frequencies with perfect and partial channel state information at the transmitter with the objective of providing secrecy. We demonstrate that frequency selectivity allows for positive secrecy rates even though the eavesdropper’s channel is not a degraded version of the desired user’s channel. We also analyse the impact of user mobility and the resulting time variations in the wireless medium on the achievable secrecy rates. Furthermore, we consider quantized channel state information at the transmitter and evaluate the secrecy rate loss due to limited feedback from the legitimate receiver to the transmitter. Our results reveal that the partial channel state information at the transmitter can still be helpful in providing positive secrecy rates.
Open Access
Power allocation and temporal fair user group scheduling for downlink NOMA
(Springer, 2021-08) Erturk, E.; Yildiz, O.; Shahsavari, S.; Akar, Nail
Non-Orthogonal Multiple Access (NOMA) has been proposed as a new radio access technique for cellular networks as an alternative to OMA (Orthogonal Multiple Access) in which the users of a group (pairs or triples of users in a group are considered in this paper) are allowed to use the wireless channel simultaneously. In this paper, for downlink single-input single-output SISO-NOMA, a heuristic power allocation algorithm within a group is first proposed which attempts to ensure that the users of a group benefit from simultaneous transmission equally in terms of achievable throughput. Moreover, a user group scheduling algorithm is proposed for downlink NOMA systems by which a user group is to be dynamically selected for transmission while satisfying long term temporal fairness among the individual contending users. The effectiveness of the proposed power allocation method along with the temporal fair scheduling algorithm for downlink NOMA is validated with simulations and the performance impact of the transmit power and the coverage radius of the base station as well as the number of users are thoroughly studied.
Open Access
Power control games between anchor and jammer nodes in wireless localization networks
(Institute of Electrical and Electronics Engineers, 2018) Sezer, Ahmet Dündar; Gezici, Sinan
In this paper, a game theoretic framework is proposed for wireless localization networks that operate in the presence of jammer nodes. In particular, power control games between anchor and jammer nodes are designed for a wireless localization network in which each target node estimates its position based on received signals from anchor nodes while jammer nodes aim to reduce localization performance of target nodes. Two different games are formulated for the considered wireless localization network: In the first game, the average Cramér-Rao lower bound (CRLB) of the target nodes is considered as the performance metric, and it is shown that at least one pure strategy Nash equilibrium exists in the power control game. Also, a method is presented to identify the pure strategy Nash equilibrium, and a sufficient condition is obtained to resolve the uniqueness of the pure Nash equilibrium. In the second game, the worst-case CRLBs for the anchor and jammer nodes are considered, and it is shown that the game admits at least one pure Nash equilibrium. Numerical examples are presented to corroborate the theoretical results.
Open Access
Random spreading for unsourced MAC with power diversity
(IEEE, 2021-10-11) Ahmadi, Mohammad Javad; Duman, Tolga M.
We propose an improvement of the random spreading approach with polar codes for unsourced multiple access, for which each user first encodes its message by a polar code, and then the coded bits are spread using a random spreading sequence. The proposed approach divides the active users into different groups, and employs different power levels for each group in such a way that the average power constraint is satisfied. We formulate and solve an optimization problem to determine the number of groups, and the corresponding user numbers and power levels. Extensive simulations show that the proposed approach outperforms the existing methods, especially when the number of active users is large.