Browsing by Subject "Communication systems"

Now showing 1 - 13 of 13

Open Access
A communication scheme by using synchronized chaotic systems
(IEEE, 1996) Morgül, Ömer; Feki, Moez
A method to synchronize systems with chaotic behavior, in a master-slave configuration adapted to communication systems, is discussed. This work is motivated by the need for secure communication. In this method, the synchronization and message transmission phases are separated, and while the synchronization is achieved in the synchronization phases, the message is only sent in the message transmission phases.
Open Access
Detection of microcalcifications in mammograms using nonlinear subband decomposition and outlier labeling
(SPIE, 1997-02) Gürcan, M. Nafi; Yardımcı, Yasemin C.; Çetin, A. Enis; Ansari, R.
Computer-aided diagnosis will be an important feature of the next generation picture archiving and communication systems. In this paper, computer-aided detection of microcalcifications in mammograms using a nonlinear subband decomposition and outlier labeling is examined. The mammogram image is first decomposed into subimages using a nonlinear subband decomposition filter bank. A suitably identified subimage is divided into overlapping square regions in which skewness and kurtosis as measures of the asymmetry and impulsiveness of the distribution are estimated. A region with high positive skewness and kurtosis is marked as a region of interest. Finally, an outlier labeling method is used to find the locations of microcalcifications in these regions. Simulation studies are presented.
Open Access
Dikgen frekans bölmeli çoklu erişim sistemlerinde telsiz erişim terminallerinin işbirliği
(IEEE, 2009-04) Tokel, Turgut Barış; Aktaş, Defne
Gelecek nesil kablosuz iletişim sistemlerinde öngörülen veri hızlarına ulaşabilmek için bu sistemlerde frekans yeniden kullanım oranının 1 olmasına ihtiyaç¸ vardır, bu ise özellikle hücre sınırlarındaki kullanıcıların önemli ölçüde hücreler arası girişime maruz kalmalarına neden olur. Telsiz erişim terminalleri arasında işbirliği hücreler arası girişimin azaltılmasında önemli bir rol oynamaktadır. Bu bildiride çok hücreli, çok girdili çok çıktılı, dikgen frekans bölmeli çoklu erişim sistemlerinde telsiz erişim terminallerinden kullanıcılara işbirlikli veri iletimi problemini ele alıyoruz. Telsiz erişim terminallerinin aralarında kısıtlı ileti paylaşımı ile çizelgeleme ve veri iletimi yaptıkları etkin bir işbirlikli algoritma öneriyoruz.
Open Access
Effects of additional independent noise in binary composite hypothesis-testing problems
(IEEE, 2009-09) Bayram, Suat; Gezici, Sinan
Performance of some suboptimal detectors can be improved by adding independent noise to their observations. In this paper, the effects of adding independent noise to observations of a detector are investigated for binary composite hypothesistesting problems in a generalized Neyman-Pearson framework. Sufficient conditions are derived to determine when performance of a detector can or cannot be improved via additional independent noise. Also, upper and lower limits are derived on the performance of a detector in the presence of additional noise, and statistical characterization of optimal additional noise is provided. In addition, two optimization techniques are proposed to calculate the optimal additional noise. Finally, simulation results are presented to investigate the theoretical results. © 2009 IEEE.
Open Access
Noise-enhanced M-ary hypothesis-testing in the minimax framework
(IEEE, 2009-09) Bayram, Suat; Gezici, Sinan
In this study, the effects of adding independent noise to observations of a suboptimal detector are studied for M-ary hypothesis-testing problems according to the minimax criterion. It is shown that the optimal additional noise can be represented by a randomization of at most M signal values under certain conditions. In addition, a convex relaxation approach is proposed to obtain an accurate approximation to the noise probability distribution in polynomial time. Furthermore, sufficient conditions are presented to determine when additional noise can or cannot improve the performance of a given detector. Finally, a numerical example is presented. © 2009 IEEE.
Open Access
Novel predistortion algorithm for OFDMA
(IEEE, 2009) Ali, S.; Markarian, G.; Arıkan, Erdal
The RF amplifier in a wireless communication system is usually non-linear in nature. If such an amplifier is used in OFDMA based systems, it will cause serious degradation. This degradation will be both in terms of the reduction in BER and the generation of out of band noise. In this paper we have worked on the linearization method of the amplifier. This work is on a hybrid methodology, in which estimation of the model is performed in frequency domain and compensation is performed in time domain. The downlink preamble of the IEEE802.16e system is used here for the estimation purpose. The results for the suppression of spectra are shown at the end.
Open Access
Optimal channel switching for average capacity maximization
(IEEE, 2014-05) Sezer, Ahmet Dündar; Gezici, Sinan; İnaltekin, H.
Optimal channel switching is proposed for average capacity maximization in the presence of average and peak power constraints. A necessary and sufficient condition is derived in order to determine when the proposed optimal channel switching approach can or cannot outperform the optimal single channel approach, which performs no channel switching. Also, it is stated that the optimal channel switching solution can be realized by channel switching between at most two different channels. In addition, a low-complexity optimization problem is derived in order to obtain the optimal channel switching solution. Numerical examples are provided to exemplify the derived theoretical results. © 2014 IEEE.
Open Access
An optimal network dimensioning and initial energy assignment minimizing the monetary cost of a heterogeneous WSN
(IEEE, 2009) Sevgi, Cüneyt; Kocyigit, A.
In this paper, a novel method is proposed to dimension a randomly deployed heterogeneous Wireless Sensor Network (WSN) of minimum monetary cost satisfying minimum coverage and minimum lifetime requirements. We consider WSNs consisting of two different types of nodes clusterheads and ordinary sensor nodes, randomly deployed over a sensing field. All devices are assumed to be stationary and have identical sensing capabilities. However, the clusterheads are more energetic and powerful in terms of processing and communication capabilities compared to sensor nodes. For such a network, finding minimum cost WSN problem is not a trivial one, since the distribution of the mixture of two different types of devices and the batteries with different initial energies in each type of device primarily determine the monetary cost of a WSN. Therefore, we formulated an optimization problem to minimize the monetary cost of a WSN for given coverage and lifetime requirements. The proposed optimization problem is solved for a certain scenario and the solution is validated by computer simulations. © 2009 IEEE.
Open Access
Power-source-aware backbone routing in wireless sensor networks
(IEEE, 2010-11) Tekkalmaz, Metin; Körpeoğlu, İbrahim
Due to the limited energy-source and mostly unattended nature of the wireless sensor networks, efficient use of energy has a critical importance on the lifetime of the applications accomplished by such networks. Although in most of the cases sensor nodes are battery-powered, there are application scenarios in which battery- and mains-powered nodes coexist. In this paper, we present an approach and algorithms based on this approach that increase the lifetime of wireless sensor networks in such heterogeneous deployment cases. In the proposed approach, a backbone, which is composed of mains-powered nodes, sink, and battery-powered nodes if required, is constructed to relay the data packets. Simulation results show that, the proposed approach is able to increase the network lifetime up to more than a factor of two, compared to the case in which battery- and mains-powered nodes are not distinguished.
Open Access
Pulse shape design using iterative projections
(IEEE, 2005-09) Güven, H. Emre; Çetin, A. Enis
In this paper, the pulse shape design for various communication systems including PAM, FSK, and PSK is considered. The pulse is designed by imposing constraints on the time and frequency domains constraints on the autocorrelation function of the pulse shape. Intersymbol interference, finite duration and spectral mask restrictions are a few examples leading to convex sets in L 2. The autocorrelation function of the pulse is obtained by performing iterative projections onto convex sets. After this step, the minimum phase or maximum phase pulse producing the autocorrelation function is obtained by cepstral deconvolution.
Open Access
Simulation of a digital communication system
(IEEE, 2005-09) Güngör, A.; Arıkan, F.; Arıkan, Orhan
In this paper, basic components of a digital communication system are simulated by a computer program. The simulation program is modular and flexible to incorporate any future additions and updates. The simulation program allows the user to choose from various channel models, transmitter and receiver antenna systems, modulation and channel coding techniques. A communication system is defined by various parameters including the source, coding, modulation, antenna systems. In order to facilitate the input of these parameters and follow the flow of the simulation, the Graphical User Interface (GUI) is designed for convenience to the user. The input parameters can both be entered from the GUI or from prepared user files. The major contribution of this simulation system to the existing communication simulators is the addition of flexible antenna systems both at the transmitting and receiving ends. With this simulation program, the antenna arrays can be located anywhere on Earth, on any platform and array elements can be placed on the platform by any desired orientation. The simulation program results are compared with both theoretical computations and commercial simulator results and excellent agreement is observed in both cases.
Open Access
Special Issue on Advances in Channel Coding
(Korean Institute of Communication Sciences, 2015) Arikan, E.; Lentmaier, M.; Montorsi, G.
Since the invention of turbo codes in 1993 there has been an enormous interest and progress in the field of capacity approaching code constructions. Many classical constructions have been replaced by newer, better performing codes with feasible decoding complexity. Most of these modern code constructions, such as turbo codes, Gallager's low-density parity-check (LDPC) codes and their generalizations, can be modeled by sparse graphical models. Spatial coupling of sparse graphical models has in the last years attracted a lot of interest due to the threshold saturation phenomenon, which leads to capacity achieving performance with iterative message passing decoding. Polar codes are a recently discovered class of capacity achieving codes that are formed by an explicit construction based on a phenomenon called channel polarization. These codes, too, have various low-complexity decoding algorithms based on message passing on a sparse graph that has a recursive structure similar to that of fast transforms in signal processing.
Open Access
Task assignment in heterogeneous computing systems
(Academic Press, 2006-01) Ucar, B.; Aykanat, Cevdet; Kaya, K.; Ikinci, M.
The problem of task assignment in heterogeneous computing systems has been studied for many years with many variations. We consider the version in which communicating tasks are to be assigned to heterogeneous processors with identical communication links to minimize the sum of the total execution and communication costs. Our contributions are three fold: a task clustering method which takes the execution times of the tasks into account; two metrics to determine the order in which tasks are assigned to the processors; a refinement heuristic which improves a given assignment. We use these three methods to obtain a family of task assignment algorithms including multilevel ones that apply clustering and refinement heuristics repeatedly. We have implemented eight existing algorithms to test the proposed methods. Our refinement algorithm improves the solutions of the existing algorithms by up to 15% and the proposed algorithms obtain better solutions than these refined solutions. © 2005 Elsevier Inc. All righs reserved.