Browsing by Subject "Telecommunication systems"

Now showing 1 - 15 of 15

Open Access
Blind phase noise estimation in OFDM systems by sequential Monte Carlo method
(Springer, 2006) Panayırcı, Erdal; Çırpan, H. A.; Moeneclaey, M.; Noels, N.
In this paper, based on a sequential Monte Carlo method, a computationally efficient algorithm is presented for estimating the residual phase noise, blindly, generated at the output the phase tracking loop employed in OFDM systems. The basic idea is to treat the transmitted symbols as "missing data" and draw samples sequentially of them based on the observed signal samples up to time t. This way, the Bayesian estimates of the phase noise is obtained through these samples, sequentially drawn, together with their importance weights. The proposed receiver structure is seen to be ideally suited for high-speed parallel implementation using VLSI technology.
Open Access
Coded-reference ultra-wideband systems
(2008-09) Gezici, Sinan
Transmitted-reference (TR) and frequency-shifted reference (FSR) ultra-wideband (UWB) systems employ pairs of reference and data signals, which are shifted in the time and frequency domains, respectively, to facilitate low-to-medium data rate communications without the need for complex channel estimation and template signal generation. On the other hand, the recently proposed coded-reference (CR) UWB systems provide orthogonalization of the reference and data signals in the code domain, which has advantages in terms of performance and/or implementation complexity. In this paper, CR UWB systems are investigated. First, it is shown that a CR UWB system can be considered as a generalized non-coherent pulse-position modulated system. Then, an optimal receiver according to the Bayes decision rule is derived for CR UWB systems. In addition, the asymptotic optimality properties of the conventional CR UWB receivers are investigated. Finally, simulation results are presented to compare the performance of the optimal and conventional CR UWB receivers. ©2008 IEEE.
Open Access
Effect of number of burst assemblers on TCP performance in optical burst switching networks
(IEEE, 2006-10) Gürel, Güray; Karasan, Ezhan
Burst assembly mechanism is one of the fundamental factors that determine the performance of an optical burst switching (OBS) network. In this paper, we investigate the influence of number of burstifiers on TCP performance for an OBS network. An ns2-based OBS network simulator is developed for simulating the optical network. The goodput of TCP flows between an ingress and an egress nodes traveling through an optical network is studied for different values of the number of assembly buffers per destination. First, the losses resulting from the congestion in the core OBS network are modeled using a burst independent Bernoulli loss model. Then, a background burst traffic is generated to create contention at a core node in order to realize a burst dependent loss model. Simulation results show that for an OBS network employing timer-based assembly algorithm, TCP goodput increases as the number of burst assemblers is increased for both types of loss models. The improvement from one burstifier to moderate number of burst assemblers is significant (15-50% depending on the burst loss probability, processing delay and the TCP version), but the goodput difference between moderate number of buffers andperflow aggregation is relatively small, implying that a cost-effective OBS edge switch implementation should use moderate number of assembly buffers per destination for enhanced TCP performance. © 2006 IEEE.
Open Access
Exact calculation of blocking probabilities for bufferless optical burst switched links with partial wavelength conversion
(IEEE, 2004-10) Akar, Nail; Karasan, Ezhan
In this paper, we study the blocking probabilities in a wavelength division multiplexing-based asynchronous bufferless optical burst switch equipped with a bank of tuneable wavelength converters that is shared per output link. The size of this bank is generally chosen to be less than the number of wavelengths on the link because of the relatively high cost of wavelength converters using current technologies; this case is referred to as partial wavelength conversion in the literature. We present a probabilistic framework for exactly calculating the blocking probabilities. Burst durations are assumed to be exponentially distributed. Burst arrivals are first assumed to be Poisson and later generalized to the more general phase-type distribution. Unlike existing literature based on approximations and/or simulations, we formulate the problem as one of finding the steadystate solution of a continuous-time Markov chain with a block tridiagonal infinitesimal generator. We propose a numerically efficient and stable solution technique based on block tridiagonal LU factorizations. We show that blocking probabilities can exactly and efficiently be found even for very large systems and rare blocking probabilities. Based on the results of this solution technique, we also show how this analysis can be used for provisioning wavelength channels and converters. © 2004 IEEE.
Open Access
Heterogeneous network-on-chip design through evolutionary computing
(Taylor & Francis, 2010) Ozturk, O.; Demirbas, D.
This article explores the use of biologically inspired evolutionary computational techniques for designing and optimising heterogeneous network-on-chip (NoC) architectures, where the nodes of the NoC-based chip multiprocessor exhibit different properties such as performance, energy, temperature, area and communication bandwidth. Focusing primarily on array-dominated applications and heterogeneous execution environments, the proposed approach tries to optimise the distribution of the nodes for a given NoC area under the constraints present in the environment. This article is the first one, to our knowledge, that explores the possibility of employing evolutionary computational techniques for optimally placing the heterogeneous nodes in an NoC. We also compare our approach with an optimal integer linear programming (ILP) approach using a commercial ILP tool. The results collected so far are very encouraging and indicate that the proposed approach generates close results to the ILP-based approach with minimal execution latencies. © 2010 Taylor & Francis.
Open Access
Model-free adaptive hysteresis for dynamic bandwidth reservation
(IEEE, 2007-10) Akar, Nail
Dynamic bandwidth reservation refers to the process of dynamically updating the bandwidth allocation to a connection between two network end points on the basis of actual aggregate traffic demand of the connection. We assume a scenario in which bandwidth updates for the connection should not be performed too frequently and the frequency of updates are thus limited to a so-called desired update rate. We propose an asynchronous model-free adaptive hysteresis algorithm for dynamic bandwidth reservations with such update frequency constraints. We validate the effectiveness of the proposed approach by comparing its bandwidth efficiency with that of a synchronous model-based dynamic bandwidth reservation mechanism from the existing literature.
Open Access
Multi-resampling Doppler compensation in cooperative underwater OFDM systems
(IEEE, 2013) Karakaya, B.; Hasna, M.O.; Duman, Tolga M.; Uysal, M.; Ghrayeb, A.
We consider a multi-carrier cooperative underwater acoustic communication (UWAC) system and investigate the Doppler scaling problem arising due to the motion of different nodes. Specifically, we assume an orthogonal frequency division multiplexing (OFDM) system with amplify and forward (AF) relaying. Our channel model is built on large-scale path loss along with the short-term frequency-selective fading. For Doppler scaling compensation, we use multi-resampling (MR) receiver designs both at the relay and destination nodes. We present an extensive Monte Carlo simulation study to evaluate the error rate performance of the proposed UWAC system. In simulations, we use the publicly available VirTEX software in conjunction with the ray-tracing based BELLHOP software to precisely reflect the characteristics of an underwater geographical location and the movement of the nodes. © 2013 IEEE.
Open Access
The network design problem with relays
(Elsevier, 2007) Cabral, E. A.; Erkut, E.; Laporte, G.; Patterson, R. A.
The network design problem with relays (NDPR) is defined on an undirected graph G = (V, E, K), where V = {1, ..., n} is a vertex set, E = {(i, j) : i, j ∈ V, i < j} is an edge set. The set K = {(o(k), d(k))} is a set of communication pairs (or commodities): o(k) ∈ V and d(k) ∈ V denote the origin and the destination of the kth commodity, respectively. With each edge (i, j) are associated a cost cij and a length dij. With vertex i is associated a fixed cost fi of locating a relay at i. The NDPR consists of selecting a subset over(E, -) of edges of E and of locating relays at a subset over(V, -) of vertices of V in such a way that: (1) the sum Q of edge costs and relay costs is minimized; (2) there exists a path linking the origin and the destination of each commodity in which the length between the origin and the first relay, the last relay and the destination, or any two consecutive relays does not exceed a preset upper bound λ. This article develops a lower bound procedure and four heuristics for the NPDR. These are compared on several randomly generated instances with |V| ≤ 1002 and |E| ≤ 1930.
Open Access
Performance analysis of turbo codes over Rician fading channels with impulsive noise
(IEEE, 2007) Ali, Syed Amjad; Ince, E.A.
The statistical characteristics of impulsive noise differ greatly from those of Gaussian noise. Hence, the performance of conventional decoders, optimized for additive white Gaussian noise (AWGN) channels is not promising in non-Gaussian environments. In order to achieve improved performance in impulsive environments the decoder structure needs to be modified in accordance with the impulsive noise model. This paper provides performance analysis of turbo codes over fully interleaved Rician fading channels with Middleton's additive white Class-A impulsive noise (MAWCAIN). Simulation results for the memoryless Rician fading channels using coherent BPSK signaling for both the cases of ideal channel state information (ICSI) and no channel state information (NCSI) at the decoder are provided. An eight state turbo encoder having (1, 13/15, 13/15) generator polynomial is used throughout the analysis. The novelty of this work lies in the fact that this is an initial attempt to provide a detailed analysis of turbo codes over Rician fading channels with impulsive noise rather than AWGN. ©2007 IEEE.
Open Access
Synthetic TEC mapping with ordinary and universal kriging
(IEEE, 2007-06) Sayın, I.; Arıkan, F.; Arıkan, Orhan
Spatiotemporal variations in the ionosphere affects the HF and satellite communications and navigation systems. Total Electron Content (TEC) is an important parameter since it can be used to analyze the spatial and temporal variability of the ionosphere. In this study, the performance of the two widely used Kriging algorithms, namely Ordinary Kriging (OrK) and Universal Kriging (UnK), is compared over the synthetic data set. In order to represent various ionospheric states, such as quiet and disturbed days, spatially correlated residual synthetic TEC data with different variances is generated and added to trend functions. Synthetic data sampled with various type of sampling patterns and for a wide range of sampling point numbers. It is observed that for small sampling numbers and with higher variability, OrK gives smaller errors. As the sample number increases, UnK errors decrease faster. For smaller variances in the synthetic surfaces, UnK gives better results. For increasing variance and decreasing range values, usually, the errors increase for both OrK and UnK. © 2007 IEEE.
Open Access
Theoretical limits and a practical estimator for joint estimation of respiration and heartbeat rates using UWB impulse radio
(IEEE, 2007) Gezici, Sinan; Arıkan, Orhan
In this paper, Cramer-Rao lower bounds are derived fo r joint estimation of respiration and heartbeat rates via impulse radio ultra-wideband signals. Generic models are employed for displacement functions due to respiration and heartbeat, and the bounds are obtained for the cases of known and unknown channel coefficients. In addition, a two-step suboptimal estimator is proposed, which is based on joint time-delay estimation followed by a least-squares approach. It is shown that the proposed estimator is asymptotically optimal under mild conditions. Simulation studies are performed to evaluate the lower bounds and performance of the proposed estimator for realistic system parameters.
Open Access
Theoretical limits on time delay estimation for ultra-wideband cognitive radios
(IEEE, 2008-09) Gezici, Sinan; Celebi, H.; Arslan, H.; Poor, H. V.
In this paper, theoretical limits on time delay estimation are studied for ultra-wideband (UWB) cognitive radio systems. For a generic UWB spectrum with dispersed bands, the Cramer-Rao lower bound (CRLB) is derived for unknown channel coefficients and carrier-frequency offsets (CFOs). Then, the effects of unknown channel coefficients and CFOs are investigated for linearly and non-linearly modulated training signals by obtaining specific CRLB expressions. It is shown that for linear modulations with a constant envelope, the effects of the unknown parameters can be mitigated. Finally, numerical results, which support the theoretical analysis, are presented. © 2008 IEEE.
Open Access
Ultra-wideband orthogonal pulse shape set design by using Hermite-Gaussian functions
(IEEE, 2012) Alp, Yaşar Kemal; Dedeoǧlu, Mehmet; Arıkan, Orhan
Ultra-Wideband (UWB) communication systems have been developed for short distance, high data rate communications. To avoid interfering with the existing systems in the same environment, very short duration pulses used by these systems should satisfy a predefined spectral mask. Data rate of UWB systems can be increased by using multiple pulse shapes simultaneously. Orthogonality of the simultaneously used pulse shapes simplifies the receiver design. In this work, design of orthogonal pulse shapes which satisfy the spectral mask is modelled as an optimization problem. First, it is converted to a convex optimization problem by constraining the pulse shapes to lie in a subspace spanned by the Hermite-Gaussian (HG) functions. Then the optimal solution is obtained. It is shown that a larger pulse shape set can be designed compared to the existing approaches, and hence, a higher data rate can be achieved. © 2012 IEEE.
Open Access
Ultra-wideband range estimation: Theoretical limits and practical algorithms
(IEEE, 2008-09) Güvenç, İ.; Gezici, Sinan; Şahinoğlu, Z.
The high time resolution of ultra-wideband (UWB) signals enables wireless devices to perform accurate range estimation. In order to realize UWB systems with accurate ranging capabilities, both theoretical limits on range estimation and practical algorithms that approach those limits should be investigated. This paper provides a survey of various UWB ranging algorithms and discusses their performance and complexity tradeoffs. In addition, theoretical limits on range estimation are discussed in terms of Cramer-Rao and Ziv-Zakai lower bounds. Index Terms- Ultra-wideband (UWB), time-of-arrival (TOA) estimation, ranging, Cramer-Rao lower bound (CRLB), Ziv-Zakai lower bound (ZZLB). ©2008 IEEE.
Open Access
Wide area telecommunication network design: Application to the Alberta SuperNet
(2008) Cabral, E.A.; Erkut, E.; Laporte G.; Patterson, R.A.
This article proposes a solution methodology for the design of a wide area telecommunication network. This study is motivated by the Alberta SuperNet project, which provides broadband Internet access to 422 communities across Alberta. There are two components to this problem: the network design itself, consisting of selecting which links will be part of the solution and which nodes should house shelters; and the loading problem which consists of determining which signal transport technology should be installed on the selected edges of the network. Mathematical models are described for these two subproblems. A tabu search algorithm heuristic is developed and tested on randomly generated instances and on Alberta SuperNet data. © 2008 Operational Research Society Ltd. All rights reserved.