| 1. |
- Haghighi, Kasra, 1978, et al.
(author)
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An LLR-based Cognitive Transmission Strategy for Higher Spectrum Reutilization
- 2011
-
In: IEEE GLOBECOM 2011 - Cognitive Radio and Networks Symposium. - 9781424492688
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Conference paper (peer-reviewed)abstract
- Reutilization of the spectrum licensed to services with low occupancy is of great interest for cognitive radios (CRs). To achieve this goal, we introduce a simple hidden Markov model which captures the primary users activity, signal uncertainties, and noise. For evaluating the performance of any CR, two new criteria are presented entitled spectrum utilization ratio (UR) and interference ratio (IR). Based on this model and new measures, a new a-posterior log-likelihood-ratio based CR is designed and implemented. Its performance is compared with standard energy-detection based spectrum-sensing CR. We demonstrate more than 300% increase in UR for up to 1% allowed interference at the SNR of -5dB.
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| 2. |
- Haghighi, Kasra, 1978, et al.
(author)
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On Optimum Causal Cognitive Spectrum Reutilization Strategy
- 2012
-
In: IEEE Journal on Selected Areas in Communications. - 0733-8716 .- 1558-0008. ; 30:10, s. 1911-1921
-
Journal article (peer-reviewed)abstract
- In this paper we study opportunistic transmission strategies for cognitive radios (CR) in which causal noisy observation from a primary user(s) (PU) state is available. PU is assumed to be operating in a slotted manner, according to a two-state Markov model. The objective is to maximize utilization ratio (UR), i.e., relative number of the PU-idle slots that are used by CR, subject to interference ratio (IR), i.e., relative number of the PU-active slots that are used by CR, below a certain level. We introduce an a-posteriori LLR-based cognitive transmission strategy and show that this strategy is optimum in the sense of maximizing UR given a certain maximum allowed IR. Two methods for calculating threshold for this strategy in practical situations are presented. One of them performs well in higher SNRs but might have too large IR at low SNRs and low PU activity levels, and the other is proven to never violate the allowed IR at the price of a reduced UR. In addition, an upper-bound for the UR of any CR strategy operating in the presence of Markovian PU is presented. Simulation results have shown a more than 116% improvement in UR at SNR of -3dB and IR level of 10% with PU state estimation. Thus, this opportunistic CR mechanism possesses a high potential in practical scenarios in which there exists no information about true states of PU.
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| 3. |
- Haghighi, Kasra, 1978, et al.
(author)
-
Sensing or Transmission: Causal Cognitive Radio Strategies with Censorship
- 2014
-
In: IEEE Transactions on Wireless Communications. - 1558-2248 .- 1536-1276. ; 13:6, s. 3031-3041
-
Journal article (peer-reviewed)abstract
- This paper introduces a novel opportunistic transmission strategy for cognitive radios (CRs). The primary user (PU) is assumed to transmit in a time-slotted manner according to a two-state Markov model, and the CR is either sensing, that is, obtaining a causal, noisy observation of a primary user (PU) state, or transmitting, but not both at the same time. In other words, the CR observations of the PU are censored whenever the CR is transmitting. The objective of the CR transmission strategy is to maximize the utilization ratio (UR), i.e., the relative number of the PU-idle slots that are used by the CR, subject to that the interference ratio (IR), i.e., the relative number of the PU-active slots that are used by the CR, is below a certain level. We introduce an a-posteriori LLR-based CR transmission strategy, called CLAPP, and evaluate this strategy in terms of the achievable UR for different PU model parameters and received signal-to-noise ratios (SNRs). The performance of CLAPP is compared with a simple censored energy detection scheme. Simulation results show that CLAPP has 52% gain in UR over the best censored energy detection scheme for a maximum IR level of 10% and an SNR of -2dB. © 2002-2012 IEEE.
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| 4. |
- Aydin, Osman, et al.
(author)
-
EU FP7 INFSO-ICT-317669 METIS, D4.2 Final report on trade-off investigations
- 2014
-
Reports (other academic/artistic)abstract
- Research activities in METIS WP4 include several aspects related to the network-level of future wireless communication networks. Thereby, a large variety of scenarios is considered and solutions are proposed to serve the needs envisioned for the year 2020 and beyond. This document provides vital findings about several trade-offs that need to be leveraged when designing future network-level solutions. In more detail, it elaborates on the following trade-offs:• Complexity vs. Performance improvement• Centralized vs. Decentralized• Long time-scale vs. Short time-scale• Information Interflow vs. Throughput/Mobility enhancement• Energy Efficiency vs. Network Coverage and CapacityOutlining the advantages and disadvantages in each trade-off, this document serves as a guideline for the application of different network-level solutions in different situations and therefore greatly assists in the design of future communication network architectures.
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| 5. |
- Beygi, Sajjad, et al.
(author)
-
Geometry-Based Stochastic Modeling and Estimation of Vehicle to Vehicle Channels
- 2014
-
In: ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings. - 1520-6149. - 9781479928927 ; , s. 4289-4293
-
Conference paper (peer-reviewed)abstract
- In this paper, a geometry-based stochastic channel model (GSCM) for vehicle-to-vehicle (V2V) wireless communica- tion is developed. The channel model reveals that the channel representation in delay-Doppler domain can be divided into four regions. In each region, the V2V channel can be modeled using a hybrid sparse/diffuse (HSD) model. Prior art on hybrid channel estimation for linear time-invariant channels is extended to the time-varying case. Furthermore, the effects of pulse shape leakage are explicitly determined and compensated. Simulation results shows that exploiting the V2V channel properties in the delay-Doppler domain, yields significantly improved channel estimates over unstructured approaches (more than 10 dB gain in SNR).
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| 6. |
- Beygi, Sajjad, et al.
(author)
-
Structured Sparse Approximation via Generalized Regularizers: With Application to V2V Channel Estimation
- 2014
-
In: Proceedings - IEEE Global Communications Conference, GLOBECOM. - 2334-0983 .- 2576-6813. - 9781479935116 ; , s. 3013-3018
-
Conference paper (peer-reviewed)abstract
- In this paper, we consider the estimation of a signal that has both group- and element-wise sparsity (joint sparsity); motivated by channel estimation in vehicle-to-vehicle channels. A general approach for the design of separable regularizing functions is proposed to adaptively induce sparsity in the estimation. A joint sparse signal estimation problem is formulated via these regularizers and its optimal solution is computed based on proximity operations. Our optimization results are quite general and they can be applied in the context of hierarchical sparsity models as well. The proposed recovery algorithm is a nested iterative method based on the alternating direction method of multipliers (ADMM). Due to regularizer separability, key operations can be performed in parallel. V2V channels are estimated by exploiting the joint sparsity (group/element-wise) exhibited in the delay-Doppler domain. Simulation results reveal that the proposed method can achieve as much as a 10 dB gain over previously examined methods.
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| 7. |
- Christoph, Mecklenbräuker, et al.
(author)
-
Vehicle-to-Vehicle Communications
- 2012
-
In: Pervasive Mobile and Ambient Wireless Communications, Roberto Verdone and Alberto Zanella, editors. Springer. - London : Springer London. - 9781447123149 ; , s. 577-608
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Book chapter (other academic/artistic)
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| 8. |
- Condo Neira, Edith, 1979, et al.
(author)
-
Evaluation of V2X Antenna Performance Using a Multipath Simulation Tool
- 2014
-
In: Antennas and Propagation (EuCAP), Proceedings of the 8th European Conference, The Hague, The Netherlands, Apr. 2014. - 9788890701849 ; , s. 2534-+, s. 2534-2538
-
Conference paper (peer-reviewed)abstract
- Antennas are one of the key components for efficient and reliable vehicular communications systems; especially for safety related applications the antenna performance is crucial. It is therefore important to be able to evaluate the antenna performance under realistic conditions so that the best antenna solution can be selected. In this paper we present a statistical method for evaluating the antenna performance by using the antennas radiation patterns and a multipath simulation tool. The multipath environment is generated by a number of incident waves with a specific angle of arrival distribution, defined by the user. In order to generate voltage samples at the antenna ports many sets of incident waves are generated. This simulates a changing environment as, e.g., when the vehicle is moving. By studying the cumulative distribution functions (CDFs) for the voltage samples we are able to compare the performance for different antenna types, positions on the vehicle, etc. The method is fast and effective and, when applied to typical vehicular propagation environments, the importance of having antennas with radiation patterns capable of covering the whole azimuth plane is demonstrated.
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| 9. |
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| 10. |
- Devassy, Rahul, 1985, et al.
(author)
-
Finite-blocklength analysis of the ARQ-protocol throughput over the Gaussian collision channel
- 2014
-
In: 6th International Symposium on Communications, Control and Signal Processing 2014. - 9781479928903 ; , s. 173-177
-
Conference paper (peer-reviewed)abstract
- We present a finite-blocklength analysis of the throughput and the average delay achievable in a wireless system where i) several uncoordinated users transmit short coded packets, ii) interference is treated as noise, and iii) 1-bit feedback from the intended receivers enables the use of a simple automatic repeat request (ARQ) protocol. Our analysis exploits the recent results on the characterization of the maximum coding rate at finite blocklength and finite block-error probability by Polyanskiy, Poor, and Verdu ́ (2010), and by Yang et al. (2013). For a given number of information bits, we determine the coded-packet size that maximize the per-user throughput and minimize the average delay. Our numerical results indicate that, when optimal codes are used, very short coded packets (of length between 50 to 100 channel uses) yield significantly lower average delay at an almost negligible throughput loss, compared to longer coded packets.
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| 11. |
- Duran, Mauricio A. Caceres, et al.
(author)
-
Terrestrial Network-Based Positioning and Navigation
- 2012
-
In: Satellite and Terrestrial Radio Positioning Techniques, Davide Dardari, Emanuela Falletti, and Marco Luise, editors. Oxford, Academic Press. - 9780123820846 ; , s. 75-153
-
Book chapter (other academic/artistic)
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| 12. |
- Fröhle, Markus, 1984, et al.
(author)
-
Multi-Step Sensor Selection with Position Uncertainty Constraints
- 2014
-
In: IEEE Globecom 2014 Workshop - Wireless Networking and Control for Unmanned Autonomous Vehicles. - 9781479974702 ; , s. 1439-1444
-
Conference paper (peer-reviewed)abstract
- Research on localization systems has shifted from focusing mainly on accuracy towards a more cognitive design, accounting for communication constraints, energy limitations, and delay. This leads to a variety of sensor selection optimization problems that are solved using techniques from convex optimization. We provide a novel formulation of the sensor selectionproblem over an extended time horizon, aiming to minimize the sensing cost of an entire path while guaranteeing a certain position accuracy. We state algorithms for determining lower and upper bounds on the sensing cost and utilize these in a path selection problem for autonomous agents. Simulation results confirm the usefulness of our approach, where we observe a benefit of optimizing over longer time horizons in low to medium noise scenarios compared to a myopic sensor selection scheme.
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| 13. |
- Gaugel, Tristan, et al.
(author)
-
In-depth Analysis and Evaluation of Self-Organizing TDMA
- 2013
-
In: IEEE Vehicular Networking Conference, VNC. - 2157-9865 .- 2157-9857. ; , s. 79-86
-
Conference paper (peer-reviewed)abstract
- Recent studies suggest that Self-organizing Time- Division Multiple Access (STDMA) might be a better medium access strategy in inter-vehicle communication networks than Carrier Sense Multiple Access (CSMA), especially when con- sidering safety focused applications. Although it is necessary to completely understand a protocol and the effect of its ‘turning knobs’ on performance before adoption, STDMA has not yet been subjected to such rigorous treatment in the literature. In order to address this shortcoming we perform and present an in-depth analysis and evaluation of STDMA’s fundamental principles. In particular, we contribute a detailed and complete description of the STDMA protocol, followed by the analysis and evaluation of two key questions: How can packet collisions occur in STDMA and whether packet collisions are ‘contagious’. We further perform a fair comparison with CSMA on the basis of which we provide recommendations on the configuration of STDMA. Our results show that STDMA coordinates multiple access effectively – even in highly congested situations – as long as all transmitted packets are decoded successfully. When non-decodable (but still carrier-sensible) transmissions are present, STDMA effectiveness drops below that achieved by CSMA due to the lack of control information. To ensure reproducibility and encourage further inquiry we release the STDMA implementation used in this paper to the wireless networks research community.
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| 14. |
- Gaugel, Tristan, et al.
(author)
-
Understanding differences in MAC performance
- 2014
-
In: IEEE WoWMoM Workshop on Smart Vehicles: Connectivity Technologies and ITS Applications. ; , s. Art. no. 6918995-
-
Conference paper (peer-reviewed)abstract
- The suitability and performance of medium access protocols in vehicular environments is already being investigated over a long period of time. Carrier Sense Multiple Access (CSMA) has been shown to perform sufficiently well in most situations and being able to support safety and efficiency vehicular applications. Recently, Self-organizing Time-Division Multiple Access (STDMA) is being considered as an alternative and has been shown to coordinate the channel slightly better under certain situations. However, when comparing both protocols the precise details of radio and network conditions and parametrization of the protocols are decisive on which protocol takes a slight lead. Consequently, scenarios can be constructed quite easily in which one protocol is superior over the other one. The focus of this work is thus not to absolutely compare both protocols, but rather to understand the strengths and weaknesses of both protocols in certain situations. In particular, we consider i) to which degree hidden nodes influence the coordination ability, ii) how an extended carrier sensing range is beneficial and iii) how temporary fading influences the performance of both MAC protocols. Our results show that while an extended carrier sensing range is only beneficial for CSMA, the existence and severity of fading is far less detrimental for STDMA than for CSMA.
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| 15. |
- Gholami, Mohammad Reza, 1976, et al.
(author)
-
A Concave-Convex Procedure for TDOA Based Positioning
- 2013
-
In: IEEE Communications Letters. - 1558-2558 .- 1089-7798. ; To appear:4, s. 765-768
-
Journal article (peer-reviewed)abstract
- This letter investigates the time-difference- of-arrival based positioning problem in wireless sensor networks. We consider the least-mean absolute, i.e., the l1 norm, minimization of the residual errors and formulate the positioning problem as a difference of convex function (DC) programming. We then employ a concave-convex procedure to solve the corresponding DC programming. Simulation results illustrate the improved performance of the proposed approach compared to existing methods.
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| 16. |
- Gholami, Mohammad Reza, 1976, et al.
(author)
-
A distributed positioning algorithm for cooperative active and passive sensors
- 2010
-
In: in Proc. 21st Annual IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC 2010). - 9781424480166 ; , s. 1711-1716
-
Conference paper (peer-reviewed)abstract
- The problem of positioning of an unknown targetin cooperative active and passive wireless sensor network isaddressed. Two-way time of arrival and time difference of arrivalmeasurements in active and passive nodes are used to estimate theposition of the target. A maximum likelihood estimator (MLE)can be employed to solve the problem. Due to nonlinear nature ofthe cost function in the MLE, the iterative search might convergeto local minima resulting in large error of estimation. To avoidthe MLE drawback, we formulate the problem of positioning asthe intersection of some convex sets. To nd the position estimate,we apply projection onto convex sets approach which is robustand can be implemented in a distributed manner. Simulationsare performed to compare the performance of the MLE andnew method.
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| 17. |
- Gholami, Mohammad Reza, 1976, et al.
(author)
-
Cooperative Wireless Sensor Network Positioning via Implicit Convex Feasibility
- 2013
-
In: IEEE Transactions on Signal Processing. - 1941-0476 .- 1053-587X. ; 61:23, s. 5830-5840
-
Journal article (peer-reviewed)abstract
- We propose a distributed positioning algorithm to estimate the unknown positions of a number of target nodes, given distance measurements between target nodes and between target nodes and number of reference nodes at known positions. Based on a geometric interpretation, we formulate the positioning problem as an implicit convex feasibility problem in which some of the sets depend on the unknown target positions, and apply a parallel projection onto convex sets approach to estimate the unknown target node positions. The proposed technique is suitable for parallel implementation in which every target node in parallel can update its position and share the estimate of its location with other targets. We mathematically prove convergence of the proposed algorithm. Simulation results reveal enhanced performance for the proposed approach compared to available techniques based on projections, especially for sparse networks.
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| 18. |
- Gholami, Mohammad Reza, 1976, et al.
(author)
-
Diffusion Estimation over Cooperative Networks with Missing Data
- 2013
-
In: IEEE Global SIP 2013. - 9781479902484 ; , s. 411-414
-
Conference paper (peer-reviewed)abstract
- In many fields, and especially in the medical and social sciences and in various recommender systems, data are often gathered through clinical studies or targeted surveys. Participants are generally reluctant to respond to all questions in a survey or they may lack information to respond adequately to the questions. The data collected from these studies tend to lead to linear regression models where the regression vectors are only known partially: some of their entries are either missing completely or replaced randomly by noisy values. There are also situations where it is not known beforehand which entries are missing or censored. There have been many useful studies in the literature on techniques to perform estimation and inference with missing data. In this work, we examine how a connected network of agents, with each one of them subjected to a stream of data with incomplete regression information, can cooperate with each other through local interactions to estimate the underlying model parameters in the presence of missing data. We explain how to modify traditional distributed strategies through regularization in order to eliminate the bias introduced by the incomplete model. We also examine the stability and performance of theresulting diffusion strategy and provide simulations in support of the findings. We consider two applications: one dealing with a mental health survey and the other dealing with a household consumption survey.
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| 19. |
- Gholami, Mohammad Reza, 1976, et al.
(author)
-
Distributed Bounding of Feasible Sets in Cooperative Wireless Network Positioning
- 2013
-
In: IEEE Communications Letters. - 1558-2558 .- 1089-7798. ; 17:8, s. 1596-1599
-
Journal article (peer-reviewed)abstract
- Locations of target nodes in cooperative wireless sensor networks can be confined to a number of feasible sets in certain situations, e.g., when the estimated distances between sensors are larger than the actual distances.Quantifying feasible sets is often challenging in cooperative positioning. In this letter, we propose an iterative technique to cooperatively outer approximate the feasible sets containing the locations of the target nodes. We first outer approximate a feasible set including a target node location by an ellipsoid. Then, we extend the ellipsoid with the measured distances between sensor nodes and obtain larger ellipsoids. The larger ellipsoids are used to determine the intersections containing other targets. Simulation results show that the proposed technique converges after a small number of iterations.
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| 20. |
- Gholami, Mohammad Reza, 1976, et al.
(author)
-
Hybrid TW-TOA/TDOA Positioning Algorithms for Cooperative Wireless Networks
- 2011
-
In: IEEE International Conference on Communications. - : IEEE. - 1550-3607. - 9781612842332
-
Conference paper (peer-reviewed)abstract
- The problem of positioning an unknown target is studied for a cooperative wireless sensor network using hybrid two-way time-of-arrival and time-difference-of-arrival measurements. A maximum likelihood estimator (MLE) can be employed to solve the problem. Due to the non-linear nature of the cost function in the MLE, a numerical method, e.g., an iterative search algorithm with a good initial point, should be taken to accurately estimate the target. To avoid drawbacks in a numerical method, we insteadlinearize the measurements and obtain a new two-step estimator that has a closed-form solution in each step.Simulation results confirm that the proposed linear estimator can attain Cram\'er-Rao lower bound for sufficiently high SNR.
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| 21. |
- Gholami, Mohammad Reza, 1976, et al.
(author)
-
Improved Position Estimation Using Hybrid TW-TOA and TDOA in Cooperative Networks
- 2012
-
In: IEEE Transactions on Signal Processing. - 1941-0476 .- 1053-587X. ; 60:7, s. 3770-3785
-
Journal article (peer-reviewed)abstract
- This paper addresses the problem of positioning multiple target nodes in a cooperative wireless sensor network in the presence of unknown turn-around times. In this type of cooperative networks, two different reference sensors, namely, primary and secondary nodes, measure two-way time-of-arrival (TW-TOA) and time-difference-of-arrival (TDOA), respectively. Motivated by the role of secondary nodes, we extend the role of target nodes such that they can be considered as pseudo secondary nodes. By modeling turn-around times as nuisance parameters, we derive a maximum likelihood estimator (MLE) that poses a difficult global optimization problem due to its nonconvex objective function. To avoid drawbacks in solving the MLE, we linearize the measurements using two different techniques, namely, nonlinear processing and first-order Taylor series, and obtain linear models based on unknown parameters. The proposed linear estimator is implemented in three steps. In the first step, a coarse position estimate is obtained for each target node, and it is refined through steps two and three. To evaluate the performance of different methods, we derive the Cramer-Rao lower bound (CRLB). Simulation results show that the cooperation technique provides considerable improvements in positioning accuracy compared to the noncooperative scenario, especially for low signal-to-noise-ratios.
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| 22. |
- Gholami, Mohammad Reza, 1976, et al.
(author)
-
Positioning Algorithms for Cooperative networks in the presence of an unknown Turn-around time
- 2011
-
In: The 12th IEEE International Workshop on Signal Processing Advances in Wireless Communications (SPAWC). - 9781424493326 ; , s. 166-170
-
Conference paper (peer-reviewed)abstract
- This paper addresses the problem of single node positioning in cooperative network using hybrid two-way time-of-arrival and time-difference-of-arrival where, the turn-around time at the target node is unknown. Considering the turn-around time as a nuisance parameter, the derived maximum likelihood estimator (MLE) brings a difficult global optimization problem due to local minima in the cost function of the MLE. To avoid drawbacks in solving the MLE, we obtain a linear two-step estimator using non-linear pre-processing which is algebraic and closed-form in each step. To compare different methods, Cramer-Rao lower bound (CRLB) is derived. Simulation results confirm that the proposed linear estimator attains the CRLB for sufficiently high signal-to-noise ratios.
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| 23. |
- Gholami, Mohammad Reza, 1976, et al.
(author)
-
Positioning of Node Using Plane Projection onto Convex Sets
- 2010
-
In: IEEE Wireless Communications and Networking Conference, WCNC. - 1525-3511. - 9781424463985
-
Conference paper (peer-reviewed)abstract
- We deal with positioning of node in wireless sensornetwork (WSN) using received signal strength (RSS) when thereis no priori knowledge about path-loss exponent and transmissionpower. Since the RSS decreases on the average with distance, itcarries some information about the distance to an unknown node.By ordering the RSS's, we conclude that there are some convexsets where the position of the unknown node can be found inthe intersection of them. We introduce a plane projection ontoconvex sets (PPOCS) approach to solve the positioning problem.Simulation results show good performance for the new methodscompared to other reduced complexity algorithms.
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| 24. |
- Gholami, Mohammad Reza, 1976, et al.
(author)
-
Range Based Sensor Node Localization in the Presence of Unknown Clock Skews
- 2013
-
In: ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings. - 1520-6149. - 9781479903566 ; , s. 4046-4050
-
Conference paper (peer-reviewed)abstract
- We deal with the positioning problem based on two-way time-ofarrival (TW-TOA) measurements in asynchronous wireless sensor networks. The optimal estimator for this problem poses a difficult global optimization problem. To avoid the drawbacks in solving the optimal estimator, we use approximations and derive linear models,which facilitate efficient solutions. In particular, we employ the least squares method and solve a general trust region subproblem to find a coarse estimate. To further refine the estimate, we linearize the measurementsand obtain a linear model which can be solved using regularized least squares. Simulation results illustrate that the proposed approaches asymptotically attain the Cram´er-Rao lower bound.
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| 25. |
- Gholami, Mohammad Reza, 1976, et al.
(author)
-
Robust Distributed Positioning Algorithms for Cooperative Networks
- 2011
-
In: The 12th IEEE International Workshop on Signal Processing Advances in Wireless Communications (SPAWC). - 9781424493326 ; , s. 156 - 160
-
Conference paper (peer-reviewed)abstract
- The problem of positioning targets based on distance estimates is studied for cooperative wireless sensor networks when there is limited a priori information about measurements noise. To solve this problem, two different methods of positioning are considered: statistical and geometrical. Based on a geometric interpretation, we show that the positioning problem can be rendered as finding the intersection of a number of convex sets. To find this intersection, we propose two different methods based on projection onto convex sets and outer-approximation. In the statistical approach, a partly novel two-step linear estimator is proposed which can be expressed in a closed-form solution. We also propose a new constrained non-linear least squares algorithm based on constraints derived in the outer-approximation approach. Simulation results show that the geometrical methods are more robust against non-line-of-sight measurements than the statistical approaches while in dense networks with line-of-sight measurements statistical approaches outperform geometrical methods.
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