Browsing by Subject "Positioning"

Now showing 1 - 15 of 15

Open Access
Autonomous navigation of robotic units in mobile sensor network
(2012) Nazlibilek, S.
This work is motivated by the problem of detecting buried anti-tank and anti-personnel mines in roads or some border regions. The problem is tried to be solved by use of small mobile robotic sensors and their some abilities such as measurement of local fields, navigation around a region, communications with each other, and constituting team within a mission area. The aim of this work is to investigate the navigation problem for the team behavior of mobile sensors within a potential field available in a small-scale environment such as an indoor area or an outdoor region. The mobile sensor network here is a collection of robotic units with sensing capability of earth magnetic field anomalies. A new kind of positioning system is needed for their collective behavior. In this work, a new method of navigation is proposed as a local positioning system. It utilizes ultrasound and radio frequency information to determine the coordinates of the points inside the operational area. The method proposed here is compared with the ultra wideband ranging ping-pong method that is used widely in recent applications. A time division multiple access method is used for the communications among the mobile sensors. The results on the positioning methods together with several simulations and experimental works are given. It is shown that the positioning method utilizing ultrasound-radio frequency method can give fairly good results. © 2012 Elsevier Ltd. All rights reserved.
Open Access
A case study : analysis of Alke Cilt Estetigi ve Sagligi AS with respect to cosmetic industry and the recommendation of new strategy development
(1996) Ertürk, Mehmet Can
The high profitability and the great potential in the cosmetic sector in Turkey is attracting many firms to this field. According to their scarce resources each firm tries to achieve a competitive position with respect to the others. They select their market segments and marketing strategies to achieve this. Alke Cilt Estetiği ve Sağlığı A.Ş. is a firm that uses party selling method in high price high quality end of the skin-care products of the sector. The company sells the products of Dr. Spiller and Aphrodie Esthétique brands, the latter being recently developed in its own trade name. Alke produces only a little amount of Dr. Spiller products under the trade name of Dr. Spiller. Alke would like to expand the Aphrodie Esthetique’s product lines and produce more of Dr. Spiller products. This thesis analyzes AJke Cilt Estetiği ve Sağlığı A.Ş. with respect to cosmetic industry, and recommends strategies that would increase its market share in skin-care products segment and improve the overall position of the company by entering other segments successfully
Open Access
Common ground and positioning in EFL classrooms : a comparison of native and non-native english-speaking teachers
(2017-05) Kuka, Seçil
This study aimed to investigate how native (NEST) and non-native English-speaking (NNEST) teachers find common ground with their students and the ways they position themselves while establishing common ground in their social interactions. The purpose of the study was to investigate NESTs’ and NNESTs’ ways of establishing common ground with their students and positioning through common ground in their social interactions in tertiary level language classrooms in an English as a Foreign Language setting. The researcher collected data through classroom observations. Three NEST and three NNEST teaching partners who teach the same classes in turn were observed and audio recorded during the first and fifth weeks of a new course. Data were transcribed and then analyzed using an analytical framework adapted from Kecskés and Zhang’s (2009) socio-cognitive perspective on common ground and Davies and Harré’s (1990) positioning theory through discourse analysis. The findings revealed several differences in terms of the ways NESTs and NNESTs established common ground and positioned themselves in their social interactions. More specifically, NESTs’ lack of shared background with their students led to more establishment of core common ground (i.e., building new common knowledge between themselves and their students), which also positioned them as outsiders in a foreign country while NNESTs maintained the already existing core common ground with their students (i.e., activating the common knowledge they shared with their students) by positioning themselves as insiders. Moreover, the real life purpose of NESTs’ common ground building acts through L2 made their teacher-student interactions good opportunities for the use of target language to the leaners’ benefit. NNESTs’ conversations involving the activation of their shared linguistic and cultural background, however, aimed to facilitate classroom instruction. These findings helped draw the conclusion that NESTs and NNESTs differed in relation to their social interactions involving common ground and positioning. NESTs created meaningful contexts that enabled opportunities for language socialization through which students not only practiced language but also negotiated meaning. On the other hand, NNESTs activated the common knowledge they shared with their students to facilitate classroom instruction. Considering the results above, this study contributed to the literature by providing insights into the differences and similarities NESTs and NNESTs have in terms of their language socialization.
Open Access
Common ground for positioning: a discourse analysis on second language socialization
(Hacettepe Universitesi, 2014) Ortaçtepe, Deniz
Applying Kecskes and Zhang's (2009) dynamic model of common ground in positioning theory (Davies & Harre, 1990), the present study aims to explore the second language (L2) socialization of Turkish students through the discursive processes as well as the skills they adopted in social interactions with the American speakers during a formal reception at an American university. The findings indicated that the Turkish students endorsed similar discursive processes not only to establish common ground as the American speakers', but also to position themselves in the speech context. This study highlights that engaging in real-life conversations with the target language speakers (Gumperz, 1996) encourages L2 learners/users (Cook, 1999) to embrace the discursive practices that are shared within a particular speech community. It also provides suggestions for future research embracing more longitudinal/ethnographic approahes to examine L2 socialization as well as teaching implications for instructional materials and contexts that reflect authentic social encounters.
Open Access
Comparative theoretical analysis of distance estimation in visible light positioning systems
(Institute of Electrical and Electronics Engineers Inc., 2016) Keskin, M. F.; Gezici, Sinan
In this paper, theoretical limits and estimators are studied for synchronous and asynchronous visible light positioning (VLP) systems. Specifically, the Cramér-Rao lower bounds (CRLBs) and maximum likelihood estimators are investigated for distance estimation based on time-of-arrival (TOA) and/or received signal strength (RSS) parameters. Hybrid TOA/RSS-based distance estimation is proposed for VLP systems, and its CRLB is compared analytically against the CRLBs of TOA-based and RSS-based distance estimation. In addition, to investigate the effects of sampling, asymptotic performance results are obtained under sampling rate limitations as the noise variance converges to zero. A modified hybrid TOA/RSS-based distance estimator is proposed to provide performance improvements in the presence of sampling rate limitations. Numerical examples are presented to illustrate the theoretical results. © 2015 IEEE.
Open Access
Consumer behavior analysis and marketing communications strategy development: the case of Tuborg
(1995) Deniz, Mehmet Ali
Efes Pilsen and Tuborg have enjoyed an oligopolistic market stiiicture m the Turkish Beer Industry for decades. This has caused the companies to adopt a sales and product orientation and exert little effort on marketing. However, the market conditions and competition have begun to change recently, by the recent introduction of a new brand, feasibility studies of world giants to enter the Turkish market, and the Customs Union which will decrease the customs tax on import beer. On the other hand, Efes Pilsen has entered into market development efforts in foreign markets. The above competitive moves in the industry by various actors have changed the long-prevailing competitive structure in the industry, especially for the disadvantage of Tuborg. Thus, in this thesis, it is argued that the study of the consumer behavior in the Turkish Beer Market, that has long been underestimated by the agents in the industry, is crucial for Tuborg to compete the changes in the market and find differentiation points that are significant in the eyes of the consumers. It is also discussed that the adoption of a consumer orientation, which takes the current needs and perceptions of the consumers into consideration, is crucial for the success of the communications strategy, which is a sustainable differentiation factor. Therefore, a marketing research has been conducted for the beer market (taking Ankara as a pilot region for application) in order to better understand the needs of the consumers, to find out significant differences as well as similarities among the consumers. Depending on the marketing research conducted, a communications strategy has been suggested for Tuborg . This strategy has been designed to serve to differentiate the brand in the market through communications and also to constitute an entry barrier against the new entrants. On the other hand, the necessary adaptations in the organizational structure of Tuborg to the suggested consumer orientation have also been discussed within the thesis.
Open Access
Cooperative localization in hybrid infrared/visible light networks: Theoretical limits and distributed algorithms
(Institute of Electrical and Electronics Engineers, 2019) Keskin, M. Furkan; Erdem, Osman; Gezici, Sinan
Light emitting diode (LED) based visible light positioning (VLP) networks can provide accurate location information in environments where the global positioning system (GPS) suffers from severe signal degradation and/or cannot achieve high precision, such as indoor scenarios. In this manuscript, we propose to employ cooperative localization for hybrid infrared/visible light networks that involve multiple LED transmitters having known locations (e.g., on the ceiling) and visible light communication (VLC) units equipped with both LEDs and photodetectors (PDs) for the purpose of cooperation. In the considered scenario, downlink transmissions from LEDs on the ceiling to VLC units occur via visible light signals, while the infrared spectrum is utilized for device-to-device communications among VLC units. First, we derive the Cramer-Rao lower bound (CRLB) and the maximum likelihood estimator (MLE) for the localization of VLC units in the proposed cooperative scenario. To tackle the nonconvex structure of the MLE, we adopt a set-theoretic approach by formulating the problem of cooperative localization as a quasiconvex feasibility problem, where the aim is to find a point inside the intersection of convex constraint sets constructed as the sublevel sets of quasiconvex functions resulting from the Lambertian formula. Next, we devise two feasibility-seeking algorithms based on iterative gradient projections to solve the feasibility problem. Both algorithms are amenable to distributed implementation, thereby avoiding high-complexity centralized approaches. Capitalizing on the concept of quasi-Fej\'er convergent sequences, we carry out a formal convergence analysis to prove that the proposed algorithms converge to a solution of the feasibility problem in the consistent case. Numerical examples illustrate the improvements in localization performance achieved via cooperation among VLC units and evidence the convergence of the proposed algorithms to true VLC unit locations in both the consistent and inconsistent cases. IEEE
Open Access
Distance and position estimation in visible light systems with RGB LEDs
(Elsevier, 2022-01-17) Demirel, I.; Gezici, Sinan
In this paper, distance and position estimation problems are investigated for visible light positioning (VLP) systems with red-green-blue (RGB) light emitting diodes (LEDs). The accuracy limits on distance and position estimation are calculated in terms of the Cramér-Rao lower bound (CRLB) for three different scenarios. Scenario 1 and Scenario 2 correspond to synchronous and asynchronous systems, respectively, with known channel attenuation formulas at the receiver. In Scenario 3, a synchronous system is considered but channel attenuation formulas are not known at the receiver. The derived CRLB expressions reveal the relations among distance/position estimation accuracies in the considered scenarios and lead to intuitive explanations for the benefits of using RGB LEDs. In addition, maximum likelihood (ML) estimators are derived in all scenarios, and it is shown that they can achieve close performance to the CRLBs in some cases for sufficiently high source optical powers. © 2022 Elsevier Inc.
Open Access
Effects of cooperation on visible light positioning
(IEEE, 2018) Erdem, Osman; Keskin, Musa Furkan; Gezici, Sinan
In this paper, cooperative localization is proposed for visible light systems. The effects of cooperation on the localization accuracy of visible light positioning systems are illustrated based on a Cramér-Rao lower bound expression. The obtained expression is generic for any three-dimensional configuration and covers all possible cooperation scenarios via definitions of connectivity sets. Numerical results are presented to investigate significance of cooperation in various scenarios.
Open Access
Fundamental limits on localization in single input multiple output visible light systems
(2017-09) Kökdoğan, Furkan
Visible light systems have recently been considered as an e ective and promising solution for indoor positioning. In this thesis, a theoretical accuracy analysis is conducted for position estimation in visible light systems based on received signal strength (RSS) measurements. Considering a single light emitting diode (LED) at the transmitter and multiple photo-detectors (PDs) at the receiver, the Cram er-Rao lower bound (CRLB) is derived for both a generic three-dimensional scenario and speci c con gurations of the PDs at the receiver. For the special case in which the height of the receiver is known, a compact expression is derived for the CRLB, considering a uniform circular layout and the same elevation angle for all the PDs. Asymptotic analysis and accuracy of derived compact expression is investigated for this con guration of the system. In addition, the optimal placement of the PDs at the receiver is investigated by taking the e ects of the elevation angle parameter of the PDs into consideration. The optimal values are obtained theoretically and also veri ed by simulations. Numerical examples are presented to illustrate the impacts of system parameters on localization accuracy, namely radius of the uniform circular layout, elevation angle and number of PDs. Finally, theoretical limits are compared against the maximum likelihood estimator (MLE) as a benchmark to evaluate the performance of receiver position estimation.
Open Access
Improved lower bounds for ranging in synchronous visible light positioning systems
(Institute of Electrical and Electronics Engineers Inc., 2016) Keskin, M. F.; Gonendik, E.; Gezici, Sinan
In this study, the Ziv-Zakai bound (ZZB) is derived for synchronous visible light positioning (VLP) systems. The proposed ZZB extracts ranging information from the prior information, the time delay parameter, and the channel attenuation factor based on the Lambertian pattern. In addition to the ZZB, the Bayesian Cramï¿½r-Rao bound (CRB) and the weighted CRB (WCRB) are calculated for synchronous VLP systems. Furthermore, a closed-form expression is obtained for the expectation of the conditional CRB (ECRB). Numerical examples are presented to compare the bounds against each other and against the maximum a posteriori probability (MAP) estimator. It is observed that the ZZB can provide a reasonable lower limit on the performance of MAP estimators. On the other hand, the WCRB and the ECRB converge to the ZZB in regions of low and high source optical powers, respectively; however, they are not tight in other regions. ï¿½ 2016 IEEE.
Open Access
Range based sensor node localization in the presence of unknown clock skews
(IEEE, 2013) Gholami, M.R.; Gezici, Sinan; Strom, E.G.
We deal with the positioning problem based on two-way time-of-arrival (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 measurements and obtain a linear model which can be solved using regularized least squares. Simulation results illustrate that the proposed approaches asymptotically attain the Cramér-Rao lower bound. © 2013 IEEE.
Open Access
TDOA based positioning in the presence of unknown clock skew
(IEEE, 2013-06) Gholami, M. R.; Gezici, Sinan; Strom, E. G.
This paper studies the positioning problem of a single target node based on time-difference-of-arrival (TDOA) measurements in the presence of clock imperfections. Employing an affine model for the behaviour of a local clock, it is observed that TDOA based approaches suffer from a parameter of the model, called the clock skew. Modeling the clock skew as a nuisance parameter, this paper investigates joint clock skew and position estimation. The maximum likelihood estimator (MLE) is derived for this problem, which is highly nonconvex and difficult to solve. To avoid the difficulty in solving the MLE, we employ suitable approximations and relaxations and propose two suboptimal estimators based on semidefinite programming and linear estimation. To further improve the estimation accuracy, we also propose a refining step. In addition, the Cramer-Rao ´ lower bound (CRLB) is derived for this problem as a benchmark. Simulation results show that the proposed suboptimal estimators can attain the CRLB for sufficiently high signal-to-noise ratios.
Open Access
Theoretical limits on localization in single input multiple output (SIMO) visible light systems
(Elsevier, 2018) Kökdoğan,Furkan; Erdem, Osman; Gezici, Sinan
In this work, a theoretical accuracy analysis is conducted for position estimation in visible light systems based on received signal strength (RSS) measurements. Considering a single light emitting diode (LED) at the transmitter and multiple photo-detectors (PDs) at the receiver, the Cramér-Rao lower bound (CRLB) is derived for both a generic three-dimensional scenario and specific configurations of the PDs at the receiver. For the special case in which the height of the receiver is known, a compact expression is derived for the CRLB, considering a uniform circular layout and the same elevation angle for all the PDs. In addition, the optimal placement of the PDs at the receiver is investigated by taking the effects of the elevation angle parameter of the PDs into consideration. The optimal values are obtained theoretically and also verified by simulations. Numerical examples are provided to illustrate the impacts of various system parameters on localization accuracy and to compare the theoretical limits against the maximum likelihood estimator (MLE) for the receiver position.
Open Access
TW-TOA based positioning in the presence of clock imperfections
(Elsevier Inc., 2016) Gholami, M. R.; Gezici, Sinan; Ström, E. G.
This manuscript studies the positioning problem based on two-way time-of-arrival (TW-TOA) measurements in semi-asynchronous wireless sensor networks in which the clock of a target node is unsynchronized with the reference time. Since the optimal estimator for this problem involves difficult nonconvex optimization, two suboptimal estimators are proposed based on the squared-range least squares and the least absolute mean of residual errors. We formulate the former approach as an extended general trust region subproblem (EGTR) and propose a simple technique to solve it approximately. The latter approach is formulated as a difference of convex functions programming (DCP), which can be solved using a concave–convex procedure. Simulation results illustrate the high performance of the proposed techniques, especially for the DCP approach. © 2016 Elsevier Inc.