11.
12.
Buendia, Ruben, 1982, et al.
(författare)
A Novel Approach for Removing the Hook Effect Artefact from Electrical Bioimpedance Spectroscopy Measurements
2009
Ingår i: Journal of Physics: Conference Series. - : Institute of Physics Publishing Ltd.. - 1742-6596.
Konferensbidrag (refereegranskat) abstract
Very often in Electrical Bioimpedance (EBI) spectroscopy measurements the presence of stray capacitances creates a measurement artefact commonly known as Hook Effect. Such an artefact creates a hook-alike deviation of the EBI data noticeable when representing the measurement on the impedance plane. Such Hook Effect is noticeable at high frequencies but it also causes a data deviation at lower measurement frequencies. In order to perform any accurate analysis of the EBI spectroscopy data, the influence of the Hook Effect must be removed. An established method to compensate the hook effect is the well known Td compensation, which consist on multiplying the obtained spectrum, Zmeas() by a complex exponential in the form of exp[jTd]. Such a method cannot correct entirely the Hook Effect since the hook-alike deviation occurs a broad frequency range in both magnitude and phase of the measured impedance, and by using a real value for Td. First, a real value only modifies the phase of the measured impedance and second, it can only correct the Hook Effect at a single frequency. In addition, the process to select a value for Td by an iterative process with the aim to obtain the best Cole fitting lacks solid scientific grounds. In this work the Td compensation method is revisited and a modified approach for correcting the Hook Effect that includes a novel method for selecting the correcting values is proposed. The initial validation results confirm that the proposed method entirely corrects the Hook Effect at all frequencies.
13.
Axelberg, Peter
(författare)
On Tracing Flicker Sources and Classification of Voltage Disturbances
2007
Doktorsavhandling (övrigt vetenskapligt/konstnärligt) abstract
Developments in measurement technology, communication and data storage have resulted in measurement systems that produce large amount of data. Together with the long existing need for characterizing the performance of the power system this has resulted in demand for automatic and efficient information-extraction methods. The objective of the research work presented in this thesis was therefore to develop new robust methods that extract additional information from voltage and current measurements in power systems. This work has contributed to two specific areas of interest. The first part of the work has been the development of a measurement method that gives information how voltage flicker propagates (with respect to a monitoring point) and how to trace a flicker source. As part of this work the quantity of flicker power has been defined and integrated in a perceptionally relevant measurement method. The method has been validated by theoretical analysis, by simulations, and by two field tests (at low-voltage and at 130-kV level) with results that matched the theory. The conclusion of this part of the work is that flicker power can be used for efficient tracing of a flicker source and to determine how flicker propagates. The second part of the work has been the development of a voltage disturbance classification system based on the statistical learning theory-based Support Vector Machine method. The classification system shows always high classification accuracy when training data and test data originate from the same source. High classification accuracy is also obtained when training data originate from one power network and test data from another. The classification system shows, however, lower performance when training data is synthetic and test data originate from real power networks. It was concluded that it is possible to develop a classification system based on the Support Vector Machine method with “global settings” that can be used at any location without the need to retrain. The conclusion is that the proposed classification system works well and shows sufficiently high classification accuracy when trained on data that originate from real disturbances. However, more research activities are needed in order to generate synthetic data that have statistical characteristics close enough to real disturbances to replace actual recordings as training data.
14.
Eliasson, Jens, et al.
(författare)
Time synchronous bluetooth sensor networks
2006
Ingår i: IEEE Consumer Communications and Networking Conference. - Piscataway, NJ : IEEE Communications Society. - 1424400856 ; , s. 336-340
Konferensbidrag (refereegranskat) abstract
Bluetooth-equipped wireless sensor nodes can be quickly integrated in small home networks. These networks can be utilized e.g. for surveillance, home monitoring and automation. Accurate time is an important factor for time-stamping of sensor data, encryption/authentication and it can also to used to implement time synchronous schemes for low power radio communication. We argue that IP-based time synchronization, such as various flavors of the NTP protocol, can be used with Bluetooth networks. This in combination with an activation schedule allows an efficient trade-off between energy consumption and communication delay, and provides easy integration with available infrastructure. The proposed approach in this paper is well suited for smaller wireless home networks, typically singlehop networks with access points that are always available. Our approach is verified by experiments performed on a COTS-based platform using Bluetooth.
15.
Johansson, Jonny, et al.
(författare)
Project: EISCAT 3D
2007
Annan publikation (populärvet., debatt m.m.)
16.
Lundberg, Magnus, et al.
(författare)
Power characterization of a bluetooth-equipped sensor node
2005
Ingår i: REALWSN 2005. - Kista : Swedish Institute of Computer Science.
Konferensbidrag (refereegranskat) abstract
Wireless Sensor Networks (WSNs) consist of small, autonomous devices with wireless networking capabilities. In order to further increase the applicability of WSNs in real world ap- plications, minimizing energy consumption and size are im- portant research topics. A WSN node itself is a complex system consisting of numerous components, and the energy consumption of the node depends heavily on the interac- tion between its components and their respective operation modes. To develop a power consumption model, we have investigated the power characteristics of a Bluetooth(BT)- equipped node based on COTS (commercial o®-the-shelf) components running standardized protocols for communica- tion. The characterization captures the transient behavior of the individual components as well as the dynamic behav- ior of the system as a whole. Although the parameters of the model are derived for a speci¯c node, the model and our conclusions can be applied to WSN nodes in general. Based on our model the estimated lifetime of a battery powered BT-equipped node can range from a couple of days to sev- eral months depending on battery and usage. This result indicates that COTS based sensor nodes can be used in a wide range of applications.
17.
Liu, Yang
(författare)
Enhancement of Short Range Wireless Communication Performance Using Adaptive Frequency Hopping
2008
Ingår i: 2008 4th International Conference on Wireless Communications, Networking and Mobile Computing. - : Institute of Electrical and Electronics Engineers (IEEE). - 9781424421077 - 9781424421084 ; , s. 1-5
Konferensbidrag (refereegranskat) abstract
In this paper, a typical commercial short range wireless communication module which has weak immunity to interference has been tested and its performance has been evaluated with test bed. An adaptive frequency hopping scheme has been proposed to improve its immunity to interference and therefore enhance the wireless communication performance for reliability and delay-critical applications. Such scheme can be easily adopted to similar short range wireless communications.
18.
Selén, Yngve, et al.
(författare)
Empirical Bayes linear regression with unknown model order
2008
Ingår i: Digital signal processing (Print). - : Elsevier BV. - 1051-2004 .- 1095-4333. ; 18:2, s. 236-248
Tidskriftsartikel (refereegranskat) abstract
We study maximum a posteriori probability model order selection for linear regression models, assuming Gaussian distributed noise and coefficient vectors. For the same data model, we also derive the minimum mean-square error coefficient vector estimate. The approaches are denoted BOSS (Bayesian order selection strategy) and BPM (Bayesian parameter estimation method), respectively. In their simplest form, both BOSS and BPM require a priori knowledge of the distribution of the coefficients. However, under the assumption that the coefficient variance profile is smooth, we derive "empirical Bayesian" versions of our algorithms which estimate the coefficient variance profile from the observations and thus require little or no information from the user. We show in numerical examples that the estimators can outperform several classical methods, including the well-known AICc and BIC for model order selection.
19.
Demetriades, G. D., et al.
(författare)
Small-signal analysis of the half-bridge soft-swithing uni-directional converter employing extended state-space averaging
2008
Ingår i: PESC Record - IEEE Annual Power Electronics Specialists Conference. - 9781424416684 ; , s. 385-391, s. 385-391
Konferensbidrag (refereegranskat) abstract
In the present paper the small-signal model of the half-bridge soft-switched Single Active Bridge is derived. In order to derive the small-signal model of the specific topology an extended state-space averaging method based on half-cycle symmetry has been used and is briefly described in the paper. The results obtained have been verified experimentally.
20.
Stigwall, Johan, 1977
(författare)
Managing non-linear signal distortion in photonic time-stretch systems
2007
Ingår i: International Microwave Symposium, Workshop on Ultrafast Analog-to-digital (A/D) Conversion Technique and its Applications.
Konferensbidrag (övrigt vetenskapligt/konstnärligt) abstract
Photonic time-stretch systems effectively boost the bandwidth of existing real-time oscilloscopes by temporally stretching a piece of a signal using dispersive optics. The stretch is, however, not perfect – the very same dispersion that actually enables the stretch also introduces signal distortions. Although the optical system is linear, the dispersive propagation and the modulator response introduce harmonic signal distortion when considering the signal from electrical input to electrical output. In this talk, two methods developed for the compensation of non-linear as well as linear distortions are presented. The first method recovers the original signal by calculation of the optical phase at the detection point followed by numerical back-propagation to the modulation point whereas the second method iteratively retrieves the signal using the Gerchberg-Saxton algorithm, which frequently is used for phase retrieval in free-space and diffraction optics. To enable fast numerical propagation, which is required for both methods, a very efficient numerical propagation technique specialized for photonic time-stretch systems is also presented.
