# September 2009, Volume 18, Number 3

**B. Geiger, T. Gigl, J. Preishuber-Pfluegl, K. Witrisal**
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Experimental Characterization of System Parameters for Ranging in IEEE 802.15.4a using Energy Detectors

The IEEE 802.15.4a standard for impulse radio ultrawide band (IR-UWB) communication systems defines a ranging scheme which relies on the measurement of the round-trip propagation time of electromagnetic pulses. Accuracy is strongly dependent on the estimation of the timeof-arrival (TOA) of the pulse that is spread in time due to multipath propagation. The major concern therefore is the proper detection of the leading edge. In this work, the ranging capabilities of the standard are analyzed for an energy detector receiver. Emphasis is put on the influence of transmitter and receiver parameters, which are evaluated for a set of measured scenarios. It is shown that sub-meter ranging accuracy can be achieved with fixed parameter settings.

- EUROPEAN COMMISSION. Commission decision of 21 April 2009: On allowing the use of the radio spectrum for equipment using ultra-wideband technology. Official Journal of the European Union, L105/9, 2009.
- IEEEWORKING GROUP 802.15.4a. Wireless Medium Access Control (MAC) and Physical Layer (PHY) Specifications for Low-Rate Wireless Personal Area Networks (WPANs): Alternate PHYs. NJ: IEEE, 2007.
- WITRISAL, K., LEUS, G., JANSSEN, G. J. M., PAUSINI, M., TROESCH, F., ZASOWSKI, T., ROMME, J.. Noncoherent ultrawideband systems. IEEE Signal Processing Magazine, 2009, vol. 26, no. 4, p. 48 - 66.
- DARDARI, D., CONTI, A., FERNER, U., GIORGETTI, A., WIN, M. Z. Ranging with ultrawide bandwidth signals in multipath environments. Proceedings of the IEEE, 2009, vol. 97, no. 2, p. 404 - 426.
- GUVENC, I., SAHINOGLU, Z. Threshold-based TOA estimation for impulse radio UWB systems. In IEEE Int. Conf. on Ultra- Wideband, ICU. 2005, p. 420 - 425.
- GUVENC, I., SAHINOGLU, Z., ORLIK, P. V. TOA estimation for IR-UWB systems with different transceiver types. IEEE Transactions on Microwave Theory and Techniques, 2006, vol. 54, no. 4, p. 1876 - 1886.
- XU, C., LAW, C. L. Experimental evaluation of UWB ranging performance for correlation and ED receivers in dense multipath environment. In Future Generation Communication and Networking. 2007, vol. 2, p. 186 - 192.
- GUVENC, I., SAHINOGLU, Z. Threshold selection for UWB TOA estimation based on kurtosis analysis. IEEE Communications Letters, 2005, vol. 9, no. 12, p. 1025 - 1027.
- LEI, Z., CHIN, F., KWOK, Y.-S. UWB ranging with energy detectors using ternary preamble sequences. In IEEE Wireless Communications & Networking Conf., WCNC. 2006, p. 872 - 877.
- KWOK, Y.-S., CHIN, F., PENG, X. Ranging mechanism, preamble generation, and performance with IEEE 802.15.4a low-rate lowpower UWB systems. In IEEE Ninth Symposium on Spread Spectrum Techniques and Applications. 2006, p. 525 - 530.
- CHIN, F., ZHI,W., KO, C.-C. System performance of IEEE 802.15.4 low rate wireless PAN using UWB as alternate-PHY layer. In IEEE Int. Symp. on Personal, Indoor and Mobile Radio Communications, PIMRC. 2003, p. 487 - 491.
- GEIGER, B. Ranging in the IEEE 802.15.4a standard using energy detectors. In IEEE EUROCON. St. Petersburg, 2009, p. 1948 - 1955.
- SAHINOGLU, Z., GEZICI, S. Ranging in the IEEE 802.15.4a standard. In Wireless and Microwave Technology Conf. 2006, p. 1 - 5.
- GIGL, T., PREISHUBER-PFLUEGL, J., WITRISAL, K. Statistical analysis of a UWB energy detector for ranging in IEEE 802.15.4a. In IEEE Int. Conf. on Ultra-Wideband, ICUWB. Vancover (Canada), 2009, in press.
- GUVENC, I., SAHINOGLU, Z. Multiscale energy products for TOA estimation in IR-UWB systems. In IEEE Global Communications Conf., GLOBECOM. St. Louis, 2005, p. 209 - 213.
- SAHINOGLU, Z., GEZICI, S., GUVENC, I. Ultra-wideband Positioning Systems – Theoretical Limits, Ranging Algorithms, and Protocols. Cambridge: Cambridge University Press, 2008.
- DIZDAREVIC, V., WITRISAL, K. Statistical UWB range error model for the threshold leading edge detector. In IEEE Int. Conf. on Information, Communications and Signal Processing, ICICS. Singapur, 2007, p. 1 - 5.
- GIGL, T., BUCHGRABER, T., ADALAN, A., PREISHUBERPFLUEGL, J., FISCHER, M., WITRISAL, K. UWB channel characterization using IEEE 802.15.4a demonstrator system. In IEEE Int. Conf. on Ultra-Wideband, ICUWB. Vancover (Canada), 2009, in press.
- GIGL, T., ARNITZ, D., PREISHUBER-PFLUEGL, J., WITRISAL, K. Experimental characterization of ranging in IEEE 802.15.4a using a coherent reference receiver. In IEEE Int. Symp. on Personal, Indoor and Mobile Radio Communications, PIMRC. Tokyo (Japan), 2009, in press.
- IRAHHAUTEN, Z., JANSSEN, G., HOMAYOUN, N., YAROVOY, A., LIGTHART, L. UWB channel measurements and results for office and industrial environments. In IEEE Int. Conf. on Ultra- Wideband, ICU. 2006, p. 225 - 230.

Keywords: Ultrawide band, IEEE 802.15.4a, energy detector, UWB measurements, ranging

**M. Aftanas, M. Drutarovsky**
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Imaging of the Building Contours with Through the Wall UWB Radar System

Any actual information about a building interior can be very useful before entering a dangerous area. It can be used to plan strategies in many rescue and security applications. The paper deals with imaging of the inner and outer building contours from the outside using through the wall UWB radar. The whole processing chain for obtaining the contours of a scanned building is explained. The image processing method of highlighting the building walls using Hough transform with assumed knowledge of the direction of walls is presented. The algorithm was tested on real measurement data acquired from a M-sequence UWB radar system.

- SACHS, J., AFTANAS, M., CRABBE, S., DRUTAROVSKY, M., KLUKAS, R., KOCUR, D., NGUYEN, T. T., PEYERL, P., ROVNAKOVA, J., ZAIKOV, E. Detection and tracking of moving or trapped people hidden by obstacles using ultra-wideband pseudonoise radar. In European Radar Conference EuRAD 2008, Amsterdam (The Netherlands), 2008, p. 408 - 411.
- BURCHETT, H. Advances in through wall radar for search, rescue and security applications. In Conference on Crime and Security. The Institution of Engineering and Technology, London (UK), 2006, p. 511 - 525.
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- Camero. XaverTM800 - Through Wall Vision, one and two persons. [Online]. Available: http://www.camero-tech.com/xaver800.shtml.
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- BORYSSENKO, A. O. et al. UWB Subsurface radar with antenna array for imaging of internal structure of concrete structural elements. Ultra-Wideband, Short-Pulse Electromagnetics 5, Springer US, 2002, p. 199 - 206.
- DORAGU, T., LE, C. Ultra-wideband radar for building interior imaging. In Army Science Conference, 2008, vol. 26.
- DUDA, R. O., HART, P. E. Use of the Hough transformation to detect lines and curves in pictures. Commun. ACM, 1972, vol. 15, p. 11 – 15.
- DANIELS, D. M-sequence Radar. In Ground Penetrating Radar. 2nd ed. Peter Peregrinus Ltd, 2004.
- AFTANAS, M. Through wall imaging using Msequence UWB radar system. Thesis to the dissertation examination, Technical University of Kosice, Department of Electronics and Multimedia Communications, Slovak Republic, Dec. 2007, p. 63.
- MARGRAVE, G. F. Numerical Methods of Exploration Seismology with Algorithms in Matlab. Master’s thesis, Department of Geology and Geophysics, University of Calgary, 2001, p. 160.
- ULANDER, L., HELLSTEN, H., STENSTROM, G. Synthetic aperture radar processing using fast factorized backprojection. Aerospace and Electronic Systems, 2003, vol. 39, p. 760 – 776.
- YILMAZ, O. Seismic Data Processing (Investigations in Geophysics, Vol 2). Society of Exploration, 1987.
- STOLT, R. H. Migration by Fourier transform. Geophysics, 1987, vol. 43, p. 23 – 48.
- AFTANAS, M., ROVNAKOVA, J., DRUTAROVSKY, M., KOCUR, D. Efficient method of TOA estimation for throughwall imaging by UWB radar. In IEEE International Conference on Ultra-Wideband (ICUWB2008), Hannover (Germany), 2008, vol. 10, p. 101 – 104.
- KHATRI, H., LE, C. Identification of electromagnetic parameters of a wall and determination of radar signal level behind a wall. In Proceedings of SPIE, the International Society for Optical Engineering, Florida (USA), 2006, vol. 6210.
- CANNY, J. A computational approach to edge detection. IEEE Transactions on Pattern Analysis and Machine Intelligence, 1986, vol. 8, p. 679 - 698.
- CHENG-LI, J., KE-FENG, J., YONG-MEI, J., GANG-YAO, K. Road extraction from high-resolution SAR imagery using Hough transform. IEEE International Geoscience and Remote Sensing Symposium, Changsha (China), 2005, vol. 1, p. 336 - 339.
- KABAKCHIEV, CH. et al. UXO Signal Multi Sensor Detection and Estimation, in Unexploded Ordnance Detection and Mitigation. Springer, 2008.
- XU, F., JIN, Y. Automatic reconstruction of building objects from multiaspect meter-resolution SAR images. IEEE Transactions on Geoscience and Remote Sensing, 2007, vol. 45, p. 2336 - 2353.
- TURAN, J., FARKAS, P. Line fitting using Hough-like procedure. Radioengineering, 2001, vol. 10, no. 1, p. 25 - 30.
- FISHER, R., PERKINS, S., WALKER, A., WOLFART, E. Hypermedia Image Processing Reference. October 2000, [online] available at: http://homepages.inf.ed.ac.uk/rbf/HIPR2/.
- SACHS, J., PEYERL, P., WOCKEL, S., KMEC, M., HERRMAN, R., ZETIK, R. Liquid and moisture sensing by ultra-wideband pseudo-noise sequence signals. Measurement Science and Technology, 2007, vol. 18, p. 1074 – 1087.
- IMMOREEV, I., FEDOTOV, P. Ultra wideband radar systems: advantages and disadvantages. In IEEE Conference on Ultra Wideband Systems and Technologies, 2002, p. 201 – 205.

Keywords: UWB radar system, through the wall imaging, SAR scanning, Hough transform, highlighting the walls

**M. Herceg, T. Matic, T. Svedek**
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Performances of Hybrid Amplitude Shape Modulation for UWB Communications Systems over AWGN Channel in a Single and Multi-User Environment

This paper analyzes the performance of the hybrid Amplitude Shape Modulation (h-ASM) scheme for the time-hopping ultra-wideband (TH-UWB) communication systems in the single and multi-user environment. h-ASM is the combination of Pulse Amplitude Modulation (PAM) and Pulse Shape Modulation (PSM) based on modified Hermite pulses (MHP). This scheme is suitable for high rate data transmission applications because b = log_{2}(MN) bits can be mapped with one waveform. The channel capacity and error probability over AWGN channel are derived and compared with other modulation schemes.

- SCHOLTZ, R. A. Multiple access with time-hopping impulse modulation. In Proc. IEEE Military Commun. Conf., October. 1993, p. 11-14.
- FCC, Revision of part 15 of the commission’s rules regarding ultra-wideband transsmision systems. Federal Communications Commission, ET Docket, 2002, pp. 98-153.
- KIM, Y., JANG, B., SHIN, C., WOMACK, B. F. Orthonormal pulses for high data rate communications in indoor UWB systems. IEEE Communications Letter, 2005, vol. 9, no. 5, p. 405-407.
- DA SILVA, J. A. N., DE CAMPOS, M. L. R. Method for obtaining spectrally efficient orthogonal UWB pulse shapes. In International Telecommunications Symposium. Fortaleza-CE (Brazil), Septemper 3-6, 2006.
- GHAVAMI, M., MICHAEL, L. B., KOHNO, R. Ultra Wideband Signals and Systems in Communication Engineering. John Wiley & Sons, Ltd, 2004.
- ZHANG, H., LI, W., GULLIVER, T. A. Pulse Position Amplitude Modulation for time-hopping multiple-access UWB communications. IEEE Trans. on Comm., 2005, vol. 53, no. 8.
- ZHANG, H., GULLIVER, T. A. Biorthogonal Pulse Position Modulation for time-hopping multiple-access UWB communications. IEEE Trans. on Wireless Comm., 2005, vol. 4, no. 3.
- MAJHI, S., MADHUKUMAR, A. S. Combining OOK with PSM modulation for TH-UWB radio systems: A performance analysis. EURASIP Journal on Wireless Comm. and Networking, 2008.
- MITCHELL, C. J., ABREU, G., KOHNO, R. Combined pulse shape and pulse position modulation for high data rate transmissions in ultra-wideband communications. International Journal of Wireless Information Networks, October 2003, vol. 10, no. 4.
- ELTAHER, A., KAISER, TH. Hybrid shape, amplitude, and position modulation for UWB communication systems. WSEAS Journal on Communications, July 2004.
- GHAVAMI, M., MICHAEL, L. B., HARUYAMA, S., KOHNO, R. A novel UWB pulse shape modulation system. Wireless Personal Communications, 2002, vol. 23, p. 105-120.
- PROAKIS, J. G. Digital Communications. 4th ed., New York: McGraw-Hill, 2001.
- DILINAR, S., DIVSALAR, D., HAMKINS, J., POLLARA, F. Capacity of Pulse-Position Modulation (PPM) on Gaussian and Webb channels. TMO Progress Report, vol. 42-142, August 15, 2000.
- DURISI, G., ROMANO, G. On the validity of Gaussian approximation to characterize the multiuser capacity of UWB TH PPM. In Proc. IEEE Conf. Ultra Wideband Systems and Technology, 2002, pp. 157-161.
- LI ZHAO, HAIMOVICH, A. M. Capacity of M-ary PPM ultrawideband communications over AWGN channels. In Proc. IEEE 54th Vehicular Technology Conference. Atlantic City (USA), October 2001, vol. 2, p. 1191-1195.
- PROAKIS, J. G., SALEHI, M. Contemporary Communication Systems Using MATLAB. PWS publishing company, 1998.
- ABEDI, O., NIELSEN, J. UWB data rate and channel capacity in modulation schemes. In Canadian Conference on Electrical and Computer Engineering. May 2006, p. 1809 – 1816.

Keywords: Ultra-Wideband, Pulse-Amplitude Modulation, Pulse-Shape Modulation

**S. Gona, V. Kresalek**
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Derivation of Equivalent Material Models for Composite Laminated Materials

In this paper, an original approach of derivation of equivalent electrical models for multilayer composite materials is presented. The purpose of the modeling is to approximate a given composite material by an equivalent dielectric slab or by a medium consisting from several dielectric layers. For each layer, an equivalent complex permittivity is set up by an optimization procedure in order to achieve the same values of reflection and transmission coefficients as are the measured values of reflection and transmission coefficients of the original composite material.

- RIKTE, S., ANDERSSON, M., KRISTENSSON, G. Homogenization of woven materials. Research report no. TEAT- 7074, Lund University of Technology, Sweden, Sept 1999, 35 pp.
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- JILKOVA, J., RAIDA, Z. Genetic homogenization of composite materials. Radioengineering. 2009, vol. 18, no.1, p. 34 - 37.
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- VARADAN, V. V. Extraction of metamaterial properties from measured S-parameters – effects of measurement accuracy, assumed constitutive models, periodicity and randomness. In Proceedings of Metamaterial. Rome (Italy), October 2007.
- WU, T. K. Frequency Selective Surfaces and Grid Arrays. 1st ed. Norwood: Artech House, 1995.
- GONA, S., KRESALEK, V. Accuracy of multilayer equivalent models for composite laminated materials. Accepted for publication on the "International Conference of Applications of Advanced Electronics (ICEAA 09)". Torino (Italy), 2009, Sept 14-18.
- REZNICEK, Z., RAIDA, Z., JILKOVA J. Analyzing small aircraft model with homogeneous composite material substitutes on HIRF. EMC Europe workshop 2009. Athens (Greece), p. 1-4.

Keywords: Composite material, reflection and transmission coefficients, equivalent model, complex permittivity, numerical inversion

**R. Sotner, J. Petrzela, J. Slezak**
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Current-Controlled Current-Mode Universal Biquad Employing Multi-Output Transconductors

This paper deals with RC active biquad working in the so-called current mode (CM). The design approach uses only three transconductors (OTA) with the minimum necessary number of outputs and with only three passive grounded elements. The proposed filter has simple circuit configuration providing all standard transfer functions such as high-pass (HP), band-pass (BP), low-pass (LP), band-reject (BR) and all-pass (AP). Electronic tuning and independent adjusting of the quality factor and bandwidth of BP filter is possible. The presented circuits are verified by PSpice simulations utilizing OTAs on transistor level of abstraction. The linear parasitic effects of the real active elements in each suggested circuit are briefly discussed. Experimental verification is also given. Designed networks can be used in many applications such as antialiasing filters, in high-speed data telecommunication systems, for signal processing in the cable modems, in regulation and measurement techniques etc.

- RANDALL, L. G., SANCHEZ-SINENCIO, E. Active filter design using operational transconductance amplifers: A tutorial. IEEE Circuits and Devices Magazine, 1985. vol. 1, p. 20-32.
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- KESKIN, A. U., BIOLEK, D., HANCIOGLU, E., BIOLKOVA, V. Current-mode KHN filter employing Current Differencing Transconductance Amplifiers. Int. J. Electronics and Communications, 2006, vol. 60, no. 6, pp. 443-446.
- TANGSRIRAT, W. Current-tunable current-mode multifunctional filter based on dual-output current-controlled conveyors. AEU – International Journal of Electronics and Communications, 2007, vol. 61, no. 8, pp. 528-533.
- JAIKLA, W., SIRIPRUCHYANUN, M. Low-component electronically controllable dual-mode universal biquad filter using DO-CCCIIs. In Proceedings of Asia-Pacific Conference on Communications, 2007, pp. 331-334.
- BIOLEK, D., SIRIPRUCHYANUN, M., JAIKLA, W. CCII and OTA based current-mode universal biquadratic filter. The sixth PSU Engineering Conference, May 2008, pp. 238-241.
- SIRIPRUCHYANUN, M., CHANAPROMMA, C., SILAPAN, P., JAIKLA, W. BiCMOS Current-controlled current feedback amplifier (CC-CFA) and its applications. WSEAS Transactions on Electronics, 2008, vol. 5, no. 6, pp. 203-219.
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- ABUELMAATTI, M. T., BENTRCIA, A. A novel mixed-mode OTA-C universal filter. International Journal of Electronics, 2005, vol. 92, no. 7, pp. 375-383.
- CHEN, H., LIAO, Y., LEE, W. Tunable mixed-mode OTA-C universal filter. Analog Integrated Circuits and Signal Processing, Springer, 2008, vol. 58, pp. 135-141.
- BHASKAR, D. R., SINGH, A. K., SHARMA, R. K., SENANI, R. New OTA-C universal current-mode/trans-admittance biquad. IEICE Electronics Express, 2005, vol. 2, no. 1, pp. 8-13.
- CHEN, H., SHEN, S., WANG, J. Electronically tunable versatile voltage-mode universal filter. International Journal of Electronics and Communications AEU, 2008, vol. 62, pp. 316- 319.
- MONGKOLWAI, P., PUKKALANUN, T., TANGSRIRAT, W. Current-mode universal biquad with orthogonal ω0 - Q tuning using OTAs. In ICICS - 6th International Conf. on Information, Communications and Signal Processing, Singapore, 2007, pp. 1-4.
- CHUNGUA, W., LING, Z., TAO, L. A new OTA-C current-mode biquad filter with single input and multiple outputs. Int. Journal of Electronics and Communications AEU, 2008, vol. 62, pp. 232-234.
- PROMMEE, P., SOMDUNYAKANOK, M., DEJHAN, K. Independent tunable-Q current-mode OTA-C universal filter. In Proc. of IEEE Asia Pacific Conf. on Circuits and Systems, 2006, pp. 900-903.
- DUMAWIPATA, T., TANGSRIRAT, W., SURAKAMPONTORN, W. Current-mode universal filter with four inputs and one output using CDTAs. In Proceedings of IEEE Asia Pacific Conf. on Circuits and Systems APCCAS 2006, 2006, pp. 892-895.
- BIOLEK, D., BIOLKOVA, V., KOLKA, Z. Universal currentmode OTA-C KHN biquad. International Journal of Electronics, Circuits and Systems, 2007, vol. 1, no. 4, pp. 214-217.
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- Texas Instruments Inc. OPA 860 Wide Bandwidth Operational Transconductance Amplifier and Buffer. 2006, 32 p. Accessible on www: http://www.ti.com
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Keywords: Current-mode, transconductor, electronic adjusting, universal filter

**M. Ma, C. Wang, S. Du**
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Low Voltage Current Mode Switched-Current-Mirror Mixer

A new CMOS active mixer topology can operate at 1 V supply voltage by use of SCM (switched currentmirror). Such current-mode mixer requires less voltage headroom with good linearization. Mixing is achieved with four improved current mirrors, which are alternatively activated. For ideal switching, the operation is equivalent to a conventional active mixer. This paper analyzes the performance of the SCM mixer, in comparison with the conventional mixer, demonstrating competitive performance at a lower supply voltage. Moreover, the new mixer’s die, without any passive components, is very small, and the conversion gain is easy to adjust. An experimental prototype was designed and simulated in standard chartered 0.18μm RF CMOS Process with Spectre in Cadence Design Systems. Experimental results show satisfactory mixer performance at 2.4 GHz.

- BRANDOLINI, G.D., ROSSI, P., MANSTRETTA, D., SVELTO, F. Toward multistandard mobile terminalsfully integrated receivers requirements and architectures. IEEE Trans. Microw. Theory and Tech., 2005, vol. 53, no 3, p 1026-1038.
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- WEN-CHIEH WANG, CHUNG-YU WU. The 1-V 24-GHz lowvoltage low-power current-mode transmitter in 130-nm CMOS technology. In Proceedings of Microelectronics and Electronics Conference. 2007, p. 49 - 52.
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- KLUMPERINK, E. A. M., LOUWSMA, S. M., WIENK, G. J. M., NAUTA, B. A CMOS switched transconductor mixer. IEEE Journal of Solid-State Circuits, 2004, vol. 39, no. 8, p. 1231 - 1240.
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- TERROVITIS, M. T., MEYER, R. G. Noise in currentcommutating CMOS mixers. IEEE Journal of Solid-State Circuits, 1999, vol. 34, p. 772 - 783.

Keywords: Current mode, switched current mirror, mixer, low voltage, receiver, RF circuit

**A. Lahiri, A. Chowdhury**
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A Novel First-Order Current-Mode All-Pass Filter Using CDTA

This paper presents a new realization of a firstorder current-mode (CM) all-pass filter (APF) using the recently proposed modern active building block (ABB), namely the current differencing transconductance amplifier (CDTA). The CM APF is made using minimum number of components, namely a single CDTA and one grounded capacitor. The circuit does not use any external resistors and offers the advantages of current-tunable pole frequency, low input impedance and high output impedance. Non-ideal analysis and sensitivity analysis are provided and PSPICE simulation results are included to verify the workability of the circuit.

- BIOLEK, D. CDTA-Building block for current-mode analog signal processing. In Proc. ECCTD 03. Cracow (Poland), 2003, vol. III, p. 397-400.
- BIOLEK, D., BIOLKOVA, V. Tunable ladder CDTA-based filters. In 4th Multiconference WSEAS. Tenerife (Spain), 2003.
- UYGUR, A., KUNTMAN, H., ZEKI, A. Multi-input multi-output CDTA-based KHN filter. In Proc. of ELECO: The 4th International Conference on Electrical and Electronics. 2005, p. 46-50.
- UYGUR, A., KUNTMAN, H. Seventh order elliptic video filter with 0.1dB pass band ripple employed CMOS CDTAs. AEU – International Journal of Electronics and Communications, 2007, vol. 61, p. 320-328.
- KESKIN, A. U., BIOLEK, D., HANCIOGLU, E., BIOLKOVA, V. Current-mode KHN filter employing current differencing transconductance amplifier. AEU – International Journal of Electronics and Communications, 2006, vol. 60, no. 6, p. 443-446.
- PRASAD, D., BHASKAR, D. R., SINGH, A. K. Realisation of single-resistance-controlled sinusoidal oscillator: a new application of the CDTA. WSEAS Transactions on Electronics, 2008 vol. 5, no. 6, p. 257-259.
- JAIKLA, W., SIRIPRUCHYANUN, M., BAJER, J., BIOLEK, D. A simple current-mode quadrature oscillator using single CDTA. Radioengineering, 2008, vol. 17, no. 4, p. 33-40.
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Keywords: Current-mode (CM), active building block (ABB), all-pass filter (APF), Current Differencing Transconductance Amplifier (CDTA)

**J. Silovsky, P. Cerva, J. Zdansky**
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Comparison of Generative and Discriminative Approaches for Speaker Recognition with Limited Data

This paper presents a comparison of three different speaker recognition methods deployed in a broadcast news processing system. We focus on how the generative and discriminative nature of these methods affects the speaker recognition framework and we also deal with intersession variability compensation techniques in more detail, which are of great interest in broadcast processing domain. Performed experiments are specific particularly for the very limited amount of data used for both speaker enrollment (typically ranging from 30 to 60 seconds) and recognition (typically ranging from 5 to 15 seconds). Our results show that the system based on Gaussian Mixture Models (GMMs) outperforms both systems based on Support Vector Machines (SVMs) but its drawback is higher computational cost.

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Keywords: Speaker recognition, Gaussian Mixture Models (GMM), Support Vector Machines (SVM), broadcast processing

**P. Foris, D. Levicky**
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Adaptive Digital Image Watermarking Based on Combination of HVS Models

In this paper two new blind adaptive digital watermarking methods of color images are presented. The adaptability is based on perceptual watermarking which exploits Human Visual System (HVS) models. The first method performs watermark embedding in transform domain of DCT and the second method is based on DWT. Watermark is embedded into transform domain of a chosen color image component in a selected color space. Both methods use a combination of HVS models to select perceptually significant transform coefficients and at the same time to determine the bounds of modification of selected coefficients. The final HVS model consists of three parts. The first part is the HVS model in DCT (DWT) domain. The second part is the HVS model based on Region of Interest and finally the third part is the HVS model based on Noise Visibility Function. Watermark has a form of a real number sequence with normal distribution.

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Keywords: Digital image watermarking, Human Visual System models, Discrete Cosine Transform, Discrete Wavelet Transform, Noise Visibility Function, color spaces, watermark embedding, watermark detection

**S. Tsakiris, A. Salis, N. Uzunoglu**
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FPGA Implementation of a Frame Synchronization Algorithm for Powerline Communications

This paper presents an FPGA implementation of a pilot–based time synchronization scheme employing orthogonal frequency division multiplexing for powerline communication channels. The functionality of the algorithm is analyzed and tested over a real powerline residential network. For this purpose, an appropriate transmitter circuit, implemented by an FPGA, and suitable coupling circuits are constructed. The system has been developed using VHDL language on Nallatech XtremeDSP development kits. The communication system operates in the baseband up to 30 MHz. Measurements of the algorithm's good performance in terms of the number of detected frames and timing offset error are taken and compared to simulations of existing algorithms.

- PAVLIDOU, N., HAN VINCK, A. J., YAZDANI, J., HONARY, B. Power line communications: state of the art and future trends. IEEE Communications Magazine, 2003, vol. 41, no. 4, p. 34 - 40.
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Keywords: Field Programmable Gate Arrays (FPGAs), frequency division multiplexing, power line communications, frame synchronization

**M. Prochazka**
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Reader’s Comment on: Application of the Global Optimization Approaches to Planar Near-Field Antenna Phaseless Measurements [1]

- PUSKELY, J., NOVACEK, Z. Application of the global optimization approaches to planar near-field antenna phaseless measurements. Radioengieering. 2009, vol. 18, no. 1, p. 9 - 17.
- BARTIK, H. Dept. of Electromagnetic Field, Czech Technical University in Prague.
- PUSKELY, J., NOVACEK, Z., POKORNY, M. Using global optimization approaches to reconstruct radiation patterns. In Proc. of the 14th Conference on Microwave Techniques. Prague (Czech Republic), April 23/24, 2008, p. 239-242.