V. Sebesta [references] [full-text] [Download Citations]
Estimating a Spectral Correlation Function under the Conditions of Imperfect Relation between Signal Frequencies and a Sampling Frequency

This paper is devoted to the estimation of the spectral correlation function. The examined signal is a simple DSB-SC signal. The aim of the paper is discovering events connected with nonstandard relations between signal frequency parameters and sampling frequency. They manifest by descending the spectral correlation function modulus. The events has been described analytically and verified using computer experiments. It is shown, that influence of the inaccuracy of the frequency is stronger for modulating frequency than for carrier frequency. Small inaccuracies of the frequencies have acceptable consequences.

1. QUAN, Z., et al. Collaborative wideband sensing for cognitive radios. IEEE Signal Processing Magazine, 2008, vol. 25, no. 6, p. 60-73.
2. LUNDEN, J., et al. Collaborative cyclostationary spectrum sensing for cognitive radio systems. IEEE Transactions on Signal Processing, 2009, vol. 57, no. 11, p. 4182-4195.
3. TURUNEN, V., et al. Implementation of cyclostationary feature detector for cognitive radios. In Conference on Cognitive Radio Oriented Wireless Networks and Communications, June 2009. p. 1 – 4.
4. GARDNER, W. A. Spectral correlation of modulated signals: Part I – Analog modulation. IEEE Transactions on Communica- tions, 1987, vol. 35, no. 6, p. 584-594.
5. ENSERINK, S., COCHRAN, D. A cyclostationary feature detector. In Proc. 28th Asilomar Conf. Signals, Systems, and Computers. Pacific Grove (CA), Nov. 1994, vol. 2, p. 806–810.
6. GARDNER, W. A. Spectral correlation of modulated signals: Part II – Digital modulation. IEEE Transactions on Communica- tions, 1987, vol. 35, no. 6, p. 595-601.
7. CHEN, H.-S., GAO, W., DAUT, D. G. Spectrum sensing using cyclostationarity properties and application to IEEE 802.22 WRAN. In GLOBECOM’07, 2007, p. 3133 – 3138.
8. MITRA, S. K. Digital Signal Processing. A Computer-Based Approach. The McGraw-Hill Companies, Inc., 1998.
9. GARDNER, W. A. Cyclostationarity in Communications and Signal Processing. IEEE PRESS, 1994.

Keywords: Spectral correlation function, feature detector, cyclic frequency, spectral frequency, frequency offset.

P. Kejík, S. Hanus [references] [full-text] [Download Citations]
Comparison of Fuzzy Logic and Genetic Algorithm Based Admission Control Strategies for UMTS System

CDMA systems have so-called soft capacity, so the total number of possible sessions has not an exact value. The capacity of CDMA system depends on the interference level in the system. There are therefore RRM (Radio Resources Management) functions, which are responsible for supplying optimum coverage, ensuring efficient use of physical resources and providing the maximum planned capacity. This paper presents and compares several algorithms that are used for admission control purposes in UMTS system. Several versions of fuzzy logic based algorithms, load factor based algorithm and genetic based algorithm are mutually compared via simulations.

1. ROMERO, J., SALLENT, O., AGUSTÍ, R., DÍAZ-GUERRA, M. Radio Resources Management Strategies in UMTS. Wiley & Sons, 2005. 345 pages. ISBN 978-0-470-02277-1.
2. ELAYOUBI, S., CHAHED, T. Admission control in the downlink of WCDMA/UMTS. In Wireless Systems and Mobility in Next Generation Internet. Springer, Heidelberg, Lecture Notes in Computer Science, vol. 3427/2005, p. 136-151. ISBN 978-3-540- 25329-7.
3. AGUSTI, R., SALLENT, O., PEREZ, J., GORIA, P., MANGANI, N., VAILLANT, A. First Report on the Evaluation of RRM Algorithms by Simulation. 2002, [online], [Cit 2008-11-24]. Document available on http://www.arrows-ist.upc.es/.
4. SOUTO, N., SOARES, A., EUSÉBIO, P., CORREIA, A., SILVA, J. C. Effective radio resource management for multimedia broadcast/multicast services in UMTS networks. EURASIP Journal on Wireless Communications and Networking, vol. 2006, Article ID 70903, 12 pages, 2006. doi: 10.1155/WCN/2006/70903.
5. MALARKKAN, S., RAVICHANDRAN, V. Performance analysis of call admission control in WCDMA systems with adaptive multi class traffic based on fuzzy logic. IJCSNS International Journal of Computer Science and Network Security. Nov. 2006, vol. 6, no. 11.
6. YENER, A., ROSE, C. Genetic algorithms applied to cellular call admission problem: Local polices. In IEEE Transactions on Vehicular Technology. Feb. 1997, vol. 46, p. 72-79.
7. SHEN, S., CHANG, C., HUANG, C., BI, Q. Intelligent call admission control for wideband CDMA cellular systems. IEEE Transactions on Wireless Communications. Sept. 2004, vol. 3, no. 5.
8. KARABUDAK, D., HUNG, C., BING, B. A call admission control scheme using genetic algorithms. In Proceedings of the 2004 ACM symposium on Applied Computing. 2004. ISBN 1-58113-812-1.
9. KEJÍK, P., HANUS, S. Fuzzy logic based call admission control in UMTS system. In CD: Proceedings of the 2009 1st International Conference on Wireless Communication, Vehicular Technology, Information Theory and Aerospace & Electronic System Technology. Aalborg (Denmark), 2009, p. 375-378. ISBN 978-1-4244-4067-2.
10. KEJÍK, P., HANUS, S. The application of fuzzy logic for admission control in UMTS system. In Proceedings of the 19th International Conference Radioelektronika 2009. Bratislava (Slovak Republic), 2009, p 203-206. ISBN 978-1-4244-3536-4.
11. LO, J., BRITO, A., CORREIA, L., CORREIA, A. Simulation of call admission control, load control, handover and power control algorithms for Enhanced-UMTS. SEACORN Project [online]. [Cit. 2009-2-3]. Document available on http://seacorn.ptinovacao.pt/.
12. KHOJA, J., AL-SHALASH, M., PRABHU, V. Dynamic system simulator for the modelling of CDMA systems. In Proceedings of the International Mobility and Wireless Access Workshop. 2002, p. 50-58. ISBN 0-7695-1843-5.

Keywords: Admission control, CDMA, UMTS, fuzzy logic, genetic algorithm.

K. B. Baltzis [references] [full-text] [Download Citations]
Closed-form Description of Microwave Signal Attenuation in Cellular Systems

The reliable and accurate description of signal attenuation characteristics is important in the simulation and performance analysis of wireless communications systems. Recent works have provided analytical expres- sions for the path loss statistics in cellular systems consid- ering distance-dependent losses and shadowing. In this paper, we extend this analysis by including small-scale fading. A closed-form expression that gives the path loss density in a cellular network is given. The impact of chan- nel parameters and cell size on signal attenuation is fur- ther investigated. Simulation results and comparisons with measured data in the literature verify the accuracy of the solution. The derived formulation is a useful tool for the modeling and analysis of cellular communications systems.

1. WIESER, V., PSENAK, V. Performance of advanced hybrid link adaptation algorithms in mobile radio channel. Radioengineering, 2008, vol. 17, no. 3, p. 81-86.
2. NOORI, N., KARIMZADEH-BAEE, R., ABOLGHASEMI, A. An empirical ultra wideband channel model for indoor laboratory environments. Radioengineering, 2009, vol. 18, no. 1, p. 68-74.
3. BALTZIS, K. B. Current issues and trends in wireless channel modeling and simulation. Recent Patents on Computer Science, 2009, vol. 2, no. 3, p. 166-177.
4. GHASSEMZADEH, S. S., JANA, R., RICE, C. W., TURIN, W., TAROKH, V. Measurement and modeling of an ultra-wide bandwidth indoor channel. IEEE Transactions on Communications, 2004, vol. 52, no. 10, p. 1786-1796.
5. MORAITIS, N., CONSTANTINOU, P. Indoor channel measurements and characterization at 60 GHz for wireless local area network applications. IEEE Transactions on Antennas and Propagation, 2004, vol. 52, no. 12, p. 3180-3189.
6. HOLIS, J., PECHAC, P. Elevation dependent shadowing model for mobile communications via high altitude platforms in built-up areas. IEEE Transactions on Antennas and Propagation, 2008, vol. 56, no. 4, p. 1078-1084.
7. HAENGGI, M. A geometric interpretation of fading in wireless networks: Theory and applications. IEEE Transactions on Information Theory, 2008, vol. 54, no. 12, p. 5500-5510.
8. CERRI, G., CINALLI, M., MICHETTI, F., RUSSO, P. Feed forward neural networks for path loss prediction in urban environment. IEEE Transactions on Antennas and Propagation, 2004, vol. 52, no. 11, p. 3137-3139.
9. BHARUCHA, Z., HAAS, H. The distribution of path losses for uniformly distributed nodes in a circle. Research Letters in Communications, 2008, vol. 2008, article ID 376895, 4 pages. DOI: 10.1155/2008/376895.
10. BALTZIS, K. B. Analytical and closed-form expressions for the distribution of path loss in hexagonal cellular networks. Wireless Personal Communications, submitted for publication.
11. ALOUINI, M.-S., GOLDSMITH, A. J. Area spectral efficiency of cellular mobile radio systems. IEEE Transactions on Vehicular Technology, 1999, vol. 48, no. 4, p. 1047–1066.
12. SIMON, M. K., ALOUINI, M.-S. Digital Communication over Fading Channels. 2nd ed. Chichester: John Wiley & Sons, Ltd, 2005.
13. RUBIO, L., REIG, J., CARDONA, N. Evaluation of Nakagami fading behaviour based on measurements in urban scenarios. AEU - International Journal of Electronics and Communications, 2007, vol. 61, no. 2, p. 135–138. L., GREENSTEIN, L., MANDAYAM, N.,
14. XIAO, PERIYALWAR, S. Distributed measurements for estimating and updating cellular system performance. IEEE Transactions on Communications, 2008, vol. 56, no. 6, p. 991-998.
15. BALTZIS, K. B., SAHALOS, J. N. A low–complexity 3–D geometric model for the description of CCI in cellular systems. Electrical Engineering, 2009, vol. 91, no. 4, p. 211-219.
16. PARSONS, J. D. The Mobile Radio Propagation Channel. Chichester: John Wiley & Sons, Ltd, 2000.
17. KILLAT, M., HARTENSTEIN, H. An empirical model for probability of packet reception in vehicular ad hoc networks. EURASIP Journal on Wireless Communications and Networking, 2009, vol. 2009, article ID 721301, 12 pages. DOI: 10.1155/2009/721301.
18. OMIYI, P., HAAS, H., AUER, G. Analysis of TDD cellular interference mitigation using busy-bursts. IEEE Transactions on Wireless Communications, 2007, vol. 6, no. 7, p. 2721-2731.
19. THIELE, L., JUNGNICKEL, V. Out-of-channel statistics at 5.2 GHz. In Proceedings of the First European Conference on Antennas and Propagation (EuCAP 2006), Nice (France), 2006, p. 1-6. DOI: 10.1109/EUCAP.2006.4584756.
20. ZHAO, X., KIVINEN, J., VAINIKAINEN, P., SKOG, K. Propagation characteristics for wideband outdoor mobile communications at 5.3 GHz. IEEE Journal on Selected Areas in Communications, 2002, vol. 20, no. 3, p. 507-514.
21. CHAN, N. H. L., MATHIOPOULOS, P. T. Efficient video transmission over correlated Nakagami fading channels for IS-95 CDMA systems. IEEE Journal on Selected Areas in Communications, 2000, vol. 18, no. 6, p. 996-1011.
22. RAPPAPORT, T. S. Wireless Communications: Principles and Practice. 2nd ed. Upper Saddle River: Prentice Hall PTR, 2002.

Keywords: Microwave propagation, path loss, fading, composite gamma-lognormal density, cellular communications.

S. D. Roy, S. Kundu [references] [full-text] [Download Citations]
Performance of Data Services in Cellular CDMA in Presence of Soft Handoff and Packet Combining

Performance analysis of data services is studied in CDMA network in presence of soft handoff (HO) and packet combining. Packet combining in conjunction with soft handoff is found to enhance throughput, reduce delay and packet delay variation (PDV) significantly. A stop and wait automatic repeat request (ARQ) scheme has been assumed. Two different packet combining schemes for packet data service, one based on log likelihood ratio (LLR) and another based on equal gain combining (EGC) have been studied. A cross layer interactions between ARQ and packet combining at link layer and soft HO in physical layer has been shown.

1. WONG, D., LIM, T. Soft handoff in CDMA mobile system. IEEE Personal Commun, Dec 1997, p. 6 –17.
2. HAI JIANG, DAVIS, C. H. Coverage expansion and capacity improvement from soft handoff for cellular CDMA. IEEE Trans on Wireless Comm, Sept 2005, vol. 4, no, 5, p. 2163-2171.
3. VITERBI, A., VITERBI, A. M., GILHOUSEN, ZEHAVI, Soft handoff extend CDMA cell coverage and increases the reverse link capacity. IEEE J. Select Areas in Commun, Oct, 1994, vol. 12, no. 8, p. 1281 –1287.
4. NARAYANAN, K. R., STÜBER, G. L. A novel ARQ technique using the turbo coding principle. IEEE Commun. Letter, March 1997, vol. 41, p. 49–51.
5. BEN LU, XIAODONG WANG, JUNSHAN ZHANG Throughput of CDMA data networks with multi user detection, ARQ and Packet combining. IEEE Transactions on Wireless Communica- tions, September 2004, vol. 3, no. 5, p. 1576-1589.
6. CHASE, D. Code combining: A maximum-likelihood decoding approach for combining an arbitrary number of noisy packets. IEEE Trans. Commun., 1985, vol. 33, p. 385–393.
7. HIROTAKE ISHIGAMI, MAYUMI SHIMOTSU, YASUNORI IWANAMI, EIJI OKAMOTO Adaptive Hybrid ARQ schemes with bit-LLR based packet combining through MIMO-OFDM eigen-mode channels. In Proceedings of IEEE TENCON, Nov. 2006, p. 1 - 4 .
8. BUTT, M. M., FRICKE, J. CH., HOEHER, P. A. Reliability-based packet combining with application to interleave-division multiple access. In Turbo – Coding – 2006. Munich (Germany), April 3–7, 2006.
9. DEEPAK AYYAGARI, ANTHONY EPHREMIDES Cellular multicode CDMA capacity for integrated (voice and data) services. IEEE J.Select. Areas.Commun., May 1999, vol. 17, no. 5, p. 928 to 938.
10. KIM, J., HONIG, M. Resource allocation for multiple class of DS- CDMA traffic. IEEE Trans on Vehicular Technol, March 2000, vol. 49, no. 2, p. 506- 518.
11. KIM, J.Y., STUBER, G.L. CDMA soft HO analysis in the presence of power control error and shadowing correlation. IEEE Trans on Wireless Comm, April 2002, vol. 1, no. 2, p. 245-255.
12. DIPTA DAS (CHOUDHURI), KUNDU, S. Performance of packet data with variable processing gain and truncated ARQ in presence of soft handoff in cellular CDMA. In Proceedings of National Conference on Communication, 2008, IIT Bombay, p. 287-291.
13. SKLAR, B. Turbo code concepts made easy, or how I learned to concatenate and reiterate. In Proceedings of IEEE MILCOM, 1997, vol. 1, p. 20-26.
14. ROY, S. D., KUNDU, S. Performance of data services in cellular CDMA in presence of soft handoff and beamforming. In PIER 88, 2008, p. 73-89.
15. ROY, S. D., KUNDU, S. Forward link data service with beamforming and soft handoff in cellular CDMA. Engineering Letter, vol. 17, no. 2, p. 63 -72.

Keywords: Packet Combining, LLR, ARQ.

P. Tesar [references] [full-text] [Download Citations]
A New Method for Generating High Non-linearity S-Boxes

Substitution boxes are important parts in many block and stream ciphers. The emergence of a range of crypto-attacks has led to the development of criteria for repelling such attacks. The non-linearity criterion provides some protection against well- known attacks, such as linear cryptanalysis and differential cryptanalysis. The open problem is constructed by generating methods which will be rapid and will generate S-boxes with the highest possible non-linearity. This paper deals with a new rapid method for generating regular 8x8 S-boxes with non-linearity up to a value of 104. The new method combines the special genetic algorithm with total tree searching.

1. MILLAN, W. How to improve the nonlinearity of bijective S- Boxes. In Australian Conference on Information Security and Privacy, 1998, p. 181 - 192.
2. CLARK, J. A., JACOB, J. L., STEPNEY, S. The design of S- Boxes by simulated annealing. New Generation Computing Archive, September 2005, vol. 23, issue 3.
3. MILLAN, W., BURNETT, L., CARTER, G., CLARK, A., DAWSON, E. Evolutionary heuristics for finding cryptographically strong S-Boxes. Springer-Verlag, Lecture Notes in Computer Science, 1999, vol. 1726, p. 263 – 274.
4. MILLAN, W., CLARK, A., DAWSON, E. Boolean function design using hill climbing methods. In 4th Australian Conference on Information Security and Privacy. Ed. Bruce Schneier, Springer-Verlag, Lecture Notes in Computer Science, 1999, vol. 1587, p. 1 – 11.
5. MILLAN, W., CLARK, A., DAWSON, E. Heuristic design of cryptographically strong balanced Boolean functions. In Advances in Cryptology EUROCRYPT´98, Springer-Verlag, Lecture Notes in Computer Science, 1998, vol. 1403, p. 489 – 499.
6. BURNETT, L., CARTER, G., DAWSON, E., MILLAN, W. Efficient methods for generating MARS-Like S-Boxes. In 7th International Workshop on Fast Software Encryption 2000, Bruce Schneier, ed. Springer-Verlag, Lecture Notes in Computer Science, 2001, vol. 1978, p. 300 – 314.
7. IZBENKO, Y., KOVTUN, V., KUZNETSOV, A. The Design of Boolean Functions by Modified Hill Climbing Method (datasheet). 17 pages. [Online] Cited 2008. Available at: http://eprint.iacr.org/2008/111.pdf
8. Mac WILLIAMS, F.J., SLOANE, N.J.A. The Theory of Error Correcting Codes. Amsterdam: North-Holland Publishing Company, 1978.

Keywords: Cryptography, regular 8x8 S-box, non-linearity criterion, generation method.

J. Blumenstein, Z. Fedra [references] [full-text] [Download Citations]
The PAPR and Simple PAPR Reduction of the 2D Spreading Based Communication Systems

This paper deals with Peak to Average Power Ra- tio (PAPR) characteristics and the theory of variable spread- ing factor orthogonal frequency and code division multiplex- ing (VSF-OFCDM) systems. Comparison and evaluation of PAPR of VSF-OFCDM systems with various 2D spreading factors (SF) are done in time and in frequency domain. The simple PAPR reduction approach based on random chip in- terleaving is also evaluated.

1. FAZEL, K., KAISER, S. Multi-Carrier and Spread Spectrum Systems. 1st ed. Chichester (England): Wiley, 2003.
2. MAEDA, N., KISHIYAMA, Y., ATARASHI, H., SAWAHASHI, M. Variable spreading factor-OFCDM with two dimensional spreading that priorizes time domain spreading for forward link broadband wireless access. IEICE Transactions on Communications, 2005, vol.E88-B, no. 2.
3. HANZO, L., MUNSTER, M., CHOI, B. J., KELLER, T. OFDM and MC-CDMA for Boardband Multi-User Communications, WLANs and Broadcasting, 1st ed. Chichester (England): Wiley, 2004.
4. HENG, K., ZENG, G., WANG, W. Performance analysis for OFDM-CDMA with joint frequency-time spreading. IEEE Transactions on Broadcasting, 2005, vol. 51, no. 1, p. 144-148.
5. ATARASHI, H. Broadband Packet Wireless Access and Its Experiments. [Online] Cited 2008-04-16. Available at: www.ctr.kcl.ac.uk/pages/4gforum/2003/presentations/Asia/Atarashi.
6. JOYDEEP, A. Two Dimensional Spreading for Doubly Dispersive Channels. Diploma thesis. New Jersey: The State University of New Jersey, 2005.
7. BLUMENSTEIN, J., FEDRA, Z. The characteristics of the 2D spreading based communication systems. In Proceedings of 19th International Conference Radioelektronika 2009. Bratislava (Slovakia), 2009, p. 277-279.
8. TELLADO J. Multicarrier Modulation with Low PAR Applications to DSL and Wireless. Norwell (USA): Kluwer Academic Publishers, 2000.
9. FEDRA Z., MARSALEK R., SEBESTA V. Chip interleaving and its optimization for PAPR reduction in MC-CDMA. Radioengineering, 2007, vol. 16, no. 4, p. 19-23.

Keywords: VSF-OFCDM, OFDM-CDMA, 2D Spreading, PAPR.

A. Kalaycioglu, H. G. Ilk [references] [full-text] [Download Citations]
A Robust Threshold for Iterative Channel Estimation in OFDM Systems

A novel threshold computation method for pilot symbol assisted iterative channel estimation in OFDM systems is considered. As the bits are transmitted in packets, the proposed technique is based on calculating a particular threshold for each data packet in order to select the reliable decoder output symbols to improve the channel estimation performance. Iteratively, additional pilot symbols are established according to the threshold and the channel is re-estimated with the new pilots inserted to the known channel estimation pilot set. The proposed threshold calculation method for selecting additional pilots performs better than non-iterative channel estimation, no threshold and fixed threshold techniques in poor HF channel simulations.

1. DONG, X., LU, W-S., SOONG, A. C. K. Linear interpolation in pilot symbol assisted channel estimation for OFDM. IEEE Transactions on Wireless Communications, 2007, vol. 6, no. 5, p. 1910-1920.
2. DOUILLARD, C., JEZEQUEL, M., BERROU, C., PICART, A., DIDIER, P., GLAVIEUX, A. Iterative correction of intersymbol interference: Turbo equalization. European Transactions on Telecommunication, 1995, vol.6, p.507-511.
3. OTNES, R., TUCHLER, M. Iterative channel estimation for turbo equalization of time-varying frequency-selective channels. IEEE Transactions on Wireless Communications, 2004, vol. 3, no. 6, p. 1918-1923.
4. SONG, S., SINGER, A. C., SUNG, K. M. Soft input channel estimation for turbo equalization. IEEE Transactions on Signal Processing, 2004, vol. 52, no. 10, p. 2885-2894.
5. DAVIS, L. M., COLLINGS, I. B., HOEHER, P., Joint MAP equalization and channel estimation for frequency-selective and frequency-flat fast fading channels. IEEE Transactions on Communications, 2001, vol. 49, no. 12, p. 2106-2114.
6. VALENTI, M. C., WOERNER, B. D. Iterative channel estimation and decoding of pilot symbol assisted turbo codes over flat-fading channels. IEEE Journal on Selected Areas in Communications, 2001, vol. 19, no. 9, p. 1697-1705.
7. FLANAGAN, M. F., FAGAN, A. D. Iterative channel estimation, equalization, and decoding for pilot-symbol assisted modulation over frequency selective fast fading channels. IEEE Transactions on Vehicular Technology, 2007, vol. 54, no. 4, p. 1661-1670.
8. NEFEDOV, N., PUKKILA, M. Iterative channel estimation for GPRS. In The 11th IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, 2000, PIMRC 2000, vol. 2, p. 999-1003.
9. LASAULCE, S., SELLAMI, N. On the impact of using unreliable data on the bootstrap channel estimation performance. In 4th IEEE Workshop on Signal Processing Advances Communications, SPAWC 2003, p. 348-352. in Wireless
10. NIU, H., RITCEY, J. A. Iterative channel estimation and decoding of pilot symbol assisted LDPC coded QAM over flat fading channels. In Conference Record of the Thirty-Seventh Asilomar Conference on Signals, Systems and Computers, 2003, vol. 2, p. 2265-2269.
11. AUER, G., BONNET, J. Threshold controlled iterative channel estimation for coded OFDM. In Proc. of IEEE 65th Vehicular Technology Conference, 2007, VTC2007-Spring, p. 1737-1741.
12. OZBEK, B., LE RUYET, D., PANAZIO, C. Pilot-symbol-aided iterative channel estimation for OFDM-based systems. In 13th European Signal Processing Conference, EUSIPCO’05. Antalya (Turkey), 2005.
13. URETEN, O., SERINKEN, N. Decision directed iterative equalization of OFDM symbols using non-uniform interpolation. In IEEE 64th Vehicular Technology Conference, 2006, VTC 2006 Fall, p. 1-5.
14. GALLAGER, R. G. Low-density parity-check codes. IRE Transactions on Information Theory, 1962, vol. 7, p. 21-28.
15. ITU-R F.1487, ITU-R Recommendation, Testing HF modems with bandwidths up to about 12 kHz using ionospheric channel simulators. Geneva, 2000.
16. CHEN, J., DHOLAKIA, A., ELEFTHERIOU, E., FOSSORIER, M. P. C., HU, X. Y. Reduced-complexity decoding of LDPC codes. IEEE Transactions on Communications, 2005, vol. 53, no. 8, p. 1288-1299.

Keywords: Adaptive threshold, additional pilot symbols, error correction decoder, soft outputs, HF.

J. Mihalik [references] [full-text] [Download Citations]
Modeling of Human Head Surface by Using Triangular B-Splines

The paper deals with modeling of human head surface on the basis of quadratic triangular B-splines for the standard videocodec MPEG-4 SNHC. First, we define a triangular B-spline surface of any degree and then we present its calculation for modeling of the quadratic form. Next, we apply the quadratic triangular B-splines on modeling of the human head surface using 3D polygonal model Candide 3-1-6. For allocation of knots belonging to vertices of triangulation of the model, the limiting conditions are specified in the method of Monte-Carlo used for their generation. To achieve smoothness of the modeled human head surface, we propose an algorithm for calculating control points. Then for the proposed net of control points as well as the allocation of knots, the results of the modeled human head surface and its textured version using a texture of selected avatar are presented.

1. JOSLIN, CH., PANDZIC, I, S., THALMANN, N. M. Trends in networked collaborative virtual environments. Computer Communications, 2003, vol. 26, no. 5, p. 430 – 437.
2. THALMANN, N. M., THALMANN, D. Handbook of Virtual Humans. Chichester (England): Wiley, 2004.
3. The special issue of the IEEE Trans. on Circuits and Systems for Video Technology on MPEG-4 SNHC, July 2004.
4. STRINTZIS, M., SARRIS, N. (Ed.). 3D modeling and Animation: Synthesis and Analysis Techniques for the Human Body. Hershey (USA): IRM Press, July 2004.
5. MIHALIK, J., MICHALCIN, V. Animation of 3D model of human head. Radioengineering, 2007, vol. 16, no. 1, p. 58 – 66.
6. MIHALIK, J., MICHALCIN, V. Texturing of surface of 3D human head model. Radioengineering, 2004, vol. 13, no. 4, p. 44 – 47.
7. PIEGL, L., TILLER, W. Parametrization for surface fitting in reverse engineering. Computer Aided Geometric Design, 2001, vol. 33, no. 11, p 593 – 603.
8. NEAMTU, M. What is the Natural Generalization of Univariate Splines to Higher Dimensions? Nashville (USA): Vanderbilt University Press, 2001.
9. FONG, P., SEIDEL, H. P. An implementation of triangular B-spline surfaces over arbitrary triangulations. Computer Aided Geometric Design, 1993, vol. 25, no. 10, p.265 – 267.
10. DAHMEN, W., MICCHELLI, C. A., SEIDEL, H. P. Blossoming begets B-splines built better by B-patches. Mathematics of Computation, 1992, vol. 59, no. 7, p.97 – 115.
11. GREINER, G., SEIDEL, H. P. Modeling with triangular B-splines. IEEE Computer Graphics and Applications, 1994, vol.14, p.56 – 60.
12. PRAUTZSCH, H., BOEHM, W., PALUSZNY, M. Bezier and B-Spline Techniques. Berlin: Springer Verlag, 2002.
13. ROSSE, C., ZEILFELDER, F., NUMBERGER, G., SIEDEL, H. P. Reconstruction of volume data with quadratic super splines. Transactions on Visualization and Computer Graphics, 2004, p. 38 – 42.
14. TRAAS, C. R. Practice of bivariate quadratic simplicial splines. Computation of Curves and Surface. Kluwer Academic, 1990.
15. HARMAN, K., LABSIK, U., GREINER, G. Remeshing tri- angulated surfaces with optimal parametrizations. Computer Aided Geometric Design, 2001, vol. 33, no. 11, p.779 – 788.
16. AHLBERG, J. Candide-3: An Updated Parameterised Face. Rep. No. LiTH-ISY-R-2326, 2001.
17. DAHMEN, W., MICCHELLI, C. A. Multivariate splines – a new constructive approach. Surfaces in Computer Aided Geometric Design. Amsterdam: North-Holland, 1992.

Keywords: Triangular B-splines, modeling, human head surface, 3D polygonal model, control net.

J. Macica, P. Farkas, S. Krile [references] [full-text] [Download Citations]
Other Computational Technique for Estimation of Lower Bound on Capacity of Two-Dimensional Diamond-1 Constrained Channel

Computational technique for lower bound on Two-dimensional Diamond-1 constrained channel capacity is presented in this paper. It is basically an amalgamation of Matrix Fractal Grow Method (MFGM) and a new Matrix Fractal Reduction Method both applicable to state transition matrices of the corresponding constrained channels and Rayleigh Quotient Iteration method. Also other programming tricks are presented which improve its implementation. Estimation of lower bound values on the mentioned capacity is made using it. The results are in good alignment with known exact results, which is a verification of the new method. The method could be generalized for other constraints which are restricted only on one neighbor symbol in 2D constrained channel such as for example Square-1 and Hexagonal-1.

1. DEMIRKAN, I., SIEGEL, P. H., WOLF, J. K. Error event characterization on 2-D ISI channels. IEEE Transactions on Information Theory, vol. 55, no., 3, March 2009, p. 1146-1152.
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Keywords: Two-dimensional, constrained channel, run-length limited (RLL) channel, hard square, Diamond-1, capacity, estimation, lower bound, Rayleigh Quotient Iteration method, state transition matrix, fractal, computation.

H. Yang, X. Sun, G. Sun, Z. Tian [references] [full-text] [Download Citations]
Lossless Authentication Watermarking Based on Adaptive Modular Arithmetic

Reversible watermarking schemes based on modulo-256 addition may cause annoying salt-and-pepper noise. To avoid the salt-and-pepper noise, a reversible watermarking scheme using human visual perception characteristics and adaptive modular arithmetic is proposed. First, a high-bit residual image is obtained by extracting the most significant bits (MSB) of the original image, and a new spatial visual perception model is built according to the high-bit residual image features. Second, the watermark strength and the adaptive divisor of modulo operation for each pixel are determined by the visual perception model. Finally, the watermark is embedded into different least significant bits (LSB) of original image with adaptive modulo addition. The original image can be losslessly recovered if the stego-image has not been altered. Extensive experiments show that the proposed algorithm eliminates the salt-and-pepper noise effectively, and the visual quality of the stego-image with the proposed algorithm has been dramatically improved over some existing reversible watermarking algorithms. Especially, the stegoimage of this algorithm has about 9.9864 dB higher PSNR value than that of modulo-256 addition based reversible watermarking scheme.

1. ZHANG, X., WANG, S. Statistical fragile watermarking capable of locating individual tampered pixels. Signal Processing Letters, 2007, vol. 14, no. 10, p. 727-730.
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6. HSIEN-WEN TSENG, CHI-PIN HSIEH Reversible data hiding based on image histogram modification. Imaging Science Journal, 2008, vol. 56, no. 5, p. 271-278.
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Keywords: Adaptive modular arithmetic, salt-and-pepper noise, lossless watermarking, visual perception.

Y. Xing, J. Tan [references] [full-text] [Download Citations]
A Color Image Watermarking Scheme Resistant against Geometrical Attacks

The geometrical attacks are still a problem for many digital watermarking algorithms at present. In this paper, we propose a watermarking algorithm for color images resistant to geometrical distortions (rotation and scaling). The singular value decomposition is used for watermark embedding and extraction. The log-polar map- ping (LPM) and phase correlation method are used to register the position of geometrical distortion suffered by the watermarked image. Experiments with different kinds of color images and watermarks demonstrate that the watermarking algorithm is robust to common image processing attacks, especially geometrical attacks.

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Keywords: Digital watermarking, geometrical attacks, LPM, phase correlation.

M. Kallel, M. S. Bouhlel, J. Lapayre [references] [full-text] [Download Citations]
Use of Multi-Watermarking Schema to Maintain Awareness in a Teleneurology Diagnosis Platform

Following the tremendous evolution of transferring images through the Internet, it is necessary to ensure security during this act, especially for medical images. The application of multiple watermarking tech- nique represents a solution to preserve the security of such data on the one hand, and the traceability of medical diagnoses made by doctors on the other hand. This falls under the remote collaborative work. This technique is applied in the TeNeCi (Collaborative tele-neurology) platform. The project allows practitioners to distribute the analyses of the medical images. In fact, we used the multiple watermarking technique in a wavelet field. The theory underlying this technique is to hide information in the medical image and at the same time to ensure its imperceptibility. The diagnosis made by the practitioner is the data inserted in the image. The fundamental challenge of this paper is how to hide the total diagnoses of each practitioner in the image ensuring a good quality of the image at the same time.

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4. MOULIN, T., BERGER, E., LEMOUNAUD, P., TATU, L., VUILLIER, F., SABLOT, D., TABAILLOUX, D., REVENCO, E., NEIDHART, A., RUMBACH, L. Consultations de neurologie en urgence dans un centre hospitalier universitaire: Apport du neurologue dans la prise en charge du patient. Revue Neurologique, 2000, vol. 156, no. 10, p. 727 – 735.
5. FOURATI KALLEL, I., BOUHLEL M.-S., LAPAYRE, J.-C., GARCIA, E. Control of dermatology image integrity using reversible watermarking. International Journal of Imaging Systems and Technology, 2009, vol. 19, no. 1, p. 5 – 9.
6. KAMSTRA, L., HEIJMANS, H. J. A. M. Reversible data embed- ding into images using wavelet techniques and sorting. IEEE Transactions on Image Processing, 2005, vol. 14, no. 12, p. 2082 – 2090.
7. BOUHLEL, M.-S., TRICHLI, H., KAMOUN, L. A review of watermarking techniques, applications, properties and domains. Journal of testing and evaluation for applied sciences and engineering, 2003, vol. 31, no. 4, p. 357 – 360.
8. FOURATI KALLEL, I., BOUHLEL, M.-S. A new fragile water- marking for medical images based on the human visual system. In 3rd International Symposium on Image/Video Communications over fixed and mobile networks ISIVC 2006. Hammamet (Tunisia), 2006,
9. CHEMAK, C., LAPAYRE, J.-C., BOUHLEL, M.-S. New water- marking scheme for security and transmission of medical images for PocketNeuro project. Radioengineering, 2007, vol. 16, no. 4, p. 58 – 63.
10. KALLEL, M., LAPAYRE, J.-C., BOUHLEL, M.-S. A multiple watermarking scheme for medical image in the spatial domain. International Journal on Graphics,Vision and Image Processing, 2007, vol. 7, no. 1, p. 37 – 42.
11. KALLEL, M., BOUHLEL, M.-S., LAPAYRE, J.-C. A new multiple watermarking schema for medical image in frequency field. In 4th International Conference: Sciences of technologies of Information and Telecommunications SETIT 2009. Hammamet (Tunisia), 2009.
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Keywords: Multiple watermarking, medical images, TeNeCi project, wavelet transform, traceability.

M. Kubicek, Z. Kolka [references] [full-text] [Download Citations]
Blind Oversampling Data Recovery with Low Hardware Complexity

The paper is focused on the optimization and implementation of fully digital feed-forward blind oversampling CDR (BO-CDR). Two new phase-decision algorithms are proposed. Their complexity is very low, enabling a very simple and fast implementation even in FPGA, which was used as a development platform as well as a target device for the BO-CDR block. The FPGA-based optimization gave the opportunity to perform on-the-fly optimization under real conditions of target link. This greatly shortened the development time as there were no errors caused by inaccurate simulation models.
Measurement results obtained on real links are included showing the jitter tolerance of the proposed algorithms to be comparable to the performance of modern PLL-based CDRs.

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10. Xilinx, Inc., 2100 Logic Drive San Jose, CA 95124-3400, USA. Data Recovery (xapp224). [online], 2000, cit. [2007-10-15]. Available at http://www.xilinx.com/support/documentation/ application_notes/xapp224.pdf.
11. Micrel Inc. 2180 Fortune Drive San Jose, CA 95131, USA. SY87701V Clock and Data Recovery. [online], 2003 [cit. 2007-09-10]. Available at http://www.micrel.com/_PDF/HBW/ sy87700v.pdf.
12. Analog Devices, Inc., 3 Technology Way Norwood, MA 02062, USA. Fiber Optic Receiver with Quantizer and Clock Recovery and Data Retiming [online], 2000 [cit. 2009-06-12]. Available at http://www.analog.com/static/imported-files/data_sheets/ AD807.pdf>

Keywords: Blind Oversampling CDR, FPGA, jitter.

P. Pocta, J. Holub, H. Vlckova, Z. Polkova [references] [full-text] [Download Citations]
Impact of Different Active-Speech-Ratios on PESQ’s Predictions in Case of Independent and Dependent Losses (in Presence of Receiver-Side Comfort-Noise)

This paper deals with the investigation of PESQ’s behavior under independent and dependent loss conditions from an Active-Speech-Ratio perspective in presence of receiver-side comfort-noise. This reference signal characteristic is defined very broadly by ITU-T Recommendation P.862.3. That is the reason to investigate an impact of this characteristic on speech quality prediction more in-depth. We assess the variability of PESQ’s predictions with respect to Active-Speech-Ratios and loss conditions, as well as their accuracy, by comparing the predictions with subjective assessments. Our results show that an increase in amount of speech in the reference signal (expressed by the Active-Speech-Ratio characteristic) may result in an increase of the reference signal sensitivity to packet loss change. Interestingly, we have found two additional effects in this investigated case. The use of higher Active-Speech-Ratios may lead to negative shifting effect in MOS domain and also PESQ’s predictions accuracy declining. Predictions accuracy could be improved by higher packet losses.

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23. CHOCHLIK, M., GRONDZAK, K., BABOS, S. Windows operating system core programming. University of Zilina, Zilina (Slovakia), 2009, ISBN 978-80-8070-970-9 (in Slovak).
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25. JIANG W., SCHULZRINNE, H. QoS Measurement of Internet Real-Time Multimedia Services. Technical Report, CUCS-015-99, Columbia University (USA), Dec. 1999.
26. SANNECK H., LE, N. T. L. Speech property-based FEC for Internet telephony applications. In Proceedings of the SPIE/ACM SIGMM Multimedia Computing and Networking Conference. San Jose (USA), 2000, p. 38–51.
27. ITU-T Rec. P.830: Subjective Performance Assessment of Digital Telephone-Band and Wideband Digital Codecs. International Telecommunication Union, Geneva (Switzerland), 1996.
28. RAAKE, A. Speech Quality of VoIP: Assessment and Prediction. Chichester (UK): John Wiley&Sons, 2006. Chapter 3, pp. 51-110, ISBN 0-470-03060-7.
29. TAKAHASHI, A. Objective Quality Evaluation Based on ITU-T Recommendation P.862 by Using Long Reference Speech (NTT), COM12-D008. International Telecommunication Union, Geneva (Switzerland), January 2005.
30. ITU-T Rec. G.191: Software Tools for Speech and Audio Coding Standardization. International Telecommunication Union, Geneva (Switzerland), 2005.
31. JIANG W., SCHULZRINNE, H. Modelling of packet loss and delay and their effect on real-time multimedia service quality. In Proceedings of 10th International Workshop Network and Operations System Support for Digital Audio and Video (NOSSDAV 2000). Chapel Hill (USA), 2000.

Keywords: Perceptual Evaluation of Speech Quality (PESQ), speech quality, intrusive measurement, Voice over Internet Protocol (VoIP), reference signal characteristic, Active-Speech-Ratio, comfort-noise.

P. Pecho, P. Hanacek, J. Nagy [references] [full-text] [Download Citations]
Simulation and Evaluation of CTP and Secure-CTP Protocols

The paper discusses characteristics and qualities of two routing protocols – Collection Tree Protocol and its secure modification. The original protocol, as well as other protocols for wireless sensors, solves only problems of ra- dio communication and limited resources. Our design of the secure protocol tries to solve also the essential security ob- jectives. For the evaluation of properties of our protocol in large networks, a TOSSIM simulator was used. Our effort was to show the influence of the modification of the routing protocol to its behavior and quality of routing trees. We have proved that adding security into protocol design does not necessarily mean higher demands for data transfer, power consumption or worse protocol efficiency. In the paper, we manifest that security in the protocol may be achieved with low cost and may offer similar performance as the original protocol.

1. LEVIS, P., LEE, N. TOSSIM: A Simulator for TinyOS Networks. 2003.
2. FONSECA, R., GNAWALI, O., JAMIESON, K., KIM, S., LEVIS, P., WOO, A. Collection Tree Protocol (CTP). TEP 123 Draft, 2006.
3. STAJANO, F., CVRCEK, D., LEWIS, M. Steel, cast iron and con- crete: security engineering for real world wireless sensor networks. In Proceedings of Applied Cryptography and Network Security Con- ference ACNS. Santa Fe (USA), 2008, p. 460-478.
4. PLATON, E., SEI, Y. Security software engineering in wireless sen- sor networks. In Progress in Informatics. National Institute of Infor- matics, 2008.
5. TinyOS 2.0.2 Documentation. [Online] Cited 2009-03-24. Available at: http://www.tinyos.net/tinyos-2.x/doc/
6. PECHO, P., ZBORIL, F., JR., DRAHANSKıY, M., HANACEK, P. Agent platform for wireless sensor network with support for crypto- graphic protocols. Journal of Universal Computer Science (in press).
7. PECHO, P. Security of Wireless Sensor Networks. PhD thesis. Brno: Brno University of Technology, 2009 (to be published).
8. FIPS 81: Operational modes of DES. Federal Information Process- ing Standard (FIPS), Publication 81. Washington D.C.: National Bu- reau of Standards, U.S. Department of Commerce.
9. BUONADONNA, P., HILL, J., CULLER, D. Active message com- munication for tiny networked sensors. In 20th Annual Joint Confer- ence of the IEEE Computer and Communications Societies. Anchor- age (Alaska), 2001.
10. Chipcon AS, Texas Instruments. CC2420: 2.4 GHz IEEE 802.15.4 / ZigBee-ready RF Transceiver. Datasheet. 2006.

Keywords: Routing protocol, wireless sensor networks, security.

M. Kovac, J. Kolouch [references] [full-text] [Download Citations]
Analysis for Design and Transformation of Autosynchronous State Machines

The paper deals with design and transformation methodology of autosynchronous state machines. The result is the design methodology for autosynchronous state machines with one-hot and Gray encodings. On the basis of their simulation models the timing parameters are defined and conditions for the correct behavior are pointed out.
In order to simplify the design of these state machines, the transformation methodology of synchronous state machine in VHDL at RTL level to autosynchronous state machine is designed. These transformed state machines are compared in their chip area, power consumption and timing.

1. REICHARDT, J., SCHWARZ, B. Digital Systems: Handout. 3rd edition. Hamburg: University of Applied Sciences. 2004. 150 p.
2. FUHRER, M. R., LIN, B., NOWICK, M. S. Algorithms for the optimal state assignment of asynchronous state machines. In 16th Conference on Advanced Research in VLSI. Chapel Hill (North Carolina, USA), 2001, p. 59-75. ISBN-13: 9780818670473.
3. TINDER, F. R. Engineering Digital Design. 2nd edition, revised. Academic Press-Elsevier, 2000. 884 p. ISBN-13: 978-0-12- 691295-1.
4. FANT, K., BRANDT, S. Null convention logic, a complete and consistent logic for asynchronous digital circuit synthesis. In International Conference on Application Specific Systems, Architectures, and Processors (ASAP '96). Chicago (Illinois, USA), 1996, p. 261–273. ISBN 0-8186-7542-X.
5. VANSCHEIK, S. W., TINDER, F. R. High speed externally asynchronous/internally clocked systems. IEEE Transactions on Computers, 1997, vol. 46, no. 7, p. 824-829, ISSN 0018-9340.
6. SPARSO, J., FURBER, S. Principles of Asynchronous Circuit Design - A System Perspective. Boston: Kluwer Academic Publishers, 2001. ISBN 0-7923-7613-7.
7. CORTADELLA, J., KONDRATYEV, A., LAVAGNO, L., SOTIRIOU, P. CH. Desynchronization: synthesis of asynchronous circuits from synchronous specifications. IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems, 2006, vol. 25, no. 10, p. 1904-1921, ISSN 0278-0070.

Keywords: Autosynchronous circuit, state machine, VHDL, RTL, transformation, one-hot encoding, Gray encoding.

J. Lacik, I. E. Lager, Z. Raida [references] [full-text] [Download Citations]
Multicriteria Optimization of Antennas in Time-Domain

An original approach to the time-domain multicriteria optimization of antennas is presented. For a given excitation pulse, the time-domain objective function takes the “time-domain impedance matching”, distortion of responses at the feeding point and in a desired radiating direction (with respect to the excitation pulse), and the radiated energy in the desired direction into account. The objective function is tested on the optimization of a bow-tie antenna using the particle swarm optimization. The proposed approach is suitable for the design of broadband antennas.

1. WEILE, S. D., PISHARODY, G., CHEN, N., SHANKER, B., MICHIELSSEN, E. A novel scheme for the solution on the time- domain integral equations of electromagnetics. IEEE Transactions on Antennas and Propagation, 2004, vol. 52, no. 1, p. 283 – 295.
2. CHUNG, Y. S., SARKAR, T. K., JUNG, B. H., SALZAR- PALMA, M., JI, Z., JANG, S., KIM, K. Solution of time domain electric field integral equation using the Laguerre polynomials. IEEE Transactions on Antennas and Propagation, 2004, vol. 52, no. 9, p. 2319 – 2328.
3. LACIK, J., RAIDA, Z., Modeling microwave structure in time domain using Laguerre polynomials. Radioengineering, 2006, vol. 15, no. 3, p. 1 – 9.
4. ANDRIULLI, F. P., BAGCI, H., VIPIANI, F., VECCHI, G., MICHIELSSEN, E., A marching on-in-time hierarchical scheme for the solution of the time domain electric field integral equation. IEEE Transactions on Antennas and Propagation, 2007, vol. 55, no. 12, p. 3734 – 3738.
5. FERNANDEZ-PANTOJA, M., MONORCHIO, A., RUBIO- BRETONES, A., GOMEZ-MARTIN, R., Direct GA-based optimisation of resistively loaded wire antennas in the time domain. Electronics Letters, 2000, vol. 36, no. 24, p. 1988 – 1990.
6. LAHTI, B. P., Signal Processing and Linear Systems, Carmichael: Cambridge press, 1998, ch. 1-2.
7. ALLEN, O. E., HILL, A., ONDREJKA, A. R., Time-domain antenna characterizations. IEEE Transactions on Electromagnetic Compatibility, 1993, vol. 35, no. 3, p. 339 – 346.
8. KRAUS, D. J., MARHEFKA, R. J., Antenna for All Applications. New York: McGraw-Hill, 2002, ch. 11.
9. MAKAROV, S. N., Antenna and EM Modelling with Matlab. New York: Wiley, 2002, ch. 4.
10. ROBINSON, J., RAMAT-SAMII, Y., Particle swarm optimization in electromagnetics. IEEE Transactions on Antennas and Propagation, 2004, vol. 52, no. 2, p. 397 – 407.
11. RAO, S. M., WILTON, D. R., GLISSON, A. W. Electromagnetic scattering by surfaces of arbitrary shape. IEEE Transactions on Antennas and Propagation, 1982, vol. 30, no. 3., p. 409 – 418.

Keywords: Multicriteria optimization, particle swarm optimization (PSO), time domain integral equation (TDIE).

G. S. Kirov, D. P. Mihaylova [references] [full-text] [Download Citations]
Circularly Polarized Aperture Coupled Microstrip Antenna with Resonant Slots and a Screen

A broadband circularly polarized (CP) Aperture Coupled Microstrip Antenna (ACMSA) is described herein. In order to decrease the back radiation of the antenna due to resonant coupling slots (a cross-slot) in the ground plane, a three-layer structure with a screen is proposed. As a result, the back radiation of the antenna is reduced by more than 12 dB and its gain is increased by about 1.3 dB compared to the conventional two-layer ACMSA with nonresonant coupling slots. The antenna is designed to operate within the Ku-band. Keeping its simple and compact construction and high mechanical characteristics it can be used as an element of CP microstrip antenna arrays with various applications in the contemporary communication systems. A comparison with two similar CP antennas with resonant slots, a two-layer ACMSA and a three-layer ACMSA with a patch reflector is accomplished.

1. WATERHOUSE, R., NOVAK, D. Printed Antennas for Wireless Communications. John Wiley & Sons, Ltd., 2007, ch. 1.
2. GARG, R., BHARTIA, P., BAHL, I., ITTIPIBOON, A. Microstrip Antenna Design Handbook. Boston, London: Artech House, 2001, ch. 9.
3. VLASITS, T., KOROLKIEWICZ, E., SAMBELL, A., ROBINSON, B. Performance of a cross-aperture coupled single feed circularly polarized patch antenna. Electronics Letters, 1996, vol. 32, no. 7, p. 612 - 613.
4. POZAR, D. M., DUFFY, S. M. A dual-band circularly polarized aperture-coupled stacked microstrip antenna for global positioning satellite. IEEE Transactions on Antennas and Propagation, 1997, vol. 45, no. 11, p. 1618 - 1625.
5. TARGONSKI, S. D., POZAR, D. M. Design of wideband circularly polarized aperture-coupled microstrip antennas. IEEE Transactions on Antennas and Propagation, 1993, vol. 41, no. 2, p. 214 - 220.
6. ALONI, E., KASTNER, R. Analysis of a dual circularly polarized microstrip antenna fed by crossed slots. IEEE Transactions on Antennas and Propagation, 1994, vol. 42, no. 8, p. 1053 - 1058.
7. MIHAYLOVA, D. P., KIROV, G. S. Circularly polarized broadband microstrip antenna. E + E, 2009, no. 9/10, p. 60 – 67. (In Bulgarian).
8. MIHAYLOVA, D. P., KIROV, G. S., SAVVA, M. N. Circularly polarized aperture coupled microstrip antenna with resonant slots and a patch reflector. Journal of Applied Electromagnetism, 2009, vol. 11, no. 2, p. 1 - 10.
9. HUANG, C.-Y., WU, J.-Y., WONG, K.-L. Cross – slot – coupled microstrip antenna and dielectric resonator antenna for circular polarization. IEEE Transactions on Antennas and Propagation, 1999, vol. 47, no. 4, p. 605 - 609.

Keywords: Aperture coupled microstrip antenna, back radiation reduction, circularly polarized microstrip antenna, cross-slot coupled, microstrip antenna with resonant slots.

P. Valtr, P. Pechac, V. Kvicera, M. Grabner [references] [full-text] [Download Citations]
A Terrestrial Multiple-Receiver Radio Link Experiment at 10.7 GHz - Comparisons of Results with Parabolic Equation Calculations

This work presents the results of a terrestrial multiple-receiver radio link experiment at 10.7 GHz. Results are shown in the form of the power levels recorded at several antennas attached to a receiving mast. Comparisons of the measurement data with theoretical predictions using a parabolic equation technique show that, due to the complex propagation environment of the troposphere in terms of the refractive index of air, closer agreement between measurements and simulations can be achieved during periods of standard refractive conditions.

1. CRAIG, K. H. Propagation modelling in the troposphere: parabolic equation method. Electronics Letters, 1988, vol. 24, p. 1136-1139.
2. BARRIOS, A. E. Parabolic equation modeling in horizontally inhomogeneous environments. IEEE Transactions on Antennas and Propagation, 1992, vol. 40, p. 791-797.
3. GUNASHEKAR, S. D., WARRINGTON, E. M., SIDDLE, D. R., VALTR, P. Signal strength variations at 2 GHz for three sea paths in the British Channel Islands: detailed discussion and propagation modeling. Radio Science, 2007, vol. 42.
4. SIRKOVA, I., MIKHALEV, M. Parabolic-equation-based study of ducting effects on microwave propagation. Microwave and Optical Technology Letters, 2004, vol. 42, p. 390-394.
5. BARRIOS, A. E. A terrain parabolic equation model for propagation in the troposphere. IEEE Transactions on Antennas and Propagation, 1994, vol. 42, p. 90-98.
6. LEVY, M. F. Parabolic equation modeling of propagation over irregular terrain. Electronics Letters, 1990, vol. 26, p. 1153-1155.
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8. ZAPOROZHETS, A. A., LEVY, M. F. Modelling of radiowave propagation in urban environment with parabolic equation method. Electronics Letters, 1996, vol. 32, p. 1615-1616.
9. DOCKERY, G. D. Modeling electromagnetic wave propagation in the troposphere using the parabolic equation. IEEE Transactions on Antennas and Propagation, 1988, vol. 36, p. 1464-1470.
10. KUTTLER, J. R., DOCKERY, G. D. Theoretical description of the parabolic approximation/Fourier split-step method of representing electromagnetic propagation in the troposphere. Radio Science, 1991, vol. 26, p. 381-393.
11. LEVY, M. F. Parabolic Equation Methods for Electromagnetic Wave Propagation. IEE Press, 2000.
12. GRABNER, M., KVICERA, V. Refractive index measurement at TV tower Prague. Radioengineering, 2003, vol. 12, p. 5-7.
13. DOCKERY, G. D., KUTTLER, J. R. An improved impedance-boundary algorithm for Fourier split-step solutions of the parabolic wave equation. IEEE Transactions on Antennas and Propagation, 1996, vol. 44, p. 1592–1599.
14. Electrical Characteristics of the Surface of the Earth. ITU-R Recommendation P.527-3, ITU 2008.

Keywords: Microwave radio propagation, radio propagation meteorological factors, refraction, microwave propagation modeling.

P. Kovacs, Z. Raida [references] [full-text] [Download Citations]
Global Evolutionary Algorithms in the Design of Electromagnetic Band Gap Structures with Suppressed Surface Waves Propagation

The paper is focused on the automated design and optimization of electromagnetic band gap structures suppressing the propagation of surface waves. For the optimization, we use different global evolutionary algorithms like the genetic algorithm with the single-point crossover (GAs) and the multi-point (GAm) one, the differential evolution (DE) and particle swarm optimization (PSO). The algorithms are mutually compared in terms of convergence velocity and accuracy. The developed technique is universal (applicable for any unit cell geometry). The method is based on the dispersion diagram calculation in CST Microwave Studio (CST MWS) and optimization in Matlab. A design example of a mushroom structure with simultaneous electromagnetic band gap properties (EBG) and the artificial magnetic conductor ones (AMC) in the required frequency band is presented.

1. YUEHE, G., ESSELLE, K. P., BIRD, T. S. A high-gain low-profile EBG resonator antenna. In Proc. of the Antennas and Propagation Society Int. Symp. Honolulu (USA), 2007, p. 1301 – 1304.
2. KERN, D.J., WERNER, D.H., MONORCHIO, A., LANUZZA, L., WILHELM, M.J. The design synthesis of multiband artificial magnetic conductors using high impedance frequency selective surfaces. IEEE Trans. Antennas Propag., 2005, vol. 53, no. 1, p. 8 – 17.
3. KOVACS, P., RAIDA, Z. Dispersion analysis of planar metallodielectric EBG structures in Ansoft HFSS. In Proc. of the 17th Int. Conf. on Microwaves, Radar and Wireless Communications. Wroclaw (Poland), 2008, p. 1 – 4.
4. KOVACS, P., RAIDA, Z., MARTINEZ-VAZQUEZ, M. Parametric study of mushroom-like and planar periodic structures in terms of simultaneous AMC and EBG properties. Radioengineering, 2008, vol. 17, no. 4, p. 19 – 24.
5. JOHNSON, J. M., RAHMAT-SAMII, Y. Genetic algorithms in engineering electromagnetics. IEEE Antennas and Propagation Magazine, 1997, vol. 39, no. 4, p. 7 – 21.
6. ZELINKA, I. Artificial Intelligence – Global Optimization. Prague: BEN, 2002. (In Czech.)
7. Differential evolution by Rainer Storn. [Online] Available at: http://www.icsi.berkeley.edu/~storn/code.html
8. ROBINSON, J., RAHMAT-SAMII, Y. Particle swarm optimization in electromagnetics. IEEE Trans. Antennas Propag., 2004, vol. 52, no. 2, p. 397 – 407.
9. SIEVENPIPER, D., ZHANG, L., BROAS, R. F. J., ALEXOPOULOS, N. G., YABLONOVITCH, E. High-impedance electromagnetic surfaces with a forbidden frequency band. IEEE Trans. Microw. Theory Tech., 1999, vol. 47, no. 1, p. 2059 – 2074.
10. SIEVENPIPER, D. F. High-Impedance Electromagnetic Surfaces. Ph.D. Thesis, Los Angeles: Univ. of California (UCLA), 1999.

Keywords: Electromagnetic band gap (EBG), optimization, genetic algorithm (GA), differential evolution (DE), particle swarm optimization (PSO), CST Microwave Studio (CST MWS), Matlab.

T. Ince [references] [full-text] [Download Citations]
FMCW Radar Performance for Atmospheric Measurements

Frequency-modulated continuous-wave radars (FMCW) have been used in the investigation of the atmosphere since the late 1960’s. FMCW radars provide tremendous sensitivity and spatial resolution compared to their pulsed counterparts and are therefore attractive for clear-air remote-sensing applications. However, these systems have some disadvantages and performance limitations that have prevented their widespread use by the atmospheric science community. In this study, system performance of atmospheric FMCW radar is analyzed and some measurement limitations for atmospheric targets are discussed. The effects of Doppler velocities and spectral widths on radar performance, radar’s near-field operation, and parallax errors for two-antenna radar systems are considered. Experimental data collected by the highresolution atmospheric FMCW radar is used to illustrate typical performance qualitatively based on morphological backscattered power information. A post-processing based on single-lag covariance differences between the Bragg and Rayleigh echo is applied to estimate clear-air component from refractive index turbulence and perform quantitative analysis of FMCW radar reflectivity from atmospheric targets.

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8. INCE, T. On performance of S-band fmcw radar for atmospheric observation. In Proceedings of the IEEE 15th Signal Processing and Communications Applications. Eskisehir (Turkey), 2007, p. 739 − 742.
9. DOVIAK, R. J., ZRNIC, D. S. Doppler Radar and Weather Observations. 2nd ed. San Diego: Academic Press, 1993.
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13. HANSEN, R. C. Microwave Scanning Antennas, vol. 1. Ed. by Hansen, R. C., Los Altos (USA): Penninsula Publishing, 1985.
14. SEKELSKY, S. M. Near-field reflectivity and antenna boresight gain corrections for millimeter wave atmospheric radars. Journal of Atmospheric and Oceanic Technology, 2002, vol. 19, no. 4, p. 468 – 477.
15. KAY, S. M. Fundamentals of Statistical Signal Processing, Volume 1: Estimation Theory, New York: Prentice-Hall, 1993.
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18. MUSCHINSKI, A., SULLIVAN, P. P., WUERTZ, D. B., HILL, R. J., COHN, S. A., LENSCHOW, D. H., DOVIAK, R. J. First synthesis of wind-profiler signals on the basis of large-eddy simulation data. Radio Science, 1999, vol. 34, no. 6, p. 1437 – 1459.

Keywords: Electromagnetic measurements, remote sensing, instruments and techniques.

C. Yang, J. Yang, M. Huang, J. Shi, J. Peng [references] [full-text] [Download Citations]
Electromagnetic Cylindrical Transparent Devices with Irregular Cross Section

Electromagnetic transparent device is very important for antenna protection. In this paper, the material parameters for the cylindrical transparent devices with arbitrary cross section are developed based on the coordinate transformation. The equivalent two-dimensional (2D) transparent devices under TE plane and cylindrical wave irradiation is designed and studied by full-wave simulation, respectively. It shows that although the incident waves are distorted in the transformation region apparently, they return to the original wavefronts when passing through the device. All theoretical and numerical results validate the material parameters for the cylindrical transparent devices with arbitrary cross section we developed.

1. PENDRY, J. B., SCHURIG, D., SMITH, D. R. Controlling electromagnetic fields. Science, 2006, vol. 312, no. 5781, p.1780 to 1782.
2. LEONHARDT, U. Optical conformal mapping. Science, 2006, vol. 312, no. 5781, p. 1777-1780.
3. SCHURIG, D., MOCK, J. J., JUSTICE, B. J., CUMMER, S. A., PENDRY, J. B., STARR, A. F., SMITH, D. R. Metamaterial electromagnetic cloak at microwave frequencies. Science, 2006, vol. 314, no. 5801, p. 977-980.
4. LEONHARDT, U., TYC, T. Broadband invisibility by non- euclidean cloaking. Science, 2009, vol. 323, no. 5910, p. 110-112.
5. LIU, R., JI, C., MOCK, J. J., CHIN, J. Y., CUI, T. J., SMITH, D.R. Broadband ground-plane cloak. Science, vol. 323, no. 5912, p. 366-369.
6. VALENTINE, J., LI, J., ZENTGRAF, T., BARTAL, G., ZHANG, X. An optical cloak made of dielectrics. Nature Materials, 2009, vol. 8, no. 7, p.568-571.
7. ALITALO, P., TRETYAKOV, S. Electromagnetic cloaking with metamaterials. Materials today, 2009, vol. 12, no. 3, p. 22-29.
8. LI, C., YAO, K., LI, F. Two-dimensional electromagnetic cloaks with non-conformal inner and outer boundaries. Optics Express, 2008, vol. 16, no. 23, p.19366-19374.
9. LI, C., LI, F. Two-dimensional electromagnetic cloaks with arbitrary geometries. Optics Express, 2008, vol. 16, no. 17, p. 13414-13420.
10. WU, Q., ZHANG, K., MENG, F. Y., LI, L. W. Material parameters characterization for arbitrary N-sided regular polygonal invisible cloak. J. Appl. Phys. D: Appl. Phys., 2009, vol. 42, no. 3, p. 035408.
11. LAI, Y., NG, J., CHEN, H. Y., HAN, D. Z., XIAO, J. J., ZHANG, Z. Q., CHAN, C. T. Illusion optics: the optical transformation of an object into another object. Phys. Rev. Lett., 2009, vol. 102, no. 25, p. 253902.
12. RAHM, M., SCHURIG, D., ROBERTS, D. A., CUMMER, S. A., SMITH, D. R., PENDRY, J. B. Design of electromagnetic cloaks and concentrators using form-invariant coordinate transformations of Maxwell’s equations. Photonics and Nanostructures- Fundamentals and Applications, 2008, vol. 6, no. 1, p. 87-95.
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18. CHEN, H. Y., LUO, X. D., MA, H. R., CHAN, C. T. The anti- cloak. Optic. Express, 2008, vol. 16, no. 19, p.14603-14608.
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21. LAI, Y., CHEN, H. Y., ZHANG, Z. Q., CHAN, C. T. Complementary media invisibility cloak that cloaks objects at a distance outside the cloaking shell. Phys. Rev. Lett., 2009, vol. 102, no. 9, p. 093901.
22. ALÙ, A., ENGHETA, N. Cloaking a sensor. Phys. Rev. Lett., 2009, vol. 102, no. 23, p. 233901.
23. YU, G. X., CUI, T. J., JIANG, W. X. Design of transparent structure using metamaterial. J. Infrared Milli Terahz Waves, 2009, vol. 30, no. 6, p. 633-641.
24. SCHURIG, D., PENDRY, J. B., SMITH, D. R. Calculation of material properties and ray tracing in transformation media. Optics Express, 2006, vol. 14, no. 21, p. 9794.

Keywords: Transparent device, transformation optics, metamaterials, finite element method.

O. Baran, M. Kasal [references] [full-text] [Download Citations]
Modeling of the Phase Noise in Space Communication Systems

Our work is focused on the investigation of an influence of an additive thermal noise and a multiplicative phase noise in space communication chains. The most important properties of both noise types are summarized. The main concern of this paper is on the multiplicative phase noise that is especially important in systems with the phase shift keying. The simulation procedure for modeling of a signal degraded by the multiplicative phase noise is described. One starts from the frequency domain, where noise properties are set up. Five basic phase noise types can be included. After a passing to the time domain, the final noisy signal is obtained. To prove the modeling correctness, two ways are used. Firstly, Allan variances are utilized as a time domain processing. Finally, for a comparison, the direct conversion formula from the frequency to the time domain is exploited. Created signal corrupted by the phase noise expresses the harmonic oscillator output signal. A pair of these oscillators, disturbed by different phase noise processes, is installed into a communication channel model and with its help, the simultaneous influence of both oscillators on the useful signal is examined. Results show a good coincidence with theoretical presumptions.

1. MARTIN, W. L., NGUYEN, T. M. CCSDS – SFCG Efficient Modulation Methods Study – A Comparison of Modulation Schemes – Phase 1: Bandwidth Utilization. Recommendation for space data system standards. CCSDS B20.0-Y, 1993.
2. SPACEK, J., KASAL, M. The low rate telemetry transmission simulator. Radioegineering, December 2007, vol. 16, no. 4, p. 24 to 31. ISSN 1210-2512.
3. KASAL, M. Frequency Synthesis in Communication Systems Experimental Satellites. Brno: Vutium, 2005. 35 p. ISBN: 80-214- 2982-8. (In Czech.)
4. PETTAI, R. Noise in Receiving Systems. New York: Wiley- Interscience, 1984. 296 pages. ISBN 0471892351.
5. HAJIMIRI, A., LEE, T. H. A General theory of phase noise in electrical oscillators. IEEE Journal of Solid-State Circuits, February 1998, vol. 33, no. 2, p. 179 – 194.
6. HAJIMIRI, A., LEE, T. Oscillator phase noise: A tutorial. IEEE Journal of Solid-State Circuits. March 2000, vol. 35, no. 3, p.326 to 336.
7. VASILESCU, G. Electronic Noise and Interfering Signals: Principals and Aplications. Berlin: Springer, 2005. 728 pages. ISBN 3540407413.
8. CHANG, K. Encyclopedia of RF and Microwave Engineering. New Jersey: John Willey & Sons, 2005. ISBN 0-471-27053-9.
9. KASAL, M. Radio Rellay and Satellite Communication. Lecture notes. Brno: MJ Servis, 2003. ISBN 80-214-2288-2. (In Czech.)
10. RILEY, J. Handbook of Frequency Stability Analysis. Beaufort: Hamilton Technical Services, 2007. Available on web: http://www.stable32.com/Handbook.pdf.
11. BAR-GUY, A. Oscillator Phase Noise Model. Matlab Central. An open exchange for the Matlab and Simulink user community. Available on web: http://www.mathworks.com/matlabcentral/fileexchange/8844.
12. HOWE, D. A., ALLAN, D. W., BARNES, J. A. Properties of Oscillator Signals and Measurement Methods. NIST, Boulder, Colorado. Available on web: http://tf.nist.gov/phase/Properties/main.htm.
13. LESAGE, P., AYI, T. Characterization of frequency stability: Analysis of the modified Allan variance and propertis of its estimate. IEEE Transactions on Instrumentation and Measurement, December 1984, vol. IM-33, no. 4, p. 332-336.

Keywords: Multiplicative phase noise, additive thermal noise, frequency stability, oscillator, Allan variances.

Y. Liu, C. Tao [references] [full-text] [Download Citations]
Feedback Compensation Algorithm for BPSK/QPSK Carrier Synchronization

This paper deals with carrier synchronization problem in coherent communication system, such as BPSK and QPSK. First, this paper surveys and analyzes currently existing carrier synchronization algorithms and relevant receiver structures. After an analysis of those methods, a novel algorithm called feedback compensation is proposed, including the receiver structures based on this new synchronization algorithm. This new algorithm can not only simplify the signal processing stage but also decouple the demodulator and carrier synchronization module. At last, FPGA implementation results are presented and discussed.

1. YUAN, H., HU, X., HUANG, J. Design and implementation of Costas loop based on FPGA. In 3rd IEEE Conference on Industrial Electronics and Applications ICIEA 2008. 3-5 June 2008, p. 2383-2388.
2. RODDEWIG, M., ZEKAVAT, S. A., NOOSHABADI, S. Design of a Costas loop downconverter. In 52nd IEEE International Midwest Symposium on Circuits and Systems MWSCAS’09. 2-5 Aug. 2009, p. 244-247.
3. MEI, X., TAO, C. Improved implementation of Costas loop for DQPSK receiver using FPGA. In International Conference on Communication Technology, ICCT’06. 27-30 Nov. 2006, p. 1-4.
4. OSBORNE, H. C. A generalized “Polarity-Type” Costas loop for tracking MPSK signals. IEEE Transactions on Communications, 1982, vol. Com-30, no. 10, p. 2289- 2296
5. PROAKIS, J. G. Digital Communication. (Fourth Edition). Chapter 6. McGraw-Hill, 2006.
6. NEZAMI, M., SUDHAKAR, R. New schemes for improving non data-aided symbol timing recovery for QAM receivers in flat fading channels. In EUROCOMM 2000. Information Systems for Enhanced Public Safety and Security. IEEE/AFCEA, p. 75 - 79.
7. NEZAMI, M., SUDHAKAR, R. M-QAM Digital symbol timing synchronization in flat Rayleigh fading channels. In PIMRC, Osaka (Japan), Nov-1999.
8. EFSTATHIO, D., AGHAYAMI, A. H. Feed forward synchronization techniques for 16-QAM TDMA demodulators. IEEE Trans. GlobeComm., 1996, vol. 2, p. 1432-1436.
9. NEZAMI, M. Symbol timing synchronization in burst wireless radios. In Fourth Wireless Symposium, SantaClara (CA), 1999.
10. NEZAMI, M. Synchronization in Digital Wireless Radio Receivers. Florida Atlantic Univ., doctoral dissertation, May 2001.

Keywords: Carrier synchronization, feedback compensation, receiver structure, FPGA based implementation.

J. Rumanek, J. Sebesta [references] [full-text] [Download Citations]
New Channel Coding Methods for Satellite Communication

This paper deals with the new progressive channel coding methods for short message transmission via satellite transponder using predetermined length of frame. The key benefits of this contribution are modification and implementation of a new turbo code and utilization of unique features with applications of methods for bit error rate estimation and algorithm for output message reconstruction. The mentioned methods allow an error free communication with very low Eb/N0 ratio and they have been adopted for satellite communication, however they can be applied for other systems working with very low Eb/N0 ratio.

1. SRIPIMANWAT, K. Turbo Code Applications. Netherlands: Springer, 2005. ISBN 10 1-4020-3686-8.
2. GIULIETTI, A., BOUGARD, B., PERRE, L. Turbo Codes: Desirable and Designable. United States of America: Kluwer Academic Publisher Group, 2004. ISBN 1-4020-7660-6.
3. VUCETIC, B. Turbo Codes. Principles and Applications. Netherlands: Springer, 2000, 386 p. ISBN 0-7923-7868-7.
4. BERROU, C., GLAVIEX, A., THITIJSHIMA P. Near Shannon limit error correcting coding and decoding: Turbo codes. In IEEE International Conference on Communications. Geneva (Switzerland), May 1993, vol. 2/3, p. 1064-1071.
5. WANG, D.; KOBAYASHI, H. On design of interleavers with practical size for turbo codes. In IEEE International Conference on Communications ICC 2000, 2000, vol. 2, p.618-622.
6. LEE, L.-N., HAMMONS, A.R., Jr., FENG-WEN SUN, EROZ, M. Application and standardization of turbo codes in third-generation high-speed wireless data services. IEEE Transactions on Vehicular Technology, November 2000, vol. 49, no. 6, p. 2198-2207.
7. HAGENAUER, J., OFFER, E., PAPKE, L. Iterative decoding of binary block and convolutional codes. IEEE Transactions on Information Theory, March 1996, vol. 42, no. 2, p.429-445.
8. BENEDETTO, S., MONTORSI, G. Unveiling turbo codes: some results on parallel concatenated coding schemes. IEEE Transactions on Information Theory, March 1996, vol. 42, no. 2, p.409-428.
9. BENEDETTO, S., MONTORSI, G. Design of parallel concate- nated convolutional codes. IEEE Transactions on Communica- tions, May 1996, vol. 44, no. 5, p. 591-600.
10. SOLEYMANI, M., GAO, Y., VILAIPORNSAWAI, U. Turbo Coding for Satelite and Wireless Communications. Netherlands: Kluwer Academic Publisher, 2002, 214 p. ISBN 1-4020-7197-3.
11. WANG, D.; KOBAYASHI, H. On design of interleavers with practical size for turbo codes. In IEEE International Conference on Communications ICC 2000, 2000, vol. 2, p.618-622.
12. STRINATI, E. C.; SIMOENS, S.; BOUTROS, J. Error rate estimation based on soft output decoding and its application to turbo coding. In IEEE Conference on Wireless Communications and Networking.WCNC 2007. 11-15 March 2007, p.72-76.
13. Ericsson Inc., Plano, United States. Method and Devices for Calculating Bit Error Rate of Received Signal. Inventor: MOELKER, D.-J., Patent No.: US 2007/0162788 A1, Public date: Jul. 12, 2007.

Keywords: Turbo code, coding, interleaving, MAP, decoding, bit error rate, bit error rate estimation, satellite communication.

L. Dordova, O. Wilfert [references] [full-text] [Download Citations]
Calculation and Comparison of Turbulence Attenuation by Different Methods

This paper is focused on the effect of turbulence in atmospheric transmission media. A short introduction of the origin of turbulent atmosphere is given. Two classical methods for the calculation of turbulence attenuation are mentioned and briefly described in the paper – the Rytov approximation and Andrews’s method, and a new technique designed by the authors of this paper – the method of available power – is presented in short as well.
We have run simulations in Matlab to compare the results of turbulence attenuation given by the classical methods and by the new technique - the method of available power. These calculations were performed for communication wavelengths of 850 nm and 1550 nm. The distance between the optical transmitter and receiver of horizontal links was set to values ranging from 0 m to 2500 m. We have taken into account the homogenous turbulence with low (10^-16 m^-2/3), medium (10^-15 m^-2/3) and high (10^-14 m^-2/3) structure parameter of refractive index Cn2.

1. ANDREWS, L. C., PHILLIPS, R. L. Laser Beam Propagation through Random Media. SPIE – The International Society for Optical Engineering, 1998.
2. NABOULSI, A., SIZUN, M., DE FORNEL, F. Propagation of optical and infrared waves in the atmosphere. In The Proceedings of the XXVIIIth URSI General Assembly in New Delhi. New Delhi (India): URSI, 2005, p. 1 – 4.
3. ANDREWS, L. C. Field Guide to Atmospheric Optics. Washington: SPIE Press, 2004,
4. WILFERT, O., KOLKA, Z. Statistical model of free-space optical data link. In Proc. of the International Symposium on Optical Science and Technology. Conference 5550. Denver: SPIE. 2004, p. 203-213.
5. DORDOVA, L.; WILFERT, O. Laser beam attenuation determined by the method of available optical power in turbulent atmosphere. Journal of Telecommunications and Information Technology, 2009, no. 2, p. 53-57.

Keywords: Free space optical links, turbulence attenuation, method of available power, the Rytov approximation.

O. Kucera [references] [full-text] [Download Citations]
Electrical Analogy to an Atomic Force Microscope

Several applications of the atomic force microscopy (AFM), such as measurement of soft samples, manipulation with molecules, etc., require mechanical analysis of the AFM probe behavior. In this article we suggest the electrical circuit analogy to AFM cantilever tip motion. Well developed circuit theories in connection with fairly accessible software for circuit analysis make this alternative method easy to use for a wide community of AFM users.

1. BINNIG, G., QUATE, C., GERBER, C. Atomic force microscope. Physical Review Letters, 1986, vol. 3, p. 930 – 933.
2. GITTES, F., SCHMIDT, C. F. Thermal noise limitations on micromechanical experiments. European Biophysics Journal, 1998, vol. 27, no. 1, p. 75 – 81.
3. BUTT, H. J., CAPPELLA, B., KAPPL, M. Force measurements with the atomic force microscope: Technique, interpretation and applications. Surface Science Reports, 2005, vol. 59, no. 1-6, p. 1 – 152.
4. ZIEGLER, C. Cantilever-based biosensors. Analytical and bioanalytical chemistry, 2004, vol. 379, no. 7, p. 946 – 959.
5. STARK, R. W., DROBEK, T., HECKL, W. M. Thermomechanical noise of a free v-shaped cantilever for atomic-force microscopy. Ultramicroscopy, 2001, vol. 86, no. 1-2, p. 207 – 216.
6. LEE, H. L., CHANG, W. J. Effects of damping on the vibration frequency of atomic force microscope cantilevers using the timoshenko beam model. Japanese Journal of Applied Physics, 2009, vol. 48, no. 6, p. 1 – 4.
7. YARALIOGLU, G. G., ATALAR, A. Noise analysis of geometrically complex mechanical structures using the analogy between electrical circuits and mechanical systems. Review of Scientific Instruments, 1999, vol. 70, p. 2379 – 2383.
8. SALAPAKA, S. M., SALAPAKA, M. V. Scanning probe microscopy. IEEE Control Systems Magazine, 2008, vol. 28, no. 2, p. 65 – 83.
9. FIRESTONE, F. A. A new analogy between mechanical and electrical systems. The Journal of the Acoustical Society of America, 1933, vol. 4, p. 249 – 267.

Keywords: Atomic Force Microscopy, electrical mechanical analogs, circuit theory.

P. Koudelka, B. Petrujova, J. Latal, F. Hanacek, P. Siska, J. Skapa, V. Vasinek [references] [full-text] [Download Citations]
Optical Fiber Distributed Sensing System Applied in Cement Concrete Commixture Research

DTS are unique optical-fiber distributed systems for measuring of temperature or mechanical tension. These systems use non-linear properties of optical fibers. Optical fiber can therefore be used not only for telecommunication purposes, as is currently the case, but also as a sensor. Optical fiber used by the DTS system can be therefore imagine as thousands of sensors placed along the route, taking all advantages of optical fiber, such as resistance to electromagnetic radiation, safe use in flammable and explosive environments, resistance to aggressive environments, small sizes, easy installation and maintenance-free operation. The properties of DTS system mentioned above seem to be ideal for detailed mapping of the hydration heat of concrete mix in the transition to a rigid structure. Values based on measurements will be used to better understanding of the processes inside the concrete mixture (individual samples) and will serve to develop better and more durable mixture.

1. LONG, D. A. The Raman Effect: A Unified Treatment of the Theory of Raman Scattering by Molecules. 2002, 650 p., ISBN: 978-0-471-49028-9
2. NIKLES, M., VOGEL, B., BRIFFOD, F., GROSSWIG, S., SAUSER, F., LUEBBECKE, S., BALS, A., PFEIFFER, T. Leakage detection using fiber optics distributed temperature monitoring. In 11th SPIE Annual International Symposium on Smart Structures and Materials [online]. c2004, [cit. 2009-09-10]. Available at: http://www.omnisens.ch/docs/1203959496_SPIE04-Leakage%20detection%20using%20DITEST%20monitoring.pdf
3. JAASKELAINEN, M. Distributed Temperature Sensing (DTS) in Geothermal Energy Applications [online]. c 2009, [cit. 2009-09-01]. Available at:
4. LATAL, J., KOUDELKA, P., HANACEK, F. The new methods of the heat borehole measuring by the help of DTS system. In Proceeding of the 7th Annual workshop WOFEX 2009. Ed. P. Moravec, J. Dvorsky, Ostrava: VSB - TU Ostrava, 2009, ISBN 978-80-248-2028-6, p. 332 - 337
5. BALL, D. W. Theory of Raman Spectroscopy [online]. c 2001. [cit. 2001-10-24]. Available at :
6. PYTLIK, J. Technologie betonu. Vysoke uceni technicke v Brne, nakladatelstvi VUTIUM, 2000, ISBN 80-214-1647-5, p. 317. (In Czech.)

Keywords: Optical-fiber distributed sensing systems, nonlinear effects, temperature-profile measurements, cement concrete commixture, hydration heat.

W. Chunhua, A. U. Keskin, L. Yang, Z. Qiujing, D. Sichun [references] [full-text] [Download Citations]
Minimum Configuration Insensitive Multifunctional Current-Mode Biquad Using Current Conveyors and All-Grounded Passive Components

This paper proposes a new current conveyorbased high-output impedance single-input three-output current mode filter with minimum configuration. It contains two dual output second generation current conveyors, one third generation dual output current conveyor, and four grounded resistors and capacitors. The circuit simultaneously provides low-pass, band-pass, and high-pass filtering outputs, without any passive component matching conditions and restrictions on input signals. Additionally, the proposed circuit offers following advantages: Minimum active and passive element count, high output and low input impedances, suitable for cascading identical currentmode sections, all passive elements are grounded (no virtual grounding), low natural frequency and Q-factor sensitivities. The influences of non-ideal current conveyors on the proposed circuit are researched in the last.

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8. SIRIPRUCHYANUN, M., JAIKLA, W. Three-input single-output electronically controllable dual-mode universal biquad filter using DO-CCCIIs. The Journal of KMITNB., 2007, vol. 17, no. 1.
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19. TOKER, A., OZOGUZ, S., ÇIÇEKOGLU, O. High output impedance current-mode multifunction filters with minimum number of active and passive elements using dual-output current conveyors. Frequenz, 1999, vol. 53, p. 206-209.
20. TOKER, A., OZOGUZ, S., ÇIÇEKOGLU, O. A new current-mode multifunction filter with minimum components using dual-output current conveyors. In Proc. of ITC-CSCC'99, 1999, vol. I, p. 301-303.
21. TANGSRIRAT, W., SURAKAMPONTORN, W. High output impedance current-mode universal filter employing dual-output current-controlled conveyors and grounded capacitors. AEU-Int J. Electron. Commun,, 2007, vol. 61, no. 2, p. 127-131.
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27. WANG, H. Y., LEE, C. T. Systematic synthesis R-L and C-D immitances using single CCIII. Electronics Letters, 2000, vol. 87, p. 293-294.
28. AHMET, M. T., KHAN, I. A., MİNHEJ, N. On transconductance quadrature oscillators. Int. Journal of Electronics, 1997, vol. 83, no. 2, p. 201-207.
29. UN, M., KACAR, F. Third generation current conveyor based current-mode fırst order all-pass fılter and quadrature oscıllator. Journal of Electrical & Electronics Engineering, 2008, vol. 8, no. 1, p. 529-535.
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Keywords: Current conveyor, current-mode circuit, filter, parasitic impedance.

W. Chunhua, L. Yang, Z. Qiujing, F. Yu [references] [full-text] [Download Citations]
Systematic Design of Fully Balanced Differential Current-Mode Multiple-Loop Feedback Filters Using CFBCCII

In this paper, a systematic design method producing balanced current-mode filters is proposed, using current controlled fully balanced second-generation current conveyor circuit (CFBCCII). In this method, many kind of all-pole multiple loop feedback (MF) current mode balanced filters can be obtained, all the produced filters have fully balance structures. Moreover, the frequency of the filters can be electronically adjustable. The produced nth-order filters are constructed by n CFBCCIIs and 2n grounded capacitors, no resistors are needed. The sensitivities of the filters and influences of CFBCCII parasitic elements on filters are analyzed.

1. PAPAZOGLOU, C. A., KARYBAKAS, C. A. Noninteracting electronically tunable CCII-based current-mode biquadratic filters. IEEE Proc G, 1997, vol. 144, no. 3, p. 178- 184.
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3. CHANG, C. M., AL-HASHIMI, B. M. Single fully differential current conveyor biquad filters. IEEE Proceedings on Circuit, Device and Systems, 2003, vol. 150, no. 5, p. 394- 398.
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5. SUN, Y., FIDLER, K. Fully-balanced structures of continuous-time MLF OTA-C filters. In Proceedings of 1998 IEEE International Conference on Electronics, Circuits and Systems, 1998, p. 157- 160.
6. SUN, Y., FIDLER, J. K. Structure generation and design of multiple loop feedback OTA-grounded capacitor filters. IEEE Transactions on Circuits and Systems—I: Fundamental Theory and Applications, 1997, vol. 44, no. 1, p. 1-11.
7. HING-KIT, K., CHUNG-MAN, C., CHI-UN, L., et al. Synthesis of optimal OTA-C filter structures with arbitrary transmission zeros via MINLP. In Proceedings of 2008 IEEE Asia Pacific Conference on Circuits and Systems, 2008, p. 944 - 947.
8. MOHAMED, O. S., SOLIMAN, A. M., SOLIMAN, A. M. High-order Gm-C filters with current transfer function based on multiple loop feedback. In 2007 IEEE International Conference on Signal Processing and Communications, 2007, p. 85-88.
9. SUN, Y., FIDLER, J. K. Current-mode multiple-loop feedback filters using dual output OTAs and grounded capacitors. International Journal of Circuit Theory and Applications, 1997, vol. 25, p. 69-80.
10. PAPAZOGLOU, C. A., KARYBAKAS, C. A. Noninteracting electronically tunable CCII-based current-mode biquadratic filters. IEE Proc G, 1997, vol. 144, no. 3, p.178- 184.
11. SUN, Y., HE, Y. Active filters using single current conveyor. In Proceedings of the 2003 IEEE International Conference on Robotics, Intelligent Systems and Signal Processing, 2003, p. 1130-1134.
12. KOKSAL, M., SAGBAS, M. A versatile signal flow graph realization of a general current transfer function. Int. Journal of Electronics and Communications, 2008, vol. 62, no. 1, p. 33-40.
13. CHUN-MING, C., SOLIMAN, A. M., SWAMY, M. N. S. Analytical synthesis of low-sensitivity high-order voltage-mode DDCC and FDCCII-grounded R and C all-pass filter structures. IEEE Transactions on Circuit and Systems-I: Regular Papers, 2007, vol. 54, no.7, p. 1430-1443.
14. JIRASEREE-AMORNKUN, A., TANGSRIRAT, W., SURAKAMPONTORN, W. Tunable elliptic filters using multioutput current controlled conveyors. In IEEE Region 10 Conference TENCON, 2004, p. 229-232.
15. WU J, EI-MAASRYA, E. Current-mode ladder filters using multiple output current conveyors. IEEE Proc Circuit Devices Syst, 1996, vol. 143, no. 4, p. 218 - 222.
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Keywords: Fully balanced, current mode, filter, current conveyor, multiple-loop feedback formatting.

D. Prasad, D. R. Bhaskar, A. K. Singh [references] [full-text] [Download Citations]
New Grounded and Floating Simulated Inductance Circuits using Current Differencing Transconductance Amplifiers

Current differencing transconductance amplifier (CDTA) is receiving considerable attention as a building block for current-mode (CM) analog signal processing / signal generation. In this paper, new CDTA based lossless grounded and floating inductance simulation circuits have been proposed. The proposed grounded simulated inductance circuit employs two CDTAs and a single grounded capacitor whereas the floating simulated inductance circuit employs three CDTAs and a grounded capacitor. The circuit for grounded inductance does not require any realization conditions whereas in case of floating inductance only equality of two transconductances is needed (which can be easily maintained in practice by ensuring equal dc bias currents in the two transconductance amplifiers). Some sample results demonstrating the applications of the new simulated inductors using CMOS CDTAs have been given to confirm the workability of the new circuits.

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Keywords: CDTA, inductance simulation, filters.