D. Vrba, M. Polivka [references] [full-text] [Download Citations]
Radiation Efficiency Improvement of Zeroth-Order Resonator Antenna

The radiation as well as antenna efficiency of very thin profile zeroth-order resonator (ZOR) antenna, implemented in negative phase velocity (NPV) microstrip transmission line (TL) structure, has been solved by the method of moment simulator IE3D. The radiation is investigated using individual portions of the ZOR antenna that shows significant values of the surface current density. Dominantly radiating parts have been identified, geometrically emphasized by means of the increase in the antenna height over the ground plane from 1/105 to 1/8 λ₀. The measured parameters of the improved antenna prototype have been enhanced so they reached the following values (compared to original ones): gain 5.0 dBi (-3.0 dBi), antenna efficiency 97.7 % (9.5 %).

1. SCHUSSLER, M., OERTEL, M., FRITSCHE, C., FREESE, J., JAKOBY, R. Design of periodically L-C loaded patch antennas. In 27th ESA Antenna Technology Workshop on Innovative Periodic Antennas. Santiago de Compostela (Spain), March 2004.
2. SCHUSSLER, M., FREESE, J., JAKOBY, R. Design of compact planar antennas using LH-transmission lines. In IEEE MTT-S International Microwave Symposium Digest, 2004, pp. 209-212.
3. SANADA, A., KIMURA, M., AKAI, I., KUBO, H., CALOZ, C., ITOH, T. A planar zero-th order resonator antenna using lefthanded transmission line. In Proc. of European Microwave Conference (CD ROM). Amsterdam (the Netherlands), 2004.
4. QURESHI, F., ANTONIADES, M. A., ELEFTERIADES, G. V. A compact and low-profile metamaterial ring antenna with vertical polarization. IEEE Antennas and Wireless Propagation Letters, vol. 4, 2005, p. 333-336.
5. PARK, J.-H., RYU, Y.-H., LEE, J.-G., LEE, J.-H. A zeroth-order resonator antenna using epsilon negative meta-structured transmission line. In Proc. of IEEE Antennas and Prop. Symposium(CD ROM). Honolulu (Hawai), 2007.
6. Inc. Zeland Software. IE3D 11.5 Users Manual. Zeland Software, Inc., 39120 Argonaut Way, Suite 499, Fremont, CA 94538, U.S.A., October 2005.
7. VESELAGO, V. The electrodynamics of substances with simultaneously negative values of ε and μ. Soviet Physics Uspekhi, vol. 10, no. 4, Jan., Feb. 1968, pp. 509-514.
8. MALYUZHINETS, G. D. A note on the radiation principle. Zhurnal technicheskoi fiziki, vol. 21, 1951, pp. 940-942 (in Russian).
9. SHELBY, R. A., SMITH, D. R., SCHULTZ, S. Experimental verification of a negative index of refraction. Science, vol. 292, April 2001, pp. 77–79.
10. CALOZ, C., ITOH, T. Electromagnetic Metamaterials: Transmission Line Theory and Microwave Applications. John Wiley & Sons, 2006.
11. ELEFTHERIADES, G. V., IYER, A. K., KREMER, P. C. Planar negative refractive index media using periodically L-C loaded transmission lines. IEEE Trans. Microwave Theory Tech., vol. 50, no. 12, 2002, pp. 2702–2712.
12. VRBA, D. Electrically Small Antenna with Lumped LC Elements Master thesis, CTU FEE, 2008.
13. SVACINA, J. Investigation of Microwave Planar Structures Using the Conformal Mapping Method. Brno: Akademicke nakladatelstvi CERM, 2006 (in Czech).

Keywords: Antenna efficiency, electrically small antenna, metamaterial, negative phase velocity, radiation efficiency, zeroth-order resonator

J. Puskely, Z. Novacek [references] [full-text] [Download Citations]
Application of the Global Optimization Approaches to Planar Near-Field Antenna Phaseless Measurements

This paper deals with a method of the radiation pattern determination of the directional antennas. The method combining both the functional minimization method and the Fourier iterative algorithm is based on the phaseless near-field measurement on two plane surfaces. The method is used for a reconstruction of the phase distribution on the aperture of the measured antenna, and for the determination of the antenna radiation pattern, consequently. The binary genetic algorithm (BGA), the realvalued genetic algorithm (RVGA), the particle swarm optimization (PSO), and differential evolutionary algorithm (DEA) were chosen for the global functional minimization. The paper is aimed to analyze the performance of the global optimizations (GOs) when solving the described problem, and to compare the GOs. GOs were examined through data achieved by measurement of a horn antenna and a parabola.

1. BUCCI, O. M., D’ELIA, G., LEONE, G., PIERRI, R. Far-field pattern determination from the near-field amplitude on two surfaces. IEEE Transaction on Antennas and Propagation. 1990, vol. 38, no. 11, p. 1772–1779.
2. YACCARINO, R. G., RAHMAT-SAMII, Y. Phaseless bi-polar planar near-field measurements and diagnostics of array antennas. IEEE Transactions on Antennas and Propagation. 1999, vol. 47, no. 3, p. 574–583.
3. TKADLEC, R. Near-Field Antenna Measurements. Dissertation Thesis. Brno: Brno University of Technology, 2005.
4. ISERNIA, T., LEONE, G., PIERRI, R. Radiation pattern evaluation from near-field intensities on planes. IEEE Transactions on Antennas and Propagation. 1996, vol. 44, no. 5, p. 701 – 710.
5. ROBINSON, J., SINTON, S., RAHMAT-SAMII, Y. Particle swarm, genetic algorithm, and their hybrids: optimization of a profiled corrugated horn antenna. In Proceedings of the IEEE International Symposium on Antennas and Propagation. San Antonio: IEEE, 2002, vol. 1, p. 314–317.
6. CARLISLE, A., DOIZIER, G. An off-the-shelf PSO. In Proc. Workshop Particle Swarm Optimization. Indianapolis (USA), 2001.
7. JOHNSON, J. M., RAHMAT-SAMII, Y. Genetic algorithms in engineering electromagnetics. IEEE Antennas and Propagation Magazine. 1997, vol. 39, no. 4, p. 7–21.
8. HAUPT, R. L., HAUPT, S. E. Practical Genetic Algorithm. A Wiley-Interscience Publication, 1998, ISBN 0-471-18873-5.
9. PUSKELY, J., NOVACEK, Z., POKORNY, M. Using global optimization approaches to reconstruct radiation patterns. In Proceedings of the 14th Conference on Microwave Techniques Comite 2008. 2008, p. 347-350. ISBN 978-1-4244-2137-4.
10. PUSKELY, J., NOVACEK, Z. Application of the global optimization approaches to planar near-field antenna phaseless measurements. In Proceedings MMS'2008 Mediterranean Microwave Symposium. Damascus (Syria), 2008, p. 231-236. ISBN 9954-8577-0-2.
11. RAZAVI, S. F., RAHMAT-SAMII, Y. A new look at phaseless planar near-field measurements: limitations, simulations, measurements, and a hybrid solution. IEEE Antennas and Propagation Magazine, 2007, vol. 49, no. 2, pp. 170-178.
12. ZELINKA, I. Artificial Intelligence in Problems of Global Optimization. Prague: BEN, 2002, 190 p. ISBN 80-7300-069-5.
13. PUSKELY, J., NOVACEK, Z. Antenna far-fields determination from phaseless measurement using the real-valued GA. In Proceedings of the Junior Scientist Conference 2008. Vienna, 2008, p. 271 - 272. ISBN 978-3-200-01612-5.

Keywords: Radiation pattern, planar near-field scanning, particle swarm optimization (PSO), binary genetic algorithms (BGA), real-valued genetic algorithm (RVGA), differential evolutionary algorithm (DEA), Fourier iterative algorithm

V. Schejbal [references] [full-text] [Download Citations]
Improved Analysis of Propagation over Irregular Terrain

An improved analysis of propagation over irregular terrain using physical optics approximation of vector problem is presented. It offers more reliable numerical simulations for low altitude propagation and diffraction field zone without any auxiliary procedures. Numerical simulations are compared with measurement results and various approximate methods.

1. LUEBBERS, R. J. Propagation prediction for hilly terrain using GTD wedge diffraction. IEEE Trans. Antennas Propag., 1984, vol. 32, no. 9, pp. 951 – 955.
2. HVIID, J. T., ANDERSON, J. B., TOFTGÅRD, J. T., BØJER, J. Terrestrial-based propagation model for rural area — an integral equation approach. IEEE Trans. Antennas Propag., 1995, vol. 43, no. 1, pp. 41–46.
3. AKORLI, F. K., COSTA, E. An efficient solution of an integral equation applicable to simulation of propagation along irregular terrain. IEEE Trans. Antennas Propag., 2001, vol. 49, no. 7, pp. 1033 -1036.
4. SCHEJBAL, V. Computing the electrical field strength of an antenna above an uneven earth. Slaboproudy obzor (in Czech), 1973, vol. 34, no. 12, pp. 541 - 547.
5. KUPCAK, D. ATC Radar Antennas. Environment Influence on ATC Radar Operation (in Czech). Prague: MNO, 1986, vol. III.
6. SCHEJBAL, V. Propagation over irregular terrain. Radioengineering, 1997, vol. 6, no. 1, pp. 19 - 22.
7. SCHEJBAL, V. Comparison of propagation over irregular terrain. Radioengineering, 1997, vol. 6, no. 3, pp. 6 - 9.
8. SCHEJBAL, V. Hybrid method for computation of propagation over irregular terrain. In COST 280 Workshop. Malvern (Great Britain), 2002, , CD-ROM.
9. SCHEJBAL, V. et al. Czech radar technology. IEEE Trans. Aerosp. Electron. Syst. 1994, vol. 30, no. 1, pp. 2 - 17.
10. UFIMTSEV, P. Ya. New insight into the classical Macdonald physical optics approximation. IEEE Antennas Propag. Mag, 2008, vol. 50, no. 3, pp. 11 - 20.
11. SILVER, S. Microwave Antenna Theory and Design. New York: McGraw-Hill, 1949.
12. Report 715-1. Propagation by diffraction. Recommendations and reports of the CCIR, 1982, vol. V, Propagation in non-ionized media, pp. 45 – 56.
13. MEEKS, M. L. Radar Propagation at Low Altitudes. Dedham: Artech, 1982, Appendix C.
14. PAPKELIS, E. G., et al. A Radio-coverage prediction model in wireless communication systems based on Physical Optics and the physical theory of diffraction. IEEE Antennas Propag. Mag., 2007, vol. 49, no. 2, pp. 157 – 165.
15. UFIMTSEV, P. Ya. Improved physical theory of diffraction: removal of the grazing singularity. IEEE Trans. Antennas Propag., 2006, vol. 54, no. 10, pp. 2698 – 2702.

Keywords: Electromagnetic propagation, electromagnetic propagation terrain factors, low altitudes propagation, numerical simulation

J. Lacik [references] [full-text] [Download Citations]
Laguerre Polynomials’ Scheme of Transient Analysis: Scale Factor and Number of Temporal Basis Functions

The paper is focused on two important parameters of the scheme with weighted Laguerre polynomials: the scale factor of time axis and the number of temporal basis functions. In the first part of the paper, the approach for the determination of the number of temporal basis functions is proposed. Its number is determined during the run of the scheme.
In the second part of the paper, the influence of the choice of the scale factor on the efficiency of the scheme, with the possibility of its optimum choice, is investigated. The investigations show that a chosen scale factor strongly influences the efficiency of the scheme. If the scale factor is not chosen close to the optimum one, the scheme becomes time-consuming. However, a simple formula for its prediction can not be given. The choice of the scale factor seems to be the weak point of the scheme with Laguerre polynomials.

1. CHUNG, Y. S., SARKAR, T. K. JUNG, B. H., SALZARPALMA, 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.
2. JUNG, B. H., SARKAR, T. K., CHUNG, Y. S., SALZARPALMA, M., JI, Z., JANG, S., KIM, K. Transient electromagnetic scattering from dielectric objects using the electric field integral equation with Laguerre polynomials as temporal basis functions. IEEE Transactions on Antennas and Propagation, 2004, vol. 52, no. 9, p. 2329 – 2340.
3. LACIK, J., RAIDA, Z. Modeling microwave structure in time domain using Laguerre polynomials. Radioengineering, 2006, vol. 16, no. 3, p. 1-9.
4. CHUNG, Y. S., SARKAR, T. K., JUNG, B. H., SALZARPALMA, M. Solving time domain electric field integral equation without the time variable. IEEE Transactions on Antennas and Propagation, 2006, vol. 54, no. 1, p. 258–262.
5. RAO, S. M. Time Domain Electromagnetics. London: Academic Press, 1999.
6. JUNG, B. H., SARKAR, T. K. Time-domain electric-field integral equation with central finite difference. Microwave and Optical Technology Letters. 2001, vol. 31, no. 6, p. 429-435.
7. WEILE, S. D., PISHARODY, G., CHEN, N., SHANKER, B., MICHIELSSEN, E. A novel scheme for the solution on the timedomain integral equations of electromagnetics. IEEE Transactions on Antennas and Propagation, 2004, vol. 52, no. 1, p. 283 – 295.
8. 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. 5, p. 409 – 418.
9. SARKAR, T. K., KOH, J., SALAZAR-PALMA, M. Generation of wideband electromagnetic response through a Laguerre expansion using early time and low frequency data. IEEE MTT-S International Microwave Symposium Digest. 2002, vol. 3, p. 1989- 1992.

Keywords: Time domain analysis, method of moments, Laguerre polynomials

T. Zvolensky, Z. Raida, P. Tobola [references] [full-text] [Download Citations]
Homogeneous Dielectric Equivalents of Composite Material Shields

The paper deals with the methodology of replacing complicated parts of an airplane skin by simple homogeneous equivalents, which can exhibit similar shielding efficiency. On one hand, the airplane built from the virtual homogeneous equivalents can be analyzed with significantly reduced CPU-time demands and memory requirements. On the other hand, the equivalent model can estimate the internal fields satisfactory enough to evaluate the electromagnetic immunity of the airplane.

1. SARTO, M. S. A new model for the FDTD analysis of the shielding performances of thin composite structures. IEEE Trans. Electromagn. Compat., 1999, vol. 41, no. 4, p. 298–306.
2. CHIN, H. K., CHU, H. C. CHEN, C. H. Propagation modeling of periodic laminated composite structures. IEEE Trans. Electromagn. Compat., 1998, vol. 40, no. 3, p. 218–224.
3. SARTO, M. S. Hybrid MFIE/FDTD analysis of the shielding effectiveness of a composite enclosure excited by a transient plane wave. IEEE Trans. Magn., 2000, vol. 36, no. 4, p. 946 to 950.
4. D’AMORE, M., SARTO, M. S. Theoretical and experimental characterization of the EMP-interaction with composite-metallic enclosures. IEEE Trans. Electromagn. Compat., 2000, vol. 42, no. 2, p. 152–163.
5. BUCCELLA, C. Two-dimensional analysis of composite structures by the finite-difference time-domain method adopting scaling approach [EM shielding]. IEEE Trans. Magn., 2002, vol. 38, no. 2, p. 845–848.
6. VEGNI, L., TOSCANO, A., BILOTTI, F. Shielding and radiation characteristics of planar layered inhomogeneous composites. IEEE Trans. Antennas Propag., 2003, vol. 51, no. 10, p. 2869–2877.
7. WAKI, H., IGARASHI, H., HONMA, T. Estimation of effective permeability of magnetic composite materials. IEEE Trans. Magn., 2005, vol. 41, no. 5, p. 1520–1523.
8. WAKI, H., IGARASHI, H., HONMA, T. Analysis of magnetic shielding effect of layered shields based on homogenization. IEEE Trans. Magn., 2006, vol. 42, no. 4, p. 847–850.
9. ROBINSON, J., RAHMAT-SAMII, Y. Particle swarm optimization in electromagnetics. IEEE Trans. Antennas Propag,. 2004, vol. 52, no. 2, p. 397–407.

Keywords: Composite material, dielectric layers, electromagnetic immunity, shielding

J. Jilkova, Z. Raida, P. Tobola [references] [full-text] [Download Citations]
Genetic Homogenization of Composite Materials

The paper is focused on numerical studies of electromagnetic properties of composite materials used for the construction of small airplanes. Discussions concentrate on the genetic homogenization of composite layers and composite layers with a slot. The homogenization is aimed to reduce CPU-time demands of EMC computational models of electrically large airplanes. First, a methodology of creating a 3-dimensional numerical model of a composite material in CST Microwave Studio is proposed focusing on a sufficient accuracy of the model. Second, a proper implementation of a genetic optimization in Matlab is discussed. Third, an association of the optimization script and a simplified 2-dimensional model of the homogeneous equivalent model in Comsol Multiphysics is proposed considering EMC issues. Results of computations are experimentally verified.

1. RAHMAT-SAMII, Y., MICHIELSSEN, E. Electromagnetic Optimization by Genetic Algorithms. New York: J. Wiley&Sons, 1999.
2. CST Microwave Studio Users’ Guide. Available: www.cst.com
3. MIYAGAWA, H., HIROSE, K., NISHIKAWA, T., WAKINO, K., KITAZAWA, T. Determination of complex permittivity and permeability of materials in rectangular waveguide using accurate hybrid numerical calculation. In Proceedings of the International Microwave Symposium 2005, vol. 1, p. 4–8.
4. SARTO, M. S. Sub-cell model of multilayer composite materials for full FDTD and hybrid MFIE/FDTD analyses. In Proc. of the IEEE International Symposium on Electromagnetic Compatibility 2002, vol. 2, p. 737–742.
5. REQUENA-PEREZ, M.E., DIAZ-MORCILLIO, A., MONZOCABRERA, J. Accurate permitivity measurement by means of inverse calculation based on genetic algorithms. In Proc. of the Int. Symp. on Antennas and Propagation IPS 2004, vol. 1. p. 511–514.
6. GONA, S., KRESALEK, V. Measurement of reflection and transmission properties of composite samples no. 1 to 8, and synthesis of equivalent models of those samples. Research report. Zlin: University of Tomas Bata, 2008.

Keywords: Composite materials, genetic algorithms, complex permittivity

V. Koudelka, Z. Raida, P. Tobola [references] [full-text] [Download Citations]
Simple Electromagnetic Modeling of Small Airplanes: Neural Network Approach

The paper deals with the development of simple electromagnetic models of small airplanes, which can contain composite materials in their construction. Electromagnetic waves can penetrate through the surface of the aircraft due to the specific electromagnetic properties of the composite materials, which can increase the intensity of fields inside the airplane and can negatively influence the functionality of the sensitive avionics.
The airplane is simulated by two parallel dielectric layers (the left-hand side wall and the right-hand side wall of the airplane). The layers are put into a rectangular metallic waveguide terminated by the absorber in order to simulate the illumination of the airplane by the external wave (both of the harmonic nature and pulse one). Thanks to the simplicity of the model, the parametric analysis can be performed, and the results can be used in order to train an artificial neural network. The trained networks excel in further reduction of CPU-time demands of an airplane modeling.

1. HAYKIN, S. Neural Networks: A Comprehensive Foundation. Englewood Cliffs: Macmillan Publishing Company, 1994.
2. RAIDA, Z. Modeling EM structures in the neural network toolbox of MATLAB. IEEE Antennas and Propagation Magazine, 2002, vol. 44, no. 6, p. 46–67.
3. COMSOL Multiphysics. Available on http://www.comsol.com
4. CST Microwave Studio. Available on http://www.cst.com
5. CERNOHORSKY, D., RAIDA, Z., SKVOR, Z., NOVACEK, Z. Analysis and Optimization of Electromagnetic Structures. Brno: VUTIUM Publishing, 1999. (In Czech.)
6. PETRIU, E. M., CORDEA, M., PETRIU, D. C. Virtual prototyping tools for electronic design automation. IEEE Instrumentation and Measurement Magazine, 1999, vol. 2, p. 28–31.
7. DEMUTH, H., BEALE, M. Neural Network Toolbox for Use with Matlab: User's Guide. Ver. 4. Natick: The MathWorks Inc., 2000.

Keywords: Electromagnetic modeling, artificial neural networks, composite materials, small airplanes

A. Prokes [references] [full-text] [Download Citations]
Modeling of Atmospheric Turbulence Effect on Terrestrial FSO Link

Atmospheric turbulence results in many effects causing fluctuation in the received optical power. Terrestrial laser beam communication is affected above all by scintillations. The paper deals with modeling the influence of scintillation on link performance, using the modified Rytov theory. The probability of correct signal detection in direct detection system in dependence on many parameters such as link distance, power link margin, refractive-index structure parameter, etc. is discussed and different approaches to the evaluation of scintillation effect are compared. The simulations are performed for a horizontal-path propagation of the Gaussian-beam wave.

1. ANDREWS, L. C., PHILLIPS, R. L. Laser Beam Propagation through Random Media. Bellingham: SPIE Press, 1998.
2. ANDREWS, L. C., PHILLIPS, R. L., HOPEN, C. Y. Laser Beam Scintillation with Applications. Washington: SPIE Press, 2001.
3. ALDA, J. Laser and Gaussian beam propagation and transformation Encyclopedia of Optical Engineering. New York: Marcel Dekker Inc, 2003.
4. SALEH, B. E., TEICH, M. C. Fundamentals of Photonics. New York: John Wiley & Sons, 1991.
5. RASOULI, S., TAVASSOLY, M. Measurement of the refractiveindex structure constant, Cn 2, and its profile in the ground level atmosphere by moire technique. Proceedings of SPIE, 2006, vol. 6364, p. 63640G.
6. AURIA, G., MARZANO, F. S., MERLO, U. Statistical estimation of mean refractive-index structure constant in clear air. Proceedings of the Seventh International Conference Antennas and Propagation, ICAP 91, 1991, vol. 1, no. 15-18, p. 177 – 180.
7. OCHS, G. R. Measurement of refractive-index structure parameter by incoherent aperture scintillation techniques. Proceedings of the SPIE, Propagation Engineering, 1989, p. 107-115.
8. PERLOT, N. Characterization of signal fluctuations in optical communications with intensity modulation and direct detection through the turbulent atmospheric channel. In Characterization of Signal Fluctuations in Optical Communications with Intensity Modulation and Direct Detection through the Atmospheric Turbulent Channel. Aachen: Shaker Verlag, 2006.
9. GIGGENBACH, D., DAVID, F., LANDROCK, R., PRIBIL, K., FISCHER, E., BUSCHNER, R., BLASCHKE, D. Measurements at a 61 km near-ground optical transmission channel. Proceedings of the SPIE, 2002, vol. 4635, p. 162-170.
10. VETELINO, F. S., YOUNG, C., ANDREWS, L., RECOLONS, J. Aperture averaging effects on the probability density of irradiance fluctuations in moderate-to-strong turbulence. Journal of Applied Optics, 2007, vol. 46, no. 11, p. 2099-2108.
11. PERLOT, N., FRITZSCHE, D. Aperture-averaging - Theory and measurements. Proceedings of the SPIE, Atmospheric Propagation, 2004, vol. 5338, p. 233-242.
12. KIM, I. I., MITCHELL, M., KOREVAAR, E. Measurement of scintillation for free-space laser communication at 785 nm and 1550 nm. Proceedings of the SPIE, 1999, vol. 3850, p. 49-62.

Keywords: FSO, atmospheric turbulence, scintillation, Gaussian beam, Rytov variance

P. Drotar, J. Gazda, D. Kocur, P. Galajda [references] [full-text] [Download Citations]
Effects of Spreading Sequences on the Performance of MC-CDMA System with Nonlinear Models of HPA

Performance evaluation and comparison of multi-carrier code division multiple access (MC-CDMA) system model for different spreading sequences at the presence of Saleh and Rapp model of high power amplifier (HPA) is investigated. Nonlinear amplification introduces degradation of bit error performance and destroys the orthogonality among subcarriers. In order to avoid performance degradation without requiring extremely large backoffs in the transmitter amplifier, it becomes convenient to use nonlinear multi-user detection techniques at the receiver side. In order to illustrate this fact, microstatistic multi-user receiver (MSF-MUD) and conventional minimum mean square error receiver (MMSE-MUD) are considered and mutually compared. The results of our analyses based on computer simulations will show very clearly, that the application of nonlinear MSF-MUD in combination with Golay codes can provide significantly better results than the other tested spreading codes and receivers. Besides this fact, a failure of Walsh codes especially at the Saleh model of HPA will be outlined by using constellation diagram.

1. HARA, S., PRASAD, R. Overview of multicarrier CDMA. IEEE Communications Magazine, Dec. 1997, vol. 35, no. 12, pp. 126-133.
2. NOBILET, S., HELARD, J., MOTTIER, D. Spreading sequences for uplink and downlink MC-CDMA Systems: PAPR an MAI minimization. European Transactions on Telecommunications, 2002.
3. CHOI, B.-J., KUAN, E.-L., HANZO, L. Crest-factor study of MCCDMA and OFDM. IEEE Vehicular Technology Conference, vol. 1, pp. 233-237, 1999.
4. MOURAD, A.-M., GUEGUEN, A., PYNDIAH, R. Impact of the spreading sequences on the performance of forward link MC-CDMA systems. IEEE 8th International Symposium on Spread Spectrum Techniques and Applications, vol. 30, pp. 683-687, Sept. 2004.
5. JIANG, T., WU, Y. An Overview: Peak-to-Average Power Ratio reduction techniques for OFDM signals. IEEE Transactions on Broadcasting, Jun. 2008, vol. 54, no. 2, pp 267-268.
6. DEUMAL, M., BEHRAVAN, A., ERIKSSON, T., PIJOAN, J. L. Evaluation of performance improvement capabilities of PAPRreduction methods. Wireless Personal Communications, Oct. 2008, vol. 47, no. 1, pp. 137-147.
7. DEUMAL, M. On OFDM-based multicarrier communication systems with low sensitivity to nonlinear amplification. Thesis for the Advanced Studies Diploma, Barcelona (Spain), 2006.
8. HATHI, N., RODRIGUES, I., DARWAZEH, I., O'REILLY, J. Analysis of the influence of Walsh-Hadamard code allocation strategies on the performance of the multicarrier CDMA systems in the presence of HPA non-linearities. In The 13th IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, 2002, vol. 3, pp. 1305–1309.
9. TELLADO, J., HOO, L. M. C., CIOFFI, J. M. Maximum likelihood detection of nonlinearly distorted multicarrier symbols by iterative decoding. IEEE Transactions on Communications, Feb. 2003, vol. 51, no. 2, pp. 218-228.
10. KRAJNAK, J., DEUMAL, M., PAVELKA, P., et al. Multiuser detection of nonlinearly distorted MC-CDMA symbols by microstatistic filtering. Wireless Personal Communications, Oct 2008, vol. 47, no. 1, pp. 147-160.
11. HANZO, L., MUNSTER, M., CHOI, B., KELLER, T. OFDM and MC-CDMA for Broadband Multi-User Communications, WLANs and Broadcasting. John Wiley & Sons, England, 2003.
12. KOCUR, D., CIZOVA, J., MARCHEVSKY , S. Nonlinear microstatistic multi-user receiver. Acta Electrotechnica et Informatica., 2003, vol.3, no.3, pp. 10-15.
13. KRAJNAK, J., PAVELKA, P., GALAJDA, P., KOCUR, D. Efficient design procedure of microstatistic multi-user detector for nonlinearly distorted MC-CDMA. In Proceedings of 17th International Conference Radioelektronika 2007, Brno (Czech Republic), 2007, pp. 147-152.
14. SALEH, A. M. Frequency-independent and frequency dependent non-linear models of TWTA. IEEE Transactions on Communications, Nov. 1981, vol. 29, pp. 1715-1720.
15. RAPP, C. Effects of HPA-nonlinearity on 4-DPSK-OFDM-signal for digital sound broadcasting system. In 2nd European Conference Satellite Communications, 1991, pp. 179-184.

Keywords: MC-CDMA, HPA, Saleh model, Rapp model, PAPR, multi-user receivers

D. Sen, R. Dasgupta, S. Chakrabarti, R. V. R. Kumar [references] [full-text] [Download Citations]
A Novel Frequency Synchronization Algorithm and its Cramer Rao Bound in Practical UWB Environment for MB-OFDM Systems

This paper presents an efficient time-domain coarse frequency offset (FO) synchronizer (TCFS) for multi-band orthogonal frequency division multiplexing (MB-OFDM) systems effective for practical ultra-wideband (UWB) environment. The proposed algorithm derives its estimates based on phase differences in the received subcarrier signals of several successive OFDM symbols in the preamble. We consider different carrier FOs and different channel responses in different bands to keep the analysis and simulation compatible for practical multiband UWB scenario. Performance of the algorithm is studied by means of bit error rate (BER) analysis of MBOFDM system. We derive the Cramer Rao lower bound (CRLB) of the estimation error variance and compare it with the simulated error variance both in additive white Gaussian noise and UWB channel model (CM) environments, CM1-CM4. Both analysis and simulation show that TCFS can estimate coarse carrier FO more efficiently in UWB fading channels for MB-OFDM applications compared to the other reported results in literature. Also, computational complexity of the proposed algorithm is analyzed for its usability evaluation.

1. BATRA, A., BALAKRISHNAN, J., AIELLO, G. R., FOERSTER, J. R., DABAK, A. Design of Multi-band system for realistic UWB channel environment. IEEE Transactions on Microwave Theory and Techniques, Sept. 2004, vol. 52, no. 9, p. 2123 - 2138.
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3. CLASSEN, F., MEYR, H. Frequency synchronization algorithms for OFDM systems suitable for communication over frequency selective fading channels. In Proceedings of the IEEE Veh. Technol. Conf. Stockholm (Sweden), Jun. 1994, p. 1655 to 1659.
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Keywords: Synchronization, MB-OFDM, Ultra-Wideband, Frequency offset correction, Cramer Rao Bound

N. Noori, R. Karimzadeh-Baee, A. Abolghasemi [references] [full-text] [Download Citations]
An Empirical Ultra Wideband Channel Model for Indoor Laboratory Environments

Channel measurement and modeling is an important issue when designing ultra wideband (UWB) communication systems. In this paper, the results of some UWB time-domain propagation measurements performed in modern laboratory (Lab) environments are presented. The Labs are equipped with many electronic and measurement devices which make them different from other indoor locations like office and residential environments. The measurements have been performed for both line of sight (LOS) and non-LOS (NLOS) scenarios. The measurement results are used to investigate large-scale channel characteristics and temporal dispersion parameters. The clustering Saleh- Valenzuela (S-V) channel impulse response (CIR) parameters are investigated based on the measurement data. The small-scale amplitude fading statistics are also studied in the environment. Then, an empirical model is presented for UWB signal transmission in the Lab environment based on the obtained results.

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Keywords: Ultra wideband measurement, propagation channel, path loss, temporal dispersion parameters, clustering channel model, small-scale amplitude fading.

Y. Ida, C. Ahn, T. Kamio, H. Fujisaka, K. Haeiwa [references] [full-text] [Download Citations]
An Interference Cancellation Scheme for TFI-OFDM in Time-Variant Large Delay Spread Channel

In the mobile radio environment, signals are usually impaired by fading and multipath delay phenomenon. In such channels, severe fading of the signal amplitude and inter-symbol-interference (ISI) due to the frequency selectivity of the channel cause an unacceptable degradation of error performance. Orthogonal frequency division multiplexing (OFDM) is an efficient scheme to mitigate the effect of multipath channel. Since it eliminates ISI by inserting guard interval (GI) longer than the delay spread of the channel. In general, the GI is usually designed to be longer than the delay spread of the channel, and is decided after channel measurements in the desired implementation scenario. However, the maximum delay spread is longer than GI, the system performance is significantly degraded. The conventional time-frequency interferometry (TFI) for OFDM does not consider timevariant channel with large delay spread. In this paper, we focus on the large delay spread channel and propose the ISI and inter-carrier-interference (ICI) compensation method for TFI-OFDM.

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Keywords: OFDM, inter-symbol-interference, inter-carrier-interference, guard interval

C. Wang, Y. Zhao, Q. Zhang, S. Du [references] [full-text] [Download Citations]
A New Current Mode SIMO-Type Universal Biquad Employing Multi-Output Current Conveyors (MOCCIIs)

This study presents a new current-mode singleinput and multi-output (SIMO) type universal biquad circuit using second generation multi-output current conveyors (MOCCII) as the active components. The proposed circuit employs three MOCCIIs, two grounded capacitors and four grounded resistors, therefore offers electroning tuning possibilities. It can simultaneously realize second order low-pass, band-pass, high-pass, notch and all-pass filters. The circuit is cascadable and has low sensitivities. It provides independent control of ω₀ (natural angular frequency) and Q (quality factor). The influences of MOCCII parasitic elements have been analyzed and simulated using PSPICE. Experimental results including frequency responses of low-pass, high-pass, band-pass and band-stop filters, as well as frequency responses of filters with different ω₀ (keeping Q invariable) and different Q (keeping ω₀ invariable) are shown to be in agreement with theory.

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Keywords: Current conveyor, current-mode circuit, filter