Algebraic number theory and code design for Rayleigh fading channels

Algebraic number theory is having an increasing impact in code design for many different coding applications, such as single antenna fading channels and more recently, MIMO systems. Extended work has been done on single antenna fading channels, and algebraic lattice codes have been proven to be an effective tool. The general framework has been settled in the last ten years and many explicit code constructions based on algebraic number theory are now available. The aim of this work is to provide both an overview on algebraic lattice code designs for Rayleigh fading channels, as well as a tutorial introduction to algebraic number theory. The basic facts of this mathematical field will be illustrated by many examples and by the use of a computer algebra freeware in order to make it more accessible to a large audience

Decoupled digital control of a three-phase four-leg inverter to feed balanced and unbalanced loads

[ES] Este trabajo presenta una estrategia de control digital para inversores trifásicos de cuatro piernas, para cumplir con el requerimiento de normas internacionales de calidad de energía para UPS cuando se alimentan cargas equilibradas y desequilibradas. La estrategia de control propuesta se desarrolla en el marco de referencia dq0 en tiempo discreto, posee un lazo interno para controlar la corriente de los inductores y un lazo externo para controlar la tensión de salida. Se demuestra que utilizando controladores convencionales pueden desacoplarse las variables de los ejes d y q, lo que permite diseñar los controladores del lazo externo de control de tensión como sistemas SISO independientes, cumpliéndose los requerimientos de régimen transitorio y de régimen permanente impuestos por norma. Para mejorar el desempeño del inversor cuando se alimentan cargas desequilibradas, se propone utilizar un controlador Proporcional-Resonante únicamente en el lazo interno del eje 0, lográndose una estrategia de control simple y de bajo costo computacional. Se presentan resultados de simulación y experimentales que permiten validar la estrategia de control propuesta.[EN] This paper presents a digital control strategy for three-phase four-leg inverters to meet the requirements of international power quality standards for UPS, when balanced and unbalanced loads are feeding. The proposed control strategy is developed in the discrete-time dq0-reference frame. It has an inner current loop to control the inductors currents and an outer voltage control loop. The analysis of this paper demonstrates that using conventional controllers, the voltages of d and q axes can be decoupled, into the whole operating range, which allows the outer voltage controllers to be designed as independent SISO systems, meeting the requirements of the transient and permanent regimes imposed by Standards. To improve the performance when the inverter feeds unbalanced loads, this paper proposes to use a Proportional-Resonant controller only in the inner loop of the axis 0, achieving a simple control strategy and, consequently with a low computational cost. Simulation and experimental results allow validating the proposed control strategy.Este trabajo fue soportado por la Secretaría de Ciencia y Técnica de la Universidad Nacional de Río Cuarto (SeCyT, UNRC), la Agencia Nacional de Promoción Científica y Tecnológica (FONCyT) a través del proyecto PICT 1663/2016 y la Red MEIHAPER CYTED.Oggier, E.; Botterón, F.; Oggier, G.; García, G. (2020). Control digital desacoplado de inversores trifásicos de cuatro piernas para alimentar cargas equilibradas y desequilibradas. Revista Iberoamericana de Automática e Informática industrial. 17(3). https://doi.org/10.4995/riai.2020.13011OJS317173Astrada, J., and DeAngelo, C. ,2019. Reducción de la impedancia de salida en inversores monofásicos para UPS con multi-lazo convencional y plug-in repetitivo. Revista Iberoamericana de Automática e Informática Industrial, 16(4), 391. https://doi.org/10.4995/riai.2019.11034Bai, H., Wang, F., Wang, D., Liu, C. L., and Wang, T. Y. ,2009. A pole assignment of state feedback based on system matrix for three-phase four-leg inverter of high speed pm generator driven by micro-turbine. 2009 4th IEEE Conference on Industrial Electronics and Applications, ICIEA 2009, 1, 1361-1366. https://doi.org/10.1109/ICIEA.2009.5138424Botterón, F., de Camargo, R., and Pinheiro, H. ,2003. New limiting algorithms for space vector modulated three-phase four-leg voltage source inverters. IEE Procedings.-Electronics Power Applications, 150(6). https://doi.org/10.1049/ip-epa:20030913Botteron, F., and Pinheiro, H. ,2007. A three-phase UPS that complies with the standard IEC 62040-3. IEEE Transactions on Industrial Electronics, 54(4), 2120-2136. https://doi.org/10.1109/TIE.2007.894782Carballo, R. E., Botterón, F., Oggier, G. G., and García, G. O. ,2016. Design approach of discrete-time resonant controllers for uninterruptible power supply applications through frequency response analysis. IET Power Electronics, 9(15), 2871-2879. https://doi.org/10.1049/iet-pel.2015.1059Chen, D., Zhang, J., Qian, Z., 2013. Research on fast transient and 6n±1 harmonics suppressing repetitive control scheme for three-phase gridconnected inverters. IET Power Electronics 6 (3) , 601-610 . https://doi.org/10.1049/iet-pel.2012.0348Corcau, J. I., Grigorie, T. L., Jula, N., Cepisca, C., and Popoviciu, N. ,2010. Dynamics and Control of Three-Phase Four-Leg Inverter. EHAC'10, 26-31.Cosner, C., Anwar, G., and Tomizuka, M. ,1990. Plug in repetitive control for industrial robotic manipulators. Proceedings., IEEE International Conference on Robotics and Automation, 1970-1975. https://doi.org/10.1109/ROBOT.1990.126295Franklin, G. F. P. ,1997. Digital Control of Dynamic Systems ,Addison Wesley (ed.); 3rd ed.Gannett, R. a., Sozio, J. C., Boroyevich, D., 2002. Application of synchronous and stationary frame controllers fornunbalanced and nonlinear load compensation in 4-leg inverters. APEC. Seventeenth Annual IEEE Applied Power Electronics Conference and Exposition (Cat. No.02CH37335) 2 (c) , 1-6 . https://doi.org/10.1109/APEC.2002.989372Houari, A., Djerioui, A., Saim, A., Ait-ahmed, M., and Machmoum, M. ,2017. Improved control strategy for power quality enhancement in standalone systems based on four-leg voltage source inverters. 1-9. https://doi.org/10.1049/iet-pel.2017.0124IEC, 1990. Electromagnetic Compatibility (EMC) - Part 2-2: Compatibility levels for low-frequency conducted disturbances and signalling in public low-voltage power supply systems. IEC 61000-2-2IEC. ,2011. Uninterruptible Power Systems (UPS)-Part 3: Method of Specifying the Performance and Test Requirements, Second Edition. IEC 62040-3.Ismail, N. M., and Mishra, M. K. ,2017. Study on the design and switching dynamics of hysteresis current controlled four-leg voltage source inverter for load compensation. https://doi.org/10.1049/iet-pel.2017.0118Li, Y. W. ,2009. Control and resonance damping of voltage-source and current-source converters with LC filters. IEEE Transactions on Industrial Electronics, 56(5), 1511-1521. https://doi.org/10.1109/TIE.2008.2009562Liang, J., Green, T. C., Feng, C., and Weiss, G. ,2009. Increasing voltage utilization in split-link, four-wire inverters. IEEE Transactions on Power Electronics, 24(6), 1562-1569. https://doi.org/10.1109/TPEL.2009.2013351Lidozzi, A., Ji, C., Solero, L., Zanchetta, P., and Crescimbini, F. ,2017. Digital Dead-Beat and Repetitive Combined Control for Stand-Alone Four-Leg VSI. IEEE Transactions on Industry Applications, 9994(c). https://doi.org/10.1109/TIA.2017.2734049Liu, C., Wang, F., and Bai, H. ,2009. High performance controller design with PD feedback inner loop for three-phase four-leg inverter. 2009 4th IEEE Conference on Industrial Electronics and Applications, ICIEA 2009, 1, 1057-1061. https://doi.org/10.1109/ICIEA.2009.5138363Miveh, M. R., Rahmat, M. F., Ghadimi, A. A., and Mustafa, M. W. ,2016. Control techniques for three-phase four-leg voltage source inverters in autonomous microgrids: A review. Renewable and Sustainable Energy Reviews, 54, 1592-1610. https://doi.org/10.1016/j.rser.2015.10.079Miveh, M. R., Rahmat, M. F., Mustafa, M. W., Ghadimi, A. A., and Rezvani, A. ,2016. An Improved Control Strategy for a Four-Leg Grid-Forming Power Converter under Unbalanced Load Conditions. Advances in Power Electronics, 2016. https://doi.org/10.1155/2016/9123747N. Mohan, T. Undeland, W. R. ,2002. Power Electronics: Converters Applications and design 3rd Ed. Wiley.Nasiri, R., and Radan, A. ,2011. Adaptive decoupled control of 4-leg voltage-source inverters for standalone photovoltaic systems: Adjusting transient state response. Renewable Energy, 36(10), 2733-2741. https://doi.org/10.1016/j.renene.2011.03.007Ortega, R., Carranza, O., Sosa, J. C., García, V., and Hernández, R. ,2016. Diseño de controladores para inversores monofásicos operando en modo isla dentro de una microrred. RIAI - Revista Iberoamericana de Automatica e Informatica Industrial, 13(1), 115-126. https://doi.org/10.1016/j.riai.2015.09.010Phillips, C. L., Nagle, H. T., and Chakrabortty, A. ,2015. State Variables. In Digital control system analysis & design (4th ed., pp. 63-71).Pichan, M., and Rastegar, H. ,2017. Sliding-mode control of four-leg inverter with fixed switching frequency for uninterruptible power supply applications. IEEE Transactions on Industrial Electronics, 64(8), 6805-6814. https://doi.org/10.1109/TIE.2017.2686346Pichan, M., Rastegar, H., and Monfared, M. ,2017. Deadbeat Control of the Stand-Alone Four-Leg Inverter Considering the Effect of the Neutral Line Inductor. IEEE Transactions on Industrial Electronics, 64(4), 2592-2601. https://doi.org/10.1109/TIE.2016.2631459Ryan, M. J., De Doncker, R. W., and Lorenz, R. D. ,2001. Decoupled control of a 4-leg inverter via a new 4×4 transformation matrix. IEEE Transactions on Power Electronics, 16(5), 694-701. https://doi.org/10.1109/PESC.1999.789001Thandi, G. S., Zhang, R., Xing, K., Lee, F. C., and Boroyevich, D. ,1999. Modeling, control and stability analysis of a PEBB based DC DPS. IEEE Transactions on Power Delivery, 14(2), 497-505. https://doi.org/10.1109/61.754094Xing, Y., Tan, C., Chen, Q., Zhang, L., Zhou, K., 2017. An improved deadbeat plus plug-in repetitive controller for three-phase four-leg inverters. Proceedings IECON 2017 - 43rd Annual Conference of the IEEE Industrial Electronics Society 2017-January (2) , 6325-6329 . https://doi.org/10.1109/IECON.2017.8217101Yaramasu, V., Rivera, M., Narimani, M., Wu, B., and Rodriguez, J. ,2014. Model predictive approach for a simple and effective load voltage control of four-leg inverter with an output LC filter. IEEE Transactions on Industrial Electronics, 61(10), 5259-5270. https://doi.org/10.1109/TIE.2013.2297291Yepes, A. G., Member, S., and Freijedo, F. D. ,2010. Effects of Discretization Methods on the Performance of Resonant Controllers. 25(7), 1692-1712. https://doi.org/10.1109/TPEL.2010.2041256Yi, H., and Jin, S. ,2004. Study on control strategy for three-phase four-leg inverter power supply. IEEE Annual Conference of Industrial Electronics (IECON), 805-809.Zhang, M. ,2013. Investigation of Switching Schemes for Three-phase Four-Leg Voltage Source Inverters. Newcastle University.Zhang, R. ,1998. High performance power converter systems for nonlinear and unbalanced load/source. Virginia Polytechnic Institute.Zhang, R., and Lee, F. C. ,2000. New high power, high performance power converter systems. Power Electronics, IEEE …, 15(3), 456-463. https://doi.org/10.1109/63.84450

An economic analysis of ischaemic heart disease in Switzerland

Aims Direct and indirect costs of ischaemic heart disease were assessed in Switzerland, for the period 1988-1993, in order to evaluate the economic consequences of more intensive treatment of the disease and of the decreasing mortality from ischaemic heart disease in the working population. Methods and Results A societal perspective was taken for a prevalence-based assessment of the direct (total resources consumed by outpatients and inpatients) and indirect (due to morbidity, invalidity, and premature death, using the human capital approach) costs. The results showed the total costs were 21 million US dollars per 100 000 population in the year 1993 (47% direct, 53% indirect costs). The largest components were the direct costs of inpatient care and indirect costs due to premature death (each approximately 25% of the total). Trends showed a large increase in direct costs (+9% per year, constant dollars). Indirect costs stabilized or decreased slightly due to the reduction of work losses. Conclusions Today's medicine and preventive measures have proven effective for ischaemic heart disease, although such remedies have required increasingly large financial resources. However, society benefits because indirect costs decrease, although this gain does not compensate for all direct cost

End-to-End Joint Antenna Selection Strategy and Distributed Compress and Forward Strategy for Relay Channels

Multi-hop relay channels use multiple relay stages, each with multiple relay nodes, to facilitate communication between a source and destination. Previously, distributed space-time codes were proposed to maximize the achievable diversity-multiplexing tradeoff, however, they fail to achieve all the points of the optimal diversity-multiplexing tradeoff. In the presence of a low-rate feedback link from the destination to each relay stage and the source, this paper proposes an end-to-end antenna selection (EEAS) strategy as an alternative to distributed space-time codes. The EEAS strategy uses a subset of antennas of each relay stage for transmission of the source signal to the destination with amplify and forwarding at each relay stage. The subsets are chosen such that they maximize the end-to-end mutual information at the destination. The EEAS strategy achieves the corner points of the optimal diversity-multiplexing tradeoff (corresponding to maximum diversity gain and maximum multiplexing gain) and achieves better diversity gain at intermediate values of multiplexing gain, versus the best known distributed space-time coding strategies. A distributed compress and forward (CF) strategy is also proposed to achieve all points of the optimal diversity-multiplexing tradeoff for a two-hop relay channel with multiple relay nodes.Comment: Accepted for publication in the special issue on cooperative communication in the Eurasip Journal on Wireless Communication and Networkin

How to obtain division algebras used for fast-decodable space-time block codes

We present families of unital algebras obtained through a doubling process from a cyclic central simple algebra D, employing a K-automorphism tau and an invertible element d in D. These algebras appear in the construction of iterated space-time block codes. We give conditions when these iterated algebras are division which can be used to construct fully diverse iterated codes. We also briefly look at algebras (and codes) obtained from variations of this method

On the Transmit Beamforming for MIMO Wiretap Channels: Large-System Analysis

With the growth of wireless networks, security has become a fundamental issue in wireless communications due to the broadcast nature of these networks. In this work, we consider MIMO wiretap channels in a fast fading environment, for which the overall performance is characterized by the ergodic MIMO secrecy rate. Unfortunately, the direct solution to finding ergodic secrecy rates is prohibitive due to the expectations in the rates expressions in this setting. To overcome this difficulty, we invoke the large-system assumption, which allows a deterministic approximation to the ergodic mutual information. Leveraging results from random matrix theory, we are able to characterize the achievable ergodic secrecy rates. Based on this characterization, we address the problem of covariance optimization at the transmitter. Our numerical results demonstrate a good match between the large-system approximation and the actual simulated secrecy rates, as well as some interesting features of the precoder optimization.Comment: Published in Lecture Notes in Computer Science 8317, pp. 90-102, 2014. (Proceedings of International Conference on Information-Theoretic Security (ICITS), Singapore, November 2013