Combined data detection scheme for zero-padded OFDM signals in MMF links

© © 2015 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.In this letter, we propose a receiver scheme for zero-padded orthogonal frequency division multiplexing (OFDM) that combines low complexity from overlap-and-add equalizer and low error rate provided by successive interference cancellation data detection from optimal ordering vertical Bell Laboratories layered space-time (V-BLAST) architecture. Results of numerical simulations on multimode optical fiber links show that the proposed scheme improves the error rate performance of zero forcing (ZF) equalization receiver, reaching results similar to V-BLAST. For example, the proposed scheme can reach 33.9 Gb/s in a 600-m link, whereas the ZF receiver would reach 29.06 Gb/s and cyclic prefix OFDM only 19.37 Gb/s. These results are obtained with a reduction in computational complexity (measured in number of real products) of 86% in detection and 66% in preprocessing with respect to the ZF receiver, and 75% and 97% with respect to the V-BLAST receiver.Manuscript received May 6, 2015; accepted May 24, 2015. Date of publication June 1, 2015; date of current version July 10, 2015. This work was supported by the Spanish Ministerio de Economia y Competitividad under Project TEC2012-38558-C02-02 and Project TEC2012-38558-C02-01, both with FEDER funds. The work of P. Medina was supported by the Formacion de Personal Investigador Grant Program of the Universitat Politecnica de Valencia.Medina Sevila, P.; Almenar Terré, V.; Corral, JL. (2015). Combined data detection scheme for zero-padded OFDM signals in MMF links. IEEE Photonics Technology Letters. 27(16):1753-1756. https://doi.org/10.1109/LPT.2015.2439158S17531756271

Transmission Over SSMF at 850 nm: Bimodal Propagation and Equalization

[EN] The combination of 850 nm vertical-cavity surfaceemitting laser (VCSEL) with standard single-mode fiber (SSMF) presents an effective and low-cost interface to increase the reach provided by multi-mode fiber links. At 850 nm, SSMF propagates two modes, and in this study, it has been experimentally shown that the different commercially available SSMF¿s present dissimilar values of differential mode delay. To cope with this unequal behavior of modal dispersion, we propose a scheme based on bidirectional decision feedback equalization (BiDFE) to overcome limited performance of other solutions as mode filtering or classical equalizers. A single span SSMF cabling model, including a measurement-derived statistical characterization of optical connectors, is simulated to evaluate the reach provided by the equalizer attending to both the conditions of the fiber excitation and the characteristics of the VCSEL. A minimum 1.45 km link length at 10 Gb/s is achieved if a linear combining BiDFE (LC-BiDFE) equalizer is included in the receiver, whatever laser launching condition and employing a single-transverse mode VCSEL. If a multitransverse mode VCSEL is used, the reach provided by LC-BiDFE is slightly reduced but assuring a minimum coverage of 1.15 km.This work was supported by the Spanish Ministerio de Economia y Competitividad under Projects TEC2015-70858-C2-2-R and TEC2015-70858-C2-1-R, both with FEDER funds. The work of P. Medina Sevila was supported by the Formacion de Personal Investigador grant program of the Universitat Politecnica de Valencia.Medina-Sevila, P.; Almenar Terré, V.; Corral, JL. (2017). Transmission Over SSMF at 850 nm: Bimodal Propagation and Equalization. Journal of Lightwave Technology. 35(19):4125-4136. https://doi.org/10.1109/JLT.2017.2726585S41254136351

Low-Complexity Time Synchronization Algorithm for Optical OFDM PON System Using a Directly Modulated DFB Laser

© 2015 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.In this paper a low-complexity time synchronization algorithm for optical orthogonal frequency division multiplexing (OFDM) is proposed. The algorithm is based on a repetitive preamble that allows the use of a short cross correlator with an exponential average filter for postprocessing before a threshold detection. The signals in the correlation have been quantized with 1 bit, and the correlations have been implemented as a hard-wired tree adder to reduce the hardware cost. This solution has been verified in a passive optical network (PON) system using a directly modulated distributed feedback (DFB) laser achieving excellent performance with low computing processing complexity even in low signal-to-noise ratio scenarios. Finally, a parallel hardware architecture has been proposed for this time synchronization algorithm, and it has been implemented in a field programmable gate array device reaching a sample rate throughput up to 7.4 Gs/s.This work was supported by the Spanish Ministerio de Economia y Competitividad under projects TEC2012-38558-C02-02 and TEC2012-38558-C02-01 and with FEDER funds.Bruno, JS.; Almenar Terre, V.; Valls Coquillat, J.; Corral, JL. (2015). Low-Complexity Time Synchronization Algorithm for Optical OFDM PON System Using a Directly Modulated DFB Laser. IEEE/OSA Journal of Optical Communications and Networking. 7(11):1025-1033. doi:10.1364/JOCN.7.001025S1025103371

Evaluation of optical ZP-OFDM transmission performance in multimode fiber links

© 2014 Optical Society of America. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modifications of the content of this paper are prohibited.In this paper, the performance of Zero Padding Orthogonal Frequency Division Multiplexing (ZP-OFDM) on intensity modulationdirect detection (IM-DD) multimode fiber (MMF) links is assessed by means of numerical simulations. The performance of ZP-OFDM is compared to classical Cyclic Prefixed form of OFDM (CP-OFDM) which is known to offer a limited performance in terms of symbol recovery in subcarriers suffering severe fading. Simulations results show that ZPOFDM is able to reach 29 Gbps in 99.5% of all installed MMF links up to 600 meters compared to 14 Gbps for CP-OFDM when a 64 points fast Fourier transform (FFT) size is used. The use of ZP-OFDM makes it possible to increase the link length up to 1200 and 2400 m with a 25 Gbps data rate if the FFT sizes are increased to 128 and 256 points, respectively; whereas the CP-OFDM scheme will offer a maximum data rate of 10 Gbps in both cases. ZP-OFDM can be an alternative to adaptive loading OFDM schemes without the need of a negotiation between transmitter and receiver, reducing the system deployment complexity and increasing the flexibility in scenarios with multiple receivers. (C) 2014 Optical Society of AmericaThe work presented in this paper has been supported by the Spanish Ministerio de Economia y Competitividad under projects TEC2012-38558-C02-02 and TEC2012-38558-C02-01.Medina Sevila, P.; Almenar Terré, V.; Corral González, JL. (2014). Evaluation of optical ZP-OFDM transmission performance in multimode fiber links. Optics Express. 22(1):1008-1017. https://doi.org/10.1364/OE.22.001008S10081017221Cunningham, J. E., Beckman, D., Zheng, X., Huang, D., Sze, T., & Krishnamoorthy, A. V. (2006). PAM-4 Signaling over VCSELs with 0.13µm CMOS Chip Technology. Optics Express, 14(25), 12028. doi:10.1364/oe.14.012028Gasulla, I., & Capmany, J. (2008). 1 Tb/s·km Multimode fiber link combining WDM transmission and low-linewidth lasers. Optics Express, 16(11), 8033. doi:10.1364/oe.16.008033Xia, C., Ajgaonkar, M., & Rosenkranz, W. (2005). On the performance of the electrical equalization technique in MMF links for 10-gigabit ethernet. Journal of Lightwave Technology, 23(6), 2001-2011. doi:10.1109/jlt.2005.849920Lowery, A. J., & Armstrong, J. (2005). 10Gbit/s Multimode Fiber Link using Power-Efficient Orthogonal-Frequency-Division Multiplexing. Optics Express, 13(25), 10003. doi:10.1364/opex.13.010003Xu, J., von Hoyningen-Huene, J., Ruprecht, C., Rath, R., & Rosenkranz, W. (2013). Robust Transmission of 29-Gb/s OFDM Signal Over 1-km OM1 MMF Under Center Launching. IEEE Photonics Technology Letters, 25(2), 206-209. doi:10.1109/lpt.2012.2233729Giacoumidis, E., Jin, X. Q., Tsokanos, A., & Tang, J. M. (2010). Statistical Performance Comparisons of Optical OFDM Adaptive Loading Algorithms in Multimode Fiber-Based Transmission Systems. IEEE Photonics Journal, 2(6), 1051-1059. doi:10.1109/jphot.2010.2092422Tang, J. M., Lane, P. M., & Shore, K. A. (2006). Transmission performance of adaptively modulated optical OFDM signals in multimode fiber links. IEEE Photonics Technology Letters, 18(1), 205-207. doi:10.1109/lpt.2005.861631Jin, X. Q., Tang, J. M., Qiu, K., & Spencer, P. S. (2008). Statistical Investigations of the Transmission Performance of Adaptively Modulated Optical OFDM Signals in Multimode Fiber Links. Journal of Lightwave Technology, 26(18), 3216-3224. doi:10.1109/jlt.2008.917088Kanprachar, S., & Jacobs, I. (2003). Diversity coding for subcarrier multiplexing on multimode fibers. IEEE Transactions on Communications, 51(9), 1546-1553. doi:10.1109/tcomm.2003.816981Muquet, B., Zhengdao Wang, Giannakis, G. B., de Courville, M., & Duhamel, P. (2002). Cyclic prefixing or zero padding for wireless multicarrier transmissions? IEEE Transactions on Communications, 50(12), 2136-2148. doi:10.1109/tcomm.2002.806518Tang, J. M., & Shore, K. A. (2007). Maximizing the Transmission Performance of Adaptively Modulated Optical OFDM Signals in Multimode-Fiber Links by Optimizing Analog-to-Digital Converters. Journal of Lightwave Technology, 25(3), 787-798. doi:10.1109/jlt.2006.890457Mestdagh, D. J. G., Spruyt, P. M. P., & Biran, B. (1993). Effect of amplitude clipping in DMT-ADSL transceivers. Electronics Letters, 29(15), 1354. doi:10.1049/el:1993090

Low Complexity Time Synchronization Algorithm for OFDM Systems with Repetitive Preambles

In this paper, a new time synchronization algorithm for OFDM systems with repetitive preamble is proposed. This algorithm makes use of coarse and fine time estimation; the fine time estimation is performed using a cross-correlation similar to previous proposals in the literature, whereas the coarse time estimation is made using a new metric and an iterative search of the last sample of the repetitive preamble. A complete analysis of the new metric is included, as well as a wide performance comparison, for multipath channel and carrier frequency offset, with the main time synchronization algorithms found in the literature. Finally, the complexity of the VLSI implementation of this proposal is discussed. © 2011 Springer Science+Business Media, LLC.This work was supported by the Spanish Ministerio de Educacion y Ciencia under grants TEC2006-14204-C02-01 and TEC2008-06787.Canet Subiela, MJ.; Almenar Terre, V.; Flores Asenjo, SJ.; Valls Coquillat, J. (2012). Low Complexity Time Synchronization Algorithm for OFDM Systems with Repetitive Preambles. Journal of Signal Processing Systems. 68(3):287-301. doi:10.1007/s11265-011-0618-6S287301683IEEE 802.11a standard (1999). Wireless LAN medium access control (MAC) and physical layer (PHY) specifications: high-speed physical layer in the 5 GHz band.IEEE 802.11 g standard (2003). Wireless LAN specifications: Further higher data rate extension in the 2.4 GHz band.IEEE 802.16-2004 (2004). Standard for local and metropolitan area networks, part 16: Air interface for fixed broadband wireless access systems.Lee, D., & Cheun, K. (2002). Coarse symbol synchronization algorithms for OFDM systems in multipath channels. IEEE Communications Letters, 6(10), 446–448.Park, B., Cheon, H., Ko, E., Kang, C., & Hong, D. (2004). A blind OFDM synchronization algorithm based on cyclic correlation. IEEE Signal Processing Letters, 11(2), 83–85.Beek, J. J., Sandell, M., & Börjesson, P. O. (1997). ML estimation of time and frequency offset in OFDM system. IEEE Transactions on Signal Processing, 45(7), 1800–1805.Ma, S., Pan, X., Yang, G., & Ng, T. (2009). Blind symbol synchronization based on cyclic prefix for OFDM systems. IEEE Transactions on Vehicular Technology, 58(4), 1746–1751.Schmidl, T., & Cox, D. (1997). Robust frequency and timing synchronization for OFDM. IEEE Transactions on Communications, 45(12), 1613–1621.Coulson, A. J. (2001). Maximum likelihood synchronization for OFDM using a pilot symbol: Algorithms. IEEE Journal on Selected Areas in Communications, 19(12), 2495–2503.Tufvesson, F., Edfors, O., & Faulker, M. (1999). Time and frequency synchronization for OFDM using PN-sequence preambles. Proceedings of the Vehicular Technology Conference (VTC), 4, 2203–2207.Shi, K., & Serpedin, E. (2004). Coarse frame and carrier synchronization of OFDM systems: a new metric and comparison. IEEE Transactions on Wireless Communications, 3(4), 1271–1284.Minn, H., Zeng, M., & Bhargava, V. K. (2000). On timing offset estimation for OFDM Systems. IEEE Communications Letters, 4, 242–244.Minn, H., Bhargava, V. K., & Letaief, K. B. (2003). A robust timing and frequency synchronization for OFDM systems. IEEE Transactions on Wireless Communications, 2(4), 822–839.Minn, H., Bhargava, V. K., & Letaief, K. B. (2006). A combined timing and frequency synchronization and channel estimation for OFDM. IEEE Transactions on Communications, 54(3), 416–422.Park, B., Cheon, H., Ko, E., Kang, C., & Hong, D. (2003). A novel timing estimation method for OFDM systems. IEEE Communications Letters, 7(5), 239–241.Chang, S., & Kelley, B. (2003). Time synchronization for OFDM-based WLAN systems. Electronics Letters, 39(13), 1024–1026.Wu, Y., Yip, K., Ng, T., & Serpedin, E. (2005). Maximum-likelihood symbol synchronization for IEEE 802.11a WLANs in unknown frequency-selective fading channels. IEEE Transactions on Wireless Communications, 4(6), 2751–2763.Larsson, E. G., Liu, G., Li, J., & Giannakis, G. B. (2001). Joint symbol timing and channel estimation for OFDM based WLANs. IEEE Communications Letters, 5(8), 325–327.Troya, A., Maharatna, K., Krstic, M., Grass, E., Jagdhold, U., & Kraemer, R. (2007). Efficient inner receiver design for OFDM-based WLAN systems: algorithm and architecture. IEEE Transactions on Wireless Communications, 6(4), 1374–1385.Yang, J., & Cheun, K. (2006). Improved symbol timing synchronization in IEEE 802.11a/g wireless LAN systems in multipath channels. International Conference on Consumer Electronics. doi: 10.1109/ICCE.2006.1598425 .Manusani, S. K., Hshetrimayum, R. S., & Bhattacharjee, R. (2006). Robust time and frequency synchronization in OFDM based 802.11a WLAN systems. Annual India Conference. doi: 10.1109/INDCON.2006.302775 .Zhou, L., & Saito, M. (2004). A new symbol timing synchronization for OFDM based WLANs under multipath fading channels. 15th IEEE International Symposium on Personal, Indoor and Mobile Radio Communications. doi: 10.1109/PIMRC.2004.1373890 .Kim, T., & Park, S.-C. (2007). A new symbol timing and frequency synchronization design for OFDM-based WLAN systems. 9th Conference on Advanced Communication Technology. doi: 10.1109/ICACT.2007.358691 .Baek, J. H., Kim, S. D., & Sunwoo, M. H. (2008). SPOCS: Application specific signal processor for OFDM communication systems. Journal of Signal Processing Systems, 53(3), 383–397.Van Kempen, G., & van Vliet, L. (2000). Mean and variance of ratio estimators used in fluorescence ratio imaging. Cytometry, 39(4), 300–305.J. Melbo, J., & Schramm, P. (1998). Channel models for HIPERLAN/2 in different indoor scenarios. 3ERI085B, HIPERLAN/2 ETSI/BRAN contribution.Abramowitz, M., & Stegun, I. A. (1972). Handbook of mathematical functions. Dover.López-Martínez, F. J., del Castillo-Sánchez, E., Entrambasaguas, J. T., & Martos-Naya, E. (2010). Iterative-gradient based complex divider FPGA core with dynamic configurability of accuracy and throughput. Journal of Signal Processing Systems. doi: 10.1007/s11265-010-0464-y .Angarita, F., Canet, M. J., Sansaloni, T., Perez-Pascual, A., & Valls, J. (2008). Efficient mapping of CORDIC Algorithm for OFDM-based WLAN. Journal of Signal Processing Systems, 52(2), 181–191

An efficient GPU implementation of fixed-complexity sphere decoders for MIMO wireless systems

The use of many-core processors such as general purpose Graphic Processing Units (GPUs) has recently become attractive for the efficient implementation of signal processing algorithms for communication systems. This is due to the cost-effectiveness of GPUs together with their potential capability of parallel processing. This paper presents an implementation of the widely employed fixed-complexity sphere decoder on GPUs, which allows to considerably decrease the computational time required for the data detection stage in multiple-input multiple-output systems. Both, the hard-and soft-output versions of the method have been implemented. Speedup results show the proposed GPU implementation boosts the runtime of the parallel execution of the methods in a high performance multi-core CPU. In addition, the throughput of the algorithm is evaluated and is shown to outperform other recent implementations and to fulfill the real-time requirements of several LTE configurations. ©2012-IOS Press and the authors. All rights reserved.This work was partially funded by the TEC2009-13741 project of the Spanish Ministry of Science and by the PROMETEO/2009/013 project of the Generalitat Valenciana.Roger Varea, S.; Ramiro Sánchez, C.; González Salvador, A.; Almenar Terré, V.; Vidal Maciá, AM. (2012). An efficient GPU implementation of fixed-complexity sphere decoders for MIMO wireless systems. Integrated Computer-Aided Engineering. 19(4):341-350. https://doi.org/10.3233/ICA-2012-0410S34135019

An efficient fixed-complexity sphere decoder with quantized soft outputs

In practical multiple-input multiple-output bit-interleaved-coded-modulation (MIMO-BICM) systems, demodulators have to deliver finite word-length (quantized) log-likelihood-ratios (LLRs). In this letter, we propose an efficient modification of the fixed-complexity sphere decoder for MIMO-BICM systems working with quantized LLRs. Our approach reduces the complexity of previously proposed schemes via pruning strategies that exploit the clipping and quantization of LLRs. Numerical results confirm that our scheme achieves a significant complexity reduction (by 37% for the case of 2 bits per LLR and by 31% for the case of 3 bits per LLR) with negligible degradation in bit error rate performance.This work was supported in part by the PROMETEO/2009/013 and TEC2009-13741 projects, by the AP2007-01417 FPU grant, and by FWF grant S10606.Roger Varea, S.; Gonzalez, A.; Almenar Terré, V.; Matz, G. (2012). An efficient fixed-complexity sphere decoder with quantized soft outputs. IEEE Communications Letters. 16(11):1828-1831. https://doi.org/10.1109/LCOMM.2012.091712.121702S18281831161

Búsqueda Tabú aplicada a detección de símbolos en L-MIMO

En la detección de símbolos para sistemas MIMO con un gran número de antenas que se conoce como L-MIMO (Large MIMO), se busca contar con esquemas eficientes cuya complejidad haga viable su implementación real. Este artículo presenta los resultados obtenidos con un esquema basado en Tabu Search, comparándolo mediante simulación con detectores lineales de referencia, demostrando que, en condiciones normales de un canal inalámbrico, es posible obtener un mejor desempeño en las evaluaciones que se realizan hasta L -MIMO 32x32

Sistemas MIMO con un elevado número de antenas

The demand for high speeds and capabilities in wireless data communication, together with an increasing traffic of services such as high definition video, video phone calls, and synchronization of photos and videos from mobile phones, pose a challenge that is expected to be overcome with the work being done to establish a 5G wireless network. Since one of the alternatives involves using a large number of antennas, there is a need to learn about and be prepared for this new paradigm as soon as possible. This article provides a review of various technologies that have currently become the center of attention and conform with the denomination of large scale MIMO systems, including, among others: massive MIMO and full dimensional MIMO systems.La demanda de altas velocidades y capacidades en comunicación inalámbrica de datos, con tráfico creciente de servicios como el video de alta definición, las videollamadas y la sincronización de fotos y videos del móvil, plantea un reto que se entiende resuelto con el trabajo que se está haciendo para la 5G inalámbrica. Una estrategia que se presenta en este marco, es el uso de un gran número de antenas, por lo que es necesario cuanto antes conocer y estar preparado para este nuevo paradigma. Este artículo hace una revisión de las tecnologías que tienen el foco de atención en la actualidad y que se enmarcan en la denominación MIMO de gran escala, entre los que se encuentran MIMO masivo y MIMO de dimensiones completas