4,164 research outputs found

    Low Complexity Time Synchronization Algorithm for OFDM Systems with Repetitive Preambles

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    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). 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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

    A Comparison of CP-OFDM, PCC-OFDM and UFMC for 5G Uplink Communications

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    Polynomial-cancellation-coded orthogonal frequency division multiplexing (PCC-OFDM) is a form of OFDM that has waveforms which are very well localized in both the time and frequency domains and so it is ideally suited for use in the 5G network. This paper analyzes the performance of PCC-OFDM in the uplink of a multiuser system using orthogonal frequency division multiple access (OFDMA) and compares it with conventional cyclic prefix OFDM (CP-OFDM), and universal filtered multicarrier (UFMC). PCC-OFDM is shown to be much less sensitive than either CP-OFDM or UFMC to time and frequency offsets. For a given constellation size, PCC-OFDM in additive white Gaussian noise (AWGN) requires 3dB lower signal-to-noise ratio (SNR) for a given bit-error-rate, and the SNR advantage of PCC-OFDM increases rapidly when there are timing and/or frequency offsets. For PCC-OFDM no frequency guard band is required between different OFDMA users. PCC-OFDM is completely compatible with CP-OFDM and adds negligible complexity and latency, as it uses a simple mapping of data onto pairs of subcarriers at the transmitter, and a simple weighting-and-adding of pairs of subcarriers at the receiver. The weighting and adding step, which has been omitted in some of the literature, is shown to contribute substantially to the SNR advantage of PCC-OFDM. A disadvantage of PCC-OFDM (without overlapping) is the potential reduction in spectral efficiency because subcarriers are modulated in pairs, but this reduction is more than regained because no guard band or cyclic prefix is required and because, for a given channel, larger constellations can be used

    Architectures and Key Technical Challenges for 5G Systems Incorporating Satellites

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    Satellite Communication systems are a promising solution to extend and complement terrestrial networks in unserved or under-served areas. This aspect is reflected by recent commercial and standardisation endeavours. In particular, 3GPP recently initiated a Study Item for New Radio-based, i.e., 5G, Non-Terrestrial Networks aimed at deploying satellite systems either as a stand-alone solution or as an integration to terrestrial networks in mobile broadband and machine-type communication scenarios. However, typical satellite channel impairments, as large path losses, delays, and Doppler shifts, pose severe challenges to the realisation of a satellite-based NR network. In this paper, based on the architecture options currently being discussed in the standardisation fora, we discuss and assess the impact of the satellite channel characteristics on the physical and Medium Access Control layers, both in terms of transmitted waveforms and procedures for enhanced Mobile BroadBand (eMBB) and NarrowBand-Internet of Things (NB-IoT) applications. The proposed analysis shows that the main technical challenges are related to the PHY/MAC procedures, in particular Random Access (RA), Timing Advance (TA), and Hybrid Automatic Repeat reQuest (HARQ) and, depending on the considered service and architecture, different solutions are proposed.Comment: Submitted to Transactions on Vehicular Technologies, April 201

    Near-Instantaneously Adaptive HSDPA-Style OFDM Versus MC-CDMA Transceivers for WIFI, WIMAX, and Next-Generation Cellular Systems

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    Burts-by-burst (BbB) adaptive high-speed downlink packet access (HSDPA) style multicarrier systems are reviewed, identifying their most critical design aspects. These systems exhibit numerous attractive features, rendering them eminently eligible for employment in next-generation wireless systems. It is argued that BbB-adaptive or symbol-by-symbol adaptive orthogonal frequency division multiplex (OFDM) modems counteract the near instantaneous channel quality variations and hence attain an increased throughput or robustness in comparison to their fixed-mode counterparts. Although they act quite differently, various diversity techniques, such as Rake receivers and space-time block coding (STBC) are also capable of mitigating the channel quality variations in their effort to reduce the bit error ratio (BER), provided that the individual antenna elements experience independent fading. By contrast, in the presence of correlated fading imposed by shadowing or time-variant multiuser interference, the benefits of space-time coding erode and it is unrealistic to expect that a fixed-mode space-time coded system remains capable of maintaining a near-constant BER

    Preamble design using embedded signalling for OFDM broadcast systems based on reduced-complexity distance detection

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    The second generation digital terrestrial television broadcasting standard (DVB-T2) adopts the so-called P1 symbol as the preamble for initial synchronization. The P1 symbol also carries a number of basic transmission parameters, including the fast Fourier transform size and the single-input/single-output as well as multiple-input/single-output mode, in order to appropriately configure the receiver for carrying out the subsequent processing. In this contribution, an improved preamble design is proposed, where a pair of training sequences is inserted in the frequency domain and their distance is used for transmission parameter signalling. At the receiver, only a low-complexity correlator is required for the detection of the signalling. Both the coarse carrier frequency offset and the signalling can be simultaneously estimated by detecting the above-mentioned correlation. Compared to the standardised P1 symbol, the proposed preamble design significantly reduces the complexity of the receiver while retaining high robustness in frequency-selective fading channels. Furthermore, we demonstrate that the proposed preamble design achieves a better signalling performance than the standardised P1 symbol, despite reducing the numbers of multiplications and additions by about 40% and 20%, respectively
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