Instituto Nacional Of Telecomunicacoes

Santa Rita do Sapucaí, Brazil

Instituto Nacional Of Telecomunicacoes

Santa Rita do Sapucaí, Brazil
Time filter
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Coelho S.T.,Instituto Nacional Of Telecomunicacoes | Ynoguti C.A.,Instituto Nacional Of Telecomunicacoes
Advances in Experimental Medicine and Biology | Year: 2010

SVMs were primarily proposed to deal with binary classification. In this work an alternative O.log2.n// method for multiple classes classification using SVMs is proposed. Experimental results showed that it can be 23 times faster than the one vs one method, and 1.3 times faster than the one vs all classic methods, with the same error rate. Tests were performed on a speaker independent, isolated word speech recognition scenario. © Springer Science+Business Media, LLC 2010.

Michailow N.,TU Dresden | Matthe M.,TU Dresden | Gaspar I.S.,TU Dresden | Caldevilla A.N.,TU Dresden | And 4 more authors.
IEEE Transactions on Communications | Year: 2014

Cellular systems of the fourth generation (4G) have been optimized to provide high data rates and reliable coverage to mobile users. Cellular systems of the next generation will face more diverse application requirements: the demand for higher data rates exceeds 4G capabilities; battery-driven communication sensors need ultra-low power consumption; and control applications require very short response times. We envision a unified physical layer waveform, referred to as generalized frequency division multiplexing (GFDM), to address these requirements. In this paper, we analyze the main characteristics of the proposed waveform and highlight relevant features. After introducing the principles of GFDM, this paper contributes to the following areas: 1) the means for engineering the waveform's spectral properties; 2) analytical analysis of symbol error performance over different channel models; 3) concepts for MIMO-GFDM to achieve diversity; 4) preamble-based synchronization that preserves the excellent spectral properties of the waveform; 5) bit error rate performance for channel coded GFDM transmission using iterative receivers; 6) relevant application scenarios and suitable GFDM parameterizations; and 7) GFDM proof-of-concept and implementation aspects of the prototype using hardware platforms available today. In summary, the flexible nature of GFDM makes this waveform a suitable candidate for future 5G networks. © 2014 IEEE.

Mendes L.L.,Instituto Nacional Of Telecomunicacoes | Baldini Filho R.,University of Campinas
IEEE Transactions on Vehicular Technology | Year: 2011

Orthogonal frequency-division multiplexing (OFDM) systems usually make use of a set of square M quadrature-amplitude modulation (M-QAM) constellations to obtain a good tradeoff between throughput and symbol-error robustness. However, the switch to the next constellation increases the number of bits per modulation symbol by two. The introduction of nonsquare M-QAM constellations in such systems brings extra advantages such as smoother transition among bit rates and a reduction of the peak-to-average ratio of the OFDM signal. Therefore, this paper unfolds analytical expressions to evaluate the symbol-error performance of nonsquare M-QAM OFDM on nonlinear time-variant additive white Gaussian noise channels, taking clipping distortion into account. Cross and overlaid M-QAM are considered. Analytical performances are evaluated and compared with computational simulations, which show good agreement. © 2011 IEEE.

Matthe M.,TU Dresden | Mendes L.,Instituto Nacional Of Telecomunicacoes | Gaspar I.,TU Dresden | Michailow N.,TU Dresden | And 2 more authors.
Eurasip Journal on Wireless Communications and Networking | Year: 2016

Future wireless communication systems are demanding a more flexible physical layer. GFDM is a block filtered multicarrier modulation scheme proposed to add multiple degrees of freedom and to cover other waveforms in a single framework. In this paper, GFDM modulation and demodulation is presented as a frequency-domain circular convolution, allowing for a reduction of the implementation complexity when MF, ZF and MMSE filters are employed as linear demodulators. The frequency-domain circular convolution shows that the DFT used in the GFDM signal generation can be seen as a precoding operation. This new point-of-view opens the possibility to use other unitary transforms, further increasing the GFDM flexibility and covering a wider set of applications. The following three precoding transforms are considered in this paper to illustrate the benefits of precoded GFDM: (i) Walsh Hadamard Transform; (ii) CAZAC transform and; (iii) Discrete Hartley Transform. The PAPR and symbol error rate of these three unitary transform combined with GFDM are analyzed as well. © 2016, Matthéet al.

Gaspar I.S.,TU Dresden | Mendes L.L.,Instituto Nacional Of Telecomunicacoes | Michailow N.,TU Dresden | Fettweis G.,TU Dresden
Eurasip Journal on Advances in Signal Processing | Year: 2014

Generalized frequency division multiplexing (GFDM) is a block filtered multicarrier modulation scheme recently proposed for future wireless communication systems. It generalizes the concept of orthogonal frequency division multiplexing (OFDM), featuring multiple circularly pulse-shaped subsymbols per subcarrier. This paper presents an algorithm for GFDM synchronization and investigates the use of a preamble that consists of two identical parts combined with a windowing process in order to satisfy low out of band radiation requirements. The performance of time and frequency estimation, with and without windowing, is evaluated in terms of the statistical properties of residual offsets and the impact on symbol error rate over frequency-selective channels. A flexible metric that quantifies the penalty of misalignments is derived. The results show that this approach performs practically as state-of-the-art OFDM schemes known in the literature, while it additionally can reduce the sidelobes of the spectrum emission. © 2014 Gaspar et al.; licensee Springer.

Zhang D.,TU Dresden | Mendes L.L.,TU Dresden | Mendes L.L.,Instituto Nacional Of Telecomunicacoes | Matthe M.,TU Dresden | And 3 more authors.
IEEE Transactions on Wireless Communications | Year: 2016

Generalized frequency division multiplexing (GFDM) as a nonorthogonal waveform aims at diverse applications in future mobile networks. To evaluate its performance, its capacity limits are of particular importance. Therefore, this paper analyzes its constellation-constrained capacities for cases where the channel state information (CSI) is unknown at the transmitter and perfectly known at the receiver. In frequency selective channels, GFDM may provide advantage over the conventional orthogonal frequency division multiplexing (OFDM) scheme. In order to achieve near-capacity performance, the interaction of data symbols in time and frequency combined with multiple antennas (MIMO) challenges the design of GFDM receivers. This paper, therefore, applies expectation propagation (EP) for systematic receiver design. It is shown that the resulting iterative MIMO-GFDM receiver with affordable complexity can approach optimum decoding performance and outperform MIMO-OFDM in a rich multipath environment. Simulations are also used to illustrate the impact of channel delay spread on the constellation-constrained capacities and on the performance of the novel receiver algorithm. © 2002-2012 IEEE.

Zhang D.,TU Dresden | Matthe M.,TU Dresden | Mendes L.L.,Instituto Nacional Of Telecomunicacoes | Fettweis G.,TU Dresden
IEEE Signal Processing Letters | Year: 2016

The coded modulation (CM) capacity represents the maximum achievable data rate for a CM scheme assuming optimal decoding at the receiver. It is an important analytical tool, providing theoretic limits for near-optimum transceiver design. Next generation wireless communications systems with the use of new technologies, such as massive antennas and nonorthogonal waveforms, tend to be large scale. However, the conventional ways developed for evaluating the CM capacity of small-scale systems expose exponential complexity with respect to the system's input dimension. Therefore, they become infeasible when the input dimension increases by one or two orders of magnitude in large-scale systems of interest. This letter resorts to a lower and upper bound of the CM capacity, allowing for a computationally efficient evaluation with polynomial complexity. In particular, two message passing algorithms, namely expectation propagation (EP) and variational message passing (VMP), are applied to evaluate the bounds. Two applications are examined in the end. The presented results bring valuable information about the system design, allowing one to evaluate the impact of suboptimal implementation in the overall system performance. © 1994-2012 IEEE.

Matthe M.,TU Dresden | Mendes L.L.,Instituto Nacional Of Telecomunicacoes | Gaspar I.,TU Dresden | Michailow N.,TU Dresden | And 2 more authors.
Eurasip Journal on Wireless Communications and Networking | Year: 2015

The challenges of future wireless networks imply that the physical layer of the next generation mobile communication system needs to be compatible with multiple-input multiple-output and allow a flexible multiple access scheme. Time-reversal space-time coding can be applied to a recent filtered multicarrier modulation scheme, named generalized frequency division multiplexing, to achieve a multiple-input multiple-output non-orthogonal multicarrier modulation with flexibility to address the requirements of future mobile networks. In this paper, the subcarriers of the physical layer block are shared between multiple users, allowing for an efficient and simple multiple access solution. A channel estimation technique that can simultaneously estimate channel frequency response and timing misalignment in generalized frequency division multiple access is described. The paper also shows that the knowledge of channel state information can improve the overall performance when used to schedule the subchannel distribution among the users. Symbol error rate performance analysis shows that the resources of the time-reversal space-time coding generalized frequency division multiple access block can be shared among users that have one or two transmit antennas simultaneously under frequency-selective time-variant channels. © 2015, Matthe et al.; licensee Springer.

Vital T.M.,Instituto Nacional Of Telecomunicacoes | Ynoguti C.A.,Instituto Nacional Of Telecomunicacoes
BIOSIGNALS 2014 - 7th Int. Conference on Bio-Inspired Systems and Signal Processing, Proceedings; Part of 7th Int. Joint Conference on Biomedical Engineering Systems and Technologies, BIOSTEC 2014 | Year: 2014

The accuracy of speech recognition systems degrades severely when operating in noisy environments, mainly due to the mismatch between training and testing environmental conditions. The use of noise corrupted training utterances is being used with success in many works. However, as the type and intensity of the noise at operation time is unpredictable, the present work proposes a step beyond: the use of the MAP method to use samples of the actual audio signal that is being processed to adapt such systems to the real noise condition. Experimental results show an increase of almost 2% on average in the recognition rates, when compared to systems trained with noisy utterances. Copyright © 2014 SCITEPRESS - Science and Technology Publications. All rights reserved.

Michailow N.,TU Dresden | Mendes L.,Instituto Nacional Of Telecomunicacoes | Matthe M.,TU Dresden | Gaspar I.,TU Dresden | And 2 more authors.
IEEE Communications Letters | Year: 2015

This paper presents the combination of generalized frequency division multiplexing (GFDM) with the Walsh-Hadamard transform (WHT) to achieve a scheme that is robust against frequency-selective channels (FSC). The proposed scheme is suitable for low-latency scenarios foreseen for 5G networks, specially for Tactile Internet. The paper also presents analytical approximations that can be used to estimate the bit error rate of GFDM and WHT-GFDM over frequency-selective channels in single shot transmission. Simulation results for encoded GFDM are included for further comparison. © 1997-2012 IEEE.

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