Time filter

Source Type

Santa Rita do Sapucaí, Brazil

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.

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.

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.

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.

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