Francisco J. Vázquez-Araújo
University of A Coruña
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Featured researches published by Francisco J. Vázquez-Araújo.
IEEE Communications Letters | 2013
Óscar Fresnedo; Francisco J. Vázquez-Araújo; Luis Castedo; Javier Garcia-Frias
Analog Joint Source-Channel Coding (JSCC) is a communication strategy that does not follow the separation principle of conventional digital systems but approaches the optimal distortion-cost tradeoff over AWGN channels. Conventional Maximum Likelihood (ML) analog JSCC decoding schemes suffer performance degradation at low Channel Signal to Noise Ratio (CSNR) values, while Minimum Mean Square Error (MMSE) decoding presents high complexity. In this letter we propose an alternative two step decoding approach which achieves the near-optimal performance of MMSE decoding at all CSNR values while maintaining a low complexity comparable to that of ML decoding. An additional advantage of the proposed analog JSCC decoding approach is that it can also be used in Multiple Input Multiple Output (MIMO) fading channels.
IEEE Transactions on Wireless Communications | 2007
Miguel González-López; Francisco J. Vázquez-Araújo; Luis Castedo; Javier Garcia-Frias
Low density generator matrix (LDGM) codes are a particular class of low density parity check (LDPC) codes with very low encoding complexity. Single LDGM codes present high error-floors, which can be substantially reduced with the serial concatenation of two LDGM (SCLDGM) codes. We propose a technique to obtain good SCLDGM codes using extrinsic information transfer (EXIT) functions in a novel way. Although the optimization is performed for AWGN channels with binary signaling, the resulting codes are also optimal for AWGN and perfectly-interleaved Rayleigh fading channels with non-binary signaling and perfect CSI at reception, provided that Gray mapping is utilized. Optimized regular and irregular SCLDGM codes outperform heuristically-designed LDGM codes existing in the literature, and have a performance similar to or better than that of irregular repeat accumulate (IRA) codes.
international conference on communications | 2011
José Antonio García-Naya; Óscar Fresnedo; Francisco J. Vázquez-Araújo; Miguel González-López; Luis Castedo; Javier Garcia-Frias
Recently, analog joint source-channel coding has been proposed as a means of achieving near-optimum performance for high data rates with a very low complexity. However, no experimental evaluation showing the practical feasibility of this scheme has been performed to date. In this paper, we describe a software-defined radio implementation of an analog joint source-channel coded wireless transmission system. Experimental evaluation carried out in an indoor environment making use of a wireless testbed show that the performance perfectly matches that originally reported by simulations in additive white Gaussian noise channels for signal-to-noise ratio values below 20 dB.
international workshop on signal processing advances in wireless communications | 2006
Francisco J. Vázquez-Araújo; Miguel González-López; Luis Castedo; Javier Garcia-Frias
Serially-concatenated low-density generator matrix (SCLDGM) codes are an attractive scheme to approach the capacity of single input single output (SISO) channels due to the low computational cost of the encoding and decoding procedures. In this paper we investigate the design of SCLDGM codes for the spatial multiplexing over multiple input multiple output (MIMO) wireless communication channels. SCLDGM codes are constructed using an optimization procedure based on tracking the decoding behaviour of the sum-product algorithm (SPA) using extrinsic information transfer (EXIT) functions. We present results for different antenna configurations, showing that the optimized SCLDGM codes exhibit better performance than standard low density parity check (LDPC) codes with similar encoding complexity
Eurasip Journal on Wireless Communications and Networking | 2014
Francisco J. Vázquez-Araújo; Óscar Fresnedo; Luis Castedo; Javier Garcia-Frias
Analog joint source-channel coding (JSCC) is a communication strategy that does not follow the separation principle of conventional digital systems but has been shown to approach the optimal distortion-cost tradeoff over additive white Gaussian noise channels. In this work, we investigate the feasibility of analog JSCC over multiple-input multiple-output (MIMO) fading channels. Since, due to complexity constraints, directly recovering the analog source information from the MIMO channel output is not possible, we propose the utilization of low-complexity two-stage receivers that separately perform detection and analog JSCC maximum likelihood decoding. We study analog JSCC MIMO receivers that utilize either linear minimum mean square error or decision feedback MIMO detection. Computer experiments show the ability of the proposed analog JSCC receivers to approach the optimal distortion-cost tradeoff both in the low and high channel signal-to-noise ratio regimes. Performance is analyzed over both synthetically computer-generated Rayleigh fading channels and real indoor wireless measured channels.
international workshop on signal processing advances in wireless communications | 2013
Óscar Fresnedo; Francisco J. Vázquez-Araújo; Luis Castedo; Javier Garcia-Frias
Recently, analog Joint Source-Channel Coding (JSCC) has been shown to approach the optimal distortion-cost trade-off when transmitting over AWGN channels. In this work we consider analog JSCC over frequency-selective channels using Orthogonal Frequency Division Multiplexing (OFDM) modulation. Due to its high complexity, optimal MMSE analog JSCC decoding is infeasible in OFDM, hence a practical two-stage decoding approach made up of a MMSE estimator followed by a Maximum Likelihood (ML) decoder is proposed. Three different alternatives for system optimization are considered: non-adaptive coding, adaptive coding, and adaptive coding with precoding. We show that the three analog JSCC transmission strategies approach the optimal distortion-cost trade-off although much better performance is obtained with the adaptive coding with precoding method, specially in Multiple Input Multiple Output (MIMO) OFDM systems.
IEEE Transactions on Wireless Communications | 2007
Francisco J. Vázquez-Araújo; Miguel González-López; Luis Castedo; Javier Garcia-Frias
We investigate the ability of serially-concatenated low density generator matrix (SCLDGM) codes to approach the capacity of ergodic multiple-input multiple-output (MIMO) channels. First, we explain how to design good SCLDGM codes using extrinsic information transfer (EXIT) analysis and optimum detection. However, optimum detection becomes unfeasible in many cases of practical interest where the number of transmitting antennas and/or the number of bits per constellation symbol is large. In this case, we resort to list sphere detection (LSD), considering two versions: maximum likelihood (ML) and maximum a posteriori (MAP). Again, we use EXIT analysis to obtain good SCLDGM codes for these specific LSD versions. We provide examples of optimized rate 1/2 SCLDGM codes and show that they perform within 1 dB from the theoretical capacity limit for a large number of antenna configurations and modulation formats. Finally, we discuss how to iteratively improve channel estimation using the soft information computed during the decoding process. We also show how the complexity of channel estimation is reduced by utilizing the candidate list calculated by the LSD.
personal, indoor and mobile radio communications | 2006
Miguel González-López; Francisco J. Vázquez-Araújo; Luis Castedo; Javier Garcia-Frias
In this work we study the ability of regular serially concatenated low-density generator matrix (SCLDGM) codes to approach the capacity of MIMO channels with two transmit antennas. We focus on two schemes: spatial multiplexing in a BICM fashion and concatenation with the Alamouti code. We show that good SCLDGM codes designed for SISO channels also approach MIMO capacity in the Alamouti concatenated scheme. These codes, however, do not perform adequately in spatial multiplexing and, in this case, have to be specifically designed for each antenna configuration and modulation format. Decoding complexity in spatial multiplexing is larger but the performance is in general better because the Alamouti code reduces the MIMO channel capacity when there is more than one receiving antenna
Sensors | 2015
José J. Lamas-Seco; Paula Maria Castro; Adriana Dapena; Francisco J. Vázquez-Araújo
Inductive Loop Detectors (ILDs) are the most commonly used sensors in traffic management systems. This paper shows that some spectral features extracted from the Fourier Transform (FT) of inductive signatures do not depend on the vehicle speed. Such a property is used to propose a novel method for vehicle classification based on only one signature acquired from a sensor single-loop, in contrast to standard methods using two sensor loops. Our proposal will be evaluated by means of real inductive signatures captured with our hardware prototype.
international conference on communications | 2011
Óscar Fresnedo; Francisco J. Vázquez-Araújo; J. Garcia-Frias; Miguel González-López; L. Castedo
Recently, the use of analog joint source-channel coding for the transmission of data samples at high rates over AWGN channels has been proposed in the literature. Simulation results have shown that this analog scheme performs close to the theoretical limits for several source distributions and transmission rates. In this paper we study the performance of such a system in comparison with optimized capacity approaching digital Bit Interleaved Coded Modulation (BICM) schemes. We show that in practical situations the analog transmission performs better than the digital scheme with a much lower encoding and decoding complexity when considering Gaussian and Laplacian source distributions.