J.M. Paredes

Technical University Darmstadt, Darmstadt, Hesse, Germany

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Publications (12)29.19 Total impact

  • S.J. Alabed, J.M. Paredes, A.B. Gershman
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    ABSTRACT: For two-way wireless relay networks (TWRNs), the simultaneous bidirectional transmission has been shown to outperform other strategies using decode-and-forward (DF) distributed space-time coding (DSTC), thanks to its high spectral efficiency. However, it has a rather high relay decoding complexity and cannot use the direct link between the communicating terminals. In this letter, we propose a simple DSTC transmission scheme for TWRNs that avoids the latter disadvantages at the same symbol rate and with a performance advantage at high powers. Our strategy allows the communicating terminals to use the direct link between them to achieve a higher diversity gain. An extension of the proposed strategy to the differential case is also discussed.
    IEEE Transactions on Wireless Communications 01/2012; 11(4):1260-1265. · 2.42 Impact Factor
  • S.J. Alabed, J.M. Paredes, A.B. Gershman
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    ABSTRACT: In this paper, a low-complexity suboptimal decoder for coherent and non-coherent quasi-orthogonal space time block codes with three and four transmit antennas is proposed. Our decoder enjoys a nearly linear complexity and approximately the same performance as the optimal maximum-likelihood (ML) decoder. Simulations show the advantages of the proposed decoder with respect to several other popular approaches to the coherent and non-coherent decoding.
    IEEE Transactions on Wireless Communications 04/2011; · 2.42 Impact Factor
  • J.M. Paredes, A.B. Gershman
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    ABSTRACT: In this paper, distributed beamforming and power control are considered for amplify-and-forward wireless relay networks with single antenna nodes. The optimal relay weights are designed by maximizing the mutual information in the case of perfect channel state information, individual node power constraints and the existence of a direct link between the source and destination nodes. In our approach, the source node transmits up to two precoded independent information streams as opposed to several previously proposed techniques in which a single symbol is always transmitted. Our solution to the relay power control given the power allocation at the source node is obtained analytically with linear complexity. Simulations show that the proposed method outperforms the previously proposed techniques in terms of mutual information, outage probability and bit error rate.
    IEEE Transactions on Wireless Communications 01/2011; 10(12):4356-4365. · 2.42 Impact Factor
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    Javier M. Paredes, Alex B. Gershman
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    ABSTRACT: A cooperative beamforming and power control scheme for amplify-and-forward wireless relay networks with single-antenna nodes is developed. Assuming perfect channel state information (CSI) and the existence of the direct link between the source and destination nodes, we design the optimal beamforming and power control weights that maximize the mutual information. In contrast to previous approaches to this problem, we consider the transmission of two independent information signals that can have different powers. The solution is obtained by considering the relay power control problem independently of the power allocation to the information signals. This results in an analytical solution that is then exploited in an iterative algorithm to obtain the final optimal beamforming weights. Our numerical results show that the proposed technique achieves a higher mutual information than previously proposed distributed beamforming and power control techniques.
    IEEE Transactions on Wireless Communications 01/2011; 10:4356-4365. · 2.42 Impact Factor
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    J.M. Paredes, B.H. Khalaj, A.B. Gershman
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    ABSTRACT: To achieve the available performance gains in half-duplex wireless relay networks, several cooperative schemes have been earlier proposed using either distributed space-time coding or distributed beamforming for the transmitter without and with channel state information (CSI), respectively. However, these schemes typically have rather high implementation and/or decoding complexities, especially when the number of relays is high. In this paper, we propose a simple low-rate feedback-based approach to achieve maximum diversity with a low decoding and implementation complexity. To further improve the performance of the proposed scheme, the knowledge of the second-order channel statistics is exploited to design long-term power loading through maximizing the receiver signal-to-noise ratio (SNR) with appropriate constraints. This maximization problem is approximated by a convex feasibility problem whose solution is shown to be close to the optimal one in terms of the error probability. Subsequently, to provide robustness against feedback errors and further decrease the feedback rate, an extended version of the distributed Alamouti code is proposed. It is also shown that our scheme can be generalized to the differential transmission case, where it can be applied to wireless relay networks with no CSI available at the receiver.
    IEEE Transactions on Signal Processing 08/2010; · 2.81 Impact Factor
  • Javier M. Paredes, Alex B. Gershman
    Proceedings of the Global Communications Conference, 2010. GLOBECOM 2010, 6-10 December 2010, Miami, Florida, USA; 01/2010
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    ABSTRACT: The use of cooperative schemes in wireless networks has recently attracted much attention in scenarios where application of multiple-antenna systems is impractical. In such scenarios, the requirement of having full channel state information (CSI) at the receiver side can be relaxed by using differential distributed (DD) transmission schemes. However, in the DD schemes proposed so far, the decoding complexity as well as the delay requirements increase with the number of relays. In this paper, we propose a low-rate feedback-based DD approach (with one-bit feedback per relay) that enjoys full diversity, linear maximum likelihood (ML) decoding complexity, and unrestrictive delay requirements. In addition, the proposed feedback scheme does not require any CSI knowledge at the receiver, and its implementation is simple. Computer simulations demonstrate substantial performance improvements of the proposed techniques as compared to several popular cooperative transmission schemes.
    Proceedings of the IEEE International Conference on Acoustics, Speech, and Signal Processing, ICASSP 2009, 19-24 April 2009, Taipei, Taiwan; 01/2009
  • CoRR. 01/2009; abs/0904.1369.
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    J.M. Paredes, B.H. Khalaj, A.B. Gershman
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    ABSTRACT: Recently, distributed space-time coding over half duplex wireless relay networks has been proposed to achieve higher diversity at the receiver. The use of orthogonal and quasi-orthogonal designs in such relay networks has the advantage of providing maximum diversity at a low decoding complexity. However, similar to their originating space-time codes, these designs are restricted in terms of rate and number of relays. In order to alleviate such restrictions, we propose an extension of group-coherent codes (GCCs) to wireless relay networks. As will be shown, with a very limited amount of feedback from receiver to the relays, it is possible to achieve a distributed code that is applicable for any number of relays without an additional rate loss. In addition, our approach offers the advantages of linear ML decoding complexity, maximum diversity, lower delay, and increased power gain. We further show that it is possible to improve the performance at the price of a higher feedback rate. Finally, the robustness of our scheme against node failures is verified.
    Signal Processing Advances in Wireless Communications, 2008. SPAWC 2008. IEEE 9th Workshop on; 08/2008
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    ABSTRACT: A new 2times2 full-rate full-diversity linear dispersion space-time block code (STBC) is designed by augmenting the generator of the lattice of the Alamouti's orthogonal STBC and optimizing it according to the criterion of the maximal worst codeword difference determinant. The proposed STBC is proved to satisfy the nonvanishing determinant property and, therefore, to achieve the optimal diversity-multiplexing gain (DMG) tradeoff, while offering a reduced computational complexity of maximum- likelihood (ML) decoding as compared to other existing full-rate STBCs. The performance of our new code is shown to be comparable to that of the best full-rate STBCs known so far.
    IEEE Transactions on Signal Processing 07/2008; · 2.81 Impact Factor
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    J.M. Paredes, A.B. Gershman
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    ABSTRACT: Orthogonal space-time block codes (OSTBCs) represent an attractive choice of space-time coding scheme because of their simple maximum-likelihood (ML) decoding and full diversity property. However, the code orthogonality property limits their achievable transmission rate. In this paper, new high-rate block codes are proposed that are referred to as orthogonal structure based STBCs. To obtain these codes, the proposed design adds extra-symbols to the OSTBC matrix using different reasonable strategies. Because of the internal OSTBC structure of the proposed designs, the ML decoder can be implemented in a fast way. Simulations validate an improved performance-to-complexity tradeoff of the proposed codes as compared to several other popular choices of space-time codes.
    Acoustics, Speech and Signal Processing, 2008. ICASSP 2008. IEEE International Conference on; 05/2008
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    ABSTRACT: A new 2timesx2 full-rate full-diversity space-time block code (STBC) is proposed that satisfies the non-vanishing determinant property and offers a reduced computational complexity as compared to the other existing full-rate codes. The performance of our new STBC is shown to be comparable to that of the best full-rate STBCs known so far. This performance is achieved at the decoding complexity which is substantially lower than that of the standard sphere decoder.
    Acoustics, Speech and Signal Processing, 2007. ICASSP 2007. IEEE International Conference on; 05/2007