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Weihua Zhuang - One of the best experts on this subject based on the ideXlab platform.

  • Channel precoding with small envelope variations for spl pi 4 qpsk and msk over frequency selective Slow Fading Channels
    IEEE Transactions on Vehicular Technology, 2003
    Co-Authors: Weihua Zhuang
    Abstract:

    This paper presents Channel precoding schemes to combat intersymbol interference (ISI) over a frequency-selective Slow Fading Channel in wireless communication systems using /spl pi//4 shifted quadrature phase-shift keying or minimum shift keying. Based on the dimension partitioning technique, the precoders predistort the phase of the transmitted symbol in the forward link to combat ISI, keeping the transmitted symbol amplitude constant. The proposed schemes can ensure the stability of the precoder even in equalizing a nonminimum-phase Channel, combat ISI without increasing the complexity of portable unit receivers, and reduce the envelope variations of transmitted signals such that power-efficient nonlinear amplifiers can be used for the precoded signals without causing a significant undue distortion. Theoretical analysis and simulation results are presented to demonstrate the effectiveness of the proposed Channel precoding schemes.

  • Channel precoding for spl pi 4 dqpsk and msk over frequency selective Slow Fading Channels
    Vehicular Technology Conference, 2000
    Co-Authors: Weihua Zhuang
    Abstract:

    This paper presents Channel precoding schemes to combat intersymbol interference (ISI) over a frequency-selective Slow Fading Channel in wireless communication systems using /spl pi//4 differential quadrature phase shift keying (/spl pi//4-DQPSK) or minimum shift keying (MSK). Based on the dimension partitioning technique, the precoders predistort the phase of the transmitted signals in the forward link to combat ISI, keeping the transmitted signal amplitude constant. The precoding schemes can (i) ensure the stability of the precoders even in equalizing a non-minimum-phase Channel, (ii) achieve ISI-free transmission without increasing the complexity of the portable unit receiver and (iii) reduce the envelope variations of transmitted signals such that a power efficient nonlinear amplifier can be used without causing undue distortion. Theoretical and simulation results are presented to demonstrate that the proposed Channel precoders can outperform DFE when the ISI is severe and the precoding scheme for /spl pi//4-DQPSK can achieve a smaller envelope variation than the standard /spl pi//4-DQPSK.

Jong-wha Chong - One of the best experts on this subject based on the ideXlab platform.

  • Improved design criterion for space-frequency trellis codes in MIMO-OFDM systems
    IEEE 60th Vehicular Technology Conference 2004. VTC2004-Fall. 2004, 2004
    Co-Authors: Jong-wha Chong
    Abstract:

    In this paper, the design problem and the robustness of space-frequency trellis codes for MIMO-OFDM systems are studied. We find that the Channel constructed by the consecutive subcarriers of an OFDM block is a correlated Fading Channel with regular correlation function of the number and time delay of the multipaths. We decompose the correlated Fading Channel into two independent components: Slow Fading Channel and fast Fading Channel. Therefore the design problem of space-frequency trellis codes is converted into the problem that we jointly design the space-time trellis code both in Slow Fading Channel and in fast Fading Channel. We also show that the space-frequency trellis codes designed according to our criterion are robust against the time delay of multipaths. Simulation results are provided to confirm our theoretic analysis.

  • Improved design criterion for space-time trellis codes over time-correlated Rayleigh Fading Channels
    IEEE 60th Vehicular Technology Conference 2004. VTC2004-Fall. 2004, 2004
    Co-Authors: Jong-wha Chong
    Abstract:

    In this paper, an improved design criterion for space-time trellis codes over time-correlated Rayleigh Fading Channels is presented. We decompose the time-correlated Fading Channel into two independent components: Slow Fading Channel and fast Fading Channel. The code design problem for time-correlated Fading Channels is converted to the joint design both in Slow Fading Channels and in fast Fading Channels, while no knowledge about correlation is needed. Simulation results are provided to confirm our theory.

M.p. Fitz - One of the best experts on this subject based on the ideXlab platform.

Cong Shen - One of the best experts on this subject based on the ideXlab platform.

Pramod Viswanath - One of the best experts on this subject based on the ideXlab platform.

  • VTC Fall - Fairness Improvement of Maximum C/I Scheduler by Dumb Antennas in Slow Fading Channel
    2010 IEEE 72nd Vehicular Technology Conference - Fall, 2010
    Co-Authors: Xiaoyan Bi, Jiayin Zhang, Yi Wang, Pramod Viswanath
    Abstract:

    Multiuser diversity is achieved by maximum C/I scheduler in both fast and Slow Fading scenarios. However, fairness among multiple users is not guaranteed in Slow Fading Channel because time and frequency resource are always occupied by the user with largest signal to interference and noise ratio(SINR). Opportunistic beamforming using dumb antennas is a multiple antennas transmit technique to increase the fluctuation rate and dynamic range of effective Channel coefficients in Slow Fading environment. In this paper, we propose a method to improve the fairness of maximum C/I scheduler with the technique of dumb antennas. The theoretical analysis of users' scheduling probability shows that the fairness of maximum C/I scheduler can be greatly improved by dumb antennas in Slow Fading Channels without significant loss in cell spectrum efficiency. The engineering issues of its application in the downlink transmission of 3GPP LTE system are discussed. The numerical results of simulation with practical LTE configurations and assumptions also verify our proposal.

  • Fairness Improvement of Maximum C/I Scheduler by Dumb Antennas in Slow Fading Channel
    2010 IEEE 72nd Vehicular Technology Conference - Fall, 2010
    Co-Authors: Xiaoyan Bi, Jiayin Zhang, Yi Wang, Pramod Viswanath
    Abstract:

    Multiuser diversity is achieved by maximum C/I scheduler in both fast and Slow Fading scenarios. However, fairness among multiple users is not guaranteed in Slow Fading Channel because time and frequency resource are always occupied by the user with largest signal to interference and noise ratio(SINR). Opportunistic beamforming using dumb antennas is a multiple antennas transmit technique to increase the fluctuation rate and dynamic range of effective Channel coefficients in Slow Fading environment. In this paper, we propose a method to improve the fairness of maximum C/I scheduler with the technique of dumb antennas. The theoretical analysis of users' scheduling probability shows that the fairness of maximum C/I scheduler can be greatly improved by dumb antennas in Slow Fading Channels without significant loss in cell spectrum efficiency. The engineering issues of its application in the downlink transmission of 3GPP LTE system are discussed. The numerical results of simulation with practical LTE configurations and assumptions also verify our proposal.

  • Approximately Universal Codes over Slow Fading Channels
    arXiv: Information Theory, 2005
    Co-Authors: Saurabha Rangrao Tavildar, Pramod Viswanath
    Abstract:

    Performance of reliable communication over a coherent Slow Fading Channel at high SNR is succinctly captured as a fundamental tradeoff between diversity and multiplexing gains. We study the problem of designing codes that optimally tradeoff the diversity and multiplexing gains. Our main contribution is a precise characterization of codes that are universally tradeoff-optimal, i.e., they optimally tradeoff the diversity and multiplexing gains for every statistical characterization of the Fading Channel. We denote this characterization as one of approximate universality where the approximation is in the connection between error probability and outage capacity with diversity and multiplexing gains, respectively. The characterization of approximate universality is then used to construct new coding schemes as well as to show optimality of several schemes proposed in the space-time coding literature.