Channel-estimation-based adaptive DFE for fading multipath radio channels

Shukla, P.K.; Turner, L.F.

doi:10.1049/ip-i-2.1991.0070

Cited by 49 publications

(42 citation statements)

References 2 publications

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“…An often cited work comparing DA and CEB equalizers on a Rayleigh fading channel is by Shukla et al [91]. The authors showed that when the channel order is known and the signal to noise ratio (SNR) is large, the DA approach had higher mean squared error than the CEB approach.…”

Section: Stojanovic Et Al Pioneered the Analysis And Application Of mentioning

confidence: 99%

“…This implies that the observation noise correlation matrix, σ −2 d R ν is a scaled identity matrix [91], such that R v = ρI, where ρ is defined as the inverse SNR,…”

Section: Channel Estimate Based Dfementioning

confidence: 99%

“…This effective noise correlation matrix is usually approximated as a scaled identity matrix with a scaling equal to the inverse signal to noise ratio (SNR). [79,91]. For the underwater channel, this turns out to be a poor estimate.…”

Section: Introductionmentioning

confidence: 99%

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Analysis of and techniques for adaptive equalization for underwater acoustic communication

Blair¹

2011

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Underwater wireless communication is quickly becoming a necessity for applications in ocean science, defense, and homeland security. Acoustics remains the only practical means of accomplishing long-range communication in the ocean. The acoustic communication channel is fraught with difficulties including limited available bandwidth, long delay-spread, time-variability, and Doppler spreading. These difficulties reduce the reliability of the communication system and make high data-rate communication challenging. Adaptive decision feedback equalization is a common method to compensate for distortions introduced by the underwater acoustic channel. Limited work has been done thus far to introduce the physics of the underwater channel into improving and better understanding the operation of a decision feedback equalizer. This thesis examines how to use physical models to improve the reliability and reduce the computational complexity of the decision feedback equalizer. The specific topics covered by this work are: how to handle channel estimation errors for the time varying channel, how to use angular constraints imposed by the environment into an array receiver, what happens when there is a mismatch between the true channel order and the estimated channel order, and why there is a performance difference between the direct adaptation and channel estimation based methods for computing the equalizer coefficients. For each of these topics, algorithms are provided that help create a more robust equalizer with lower computational complexity for the underwater channel.

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Section: Stojanovic Et Al Pioneered the Analysis And Application Of mentioning

confidence: 99%

“…This implies that the observation noise correlation matrix, σ −2 d R ν is a scaled identity matrix [91], such that R v = ρI, where ρ is defined as the inverse SNR,…”

Section: Channel Estimate Based Dfementioning

confidence: 99%

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Analysis of and techniques for adaptive equalization for underwater acoustic communication

Blair¹

2011

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“…Imperfect channel estimation directly causes performance degradation of a channel estimate based equalizer [Pre05] [Sto95]. For time-varying channels, it has been shown in [Shu91] that channel estimate based equalizer (see Figure 1-2 ) has superior performance over the directly adapted linear equalizer (LE) or decision feedback equalizer (DFE).…”

Section: The Problemmentioning

confidence: 99%

Estimation and tracking of rapidly time-varying broadband acoustic communication channels

Li¹

2006

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This thesis develops methods for estimating wideband shallow-water acoustic communication channels. The very shallow water wideband channel has three distinct features: large dimension caused by extensive delay spread; limited number of degrees of freedom (DOF) due to resolvable paths and inter-path correlations; and rapid fluctuations induced by scattering from the moving sea surface. Traditional LS estimation techniques often fail to reconcile the rapid fluctuations with the large dimensionality. Subspace based approaches with DOF reduction are confronted with unstable subspace structure subject to significant changes over a short period of time.Based on state-space channel modeling, the first part of this thesis develops algorithms that jointly estimate the channel as well as its dynamics. Algorithms based on the Extended Kalman Filter (EKF) and the Expectation Maximization (EM) approach respectively are developed. Analysis shows conceptual parallels, including an identical second-order innovation form shared by the EKF modification and the suboptimal EM, and the shared issue of parameter identifiability due to channel structure, reflected as parameter unobservability in EKF and insufficient excitation in EM. Modifications of both algorithms, including a two-model based EKF and a subspace EM algorithm which selectively track dominant taps and reduce prediction error, are proposed to overcome the identifiability issue. The second part of the thesis develops algorithms that explicitly find the sparse estimate of the delay-Doppler spread function.The study contributes to a better understanding of the channel physical constraints on algorithm design and potential performance improvement. It may also be generalized to other applications where dimensionality and variability collide.

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“…Adaptive equalizers using a decision feedback type structure (22) have been shown to be successful when used in receivers for UWA communications particularly when estimates of the channel impulse response are used to adapt the taps of the equalizer (31,34). Despite the significant progress made in past decade or so in designing adaptive algorithms for UW A communication systems, there are stil many underwater acoustic channels over which such algorithms are unable to establish reliable communications.…”

Section: Receiver Design: Current Techniques and Obstaclesmentioning

confidence: 99%

A channel subspace post-filtering approach to adaptive equalization

Nadakuditi¹

2002

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Channel-estimation-based adaptive DFE for fading multipath radio channels

Cited by 49 publications

References 2 publications

Analysis of and techniques for adaptive equalization for underwater acoustic communication

Analysis of and techniques for adaptive equalization for underwater acoustic communication

Estimation and tracking of rapidly time-varying broadband acoustic communication channels

A channel subspace post-filtering approach to adaptive equalization

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