Estimation and tracking of rapidly time-varying broadband acoustic communication channels
Citable URI
https://hdl.handle.net/1912/1509DOI
10.1575/1912/1509Keyword
Underwater acousticsAbstract
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.
Description
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2006
Suggested Citation
Thesis: Li, Weichang, "Estimation and tracking of rapidly time-varying broadband acoustic communication channels", 2006-02, DOI:10.1575/1912/1509, https://hdl.handle.net/1912/1509Related items
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