14,504 research outputs found
Reversible watermarking scheme with image-independent embedding capacity
Permanent distortion is one of the main drawbacks of all the irreversible watermarking schemes. Attempts to recover the original signal after the signal passing the authentication process are being made starting just a few years ago. Some common problems, such as salt-and-pepper artefacts owing to intensity wraparound and low embedding capacity, can now be resolved. However, some significant problems remain unsolved. First, the embedding capacity is signal-dependent, i.e., capacity varies significantly depending on the nature of the host signal. The direct impact of this is compromised security for signals with low capacity. Some signals may be even non-embeddable. Secondly, while seriously tackled in irreversible watermarking schemes, the well-known problem of block-wise dependence, which opens a security gap for the vector quantisation attack and transplantation attack, are not addressed by researchers of the reversible schemes. This work proposes a reversible watermarking scheme with near-constant signal-independent embedding capacity and immunity to the vector quantisation attack and transplantation attack
Context-Tree-Based Lossy Compression and Its Application to CSI Representation
We propose novel compression algorithms for time-varying channel state
information (CSI) in wireless communications. The proposed scheme combines
(lossy) vector quantisation and (lossless) compression. First, the new vector
quantisation technique is based on a class of parametrised companders applied
on each component of the normalised CSI vector. Our algorithm chooses a
suitable compander in an intuitively simple way whenever empirical data are
available. Then, the sequences of quantisation indices are compressed using a
context-tree-based approach. Essentially, we update the estimate of the
conditional distribution of the source at each instant and encode the current
symbol with the estimated distribution. The algorithms have low complexity, are
linear-time in both the spatial dimension and time duration, and can be
implemented in an online fashion. We run simulations to demonstrate the
effectiveness of the proposed algorithms in such scenarios.Comment: 12 pages, 9 figures. Accepted for publication in the IEEE
Transactions on Communication
Circle actions and geometric quantisation
The aim of this article is to present unifying proofs for results in
geometric quantisation with real polarisations by exploring the existence of
symplectic circle actions. It provides an extension of Rawnsley's results on
the Kostant complex, and gives an alternative proof for Sniatycki's and
Hamilton's theorems; as well as, a partial result for the focus-focus
contribution to geometric quantisation.Comment: 28 pages; issues concerning flat hermitian line bundles were
addressed, results unchange
That strange procedure called quantisation
This is a pedagogical and (almost) self-contained introduction into the
theorem of Groenewold and van Howe, which states that a naive transcription of
Dirac's quantisation rules cannot work. Some related issues in quantisation
theory are also discussed. First-class constrained systems are briefly
described in a slightly more `global' fashion.Comment: 28 pages, no figures, contribution to the conference ``Aspects of
Quantum Gravity -- From Theory to Experimental Search'', Bad Honnef (Ger)
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