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E - Limits of Applicability of the Theory — Caveat Reader

from APPENDICES

Published online by Cambridge University Press:  06 July 2010

Bernard Widrow
Affiliation:
Stanford University, California
István Kollár
Affiliation:
Budapest University of Technology and Economics
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Summary

The theory described in this book is very general: it describes well most quantization and roundoff situations. However, assumptions have been made which are necessary for proper application. In this appendix, some of these will be briefly described.

LONG–TIME VS. SHORT–TIME PROPERTIES OF QUANTIZATION

Statistical theory of quantization deals with statistics of signals: PDFs, CFs and moments. The basic idea is coined at the beginning of Chapter 4: “Instead of devoting attention to the signal being quantized, let its probability density function be considered.”

Having extensively explored the theory, a few basic questions need to be discussed, like:

  • when may the PDF be used?

  • what are the consequences of the use of the PDF in the application of the theory?

  • what has to be done if the PDF may not used, e.g. when the signal is deterministic?

For the introduction of the probability density function, Fig. 3.1(a) shows an ensemble of random time functions. These random time functions are realizations of a stochastic process. In practice, usually just one realization is measured, thus averaging is performed as averaging in time — which means that time averages are assumed to be equal to ensemble averages. In this case, the process is called ergodic (see page 43).

Quantization theory deals with statistical properties of ergodic processes. Fulfillment of QT I ensures that the PDF of x can be determined from the PDF of x′.

Type
Chapter
Information
Quantization Noise
Roundoff Error in Digital Computation, Signal Processing, Control, and Communications
, pp. 621 - 632
Publisher: Cambridge University Press
Print publication year: 2008

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