Abstract-The effect of the companding process on QAM signals
has been under investigation for the past several years. The
compander, included in the PCM telephone network to improve
voice performance, has an unusual affect on digital QAM data
signals which are transmitted over the same channel. The quantization
noise, generated by the companding process which is multiplicative
(and asymmetric), degrades the detectability performance
of the outermost points of the QAM constellation more
than that of the inner points.
The combined effect of the companding noise and the inherent
white gaussian noise of the system, leads us to a re-examination of
signal constellation design.
In this paper we investigate the detectability performance of a
number of candidates for signal constellations including, a typical
rectangular QAM constellation, the same constellation with the
addition of a smear-desmear operation, and two new improved
QAM constellation designs with two-dimensional warpi
標簽：
investigation
Abstract-The
companding
the
上傳時間：
2013-12-20
上傳用戶：英雄
Abstract—In the future communication applications, users
may obtain their messages that have different importance levels
distributively from several available sources, such as distributed
storage or even devices belonging to other users. This
scenario is the best modeled by the multilevel diversity coding
systems (MDCS). To achieve perfect (information-theoretic)
secrecy against wiretap channels, this paper investigates the
fundamental limits on the secure rate region of the asymmetric
MDCS (AMDCS), which include the symmetric case as a special
case. Threshold perfect secrecy is added to the AMDCS model.
The eavesdropper may have access to any one but not more than
one subset of the channels but know nothing about the sources,
as long as the size of the subset is not above the security level.
The question of whether superposition (source separation) coding
is optimal for such an AMDCS with threshold perfect secrecy
is answered. A class of secure AMDCS (S-AMDCS) with an
arbitrary number of encoders is solved, and it is shown that linear
codes are optimal for this class of instances. However, in contrast
with the secure symmetric MDCS, superposition is shown to
be not optimal for S-AMDCS in general. In addition, necessary
conditions on the existence of a secrecy key are determined as a
design guideline.
標簽：
Fundamental
Limits
Secure
Class
on
of
上傳時間：
2020-01-04
上傳用戶：kddlas
