735 research outputs found
Low Complexity Decoding for Higher Order Punctured Trellis-Coded Modulation Over Intersymbol Interference Channels
Trellis-coded modulation (TCM) is a power and bandwidth efficient digital
transmission scheme which offers very low structural delay of the data stream.
Classical TCM uses a signal constellation of twice the cardinality compared to
an uncoded transmission with one bit of redundancy per PAM symbol, i.e.,
application of codes with rates when denotes the
cardinality of the signal constellation.
Recently published work allows rate adjustment for TCM by means of puncturing
the convolutional code (CC) on which a TCM scheme is based on.
In this paper it is shown how punctured TCM-signals transmitted over
intersymbol interference (ISI) channels can favorably be decoded. Significant
complexity reductions at only minor performance loss can be achieved by means
of reduced state sequence estimation.Comment: 4 pages, 5 figures, 3 algorithms, accepted and published at 6th
International Symposium on Communications, Control, and Signal Processing
(ISCCSP 2014
Low Complexity Decoding for Punctured Trellis-Coded Modulation Over Intersymbol Interference Channels
Classical trellis-coded modulation (TCM) as introduced by Ungerboeck in
1976/1983 uses a signal constellation of twice the cardinality compared to an
uncoded transmission with one bit of redundancy per PAM symbol, i.e.,
application of codes with rates when denotes the
cardinality of the signal constellation. The original approach therefore only
comprises integer transmission rates, i.e., , additionally, when transmitting over an intersymbol interference
(ISI) channel an optimum decoding scheme would perform equalization and
decoding of the channel code jointly. In this paper, we allow rate adjustment
for TCM by means of puncturing the convolutional code (CC) on which a TCM
scheme is based on. In this case a nontrivial mapping of the output symbols of
the CC to signal points results in a time-variant trellis. We propose an
efficient technique to integrate an ISI-channel into this trellis and show that
the computational complexity can be significantly reduced by means of a reduced
state sequence estimation (RSSE) algorithm for time-variant trellises.Comment: 4 pages, 7 pictured, accepted for 2014 International Zurich Seminar
on Communication
Punctured Trellis-Coded Modulation
In classic trellis-coded modulation (TCM) signal constellations of twice the
cardinality are applied when compared to an uncoded transmission enabling
transmission of one bit of redundancy per PAM-symbol, i.e., rates of
when denotes the cardinality of the signal
constellation. In order to support different rates, multi-dimensional (i.e.,
-dimensional) constellations had been proposed by means of
combining subsequent one- or two-dimensional modulation steps, resulting in
TCM-schemes with bit redundancy per real dimension. In
contrast, in this paper we propose to perform rate adjustment for TCM by means
of puncturing the convolutional code (CC) on which a TCM-scheme is based on. It
is shown, that due to the nontrivial mapping of the output symbols of the CC to
signal points in the case of puncturing, a modification of the corresponding
Viterbi-decoder algorithm and an optimization of the CC and the puncturing
scheme are necessary.Comment: 5 pages, 10 figures, submitted to IEEE International Symposium on
Information Theory 2013 (ISIT
Reduced Complexity Super-Trellis Decoding for Convolutionally Encoded Transmission Over ISI-Channels
In this paper we propose a matched encoding (ME) scheme for convolutionally
encoded transmission over intersymbol interference (usually called ISI)
channels. A novel trellis description enables to perform equalization and
decoding jointly, i.e., enables efficient super-trellis decoding. By means of
this matched non-linear trellis description we can significantly reduce the
number of states needed for the receiver-side Viterbi algorithm to perform
maximum-likelihood sequence estimation. Further complexity reduction is
achieved using the concept of reduced-state sequence estimation.Comment: 6 pages, 8 figures, accepted for ICNC'13. (see also: arXiv:1205.7031
Gate control of low-temperature spin dynamics in two-dimensional hole systems
We have investigated spin and carrier dynamics of resident holes in
high-mobility two-dimensional hole systems in GaAs/AlGaAs
single quantum wells at temperatures down to 400 mK. Time-resolved Faraday and
Kerr rotation, as well as time-resolved photoluminescence spectroscopy are
utilized in our study. We observe long-lived hole spin dynamics that are
strongly temperature dependent, indicating that in-plane localization is
crucial for hole spin coherence. By applying a gate voltage, we are able to
tune the observed hole g factor by more than 50 percent. Calculations of the
hole g tensor as a function of the applied bias show excellent agreement with
our experimental findings.Comment: 8 pages, 7 figure
Electrical spin injection and detection in lateral all-semiconductor devices
Electrical injection and detection of spin-polarized electrons is
demonstrated for the first time in a single wafer, all-semiconductor,
GaAs-based lateral spintronic device, employing p+-(Ga,Mn)As/n+-GaAs
ferromagnetic Esaki diodes as spin aligning contacts. The conversion of
spin-polarized holes into spin-polarized electrons via Esaki tunnelling leaves
its mark in a bias dependence of the spin-injection efficiency, which at
maximum reaches the relatively high value of 50%.Comment: 11 pages, 3 figures, sent to PR
Electron g-Factor Anisotropy in Symmetric (110)-oriented GaAs Quantum Wells
We demonstrate by spin quantum beat spectroscopy that in undoped symmetric
(110)-oriented GaAs/AlGaAs single quantum wells even a symmetric spatial
envelope wavefunction gives rise to an asymmetric in-plane electron
Land\'e-g-factor. The anisotropy is neither a direct consequence of the
asymmetric in-plane Dresselhaus splitting nor of the asymmetric Zeeman
splitting of the hole bands but is a pure higher order effect that exists as
well for diamond type lattices. The measurements for various well widths are
very well described within 14 x 14 band k.p theory and illustrate that the
electron spin is an excellent meter variable to map out the internal -otherwise
hidden- symmetries in two dimensional systems. Fourth order perturbation theory
yields an analytical expression for the strength of the g-factor anisotropy,
providing a qualitative understanding of the observed effects
Tunneling anisotropic magnetoresistance in Fe/GaAs/Au junctions: orbital effects
We report experiments on epitaxially grown Fe/GaAs/Au tunnel junctions
demonstrating that the tunneling anisotropic magnetoresistance (TAMR) effect
can be controlled by a magnetic field. Theoretical modelling shows that the
interplay of the orbital effects of a magnetic field and the Dresselhaus
spin-orbit coupling in the GaAs barrier leads to an independent contribution to
the TAMR effect with uniaxial symmetry, whereas the Bychkov-Rashba spin-orbit
coupling does not play a role. The effect is intrinsic to barriers with bulk
inversion asymmetry.Comment: 5 pages, 3 figure
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