71 research outputs found
Decoding options for trellis codes in the two-way relay channel
No full textWe study the application of trellis codes to physical-layer network coding in the two-way relay channel. In particular, we consider quaternary decoding on a combined trellis as an alternative to binary decoding and evaluate its gain in several scenarios, including asymmetric channels and the combination of different codes. We focus on the multiple-access phase, in which both terminals transmit their messages simultaneously, while in the second phase the relay retransmits the network-coded combination of both messages. We also evaluate the performance of both options when decoding the individual message of each terminal. © 2013 IEEE
Joint Decoding of Multiple Non-Binary LDPC Codewords
No full textWe develop a belief-propagation (BP) decoder for the joint decoding of multiple codewords which belong to the same non-binary LDPC code. Decoding is based on soft information in form of joint channel-posterior probabilities of all codeword symbols. We extend the BP algorithm for q-ary LDPC codes such that the FFT-based check node processing is preserved and the complexity remains manageable. This joint decoding is useful in settings in which multiple codewords are transmitted in a non-orthogonal way over the same channel, including multiple-access with packet collisions, physical-layer network coding and multi-resolution broadcasting. We show in an example that joint decoding can be far superior to separate decoding.Grant numbers : This work was supported by the Catalan and Spanish Governments under SGR (2009SGR1046) and CICYT (TEC2011-29006-C03-01), respectively.© 2014 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works
Network Coding and Decoding Options for Trellis-coded Relay Communications
No full textI study the application of trellis codes to physical layer network coding in relay communications, with two, three or four users. In particular, I consider non-binary decoding on a combined trellis as an alternative to binary decoding and evaluate its gain in several scenarios, including asymmetric channels and the combination of different codes. I focus on the multiple-access phase, in which the terminals transmit their messages simultaneously, while in the second phase the relay will retransmit the network-coded combination of every messages. I also evaluate the performance of both options for the decoding of the individual message of each terminal
Adaptive coded modulation with retransmission for partial channel state information
No full textA promising way of improving the spectral efficiency of radio interfaces beyond
3G is by performing fast link adaptation. Since the channel is fluctuating due to
fading and shadowing effects, the transmission parameters of a wireless communication
system have to be adjusted according to the current channel state in order
to make best use of the available resources. In real-world systems, anyway, only
partial channel information is available at the transmitter. This has a strong impact
on achievable performances since, without exact knowledge of the fading state, it
is no longer possible to accurately adapt coding and modulation. The main objective
of this thesis is to design a link adaptation scheme which is robust despite
of this uncertainty about the channel. To this end, in a preliminary phase it is at
first quantified the performance loss with respect to the ideal case of complete information
and consequently it is studied how it can be minimized with the use of
channel prediction. Since a severe degradation can still be observed in some fading
conditions, an additional mechanism for fast link-level retransmissions based
on soft-combining of information is suggested. The retransmission protocol is used
not just to recover from incorrectly received codewords, but the link adaptation
strategy is defined anew so as to enhance throughput with the new degree of freedom
represented by delay. With this perspective, we get closed-form expressions
of the interesting parameters for the case of block fading and Chase combining, whilst a remarkable improvement of the outage probability approximation of the
word error rate for the case of incremental redundancy and/or selective channels is
also presented. With this analytical framework an optimization of the adaptive system
for any criterion and constraints is thus feasible at low computational cost without
necessarily resorting to time-consuming link-level simulations. In the examples
provided, encouraging results are obtained since it is observed that the achieved
throughput comes relatively close to the throughput of an ergodic fading channel at
the expense of few retransmissions, even when no channel state information apart
from the long-term average SNR is available at the transmitter
ITERATIVE DEMODULATION OF ZERO-PADDED OFDM WITH MMSE EQUALIZATION USING A PRIORI INFORMATION
No full textPublication in the conference proceedings of EUSIPCO, Viena, Austria, 200
Frame Synchronization for a Single Packet
No full textWe derive the optimum method for locating a single packet in a received frame of symbols, using not only the samples that correspond to a known preamble but those of the entire transmitted packet. This approach leads to significant improvements compared to detection methods based on the preamble alone. For BSPK and on-off keying and their combinations with Manchester coding, we present simplified maximum likelihood metrics which are near-optimum while their computational complexity is only slightly higher than a simple correlation. Finally, we show how this metric can be derived for other modulations with memory
Verfahren und Vorrichtung zur Rahmensynchronisation (DE102024111661B4)
No full textDie Erfindung betrifft ein Verfahren zur Rahmensynchronisation für ein digitales Empfangssignal, welches an einem Ausgang eines Übertragungskanals als Folge eines einem Eingang des Übertragungskanal zugeführten binären digitalen Sendesignals empfangen wird, wobei das binäre digitale Sendesignal eine zu übertragende Information in einem Datenpaket beinhaltet, welches in einem Datenabschnitt eine vorgegebene Anzahl D von Datensymbolen und in einem optionalen Synchronisationsabschnitt eine vorgegebene Anzahl S von Synchronisationssymbolen aufweist, und wobei das binäre digitale Sendesignal eine vorgegebene Symbolrate aufweist, wobei das digitale Empfangssignal durch eine Folge von digitalen Abtastwerten dargestellt wird und wobei eine Abtastfrequenz verwendet wird, die größer oder gleich der Symbolrate ist. Nach der Erfindung wird ein Sliding-Window definiert, welches eine der zeitlichen Länge eines Datenpakets oder des Datenabschnitts eines Datenpakets entsprechende zeitliche Länge aufweist. In jeder Position µ des Sliding-Window wird jedem Symbolabschnitt des Datenabschnitts und optional jedem Symbolabschnitt des Synchronisationsabschnitts des Sliding-Window ein Abtastwert zugeordnet. Für jede Position µ des Sliding-Window wird unter Verwendung einer vorgegebenen Metrik ein Positionswert &Lgr;met[µ] ermittelt, wobei hierfür zumindest die den Symbolabschnitten des Datenabschnitts zugeordneten Abtastwerte verwendet werden. Die Metrik basiert auf der Verwendung eines Modells für den Übertragungskanal, welches einen gedächtnisfreien Übertragungskanal annimmt und bei welchem das digitale Empfangssignal für die möglichen binären Werte des Sendesignals jeweils mit einer bedingten Wahrscheinlichkeitsdichtefunktion beschrieben wird. Aus dem Anfangszeitpunkt des Sliding-Window in einer Position, für welche die Positionswerte &Lgr;metein Maximum annehmen oder für welche der Positionswert &Lgr;meteinen vorgegebenen Schwellwert übersteigt, wird ein Startzeitpunkt eines Datenpakets in dem digitalen Empfangssignal ermittelt. Weiterhin betrifft die Erfindung eine Vorrichtung und ein Computerprogramm zur Realisierung des Verfahrens
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