1,720,982 research outputs found
Non-Binary Message-Passing Algorithms for Magnetic Channels with Data-Dependent Noise
Full text linkThe paper proposes an implementation of the message
passing algorithm adapted to iterative channel detection.
The algorithm uses soft messages associated to non binary
symbols in order to cancel cycles in the equivalent Tanner graphs,
achieving optimal performance after a low number of iterations.
This architecture, suited to very fast channel detectors, is applied
to magnetic recording channels and adapted to the non stationary
nature of the magnetic media noise
On the Reduction of Additive Complexity of Cyclotomic FFTs
No full textWe investigate a property that we have found in
many efficient bilinear cyclic convolutions in GF(2^m). We
show that this property can reduce the additive complexity of
cyclotomic FFTs. We explain how it arises, and why the most
common constructions of cyclic convolutions yield this beneficial
feature
Safe Early Stopping for Layered LDPC Decoding
Full text linkIn this letter, we address the problem of early stopping
of iterative decoding of LDPC codes, driven by criteria
ensuring that no errors occur from premature termination. A safe
termination strategy developed for Turbo codes is generalized to
layered LDPC decoding. Then, a more efficient version and also
two less efficient, but less complex, criteria are proposed
Method and apparatus for channel estimation in communication systems, and related computer program product
No full textA method of channel estimation in orthogonal frequency-division multiplexing communication employing three or more subcarriers, wherein frequency correlation exists between the subcarriers. The method includes: calculating a coarse channel estimate for each of the subcarriers, and calculating from the coarse channel estimates refined channel estimates for each of the subcarriers, wherein calculation of the refined channel estimates includes calculating the parameters of a Wiener Filter having a length of 2 L+1, where L is a positive integer, and filtering the coarse channel estimates with the Wiener Filter
Low-Complexity Z_4 LDPC Code Design under a Gaussian Approximation
No full textIn this paper we propose low complexity LDPC code design and decoding in Z_4 which may be useful to combat phase ambiguities in wireless links affected by strong phase noise. We approximate messages exchanged on the Tanner graph using separable probability density functions. This allows a substantial reduction of decoder memory and complexity, with a negligible performance penalty, compared to ideal Z_4 decoding. Furthermore, we show that the Density Evolution analysis of this suboptimal decoder leads to irregular LDPC designs matching the criteria of binary LDPC codes
On the constrained capacity of block differential modulation and detection
No full textIn this paper, we consider Block Differential Modulation
(BDM), to tackle the phase slip problem in digital
communication systems. When the received signal phase can
drift, the synchronizer can suddenly choose a wrong reference
phase, e.g. adding multiples of 2π/M in case of M-ary Phase
Shift Keying. Phase slips are detrimental for any coherent system
since they cause long error bursts, till an opposite phase slip
occurs.
BDM is a generalization of Differential Modulation (DM).
Neither of them relies on the absolute carrier phase. However,
BDM differentially encodes information between small blocks
of symbols and exploits couples of adjacent blocks to decode.
This allows simple and practical demapping, without sacrificing
capacity.
We show that for low and moderate phase slip probabilities,
BDM approaches the constrained capacity of coherent transmission,
in particular at high spectral efficiencies.We provide closedform
results for the constrained capacity in absence of phase slips
for Phase Shift Keying and Quadrature Amplitude Modulation,
and we evaluate numerically the constrained capacity through an
efficient Monte Carlo method, when phase slips occur. Besides,
we provide simple upper and lower bounds
Method for channel estimation, related channel estimator, receiver, and computer program product
No full textAn embodiment of a method for channel estimation for an Orthogonal Frequency Division Multiplexing communication system, including estimating a Time Domain Least Squares channel impulse response having a given maximum number of L taps based on a channel covariance matrix Q, and for each tap l=1, . . . , L a respective channel impulse response in the time-domain hl, wherein the channel impulse responses in the time-domain are grouped as a channel impulse response vector in the time domain h. Specifically, an updated channel-impulse-response vector in the time domain {tilde over (h)} is determined by computing for each tap l the solution of the following system: Q1:l, 1:l{tilde over (h)}l1=h1:l, wherein the updated channel-impulse-response vector in the time domain {tilde over (h)} is computed recursively via a Levinson Durbin algorithm
Method and device for soft-output detection in multiple antenna communication systems
No full textAn embodiment of a method and device for detecting and generating bit soft-output of a multiple-input-multiple-output system is provided. The device includes at least one channel estimates preprocessing unit, one received vector processing and one detection and soft-output generation unit
Low Complexity, Quasi-Optimal MIMO Detectors for Iterative Receivers
No full textWe propose a novel family of Soft-Input Soft-
Output detectors for iterative, point-to-point, MIMO receivers.
Compared to the optimal Maximum A Posteriori receiver, low
complexity is achieved restricting the detector search to small
subsets of the entire QAM hyper-symbol constellation, through
simple criteria. These criteria are applied to an improved version
of the non-iterative Layered ORthogonal lattice Detector. We
show that, notwithstanding the suboptimal low-complexity implementation,
this detector approaches the EXtrinsic Information
Transfer of the MAP detector. Therefore, when included in an
iterative receiver it delivers the same performance. Furthermore,
the deterministic complexity and highly parallelizable structure
of the proposed detector are well suited for HDL and ASIC
implementation. To focus on a specific setting, we consider
the indoor MIMO wireless LAN 802.11n standard, taking into
account errors in Channel Estimation and a frequency selective,
spatially correlated channel model
On the Structure of Cyclotomic Fourier Transforms and Their Applications to Reed-Solomon Codes
No full textThis paper is focused on cyclotomic Fourier transforms in GF(2m), and on their applications to algebraic decoding of Reed-Solomon codes, like the evaluation of syndromes and of error locator (or evaluator) polynomials. Cyclotomic transforms are much more efficient than straightforward evaluation. In particular, the number of multiplications is quite small. In this paper it is shown that also the number of additions can be considerably reduced with respect to previous analyses. A simple interpretation of the cyclotomic Fourier transform best suited for the evaluation of syndromes allows to assemble the required matrix easily and quickly, even in large fields. Fast construction of such matrices is important to obtain the best results, since as many matrices as possible must be generated and compared. It is shown that both the structure of the matrix and of bilinear convolutions need to be exploited, to reduce the complexity of the costly part of cyclotomic Fourier transforms, which is a matrix-vector product. Heuristic algorithms for matrix-vector product are to be run as many times as possible to obtain the best transform. It is shown with several examples that very good results can be obtained even with very simple algorithms
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