Results 1  10
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116
Extrinsic Information Transfer Functions: A Model and Two Properties,”
 in Proc. Conference on Information Sciences and Systems (CISS),
, 2002
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Generalized Approximate Message Passing for Estimation with Random Linear Mixing
, 2012
"... We consider the estimation of an i.i.d. random vector observed through a linear transform followed by a componentwise, probabilistic (possibly nonlinear) measurement channel. A novel algorithm, called generalized approximate message passing (GAMP), is presented that provides computationally effici ..."
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Cited by 123 (18 self)
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We consider the estimation of an i.i.d. random vector observed through a linear transform followed by a componentwise, probabilistic (possibly nonlinear) measurement channel. A novel algorithm, called generalized approximate message passing (GAMP), is presented that provides computationally efficient approximate implementations of maxsum and sumproblem loopy belief propagation for such problems. The algorithm extends earlier approximate message passing methods to incorporate arbitrary distributions on both the input and output of the transform and can be applied to a wide range of problems in nonlinear compressed sensing and learning. Extending an analysis by Bayati and Montanari, we argue that the asymptotic componentwise behavior of the GAMP method under large, i.i.d. Gaussian transforms is described by a simple set of state evolution (SE) equations. From the SE equations, one can exactly predict the asymptotic value of virtually any componentwise performance metric including meansquared error or detection accuracy. Moreover, the analysis is valid for arbitrary input and output distributions, even when the corresponding optimization problems are nonconvex. The results match predictions by Guo and Wang for relaxed belief propagation on large sparse matrices and, in certain instances, also agree with the optimal performance predicted by the replica method. The GAMP methodology thus provides a computationally efficient methodology, applicable to a large class of nonGaussian estimation problems with precise asymptotic performance guarantees.
Asynchronous physicallayer network coding,” technical report. Available: http://arxiv.org/abs/1105.3144
"... Abstract—A key issue in physicallayer network coding (PNC) is how to deal with the asynchrony between signals transmitted by multiple transmitters. That is, symbols transmitted by different transmitters could arrive at the receiver with symbol misalignment as well as relative carrierphase offset. ..."
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Cited by 100 (11 self)
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Abstract—A key issue in physicallayer network coding (PNC) is how to deal with the asynchrony between signals transmitted by multiple transmitters. That is, symbols transmitted by different transmitters could arrive at the receiver with symbol misalignment as well as relative carrierphase offset. A second important issue is how to integrate channel coding with PNC to achieve reliable communication. This paper investigates these two issues and makes the following contributions: 1) We propose and investigate a general framework for decoding at the receiver based on belief propagation (BP). The framework can effectively deal with symbol and phase asynchronies while incorporating channel coding at the same time. 2) For unchannelcoded PNC, we show that for BPSK and QPSK modulations, our BP method can significantly reduce the asynchrony penalties compared with prior methods. 3) For QPSK unchannelcoded PNC, with a half symbol offset between the transmitters, our BP method can drastically reduce the performance penalty due to phase asynchrony, from more than 6 dB to no more than 1 dB. 4) For channelcoded PNC, with our BP method, both symbol and phase asynchronies actually improve the system performance compared with the perfectly synchronous case. Furthermore, the performance spread due to different combinations of symbol and phase offsets between the transmitters in channelcoded PNC is only around 1 dB. The implication of 3) is that if we could control the symbol arrival times at the receiver, it would be advantageous to deliberately introduce a half symbol offset in unchannelcoded PNC. The implication of 4) is that when channel coding is used, symbol and phase asynchronies are not major performance concerns in PNC. Index Terms—Physicallayer network coding, network coding, synchronization. I.
Asymptotic analysis of MAP estimation via the replica method and applications to compressed sensing
, 2009
"... The replica method is a nonrigorous but widelyaccepted technique from statistical physics used in the asymptotic analysis of large, random, nonlinear problems. This paper applies the replica method to nonGaussian maximum a posteriori (MAP) estimation. It is shown that with random linear measureme ..."
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Cited by 77 (9 self)
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The replica method is a nonrigorous but widelyaccepted technique from statistical physics used in the asymptotic analysis of large, random, nonlinear problems. This paper applies the replica method to nonGaussian maximum a posteriori (MAP) estimation. It is shown that with random linear measurements and Gaussian noise, the asymptotic behavior of the MAP estimate of anndimensional vector “decouples ” asnscalar MAP estimators. The result is a counterpart to Guo and Verdú’s replica analysis of minimum meansquared error estimation. The replica MAP analysis can be readily applied to many estimators used in compressed sensing, including basis pursuit, lasso, linear estimation with thresholding, and zero normregularized estimation. In the case of lasso estimation the scalar estimator reduces to a softthresholding operator, and for zero normregularized estimation it reduces to a hardthreshold. Among other benefits, the replica method provides a computationallytractable method for exactly computing various performance metrics including meansquared error and sparsity pattern recovery probability.
SoftInput SoftOutput Lattice Sphere Decoder for Linear Channels
 Proc. of the IEEE GLOBECOM’03
, 2003
"... Soft output detection for signals transmitted on linear channels is investigated. A particular emphasis is made for signal detection on multiple antenna channels. The a posteriori information at the detector output is evaluated from a shifted spherical list of point candidates. The spherical list is ..."
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Cited by 51 (11 self)
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Soft output detection for signals transmitted on linear channels is investigated. A particular emphasis is made for signal detection on multiple antenna channels. The a posteriori information at the detector output is evaluated from a shifted spherical list of point candidates. The spherical list is centered on the maximum likelihood point, which has the great advantage of stabilizing the list size. Thus, the sphere radius is selected in order to control the list size and to cope with the boundaries of the finite multiple antenna constellation. Our new soft output sphere decoder is then applied to the computation of constrained channel capacity and to the iterative detection of a coded transmission. For example, we achieved a signaltonoise ratio at 1.25dB from capacity limit on a 44 MIMO channel with 16QAM modulation and a 4state rate 1/2 parallel turbo code.
Design methods for irregular repeat accumulate codes
, 2002
"... We optimize the randomlike ensemble of Irregular Repeat Accumulate (IRA) codes for binaryinput symmetric channels in the large blocklength limit. Our optimization technique is based on approximating the Evolution of the Densities (DE) of the messages exchanged by the BeliefPropagation (BP) messa ..."
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Cited by 41 (5 self)
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We optimize the randomlike ensemble of Irregular Repeat Accumulate (IRA) codes for binaryinput symmetric channels in the large blocklength limit. Our optimization technique is based on approximating the Evolution of the Densities (DE) of the messages exchanged by the BeliefPropagation (BP) messagepassing decoder by a onedimensional dynamical system. In this way, the code ensemble optimization can be solved by linear programming. We propose four such DE approximation methods, and compare the performance of the obtained code ensembles over the binary symmetric channel (BSC) and the binaryantipodal input additive white Gaussian channel (BIAWGNC). Our results clearly identify the best among the proposed methods and show that the IRA codes obtained by these methods are competitive with respect to the bestknown irregular LowDensity ParityCheck codes (LDPC). In view of this and the very simple encoding structure of IRA codes, they emerge as attractive design choices.
Analysis of lowdensity paritycheck codes for the GilbertElliott channel
 IEEE TRANS. INF. THEORY
, 2005
"... Density evolution analysis of lowdensity paritycheck (LDPC) codes in memoryless channels is extended to the Gilbert–Elliott (GE) channel, which is a special case of a large class of channels with hidden Markov memory. In a procedure referred to as estimation decoding, the sum–product algorithm (S ..."
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Cited by 34 (8 self)
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Density evolution analysis of lowdensity paritycheck (LDPC) codes in memoryless channels is extended to the Gilbert–Elliott (GE) channel, which is a special case of a large class of channels with hidden Markov memory. In a procedure referred to as estimation decoding, the sum–product algorithm (SPA) is used to perform LDPC decoding jointly with channelstate detection. Density evolution results show (and simulation results confirm) that such decoders provide a significantly enlarged region of successful decoding within the GE parameter space, compared with decoders that do not exploit the channel memory. By considering a variety of ways in which a GE channel may be degraded, it is shown how knowledge of the decoding behavior at a single point of the GE parameter space may be extended to a larger region within the space, thereby mitigating the large complexity needed in using density evolution to explore the parameter space pointbypoint. Using the GE channel as a straightforward example, we conclude that analysis of estimation decoding for LDPC codes is feasible in channels with memory, and that such analysis shows large potential gains.
Random Sparse Linear Systems Observed Via Arbitrary Channels: A Decoupling Principle
"... Abstract—This paper studies the problem of estimating the vector input to a sparse linear transformation based on the observation of the output vector through a bank of arbitrary independent channels. The linear transformation is drawn randomly from an ensemble with mild regularity conditions. The c ..."
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Cited by 33 (0 self)
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Abstract—This paper studies the problem of estimating the vector input to a sparse linear transformation based on the observation of the output vector through a bank of arbitrary independent channels. The linear transformation is drawn randomly from an ensemble with mild regularity conditions. The central result is a decoupling principle in the largesystem limit. That is, the optimal estimation of each individual symbol in the input vector is asymptotically equivalent to estimating the same symbol through a scalar additive Gaussian channel, where the aggregate effect of the interfering symbols is tantamount to a degradation in the signaltonoise ratio. The degradation is determined from a recursive formula related to the score function of the conditional probability distribution of the noisy channel. A sufficient condition is provided for belief propagation (BP) to asymptotically produce the a posteriori probability distribution of each input symbol given the output. This paper extends the authors ’ previous decoupling result for Gaussian channels to arbitrary channels, which was based on an earlier work of Montanari and Tse. Moreover, a rigorous justification is provided for the generalization of some results obtained via statical physics methods. I.
Multiple access demodulation in the lifted signal graph with spatial coupling
 IEEE Transactions on Information Theory
, 2013
"... Abstract—Demodulation in a random multiple access channel is considered where the signals are chosen uniformly randomly with unit energy, a model applicable to several modern transmission systems. It is shown that by lifting (replicating) the graph of this system and randomizing the graph connectio ..."
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Cited by 22 (8 self)
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Abstract—Demodulation in a random multiple access channel is considered where the signals are chosen uniformly randomly with unit energy, a model applicable to several modern transmission systems. It is shown that by lifting (replicating) the graph of this system and randomizing the graph connections, a simple iterative cancellation demodulator can be constructed which achieves the same performance as an optimal symbolbysymbol detector of the original system. The iterative detector has a complexity that is linear in the number of users, while the direct optimal approach is known to be NPhard. However, the maximal system load of this lifted graph is limited to α < 2.07, even for signaltonoise ratios going to infinity – the system is interference limited. We then show that by introducing spatial coupling between subsequent lifted graphs, and anchoring the initial graphs, this limitation can be avoided and arbitrary system loads are achievable. Our results apply to several welldocumented system proposals, such as IDMA, partitioned spreading, and certain forms of MIMO communications. Index Terms—random signaling, iterative decoding, optimal joint detection I.