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An unilateral nuclear magnetic resonance (UMR) sensor was designed to measure wood moisture nondestructively. The sensor consisted of a unilateral magnet, an anti-eddy current module, a radiofrequency (RF) coil and an impedance matching and tuning circuit. The sensor produced a static magnetic field of 71.1 mT (resonant frequency:3.027 MHz) in a 50 mm×50 mm plane locating 75 mm above the sensor's surface. Preliminary nondestructive measurement of wood moisture was carried out with the sensor. The moisture distribution in the radical direction of a cylindrical wood sample was scanned. Variations in transverse relaxation time (T2) from the bark to core were obtained. Evaporation of moisture during wood drying was also measured with the UMR sensor. Experimental results showed that:the peak of long T2 component in the T2 spectrum moved to left and the peak integral area decreased gradually during drying. The integral area was proportional to the moisture content of the sample. The work presents a portable UMR device for wood research which may potentially be used for nondestructive moisture measurement on living trees in situ.

Consider a file synchronization problem at two remote nodes A and B connected by a noiseless link. The node A has a binary file $X$ , and node B has a binary file $Y$ which is an edited version of $X$ with random insertions and deletions (indels). The goal is to reconstruct $X$ at node B from $Y$ with minimal exchange of information between A and B. In this letter, we design a single-round, thus low latency, file synchronization scheme with low redundancy. In particular, a series of redundancy bits, including markers, check symbols of Reed-Solomon (RS) codes for hashes and Varshamov-Tenengolts (VT) syndromes, are constructed from $X$ at node A and send to node B. According to the received redundancy and $Y$ , we develop a recovery algorithm at node B to reconstruct $X$. The amount of exchanged information of the proposed scheme is significantly reduced when compared with the existing single-round synchronization scheme under random indels. [ABSTRACT FROM AUTHOR]

The structures of convolutional self-orthogonal codes and convolutional self-doubly-orthogonal codes for both belief propagation and threshold iterative decoding algorithms are analyzed on the basis of difference sets and computation tree. It is shown that the double orthogonality property of convolutional self-doubly-orthogonal codes improves the code structure by maximizing the number of independent observations over two successive decoding iterations while minimizing the number of cycles of lengths 6 and 8 on the code graphs. Thus, the double orthogonality may improve the iterative decoding in both convergence speed and error performance. In addition, the double orthogonality makes the computation tree rigorously balanced. This allows the determination of the best weighing technique, so that the error performance of the iterative threshold decoding algorithm approaches that of the iterative belief propagation decoding algorithm, but at a substantial reduction of the implementation complexity. Index Terms--Belief propagation, convolutional self-doubly-orthogonal codes, convolutional self-orthogonal codes, iterative decoding, threshold decoding.

The prefixed Varshamov-Tenengolts (VT) codes, which are subsets of VT codes with predetermined prefixes, can be used for error correction over segmented edit channels. In this paper, we investigate the construction and analysis of this class of codes. First, we derive upper bounds on the size of zero-error codes for segmented edit channels with segment-by-segment decoding. Second, we establish a one-to-one correspondence between prefixed VT codes and Levenshtein codes. Based on this relation, we can obtain explicit formulas on the size of prefixed VT codes via the existing results on the size of Levenshtein codes. Third, we construct a new zero-error prefixed VT code and show that the size of the constructed code is strictly larger than that of the existing prefixed VT code for the segmented deletion channel. Finally, an efficient systematic encoding method of prefixed VT codes is proposed for the segmented edit channels. [ABSTRACT FROM AUTHOR]

Guess & check (GC) codes can correct multiple deletions with high probability by guessing all possible deletion patterns at a polynomial complexity. This paper investigates an efficient way of guessing deletion patterns with the aid of markers. The marker are inserted as block identifiers into GC codewords and examined for implementing maximum-likelihood inference of deletion patterns in trellis graph. The resulting number of guesses for decoding marker GC codes can be reduced significantly by an increasing order of magnitude as the code length grows. [ABSTRACT FROM AUTHOR]

Probabilistic amplitude shaping (PAS) has proved to be a promising way to achieve the shaping gain for an additive white Gaussian noise channel with a distribution matcher (DM). However, the DM schemes may suffer a rate loss and increase both complexity and latency, when they are not suited for the input bit stream with redundancy. In this paper, a novel PAS strategy is proposed for a joint source and channel coded modulation system, where the residual source redundancy after source coding can be exploited to obtain both shaping and coding gains. It is shown that the residual source redundancy can be controlled by choosing the row weight distribution for source code, thus making the probability distribution of the modulated symbols be optimized under an appropriate interleaver design. To guarantee the error-floor performance, the source code is constrained by predicting the probability distribution of source bits within target finite-length frames. By jointly designing source and channel codes, the residual source redundancy can also be exploited to achieve the coding gain. Compared with the state-of-the-art code pairs, the proposed code pairs have better error-floor performance, and achieve higher coding and shaping gains without suffering from the rate-loss and the latency caused by DM. [ABSTRACT FROM AUTHOR]

The alternating direction method of multipliers (ADMM) has been adapted for decoding low-density parity-check (LDPC) codes over intersymbol interference (ISI) channels in order to reduce the complexity of the traditional Turbo equalization (TE) method. However, the error rate performance of ADMM decoding may be degraded in certain ISI channels when compared with the TE at high signal-to-noise ratio regions. In order to address the problem, we derive a novel ADMM-based decoding method, called l2-box ADMM decoding, for LDPC codes over ISI channels. By introducing suitable penalty functions to l2-box ADMM decoding, we present an enhanced method, called l2-box ADMM penalized decoding, to further improve the performance. Simulation results on several ISI channels indicate that the proposed l2-box ADMM penalized decoding can achieve better error rate performances compared with the TE and the existing ADMM penalized decoding methods, especially for ISI channels with long memory, while maintaining the low-complexity advantage of the ADMM penalized decoding. [ABSTRACT FROM AUTHOR]

Permutation codes are widely studied due to their promising applications in flash memories. Based on the theory of permutation groups and subgroups, two classes of permutation codes are constructed to correct a single burst deletion of length up to a designated parameter. The proposed codes can achieve larger rates than available codes while maintaining simple interleaving structures. The decoding methods for the proposed codes are provided in proofs and verified by examples. [ABSTRACT FROM AUTHOR]

Multi-permutation codes for rank modulation scheme have been recently proposed for efficiently storing data in flash memories. In this letter, we investigate the problem of a single burst unstable deletion (BUD) of length $t$ in a $t$ -balanced multi-permutation and this problem can be decomposed into the sub-problems of a single permutation-invariant deletion (PID) in $t$ permutations by a rank demodulation method. Based on the rank demodulation method and the interleaving of $t$ single-PID-correcting permutation codes, we construct two classes of $t$ -balanced multi-permutation codes that are capable of correcting a single BUD of length $t$. Moreover, the constructed codes can achieve higher rates compared with the existing code. The decoding methods are provided in the proofs and verified by some examples. [ABSTRACT FROM AUTHOR]

This letter investigates the application of alternating direction method of multipliers (ADMM) in decoding low-density parity-check (LDPC) codes over partial response (PR) channels. Unlike the ADMM decoding in memoryless channels, the ADMM decoding in PR channels becomes involved with the correlation among adjacent code symbols. As the update equations for code symbols constitute the most complicated part of the ADMM decoding in PR channels, this letter focuses on their derivation by making use of the iterative fashion of ADMM and incorporating the use of a penalty function. A notable advantage of the proposed ADMM penalized decoding algorithm is that its complexity increases linearly with the memory length of PR channels. Simulation results show that the proposed algorithm can achieve error performance comparable with that of Turbo equalization (TE) in the waterfall region. It can also outperform TE at high signal-to-noise ratios as iteration grows. [ABSTRACT FROM AUTHOR]

The rank-modulation scheme has been recently proposed to write and store data in flash memories efficiently. In this paper, a new construction of systematic error-correcting codes for permutations is presented under the Chebyshev distance. By constructing a subgroup code and using its coset codes to partition the set of information permutations, the proposed code construction can achieve much larger code cardinality and hence higher code rates. To facilitate the encoding and decoding of the constructed codes, we also investigate the concepts of ranking and unranking for permutations, and generalize them to $M$ -ranking and $M$ -unranking for multi-permutations. Examples are provided to demonstrate the relevant concepts and the encoding/decoding algorithms. [ABSTRACT FROM AUTHOR]

Error-correcting codes on permutations and multi-permutations have recently attracted much attention for their applications in flash memories through rank modulation. We propose a new rank demodulation method to transform the problem of a single burst unstable erasure (BUE) in a $t$ -balanced multi-permutation into the sub-problems of a single permutation-invariant erasure (PIE) in $t$ permutations. Based on the rank demodulation method, we propose two classes of $t$ -balanced multi-permutation codes to correct a single BUE of length up to $t$ by interleaving $t$ single-PIE-correcting permutation codes. The decoding methods for the proposed codes are included in the proofs and demonstrated by examples. [ABSTRACT FROM AUTHOR]

To improve the secrecy performance of the untrusted relay system with a multiple-antenna destination, a novel full-duplex destination jamming scheme with optimal antenna selection (FDJ-OAS) is proposed in this paper. The approximate closed-form expressions of the average achievable secrecy rate are derived for the proposed scheme. To attain more insightful results, the approximated closed-form expressions for the average achievable secrecy rate and the optimal power allocation factor for FDJ-OAS are derived in the case with a large-scale antenna array, and simple power allocation solutions are also provided in the high and low SNR regimes, respectively. Furthermore, we derive the asymptotic expressions for the secrecy outage probability under different asymptotic conditions for the proposed scheme, and the analysis results indicate that the secrecy diversity order of FDJ-OAS is significantly superior to that of the comparable schemes. Simulation results show that the analytical curves match well with the simulation results, and the advantage of FDJ-OAS is also clearly demonstrated through performance comparison. [ABSTRACT FROM AUTHOR]

This paper proposes an efficient method for joint power and subcarrier allocation in a multicell multiuser OFDMA downlink network. The joint optimization problem is formulated with the objective of maximizing the energy efficiency subject to the constraints on the quality of service in sum transmission rates for each cell and the total transmit power for the network. Due to intercell cochannel interferences and multiple variable coupling, the problem is intractable in its original form. To relax the difficulties in coordinating cochannel interferences, we introduce the tolerable interferences constraints for interference channels. To cope with the multiple variable coupling, we decompose the joint optimization problem into two iterative processes of user scheduling and a parametric convex optimization problem, where the energy efficiency is treated as the parameter and approached by bisection search. Then, by double dual decomposition, the parametric convex problem is transformed into Lagrangian dual problems at two levels of cells and subcarriers, and a decentralized solution is obtained in closed form. Based on the reformulations, an iterative subgradient algorithm is presented for approaching the joint optimization problem with acceptable complexity. Computer simulations are conducted to validate the proposed algorithm and examine the effects of various system parameters. [ABSTRACT FROM AUTHOR]

Codes over permutations and multi-permutations have been recently proposed for efficiently storing data in flash memories. Based on the interleaving techniques for permutations, we construct two classes of permutation codes which can correct a single burst symbol-invariant deletion (SID) of length up to $t$. Moreover, a class of balanced multi-permutation codes capable of correcting a single burst SID of length up to $t$ is presented. The simple decoding procedures for the constructed codes are included in proofs and verified by examples. [ABSTRACT FROM AUTHOR]

This paper investigates secure cooperative transmissions in a dual-hop MIMO relay system using a combined transmit antenna selection (TAS) and maximal-ratio combining (MRC) scheme over the Nakagami- $m$ fading channels, where an adaptive decode-and-forward relaying protocol and an multi-antenna eavesdropper are considered. Due to the feedback delay, channel state information (CSI) for TAS might be outdated at both the source and the relay. To evaluate the secrecy performance of the TAS/MRC scheme and the impacts of outdated CSI, the closed-form expressions for the metrics of exact ergodic secrecy rate and exact secrecy outage probability are derived under both perfect and outdated CSI conditions in a channel feedback error model. In order to explicitly reveal the behaviors of the secrecy performance in high signal-to-noise ratio regime, asymptotic expressions for both the metrics are further derived. As validated by simulation results, analytically numerical results demonstrate that outdated the CSI always results in a loss in the secrecy performance, but the loss can be recovered by increasing the number of antennas at legitimate receivers. Furthermore, the outdated CSI yields a reduced secrecy diversity order, whereas only the perfect CSI leads to the full secrecy diversity order. [ABSTRACT FROM PUBLISHER]

This paper addresses robust designs of secure simultaneous wireless information and power transfer for multiple-input single-output (MISO) multiuser systems. By using a bounded uncertainty model for the channel state information (CSI) from transmitters to legitimate receivers and under the assumption of only available statistic knowledge of the CSI to eavesdroppers, we consider the robust designs with both worst-case and chance-constrained optimizations. To jointly optimize transmit beamforming vectors and power splitting factors, we formulate three problems aiming at minimizing the system power, maximizing the sum secrecy rate, and maximizing the minimal secrecy rate, respectively, subject to both energy harvesting and secrecy outage constraints. These problems are intractable in their original forms due to the CSI models and their non-convexity. To reach computationally efficient solutions, we first rewrite the original problems by semi-definite relaxation, then transform the CSI uncertainty related constraints by S-procedure, and finally approximate the non-convex constraints by the first-order Taylor expansion. By the reformulations, we present iterative successive convex approximation algorithm for approaching the optimized solutions. Simulation results under various setups of system parameters are provided to examine the system performance and validate the effectiveness of the proposed schemes. [ABSTRACT FROM PUBLISHER]

This paper investigates full-duplex (FD) secure transmissions with simultaneous wireless information and power transfer (SWIPT) on downlink (DL), where an FD base station, with multiple transmit antennas and multiple receive antennas, serves a group of single-antenna users on both DL and uplink (UL). An optimization problem with non-convex form is formulated for minimizing the system power under constraints on energy harvesting (EH) and security rates. In order to efficiently solve it, the original non-convex problem is first approximated to a convex one and then casted into a form of second-order cone programming (SOCP). Iterative solving algorithms are presented with the computational complexity analysis. Simulation results show that the proposed FD secure scheme is more power-efficient than conventional one, and the SOCP formulation is more computationally efficient than its semi-definite programming alternative. Compared with half-duplex schemes, the FD scheme is also advantageous in power performance especially under high DL and low UL security rate requirements. [ABSTRACT FROM AUTHOR]

Linear programming decoding with the alternating direction method of multipliers (ADMM) is a promising decoding technique for low-density parity-check (LDPC) codes, where the computational complexity of Euclidean projections onto check polytopes becomes a prominent problem. In this paper, the problem is circumvented by building lookup tables (LUTs) and quantizing the inputs to approach approximate Euclidean projections at low computational complexities. To challenge the huge memory cost of LUTs, we first propose two commutative compositions of Euclidean projection and self-map, and show the existence of a small quantization range which does not alter the Euclidean projection. Then, we investigate the design and simplification of the LUTs by exploiting the commutative compositions and check node decomposition techniques. An efficient algorithm for the LUT-based projection is demonstrated by using one simplification method. Simulation results show that for both the regular and irregular LDPC codes, the ADMM decoding using LUT-based projection can substantially reduce the decoding time while maintaining the error rate performance at a comparatively large memory cost. [ABSTRACT FROM PUBLISHER]

This paper investigates the physical layer security problem of cognitive decode-and-forward relay networks over Nakagami- $m$ fading channels. We consider the relaying communication between one secondary user (SU) source and one SU destination by using an opportunistic relay selection from multiple SU relays and sharing the licensed spectrum of multiple primary users (PUs) in the underlay network. While the transmission between the SUs imposes interference on each PU, the relayed transmission is intercepted by one SU eavesdropper. In the absence of the eavesdropper’s channel state information, the relay selection is based on the largest channel gain of relay-to-destination link, which is assumed to be outdated due to feedback delay. We derive the exact probability of non-zero secrecy capacity and the exact secrecy outage probability (SOP) in the closed form. Furthermore, we derive the asymptotic SOP in two different cases, and explicitly show the effects of system parameters on the secrecy diversity order and the secrecy diversity gain, respectively. Both asymptotic analysis and simulation results show that the secrecy performance can be improved by increasing either the number of relays or the Nakagami parameter of the legitimate relay channels, whereas the secrecy diversity gain deteriorates as the number of the PUs increases. [ABSTRACT FROM PUBLISHER]

A blind signal-to-interference-plus-noise ratio (SINR) estimation method is proposed for orthogonal frequency division multiplexing (OFDM) systems in the presence of impulsive noise over multi-path fading channels. By exploiting the cyclostationarity of the OFDM signal, the received signal power is decomposed into the transmitted signal power and the impulsive interference plus the Gaussian noise power, which are estimated respectively using the cyclic correlations of the received signal. Simulation results are provided to examine the performance of the proposed estimation method and show that the estimated results approach the true values of SINR. [ABSTRACT FROM PUBLISHER]

An efficient impulsive noise estimation algorithm based on alternating direction method of multipliers (ADMM) is proposed for OFDM systems using quadrature amplitude modulation (QAM). Firstly, we adopt the compressed sensing (CS) method based on the l1-norm optimization to estimate impulsive noise. Instead of the conventional methods that exploit only the received signal in null tones as constraint, we add the received signal of data tones and QAM constellations as constraints. Then a relaxation approach is introduced to convert the discrete constellations to the convex box constraints. After that a linear programming is used to solve the optimization problem. Finally, a framework of ADMM is developed to solve the problem in order to reduce the computation complexity. Simulation results for 4-QAM and 16-QAM demonstrate the practical advantages of the proposed algorithm over the other algorithms in bit error rate performance gains. [ABSTRACT FROM AUTHOR]