Table of Content

28 May 2013, Volume 31 Issue 3

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Communication Engineering

Adaptive Device-to-Device Cooperative Retransmission for Improving Multicast Efficiency in Cellular Systems

ZHOU Bin1, HU Hong-lin2,3

2013, 31(3):  221-227.  doi:10.3969/j.issn.0255-8297.2013.03.001

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We focus on device-to-device (D2D) enhanced multicast transmission in cellular systems, formulate the relationship between the number of retransmitters and the efficiency of D2D retransmission, and derive a closed-form expression to search the optimal number of D2D retransmitters and the optimal sub-cluster partition. Based on the analysis, we propose an adaptive D2D cooperative retransmission scheme with limited channel feedback, which adaptively selects the number of retransmitters and the optimal routing. Exploiting the multicast gain and multi-channel diversity jointly, the proposed scheme achieves a significant gain in terms of spectrum efficiency compared to its counterparts with a fixed number of retransmitters.

Performance of Zero-Forcing Beam Forming System with Channel Prediction

LU Min, ZENG Gui-gen, FENG Guang-zeng

2013, 31(3):  228-232.  doi:10.3969/j.issn.0255-8297.2013.03.002

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 In this paper, capacity degradation of zero-forcing beam forming (ZFBF) system due to outdated CSI is investigated. A linear minimum mean square error (MMSE) channel predictor is employed to cope with the feedback delay and improve the capacity performance. Based on the power density function of the system’s signal to interference plus noise ratio (SINR), the analytic sum capacity expression relevant to the prediction error is derived. Numerical simulations show effectiveness of the predictor that exploits the channel’s temporal correlation against feedback delay. The simulation results are consistent with the analytic research.

Physical Layer Secrecy of Wideband System by Adding Random Noise Based on Channel’s Weak Characteristics

PANG Hong-wei, JIN Liang, HUANG Kai-zhi, JI Jiang

2013, 31(3):  233-238.  doi:10.3969/j.issn.0255-8297.2013.03.003

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To combat wiretapping of wireless wideband system, this paper presents a method for wireless wideband system physical layer secrecy in the time domain. The method adds random noise based on weak channel characteristic. First, the transmitter decomposes the nonsingular channel characteristic matrix into
some sub-channels. The sub-channels with strong characteristic are selected to transmit useful information, and weak ones are transformed into a random channel. The signal received by legitimate receivers becomes steady, while the eavesdropper’s turns random. Simulation results show that the method can lower the requirements to the legitimate channel state while decrease SINR at eavesdroppers to keep its error probability high so as to enhance system security.

Three-Core LPFG Coupled Mode and Effective Refractive Index Calculation Method

WANG Xue1, LIU Ke-qiang2

2013, 31(3):  239-244.  doi:10.3969/j.issn.0255-8297.2013.03.004

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Based on the coupled-mode theory, we study the coupling of three-core long period fiber gratings with two different structures and derive the mode coupling equations. The calculation method of cladding mode’s effective refractive index is also investigated. The rule of cladding mode’s effective refractive index
change with the wavelength is discussed by numerical simulation. The results show that, the indices of both odd and even modes reduce as the wavelength increases. Different arrangements of three cores affect the extent of the index decrease. The results of this study provide theoretical guidance to the application of three-core fiber LPFG.

Signal and Information Processing

Sparse Channel Estimation Based on Compressed Sensing for MIMO-OFDM Systems

YE Xin-rong1,2, ZHU Wei-ping1, MENG Qing-min1

2013, 31(3):  245-251.  doi:10.3969/j.issn.0255-8297.2013.03.005

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 To improve accuracy of sparse channel estimation and reduce the pilot number in MIMO-OFDM systems, we use the sparse prior information of the channel impulse response in the time domain, and model the estimation of frequency selective fading channel for MIMO-OFDM systems as the reconstruction of complex sparse signal interfered by noise in compressed sensing. Two methods of sparse channel estimation in MIMOOFDM systems are proposed, based on sparsity adaptive matching pursuit (SAMP) and sparse reconstruction by separable approximation (SRSA), respectively. Simulation shows that, under the same signal-to-noise ratio and for the same performance of MSE and BER without prior information of the sparsity, the two proposed methods can reduce pilot signals by 40% as compared to the conventional least square method. In the two methods, the one based on SAMP runs faster and is closer to the Cramer-Rao bound, while parameters of the one based on SRSA are easier to be set in practical applications.

Joint Estimation of DOA and Polarization for LFM Signals Using Conformal Array Antenna

ZHANG Shu-yin, GUO Ying, QI Zi-sen, SU Ling-hua

2013, 31(3):  252-258.  doi:10.3969/j.issn.0255-8297.2013.03.006

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Using the energy concentration ability of fractional Fourier transform (FRFT) to linear frequency modulation (LFM) signal, this paper presents a simplified data model for conformal array, and proposes a method to de-couple DOA and polarization estimation using an algorithm of noise subspace fitting. As it uses
a multi-dimensional and multi-peak search procedure to resolve the DOA estimation problem, the proposed scheme forms a single peak objection function by reforming the noise subspace vector and manifold matrix. 2D DOA estimation is performed with particle swarm optimization. The polarization parameter is then acquired based on the ESPRIT theory. Simulation results show that the proposed method can reduce the computation complexity with a favorable parameter estimation performance.

Subword-Based Position Specific Posterior Lattices for Chinese Spoken Document Indexing

LU Ming-ming, ZHANG Lian-hai, QU Dan

2013, 31(3):  259-265.  doi:10.3969/j.issn.0255-8297.2013.03.007

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A spoken document indexing method based on subword-based position specific posterior lattices (SPSPL) is proposed to overcome inconsistency between optimal recognition unit and retrieval unit in the existing Chinese spoken document indexing methods. In the proposed method, a word-based PSPL is generated with a word-based speech recognizer. Each word in the PSPL is replaced by its constituent subword units. According to the posterior probability relationship between each word and its constituent subword units, the original PSPL can be converted to the corresponding S-PSPL to be used in generating a subword-based index for retrieval. Experimental results show that the new method can make use of a well-trained language model, and avoid incorrect segmentation in the word-based recognizer as well. Better performance is obtained compared to the current indexing methods that use words as both recognition and retrieval units.

Classification of Layered Structures Using Phase Information of Reflected Sound

WANG Lu-xian1, WANG Shuo-zhong1, CHEN Yun-fei2, WANG Run-tian3, ZOU Ting-ting1

2013, 31(3):  266-270.  doi:10.3969/j.issn.0255-8297.2013.03.008

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This paper presents a method for classification of layered materials with unknown physical properties based on the phase-frequency characteristics of acoustic reflection coefficients. Layered structures under consideration include a single layer material, double-layered plates with harder and softer materials on the two sides respectively, and a sandwich structure with a harder material as the outer layers and a softer material in the middle. A set of criteria for differentiating the types of structure is given. Numerical simulation shows effectiveness of the method with a high rate of correct classification.

PTS Phase Search with Symmetrical Dual Binary Tree

HE Xuan-sen, ZENG Qing-fang, WU Liang-min

2013, 31(3):  271-277.  doi:10.3969/j.issn.0255-8297.2013.03.009

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To reduce computation complexity of the partial transmit sequence (PTS) for OFDM systems, a symmetrical dual binary tree search method is proposed, in which the search of the optimum phase factor is mapped to the search of a minimum cost path of a full binary tree. By selecting the number of intermediate
nodes and the search depth, the proposed method effectively reduce both peak-to-average power ratio (PAPR) and the computation complexity of PTS. Simulation results show that the method can make a good tradeoff between the computation complexity and the OFDM performance.

Multi-flow Attack Resistance Based on Reordering of Watermark Bits

WANG Zhen-xing1, ZHANG Lian-cheng1, GUO Yi1, LI Shuo2

2013, 31(3):  278-284.  doi:10.3969/j.issn.0255-8297.2013.03.010

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Network flow watermarking is a technique for active tracing of network attacks. Multi-flow attack makes use of dependences among different watermarked network flows, and thus poses a great challenge to the applicability of flow watermarking. This paper proposes a multi-flow attack resistance method based on reordering of watermark bits that combats the multi-flow attack. The method randomizes the bit order of the watermark message across multiple flows based on different random seeds, therefore effectively removing cross-correlations among watermarked flows. Theoretical analysis and experimental evaluation show that the proposed method is robust against multi-flow attack. Compared with insertion position randomization, the method is more effective in resisting multi-flow attack. It neither increase false positive rate, nor requires high computation cost.

Control and System

Novel Particle Filtering Based on Adaptive Particle Swarm Optimization and Its Application

CHEN Zhi-min, BO Yu-ming, WU Pan-long, SONG Gong-fei, DUAN Wen-yong

2013, 31(3):  285-293.  doi:10.3969/j.issn.0255-8297.2013.03.011

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Particle filter based on particle swarm optimization (PSO-PF) algorithm suffers from low precision and high computation complexity, therefore is difficult to be used in practical applications. This paper proposes   novel dynamic particle filter algorithm based on neighborhood adaptive particle swarm optimization (DPSOPF). The method takes the neighborhood information of particles into consideration. Factors of diversity, neighborhood extension, and neighborhood limiting are jointly used to realize self-adaption of neighborhood particle numbers. Thus the influence of particles on the neighborhood is under control, and the local optimization phenomenon is alleviated. Optimal balance is achieved between convergence speed and search ability. By using the univariate nonstationary growth model (UNGM), target tracking model and failure detection model, a simulation test of the algorithm is performed. The results show that, compared to PSO-PF, the proposed algorithm improves precision and computation speed, showing its applicability to practical engineering.

Direct Adaptive Neural Network Tracking Control with Input Saturation

LI Jun-fang, LI Tie-shan

2013, 31(3):  294-302.  doi:10.3969/j.issn.0255-8297.2013.03.012

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Based on the Lyapunov stability theory and the backstepping technique, a direct adaptive neural networks controller is proposed for a class of uncertain nonlinear single-input-single-out systems in the presence of input saturation. It is shown that all signals in the closed-loop system are uniformly ultimately bounded, and the tracking error converges to a small neighborhood of the origin. Using the dynamic surface control (DSC) technique and neural networks, the problem of explosion of complexity inherent in the conventional backstepping method is avoided. The controller’s singularity problem is removed completely by using a special property of the affine term. A stability analysis subject to the effect of input saturation constrains is conducted with the help of an auxiliary design system. Simulation studies of an application case of a Dalian Maritime University training ship YULONG are given to demonstrate effectiveness and good performance of the proposed scheme.

Adaptive Predictive Control of Networked Control System

TIAN Zhong-da, GAO Xian-wen, LI Kun

2013, 31(3):  303-308.  doi:10.3969/j.issn.0255-8297.2013.03.013

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This paper proposes an adaptive predictive control method for networked control systems with random time-delay. By using the Elman neural network, online prediction of the random time-delay of network is realized. Compensation of time-delay is done using an improved implicit generalized predictive control
algorithm with derivative functions. Finally, adaptive predictive control for the networked control system with random time-delay is achieved. Simulation results show that the method has a good compensation effect. It can improve the system output performance and ensure stability and rapidity.

Relationship between Ship Roll Attitude and Added Resistance

JIN Hong-zhang, LIU Zhi-quan, JIANG Shu-qiang

2013, 31(3):  309-314.  doi:10.3969/j.issn.0255-8297.2013.03.014

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With the increasing needs of energy saving and emission reduction, the effects of added resistance on ship navigation performance and the control quality have attracted considerable research interests. The added resistance of ship roll is analyzed based on the potential flow theory, and an added resistance model is presented. The added resistance induced by ship roll is calculated with the hydrodynamic computation software ANSYS-AQWA. The rolling added resistance model is modified with regression analysis, and feasibility of model validated. The relationship between roll attitude and added resistance in the time domain is analyzed based on this model. The results provide a theoretical foundation for controlling ships’ anti-roll capability with minimum speed loss.

Area Re-entry for Multi-UAV Search in Unknown Environment

DU Ji-yong1, ZHANG Feng-ming2, MAO Hong-bao3, YANG Ji1, ZHANG Chao1

2013, 31(3):  315-320.  doi:10.3969/j.issn.0255-8297.2013.03.015

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 This paper addresses a cooperative search problem where a team of unmanned aerial vehicles (UAVs) seeks to reduce uncertainty in an unknown environment. The gird-based representation of search environment is established, and a UAV dynamic model and a predictive model of UAV systems are presented.Taking into account the practical tactical requirements, an area re-enter model is formulated, considering some maneuverability constraints. The corresponding shortest re-enter path is formulated. We develop a cooperative search strategy based on “retractable” mechanism, which can enhance adaptability to unknown environments. We also propose a global information base to make full use of the real-time local environmental information
detected by the UAVs, and generate the search path on-line in a rolling style. Simulation results are presented to demonstrate the main feature of the proposed method.

Distributed Fault-Tolerant Control for Quadrotor

YANG Cheng-shun1, YANG Zhong1, HUANG Xiao-ning2, XU De-zhi 1

2013, 31(3):  321-330.  doi:10.3969/j.issn.0255-8297.2013.03.016

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In this paper, a fault accommodation scheme is proposed for a quadrotor attitude dynamics that has composite disturbance and actuator fault. The attitude model and the attitude model with composite disturbance of the quadrotor are described, and an actuator loss-of-effectiveness failure model presented. An
algorithm for composite disturbance estimation and a local fault diagnosis and identification (FDI) algorithm are proposed for composite disturbance and for actuator loss-of-effectiveness failures of the quadrotor system respectively. The composite disturbance estimator is driven by the disturbance estimation error rather than directly related to the state tracking or prediction errors. The local actuator FDI structure is similar to the model reference adaptive control for actuator model. A backstepping fault tolerant control (FTC) based on composite disturbance estimate and local FDI is designed for the quadrotor. Simulation results show effectiveness of the proposed FTC scheme.