Table of Content

31 May 2008, Volume 26 Issue 3

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Articles

Multistage Soft Decision Equalizers Based on Minimum Bit Error Rate



ZHU Ren-xiang;WU Le-nan

2008, 26(3):  221-221 . 

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A multistage soft decision equalizer based on minimum bit error rate is proposed for interference suppression in communications. Bit error rate and computational complexity can be compromised by controlling rejection threshold of each stage. Simulation results show that when extended binary phase shifting keying signals are contaminated by the mix of relatively strong interference signals of amplitude modulation and frequency modulation, multistage soft decision equalizers based on minimum bit error rate can provide very low bit error rate, and the computational complexity is greatly reduced. Furthermore, it is found that by combining different nonlinear equalizers, performance superior to single equalizers can be obtained.


Multi-user Blind Detection Based on Optimum Step Size with Linear Constraint and Conjugate Gradient Constant Modulus


PAN Zi-yu;FENG Guang-zeng;WANG Xin

2008, 26(3):  228-228 . 

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This paper studies multi-user detection for CDMA downlink and proposes a new approach for blind detection to overcome multi-access interference (MAI) in CDMA systems. The method is called linear constraint conjugate gradient constant modulus algorithm based on adaptive step size. The best step size is used to achieve optimization. An analytical form is obtained. Simulations for additive white Gaussian channel and multi-path fading channel environments show that the proposed technique can provide SIR and BER improvement with respect to other adaptive step size CMA.


An Unlicensed Access Scheme for Up-band of Fixed Satellite Service


ZHAO Lu-wen;ZHOU Zhi-jie;MIAO Zhi-min

2008, 26(3):  234-234 . 

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In order to improve the spectrum usage of the up-band of fixed satellite service (FSS), an unlicensed access scheme is presented. The satellite’s idle channel is used for cognitive radio service channel, and a common coordinate channel with lower transmitting power and better anti-jamming ability is proposed. The two basic unlicensed access modes, Ad hoc and star mode, are considered. According to interference temperature, the interference of the cognitive radios to satellite receiver is analyzed. Analysis and simulation results show that, by using this scheme to avoid interference to satellite receiver with the jam-probability lower than 1%, many cognitive radios can access the band without special authorization.


A Multi-object Optimization Routing Algorithm with Constraint for Wireless Sensor Networks




MI Zhi-Chao;ZHOU Jian-Jiang

2008, 26(3):  239-239 . 

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Using characteristics of wireless sensor networks, this paper presents a multi-object optimization model to optimize routing energy and delay with bandwidth constraint. A modified ideal point algorithm is proposed to solve the dimension problem caused by different targets. By adjusting corresponding parameters, the algorithm adapts well to various services whose requirements for energy and delay are different. Feasibility of the algorithm is shown with an example. Simulation results confirm that, compared with the minimum delay routing algorithm and maximum available power routing algorithm, the proposed algorithm is a better approach in terms of the overall performance of the evaluation function based on the available power and routing delay.


Low Complexity Iterative Receiver with Bit-Level Cancellation and Detection for Multiuser Space-Time Coding Systems



DU Na;XU Da-zhuan

2008, 26(3):  244-244 . 

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A multiuser space-time coding system combined with the Turbo-BLAST scheme is presented. Since the conventional iterative receiver with symbol-level cancellation (SLC) has high computation complexity, a low complexity iterative receiver scheme with bit-level cancellation (BLC) and detection is proposed which can perform bit-level cancellation by decomposing an M-QAM constellation into a linear combination of binary constellations. Theoretical analysis and simulation results show that the proposed scheme has lower complexity compared with the conventional receiver without introducing performance degradation, while the spectral efficiency is improved due to the BLAST structure used at the transmitter.


Security Analysis of Secure Routing Protocols for Ad Hoc Networks Based on Improved Meadows Model



LIU Jing;FU Fei;XIAO Jun-mo

2008, 26(3):  250-250 . 

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Many secure routing protocols for ad hoc networks have been proposed so far, but few formal analysis methods are available. Although Meadows model is a well-known cryptographic analysis method, it is unsuitable for ad hoc network secure routing protocols because it lacks ability to describe and analyze routing. By adding routing description and analysis scheme based on graphic theory, we extend the Meadows model to have the analysis ability. The extended Meadows model can analyze secure routing protocols for ad hoc networks. As an example, the extended model is used to analyze the routing protocol, Ariadne, and the result shows that Ariadne can generate fault routing.


On Demand Mesh Routing Protocol for Ad Hoc Networks



GUAN Jun-ming;LU Yang;SHENG Feng

2008, 26(3):  257-257 . 

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Both node mobility and network congestion may lead to invalidation of RREP and failure of existing routes in ad hoc networks. Therefore the source node has to perform network-wide flooding again for rediscovering a new route, leading to an increase of the network load and consumption of a large amount of node energy and bandwidth. Based on route interception and MAC cache technique, a new On Demand Mesh Routing (ODMR) protocol is presented using the cross-layer concept. By spreading bypass RREP packets during route reply phase, the proposed protocol sets up multiple bypass routes to the destination in order to reduce route discovery frequency and improve protocol robustness. Simulation results show that ODMR can reduce the end-to-end delay with significantly less protocol overhead and higher network throughput as compared to AODV, AOMDV, and AODV-BR.


Improved EM Algorithm of Blind Multiuser Detection for CDMA Systems




HU Yan-jun

2008, 26(3):  264-264 . 

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Blind CDMA multiuser detection based on the expectation-maximization (EM) algorithm is studied, and an improved blind multiuser detection method based on the EM algorithm is proposed. To overcome conflict between computational complexity and the system performance, both multiuser interferences and noise are taken into account in the maximization likelihood estimate, and the likelihood function is modified. Simplification is achieved by decomposition of the estimation process. Numerical experiment is carried out. The results show that the proposed algorithm has good performance and low computation complexity.



SNR-Optimized User Selection Scheme in MIMO Broadcast Channels



WANG Jing;WANG Yan;YOU Xiao－hu

2008, 26(3):  269-269 . 

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In this paper, we investigate the user selection algorithm in MIMO BC systems with many users. Consider frequency division duplex (FDD) systems, where channel state information (CSI) at the base station is obtained via feedback mechanisms from the users. An algorithm aiming to optimize the average signal-to-noise ratio (SNR) is presented. After setting a threshold value, only users whose channel gains are above the set threshold are considered. Among these candidate users, the transmitter selects a set of users whose minimum eigenvalue is maximal among the possible user sets. The proposed algorithm can achieve the full multiplex gain and get a desirable sum capacity and BER performance. Meanwhile, compared with the exhaustive search scheme, the system overheads, such as the amount of feedback and number of selections in the base station, decrease evidently.


Medical Image Registration Based on Differential Evolution


CAO Guo-gang;RONG Cheng-cheng;LUO Li-min

2008, 26(3):  274-274 . 

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Medical image registration using mutual information can be viewed as a optimization problem. In optimization problems, the objective function is often trapped into a local minimum. In this paper, differential evolution is proposed for medical image registration, and applied to registration of multi-modality medical images. The proposed method can avoid local minimum due to its converging characteristics. Experimental results show that, using mutual information and affine transformation as objective functions, the differential evolution algorithm outperforms the Powell algorithm and the simulated annealing for medical image registration.


Detection of Composite Images Based on JPEG Compression Properties



LI Sheng;ZHANG Xin-peng

2008, 26(3):  281-281 . 

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This paper proposes an image forgery detection scheme based on JPEG compression properties, which aims to identify a special type of images that are composed of contents from different JPEG images. Inconsistency in compression qualities and block boundaries in a suspicious image can provide a clue for forgery detection. By recompressing the image with different quality factors and analyzing the induced distortion, we can estimate the quality factor initially used in the main area of the image. Thus, inconsistency can be found from fluctuation of distortion energy in different areas. The proposed scheme is capable of identifying objects from different origins, and provides a useful means of digital forensics.


Improved Method of Feature Extraction and Matching for Image Mosaic


ZHANG Jing;YAN Zhuang-zhi;SHAO Shi-jie;WANG Mu-yun;WANG Li-ming

2008, 26(3):  288-288 . 

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By comparing with some common approached of feature extraction and matching, the paper proposes an improved method of feature extraction and matching for image mosaic which improves image quality and processing speed. It uses scale invariant feature transform (SIFT) to extract invariant features from images, approximate nearest neighbor searching and random sample consensus (RANSAC) to perform reliable matching. Parameters of the transformation between images are obtained from the matched feature points to realize image stitching and blending. The feature points are invariant to affine transformation, noise contamination and illumination variation, leading to robustness of the method. Experimental results show that the proposed method is fast and can produce high quality image mosaic.


Solution to Inverse Problem of Elastic Modulus for Biologic Tissue Using Genetic-Algorithm


CAI Chuan-bao;TANG Wen-cheng

2008, 26(3):  295-295 . 

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Since pathological changes of biologic tissues cause physical changes, research of the physics of biologic tissues can provide references to diagnosis. A method for finding elastic modulus of biologic tissues is presented by using the genetic algorithm, given part of the boundary displacement, outer load, boundary condition and a finite element model. Solution to the elastic modulus is described as an inverse problem in mechanics. A mathematical model of the inverse system recognition process is established. Principles of the genetic algorithm are used to provide a solution to elastic modulus of the biologic tissues. The algorithm is verified with a numeric example. Parts of boundary displacement are obtained by combining image recognition. Log arithmetic operator is used for edge detection, and bilinear coordinate transformation formula is used for image interior orientation. The elastic modulus is solved with a relative error 0.914%.


Flush Air Data Sensing and Its Calibration



Song Xiu-yi;Lu Yu-ping

2008, 26(3):  301-301 . 

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An algorithm for flush air data sensing system is designed and improved. A Kalman algorithm is proposed in which iterative computation for the shape and compressibility parameters are avoided. Instead, these parameters are obtained from pressure modification coefficient. A neural network basing algorithm for the modularization is described, and the attack angle and sideslip angle are calibrated by modularization MRCa and MRCb respectively. Methods for getting optimal attack and sideslip angles are developed, solving the multiple solution problem. Calculation and calibration results are presented with improved precision and real-time characteristic, indicating that the design method is feasible.


Analysis of Circular Groove Guide Loaded with Plasmas



SUN Yong-zhi;YANG Hong-sheng;SHEN Chang-sheng

2008, 26(3):  307-307 . 

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A circular groove guide loaded with plasmas is analyzed using the mode matching method. The characteristic equation of circular groove guide loaded with plasmas is derived. Effects of plasma physical parameters on dispersion curve of TE11 mode are calculated using the characteristic equation. The calculated results show that the physical parameters of plasmas have great effect on the characteristic of TE11 mode. For instance, when the plasma density rises from 5×10^15/m3 to 5×10^16/m3, the cutoff frequency of TE11 mode changes from 4.6 GHz to 13.8 GHz. The changes of cutoff frequency of TE11 mode loaded with different plasma parameters can be found. The results provide guidelines for applications of circular groove guide loaded with plasmas.


Role-Based Policy Delivery Model for Distributed Firewall


CHEN Bing;HU Ying;DING Qiu-lin

2008, 26(3):  312-312 . 

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To deliver policies to all clients in distributed firewalls, a role-based access control policy model is proposed. The policy server creates a global policy and a rule restricted policy, deduces role policy, and divides it into user-role policies. All clients in the same role set own the same security level and access rights. Complexity due to making policy individually for each client is reduced. Rules can be retrieved with high speed, and the time complexity is O(1) using a hash algorithm. Test results show that the flow produced by interactive communication on the network traffic can be ignored by applying this model.


Breast Cancer Assistant Diagnosis by Combining Cost Sensitive Feature Selection with Semi-supervised Learning



DING Xiao-nian;CHEN Song-can

2008, 26(3):  319-319 . 

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Masses and microcalcification clusters are the main characteristics in the digital mammography of breast cancer. It is traditionally thought that the features extracted from the masses and microcalcification clusters are always correct and effective, and therefore used for a supervised design of classifier to diagnose. In practice, however, one cannot necessarily promise effectiveness of the features. Furthermore, not all labels of the samples can be obtained due to the expensive labeling cost. In this paper, we design a novel diagnosis method for microcalcification clusters. The proposed method first uses an algorithm of modified cost sensitive selective ensemble (CSSE) to select the features that are most useful for classification and without redundant information. Then we design a semi-supervised consistent co-training (CoCo-Training) algorithm as a diagnosis classifier by taking sufficient advantage of the unlabeled samples. Experiments on the benchmark DDSM show that the proposed diagnose method outperforms others.


New Algorithm for Attacking Nonlinear Combined Sequences



SUN Bing;LI Chao

2008, 26(3):  326-326 . 

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To attack nonlinear combined sequences, we propose a new method that only requires the stage of the linear feedback shift register's (LFSR) and enough sample bits to recover the initial states and the feedback polynomial. Complexity of the algorithm is studied. We show that security cannot be improved essentially by just increasing the number of LFSRs. We propose a new metric to evaluate the cryptographic ability of Boolean functions in order to resist this kind of attack, and study some properties of the metric. We show that this metric should be small in designing a nonlinear combined sequence. We gave all the functions that the new metric is 0 when the variable number is 2 and 3. An up-bound of the metric is given when the number of variable is equal to or greater than 4.