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China Communications
(ISSN 1673-5447)
(CN 11-5439/TN)
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2016 Vol. 13, No. 9
Published: 19 September 2016

WIRELESS COMMUNICATIONS
COMMUNICATION NETWORKS
OPTICAL COMMUNICATIONS
SERVICES AND APPLICATIONS
 
   
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       WIRELESS COMMUNICATIONS

Resource Allocation and User Association for HTTP Adaptive Streaming in Heterogeneous Cellular Networks with Small Cells

Jiang Liu, Renchao Xie, F.Richard Yu
China Communications, 2016, 13(9): 1-11
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Video streaming, especially hypertext transfer protocol based (HTTP) adaptive streaming (HAS) of video, has been expected to be a dominant application over mobile networks in the near future, which brings huge challenge for the mobile networks. Although some works have been done for video streaming delivery in heterogeneous cellular networks, most of them focus on the video streaming scheduling or the caching strategy design. The problem of joint user association and rate allocation to maximize the system utility while satisfying the requirement of the quality of experience of users is largely ignored. In this paper, the problem of joint user association and rate allocation for HTTP adaptive streaming in heterogeneous cellular networks is studied, we model the optimization problem as a mixed integer programming problem. And to reduce the computational complexity, an optimal rate allocation using the Lagrangian dual method under the assumption of knowing user association for BSs is first solved. Then we use the many-to-one matching model to analyze the user association problem, and the joint user association and rate allocation based on the distributed greedy matching algorithm is proposed. Finally, extensive simulation results are illustrated to demonstrate the performance of the proposed scheme.
       WIRELESS COMMUNICATIONS

Adaptive Antenna-Activation Based Beamforming for Large-Scale MIMO Communication Systems of High Speed Railway

Meng Cheng, Shaoshi Yang, Xuming Fang*
China Communications, 2016, 13(9): 12-23
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Large-scale array aided beamforming improves the spectral efficiency (SE) as a benefit of high angular resolution. When dual-beam downlink beamforming is applied to the train moving towards cell edge, the inter-beam ambiguity (IBA) increases as the directional difference between beams becomes smaller. An adaptive antenna activation based beamforming scheme was proposed to mitigate IBA. In the district near the base station (BS), all antenna elements (AEs) were activated to generate two beams. As the distance from the train to the BS increased, only the minimum number of AEs satisfying the resolution criterion would be activated. At the cell edge, one beam was switched off due to intolerable IBA. The proposed scheme can achieve SE gain to the non-adaptive scheme and show more robustness against the direction-of-arrival (DOA) estimation error.
       WIRELESS COMMUNICATIONS

Downlink SINR and Rate Distribution of Ultra-Dense HetNets with Burst Traffic

Xin Liu, Zhiwen Pan, Nan Liu, Xiaohu You
China Communications, 2016, 13(9): 24-32
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SINR distribution and rate overage distribution are crucial for optimization of deployment of Ultra-dense HetNets. Most existing literatures assume that BSs have full queues and full-buffer traffic. In fact, due to ultra-dense deployment of small cells, traffic in small cell varies dramatically in time and space domains. Hence, it is more practical to investigate scenario with burst traffic. In this paper, we consider a two-tier non-uniform ultra-dense HetNet with burst traffic, where macro BSs are located according to Poisson Point Process (PPP), and pico BSs are located according to Poisson Hole Process (PHP). The closed-form expressions of SINR distribution and rate distribution are derived, and then validated through simulation. Our study shows that different from the result of full buffer case, the SINR distribution and rate distribution of users depend on the average transmission probabilities of BSs in burst traffic case.
       WIRELESS COMMUNICATIONS

Power Allocation for Sensing-Based Spectrum Sharing Cognitive Radio System with Primary Quantized Side Information

Shuying Zhang, Xiaohui Zhao*
China Communications, 2016, 13(9): 33-43
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Spectrum access approach and power allocation scheme are important techniques in cognitive radio (CR) system, which not only affect communication performance of CR user (secondary user, SU) but also play decisive role for protection of primary user (PU). In this study, we propose a power allocation scheme for SU based on the status sensing of PU in a single-input single-output (SISO) CR network. Instead of the conventional binary primary transmit power strategy, namely the sensed PU has only present or absent status,we consider a more practical scenario when PU transmits with multiple levels of power and quantized side information known by SU in advance as a primary quantized codebook. The secondary power allocation scheme to maximize the average throughput under the rate loss constraint (RLC) of PU is parameterized by the sensing results for PU, the primary quantized codebook and the channel state information (CSI) of SU. Furthermore, Differential Evolution (DE) algorithm is used to solve this non-convex power allocation problem. Simulation results show the performance and effectiveness of our proposed scheme under more practical communication conditions.
       WIRELESS COMMUNICATIONS

On the Probability Density Function of the Real and Imaginary Parts in WFRFT Signals

Xiaolu Wang, Lin Mei*, Zhenduo Wang, Naitong Zhang
China Communications, 2016, 13(9): 44-52
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Recently a Hybrid Carrier (HC) scheme based on Weighted-type Fractional Fourier Transform (WFRFT) was proposed and developed, which contains Single Carrier (SC) and Multi-Carrier (MC) synergetic transmission. The wide interest is primarily due to its appealing characteristics, such as the robust performances in different types of selective fading channels and a great deal of potential for secure communications. According to the literatures, the HC signal and SC or MC signal probability distributions are different. In particular, some benefits of this HC scheme are brought by the quasi-Gaussian distribution of WFRFT signals. However, until now researchers have only presented statistic properties through computer simulations, and the accurate expressions of signals are not derived yet. In this paper, we derive the accurate and rigorously established closed-form expressions of Probability Density Function (PDF) of WFRFT signal real and imaginary parts with a large number of QPSK subcarriers, and this PDF can describe the behavior of data modulated by WFRFT, avoiding the complex computation for extensive computer simulations. Furthermore, the components of PDF expression are described and analyzed, and it is revealed that the tendency of signal quasi-Gaussian changes with the increasing of the parameter α (α in (0,1]). To validate the analytical results, extensive simulations have been conducted, showing a very good match between the analytical results and the real situations. The contribution of this paper may be useful to deduce the closed form expressions of Bit Error Ratio (BER), the Complementary Cumulative Distribution Function (CCDF) of Peak to Average Power Ratio (PAPR), and other analytical studies which adopt the PDF.
       WIRELESS COMMUNICATIONS

Robust Digital Non-Linear Self-Interference Cancellation in Full Duplex Radios with Maximum Correntropy Criterion

Zhirong Luan, Hua Qu, Jihong Zhao, , Badong Chen
China Communications, 2016, 13(9): 53-59
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Full duplex radio increases the frequency efficiency but its performance is limited by the self-interference (SI). We first analyze the multiple noises in the full duplex radio system and model such noises as an distribution. Then we formulate a novel non-Gaussian SI problem. Under the maximum correntropy criterion (MCC), a robust digital non-linear self-interference cancellation algorithm is proposed for the SI channel estimation. A gradient descent based algorithm is derived to search the optimal solution. Simulation results show that the proposed algorithm can achieve a smaller estimation error and a higher pseudo signal to interference plus noise ratio (PSINR) than the well-known least mean square (LMS) algorithm and least square (LS) algorithm.
       WIRELESS COMMUNICATIONS

Dual-Band Coupled-Line Bandpass Filter with Independently Tunable Bandwidths

Yongle Wu, Lixia Nan, Lingxiao Jiao, Weimin Wang, Yuanan Liu
China Communications, 2016, 13(9): 60-64
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This paper reports a novel dual-band coupled-line bandpass filter. Comprising a quadruple-mode coupled-line resonator, this proposed filter could filter signals on two frequency bands. After introducing two varactors, one of the four resonances could be continuously altered by changing the capacitance of the varactors, thus the two frequency bandwidths could be independently tunned. In this paper, the detailed explanation for its operation is given, and the agreement between the expected and practical performance sufficiently confirms the robustness and effectiveness of this proposed filter.
       WIRELESS COMMUNICATIONS

Fractional Frequency Offset Estimation for OFDM Systems in Non-Cooperative Communication

Mingqian Liu, Jian Chen, Bingbing Li, Junfang Li
China Communications, 2016, 13(9): 65-71
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The traditional fractional frequency offset (FFO) estimation schemes for orthogonal frequency division multiplexing (OFDM) in non-cooperative communication have the problems of susceptible performance with the frequency offset values and the number of OFDM symbols, a novel fractional frequency offset blind estimation scheme based on EKF for OFDM systems is conceived. The nonlinear function of the frequency offset is calculated by employing the correlation. And then the frequency offset is estimated by means of the iterative algorithm of EKF. The finally fractional frequency offset is estimated by adopting repeated the above process. Simulation results demonstrate that the proposed scheme is robust to the frequency offset values without any requirements of a prior knowledge.
       WIRELESS COMMUNICATIONS

Semi-Blind Pilot-Aided Channel Estimation in Uplink Cloud Radio Access Networks

Yourong Ban, Qiang Hu, Zhendong Mao, Zhongyuan Zhao
China Communications, 2016, 13(9): 72-79
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In this paper, a quasi-Newton method for semi-blind estimation is derived for channel estimation in uplink cloud radio access networks (C-RANs). Different from traditional pilot-aided estimation, semi- blind estimation utilizes the unknown data symbols in addition to the known pilot symbols to estimate the channel. An initial channel state information (CSI) obtained by least-squared (LS) estimation is needed in semi-blind estimation. BFGS (Brayben, Fletcher, Goldfarb and Shanno) algorithm, which employs data as well as pilot symbols, estimates the CSI though solving the problem provided by maximum-likelihood (ML) principle. In addition, mean-square-error (MSE) used to evaluate the estimation performance can be further minimized with an optimal pilot design. Simulation results show that the semi-blind estimation achieves a signi?cant improvement in terms of MSE performance over the conventional LS estimation by utilizing data symbols instead of increasing the number of pilot symbols, which demonstrates the estimation accuracy and spectral ef?ciency are both improved by semi-blind estimation for C-RANs.
       WIRELESS COMMUNICATIONS

A Dynamic Bandwidth Allocation Solution Based on User Behavior and Software Defined EPS

Bo Zhu, Hao Jiang, Lihua Wu, Shuwen Yi, Hai Wang
China Communications, 2016, 13(9): 80-90
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For telecommunication operators, how to improve the utilization of bandwidth resources is always a problem which worthy of study, nowadays, this issue has become more and more important, since the traffic load bursting in the mobile Internet. So the key to solving this problem is that we need to find a kind of traffic model to predict the traffic load that users need. According to the predicted traffic load to allocate bandwidth to each base station dynamically.But the traffic consumption behavior of a single base station is random, it is difficult to predict[1].For this reason, we based on reality that, when the user moves, it may get traffic load from different base stations, therefore, there will have some kind of relationship between those base stations.We use this relationship to establish a kind of Spatial Collaborative Network.consequently, we make use of stability algorithm to divided those base station cluster into different communities, According to the traffic load usage rules which these communities indicated to us, we get a traffic model.At the same time, we studied how to use this traffic model in the future networks to dynamically allocate bandwidth resources, then we propose a new kind of EPS architecture based on SDN, on this platform, we can deploy our strategy through it's programmable interface.Finally, we designed an experiment to test the performance of our dynamic strategy, and the result shows that our method enables bandwidth utilization has been greatly improved.
       COMMUNICATION NETWORKS

PLC-Oriented Access Point Location Planning Algorithm in Smart-Grid Communication Networks

Ningzhe Xing, Sidong Zhang, Yue Shi, Shaoyong Guo
China Communications, 2016, 13(9): 91-102
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In this study, we investigate the optimal location of access points (APs) to connect end nodes with a service provider through power-line communication in smart-grid communication networks. APs are the gateways of power-distribution communication networks, connecting users to control centers. Hence, they are vital for the reliable, safe, and economical operation of a power system. This paper proposes a planning method for AP allocation that takes into consideration economics, reliability, network delay, and (n-1) resilience. First, an optimization model for the AP location is established, which minimizes the cost of installing APs, while satisfying the reliability, network delay, and (n-1) resilience constraints. Then, an improved genetic algorithm is proposed to solve the optimization problem. The simulation results indicate that the proposed planning method can deal with diverse network conditions satisfactorily. Furthermore, it can be applied effectively with high flexibility and scalability.
       COMMUNICATION NETWORKS

ICN Based Vehicle-to-Cloud Delivery for Multimedia Streaming in Urban Vehicular Networks

Wei Quan, Fei Song, *, Chengxiao Yu, Mingchuan Zhang,
China Communications, 2016, 13(9): 103-112
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Mobile multimedia streaming is an open topic in vehicular environment. Due to the high intermittent links, it has become a critical challenge to deliver high quality video streaming in vehicular networks. In this paper, we reform the Information Centric Networking (ICN) concept for multimedia delivery in urban vehicular networks. By leveraging the ICN perspective, we highlight that vehicular peers can obtain multimedia chunks via the vehicle-to-cloud (V2C) approach to improve the delivery quality. Based on this, we propose a lightweight multipath selection strategy to guide the network system to adaptively adjust the forwarding means. Extensive simulations show that the proposed solution can optimize the utilization of network paths, lighten network loads as well as avoid wasting resources.
       OPTICAL COMMUNICATIONS

Performance Analysis of Optical Transmission Based on Seven Cores Fiber

Hang Zhou*, Fu Wang, Borui Li, Ming Tang, Xiangjun Xin
China Communications, 2016, 13(9): 113-120
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This essay designed a kind of new seven-core fiber with lower crosstalk and loss, and made space division multiplexing transmission experiment based on this seven-core fiber. It is known that crosstalk has the most serious influence in multicore fiber transmission process. Before the experiment, the affecting factors of fiber crosstalk were analyzed through simulation, such as core space, bending radius, and fiber length. Combined with the simulation analysis, the design scheme of multicore fiber with low crosstalk was obtained. Before the fiber design, various factors of influence crosstalk such as the core-to-core distance, bending radius, fiber length and so on. Based on the simulation analysis, conclusion has made on the design scheme of multi-core optimal fiber with low crosstalk. The space division multiplexing and wavelength division multiplexing technology, was adopted to conduct seven-core optical fiber transmission of 58.7km.The crosstalk of adjacent core was suppressed to as low as 45dB /km, the attenuation of inner core was 0.24dB/km, the outer cores’ 0.32dB/km. Different bit error rate (BER) performances were also studied under different conditions, through reasonably designing the system to reduce the error rate, improve the performance of the system, and realize long distance and large capacity transmission with fiber.
       SERVICES AND APPLICATIONS

No-Reference Quality Assessment of Enhanced Images

Leida Li, Wei Shen, Ke Gu, Jinjian Wu, Beijing Chen, Jianying Zhang*
China Communications, 2016, 13(9): 121-130
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Image enhancement is a popular technique, which is widely used to improve the visual quality of images. While image enhancement has been extensively investigated, the relevant quality assessment of enhanced images remains an open problem, which may hinder further development of enhancement techniques. In this paper, a no-reference quality metric for digitally enhanced images is proposed. Three kinds of features are extracted for characterizing the quality of enhanced images, including non-structural information, sharpness and naturalness. Specifically, a total of 42 perceptual features are extracted and used to train a support vector regression (SVR) model. Finally, the trained SVR model is used for predicting the quality of enhanced images. The performance of the proposed method is evaluated on several enhancement-related databases, including a new enhanced image database built by the authors. The experimental results demonstrate the efficiency and advantage of the proposed metric.
       SERVICES AND APPLICATIONS

Robust Watermarking of Mobile Video Resistant against Barrel Distortion

Huawei Tian*, Yanhui Xiao, Gang Cao, Jianwei Ding, Bo Ou
China Communications, 2016, 13(9): 131-138
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In head mounted display (HMD), in order to cancel pincushion distortion, the images displayed on the mobile should be pre-warped with barrel distortion. The copyright of the mobile video should be verified on both the original view and the pre-warped virtual view. A robust watermarking resistant against barrel distortion for HMDs is proposed in this paper. Watermark mask is embedded into image in consideration of imperceptibility and robustness of watermarking. In order to detect watermark from the pre-warped image with barrel distortion, an estimation method of the barrel distortion is proposed for HMDs. Then, the same warp is enforced on the embedded watermark mask with the estimated parameters of barrel distortion. The correlation between the warped watermark and the pre-warped image is computed to predicate the existence of watermark. As shown in experimental results, watermark of mobile video can be detected not only from the original views, but also from the pre-warped virtual view. It also shows that the proposed scheme is resistant against combined barrel distortion and common post-processing, such as JPEG compression.
       SERVICES AND APPLICATIONS

A Novel Provable Data Possession Scheme Based on Geographic Location Attribute

Yaxing Zha*, Shoushan Luo, Jianchao Bian, Wei Li
China Communications, 2016, 13(9): 139-150
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Increment of mobile cloud video motivates mobile users to utilize cloud storage service to address their demands, cloud storage provider always furnish a location-independent platform for managing user’s data. However, mobile users wonder if their cloud video data leakage or dynamic migration to illegal service providers. In this paper, we design a novel provable data possession protocol based on data geographic location attribute, which allows data owner to auditing the integrity of their video data, which put forward an ideal choice for remote data possession checking in the mobile cloud storage. In our proposed scheme, we check out whether the video data dynamic migrate to an unspecified location (such as: overseas) by adding data geographic location attribute tag into provable data possession protocol. Moreover, we make sure the security of our proposed scheme under the Computational Diffie-Hellman assumption. The analysis and experiment results demonstrate that our proposed scheme is provably secure and efficient.
       SERVICES AND APPLICATIONS

Modeling and Optimization of Bandwidth Supply Performance for Cloud-Assisted Video Systems under Flash Crowd

Shijie Jia, , Ruiling Zhang, , Youzhong Ma, , Lujie Zhong*, Changqiao Xu
China Communications, 2016, 13(9): 151-162
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The large-scale and sudden video content access such as flash crowds results in huge bandwidth demand, which severely influence user quality of experience and quality of service of video systems. In this paper, we firstly discuss the main reason of generation of flash crowds for video streaming services and analyze key factor for balance recovery between supply and demand of upload bandwidth. We construct two models: bandwidth supply capacity model of video systems and bandwidth demand model of users, which measures usage amount of bandwidth of the cloud. Based on the built models, we further employ a community-based cooperative caching strategy of video resources to promote supply capacity of upload bandwidth of video systems. Extensive tests show how the proposed cooperative caching strategy achieves much better performance results in comparison with original solution.
       SERVICES AND APPLICATIONS

Service-Oriented Network Virtualization Architecture for Internet of Things

Yongan Guo, Hongbo Zhu, Longxiang Yang
China Communications, 2016, 13(9): 163-172
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As a key technology to realize smart services of Internet of Things(IoT), network virtualization technology can support the network diversification and ubiquity, and improve the utilization rate of network resources. This paper studies the service-oriented network virtualization architecture for IoT services. Firstly the semantic description method for IoT services is proposed, then the resource representation model and resource management model in the environment of network virtualization are presented. Based on the above models, the service-oriented virtual network architecture for IoT is established. Finally, a smart campus system is designed and deployed based on the service-oriented virtual network architecture. Moreover, the proposed architecture and models are verified in experiments.
       SERVICES AND APPLICATIONS

An Overview of Social Analysis from Mobile Telephone Calls of Different Operators

Changyuan Wang, Yang Liu, Zongfei Lu, Shanqing Guo*, Lizhen Cui
China Communications, 2016, 13(9): 173-182
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We construct a call network digraph G with attribution using mobile phone call records within 21 days collected by three operators and analyze the social call behavior features through analyzing the degree distribution of nodes of the network digraph under the help of Graphx based on the Spark Platform. We get the following social conclusions from the communication relationship between phone users: on average, users make about 5~7 mobile telephone calls and connect about 2~3 persons one day; on weekends, people make less calls but spend longer time on each call, revealing that working calls account for a large part of calls on weekdays; among these telephone calls on weekdays, most are less than one minute, and on average, mobile users that call more people also tend to be called by more individuals.
       SERVICES AND APPLICATIONS

Lightweight SOA-Based Twin-Engine Architecture for Enterprise Systems in Fixed and Mobile Environments

Tongguang Zhang, Shuai Zhao, Budan Wu, Maurizio Farina, Bo Cheng, Junliang Chen
China Communications, 2016, 13(9): 183-194
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Mobile devices as a popular computing platform for enterprise systems have enabled certain tasks to be executed out of office. However, the work may be interrupted due to the server shutdown or network disconnection when employees access traditional single-engine Business Process Management System. To overcome this defect, we present a lightweight twin-engine architecture based on Service Oriented Architecture (SOA). In this paper, we discuss in detail the design and implementation of the architecture, and present a trigger mechanism to activate engines according to the states of hybrid environments since it is critical for the two types of engines to cooperate closely in hybrid environments with fixed and mobile computing resources. The experimental results validate the usability of the architecture.
       SERVICES AND APPLICATIONS

Efficient Security Sequencing Problem over Insecure Channel Based on Homomorphic Encryption

Mingxu Yi, Lifeng Wang*, Yunpeng Ma
China Communications, 2016, 13(9): 195-202
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In the field of sequencing of secret number, an important problem is how to establish an efficient and secure protocol for sorting the secret number. As a powerful tool in solving privacy sequencing problems, secure multipart computation is more and more popular in anonymous voting and online auction. In the present study, related secure computation protocol for sequencing problem is not many by far. In order to improve the efficiency and safety, we propose a security sequencing protocol based on homomorphic encryption. We also give analysis of correctness and security to highlight its feasibility.
       SERVICES AND APPLICATIONS

Coping with the Big Data: Convergence of Communications, Computing and Storage

Pingzhi Fan
China Communications, 2016, 13(9): 203-207
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To cope with the impact of big data, it is proposed to integrate the traditionally individual computing, communications and storage systems, which are getting inevitably converged. An effective information system capacity is introduced and discussed, aimed at excavating potentials of information system under a new paradigm with more degrees of freedom.
       SERVICES AND APPLICATIONS

Mitigating ROP Attacks via ARM-Specific In-Place Instruction Randomization

Yu Liang, Guojun Peng*, Yuan Luo, Huanguo Zhang
China Communications, 2016, 13(9): 208-226
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Defending against return-oriented programing (ROP) attacks is extremely challenging for modern operating systems. As the most popular mobile OS running on ARM, Android is even more vulnerable to ROP attacks due to its weak implementation of ASLR and the absence of effective control-flow integrity enforcement. In this paper, leveraging specific ARM features, an instruction randomization strategy to mitigate ROP attacks in Android even with the threat of single pointer leakage vulnerabilities is proposed. By popping out more registers in functions’ epilogue instructions and reallocating registers in function scopes, branch targets in all (direct and indirect) branch instructions potential to be ROP gadgets are changed randomly. Without the knowledge of binaries’ runtime instructions layout, adversary’s repeated control flow transfer in ROP exploits will be subverted. Furthermore, this instruction randomization idea has been implemented in both Android Dalvik runtime and ART. Corresponding evaluations proved it is capable to introduce enough randomness for more than 99% discovered functions and thwart about 95% ROP gadgets in application’s shared libraries and oat file compiled from Dalvik bytecode. Besides, evaluations on real-world exploits also confirmed its effectiveness on mitigating ROP attacks within acceptable performance overhead.
       SERVICES AND APPLICATIONS

Automatic GUI Test by Using SIFT Matching

Xiaoxin Fang, Bin Sheng*, Ping Li, Dan Wu, Enhua Wu
China Communications, 2016, 13(9): 227-236
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In software development process, the last step is usually the Graphic User Interface(GUI) test, which is part of the final user experience (UE) test. Traditionally, there exist some GUI test tools in the market, such as Abbot Java GUI Test Framework and Pounder, in which testers pre-configure in the script all desired actions and instructions for the computer, nonetheless requiring too much of invariance of GUI environment; and they require reconfiguration in case of GUI changes, therefore still to be done mostly manually and hard for non-programmer testers to. Consequently, we proposed GUI tests by image recognition to automate the last process; we managed to innovate upon current algorithms such as SIFT and Random Fern, from which we develop the new algorithm scheme retrieving most efficient feature and dispelling inefficient part of each algorithm. Computers then apply the algorithm, to search for target patterns themselves and take subsequent actions such as manual mouse, keyboard and screen I/O automatically to test the GUI without any manual instructions. Test results showed that the proposed approach can accelerate GUI test largely compared to current benchmarks.
       SERVICES AND APPLICATIONS

Evaluation and Optimization of the Mixed Redundancy Strategy in Cloud-Based Systems

Pan He*, Xueliang Zhao, Chun Tan, Zhihao Zheng, Yue Yuan
China Communications, 2016, 13(9): 237-248
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Mixed redundancy strategies are generally used in cloud-based systems, with different node switch mechanisms from traditional fault-tolerant strategies. Existing studies often concentrate on optimizing a single strategy in cloud computing environment and ignore the impact of mixed redundancy strategies. Therefore, a model is proposed to evaluate and optimize the reliability and performance of cloud-based degraded systems subject to a mixed active and cold standby redundancy strategy. In this strategy, node switching is triggered by a continual monitoring and detection mechanism when active nodes fail. To evaluate the transient availability and the expected job completion rate of systems with such kind of strategy, a continuous-time Markov chain model is built on the state transition process and a numerical method is used to solve the model. To choose the optimal redundancy for the mixed strategy under system constraints, a greedy search algorithm is proposed after sensitivity analysis. Illustrative examples were presented to explain the process of calculating the transient probability of each system state and in turn, the availability and performance of the whole system. It was shown that the near-optimal redundancy solution could be obtained using the optimization method. The comparison with optimization of the traditional mixed redundancy strategy proved that the system behavior was different using different kinds of mixed strategies and less redundancy was assigned for the new type of mixed strategy under the same system constraint.
 
 
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