Artificial noise–aided secure communication in a bidirectional relaying network

An artificial noise strategy is proposed for amplify‐and‐forward bi‐directional relay network where the eavesdropper can wiretap the relay channels in both hops. Artificial noise is used to confuse the eavesdropper and improve its secrecy. Specifically, the source and the relay are allowed to split their available transmit power into 2 parts: a useful information portion and a jamming portion to transmit a jamming signal. The mathematical model is established for 2‐way relay network with an eavesdropper. The secrecy rate achieved by using artificial jamming is derived from the above model. The optimal power allocation with individual power constraint is obtained via sequential quadratic programming to maximize the secrecy sum rate, and 2 special cases are investigated. Furthermore, the benchmark is provided for the purpose of performance comparison. Simulation results show that the proposed strategy can significantly improve the secrecy sum rate by using artificial noise to jam the eavesdropper.     

A novel model for implicit cooperation between primary users and secondary users in cognitive radio‐cooperative communication systems

Recently, cooperative communications are used to improve the communications performance in cognitive radio networks. In this paper, we present a new model for implicit cooperation between primary users and secondary users (SUs), where SUs transparently relay packets of primary transmitters (PTs) towards their primary receivers encouraging PTs to reduce their transmit power, which in turn will reduce the total interference at some intended secondary receivers (SRs). Secondary relays work as full‐duplex amplify‐and‐forward (AF) cooperative nodes. The system is modeled as a multi‐armed restless bandit problem where the optimal policy for joint relay selection and transmit power allocation is obtained in a distributed way taking both instantaneous channel states and residual energy into consideration. We solve the problem using primal‐dual priority‐index heuristic, which can reduce the online computations and implementation complexity. Simulation results show that this model can benefit both sides where the energy consumption at PTs is reduced significantly and signal to interference plus noise ratio (SINR) at the intended SUs is increased about 50% in average.     

Channel assignment scheme in clustered multichannel cognitive radio networks with outdated CSI over Rayleigh fading channels

This work investigates channel assignment for cooperative spectrum sensing in multichannel cognitive radio networks, where the heterogeneity of primary user (PU) activity and the effect of varying channel condition on the received signal‐to‐noise ratio during cluster formation are considered. With the objective to minimize interference to the PU while enhancing multiple spectrum utilization of the secondary user (SU), an overlapping cluster‐based assignment is formulated into a nonlinear integer optimization problem. To obtain an efficient solution, the nonlinear integer problem is transformed into a mixed integer linear problem, based on which, this paper proposes an exact solution and then two new heuristic algorithms for suboptimal solutions, respectively. Furthermore, a comparative study of four different cluster head selection schemes with respect to their performance in cooperative spectrum sensing, under cluster's heterogeneity in terms of SUs distribution relative to PU transmitter location is presented. Based on the study, a robust cluster head selection scheme is proposed. Simulation results show that good sensing performance and increased opportunistic spectrum utilization in multichannel cognitive radio networks are two sides of a coin that depend on the ratio of the SUs to the number of PU channels. How far away the PU is from the cluster center is also seen to be key in the optimal selection of cluster heads in cooperative spectrum sensing.     

A comprehensive performance analysis of relay-aided CDMA communications over dissimilar fading channels

In this paper, bit error probability (BEP), outage probability (OP) and channel capacity (CC) of direct-sequence code-division multiple access systems with amplify-and-forward relaying are presented for different fading scenarios. In the first scenario, the source-destination link is assumed to experience Rayleigh fading while it is subject to Nakagami-m fading in the second scenario. The source-relay and relay-destination channels are considered to have Nakagami-m fading conditions in two scenarios. First, analytical expressions for the end-to-end probability density function (PDF) are derived by using the convolution integral. Then, BEP, OP and CC are obtained based on these PDFs in terms of infinite series. Truncation error analyses are presented for different parameter values in order to show that truncation error arising from the infinite series is negligible. Simple and easy-to-compute asymptotic expressions are also introduced for BEP and OP in order to simplify the performance analysis in high signal-to-noise ratio region. Simulation results are provided to show the accuracy of the proposed approximate and asymptotic expressions.     

An integrated numerical and experimental framework for modeling of CTB and GD1b ganglioside binding kinetics

A mathematical model is developed and validated for a multistep binding process between cholera toxin subunit B (CTB) and GD1b receptors that precedes cholera infection. To study the dynamics of the complex CTB‐GD1b binding mechanisms, cooperative binding effect and GD1b receptor aggregation in the host cell membrane are considered. More reliable parameters for the CTB‐GD1b binding kinetics are estimated by quantitatively calibrating the proposed multistep binding model against the experimental measurements obtained from the novel nanocube‐based biosensor. Specifically, a numerical scheme that includes the sensitivity analysis, parameter estimation and dynamic optimization is implemented for the model calibration. Through this scheme, identifiable model parameters are determined. After those selected parameters are estimated, the calibrated model and the experimental measurements were in reasonable agreement for different CTB and GD1b concentrations, which shows a promising approach for identification of the kinetics of CTB binding to the host cell membrane. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3882–3893, 2018     

存在干扰的星地混合协作传输性能分析

分析了地面多个中继节点采用放大转发协议辅助卫星通信构成的星地混合协作网存在同信道干扰时的性能.首先在用户端采用最大比合并方案并受到同信道干扰的情况下,得到其输出信干噪比的表达式.其次针对卫星链路服从阴影莱斯分布和地面链路服从瑞利分布的情况,推导出输出信干噪比的矩母函数,并进一步得到系统平均误符号率的解析表达式.接着,推导出高信噪比条件下系统平均误符号率的近似表达,为估算系统的性能提供了更加快速的方法.最后,计算机仿真验证了理论计算公式的准确性,并分析了信道参数、中继数目和调制方式对星地混合协作传输的影响.     

基于面向对象技术构建的并行液压CAD绘图平台

利用面向对象以及网络开发技术，构建了并行液压CAD绘图平台。在分析当前液压CAD的特点之后，提出了用并行协同设计模式规划液压CAD，运用面向对象（object-oriented）技术、对话框和控件技术、数据库图库存储提取技术、导入导出图形图像技术和socket技术，具体实现了辅助图元绘制、原理图生成、数据交换、网络通讯和后台数据库服务各个功能，使液压系统计算机辅助设计得到进一步的完善。     

An integrating view on the viewing abstraction: Contexts and perspectives in software development,AI, and databases

Viewing entities from different situations and representing and processing them in different contexts constitutes a fundamental concern in various disciplines of computer science. Not surprisingly, the viewing abstraction is supported by many languages and techniques employed either for programming or world modelling. This paper presents an overview on various manifestations of viewing mechanisms in formal notations including software development techniques, knowledge representation languages, and data models. The concepts of context and perspective are introduced in form of a language-independent framework in order to capture and systematically discuss features that characterize viewing mechanisms, such as the relationship between the two, the relation between different perspectives on the same conceptual entity, or operations supporting effective construction of contexts. In addition, it is argued that the full power of viewing can be exploited by supporting both notions: contexts as well as perspectives. In order to achieve this support, any formal notation has to fulfill a number of general requirements which are stated as a result of the investigation and the survey.     

基于C-V2X的车路群体协同混合组网

车联网是支持未来自动驾驶和智能交通的重要基础设施,也是5G交通新基建的重点建设方向。针对大规模车路协同智能驾驶业务场景,建立并分析了通信流量模型,测算了不同发展阶段车路群体协同带宽需求,分析了当前C-V2X独立组网和叠加组网等不同组网模式在支持车路群体协同过程中面临的困境。针对车路群体协同服务带来的通信高带宽、用户规模大和资源调度复杂挑战,提出了网络协调下的混合组网模式,为基于5G C-V2X的车联网支撑大规模车路群体协同服务提供了可行方案。     

一种协同问答信号配对规则提取方法

针对通信协议未知或部分已知条件下询问和应答信号配对难、配对准确度不高等问题,利用询问与应答信号间时序的模式规律,提出了一种询问应答信号配对规则提取方法,实现了问答信号精准配对。以非合作侦察获得的询问和应答信号特征参数时间序列为基础,首先根据询问、应答节点定位信息和侦察节点位置信息估计时间窗,在此基础上以询问信号到达时间为起始,在应答信号序列中搜索时间窗范围内的应答信号,交叉构建询问-应答信号2-项候选项集;再采用DBSCAN(Density-based Spatial Clustering of Applications with Noise)算法对候选项集进行特征聚类并挖掘频繁项集,通过频繁项集中问答信号频率、到达时间、脉冲宽度等参数,提取信号时序和特征配对规则;最后利用规则进行问答信号配对。计算机仿真和实采数据验证了该方法的有效性,当设置时间窗大小符合信号传播时间差且规则偏差小于50%时,置信度可达90%以上。