基于随机变量相似度的ICA方法

从随机变量(微分)熵的概念出发,定义了随机变量的相似度,讨论了用求相似度极点的方法实现观测数据线性组合非高斯性最大化,从而串行估计独立分量分析(ICA)模型中的独立分量的原理和算法。对非多项式矩定理进行了更为一般化的证明,以此定理为根据阐明了以一般的非二次型光滑偶函数的数学期望近似代替相似度的可行性。给出梯度算法中的符号因子计算公式,避免了现有的相应算法中符号因子计算公式与目标函数之间的矛盾。通过与极大似然ICA方法对比,表明所定义的相似度就是在预白化条件下单个源变量的极大似然函数。     

A new DOA estimation approach for QPSK Alamouti STBC using ICA technique‐based PSO algorithm

Alamouti space time block code (STBC) has been a revolutionary technology in multiple‐input multiple‐output (MIMO) wireless communication since it provides full transmission diversity. To reduce a multi‐path effect and a consumed power, the dynamic beam‐forming technique should be used to enable antennas focusing on a particular area. The aim of this paper is how to reduce the computational complexities of independent component analysis (ICA) and speed up the algorithm used in estimating the direction of arrival (DOA) angles. First, we derive a simple formula to reduce the number of unknown DOA to be one only. Then, real‐imaginary (Re‐Im) decomposition for MIMO system is used to reduce the computational complexities of ICA algorithm. The novel criteria used in this paper is that the kurtosis measuring for the extracted source will be minimum at one of the unknown values of DOA angles. Finally, particle swarm optimization (PSO) will be used as an effective tool to locate the DOA angle positions that minimize the kurtosis measuring. Performance analysis of the proposed approach with QPSK Alamouti STBC in MIMO channel was implemented using MATLAB. The validated criterions for the new approach were first examined. Then, root‐mean‐square‐error (RMSE) was employed to test the proposed approach at different SNR levels. The main parameters that influence on this approach were evaluated. It was found that superior performance could be obtained at ?DOA > 10⁰ when antenna spacing set to be λ/2 using at least 10³ snapshots. The important point observed during simulations was computational complexity (and latency) of the proposed approach was reduced to the minimum by employing Re‐Im decomposition model and PSO algorithm. Consequently, this approach is very efficient for hardware implementations.     

基于加权模糊解耦策略的注塑机料筒温度控制

着重研究注塑机的料筒温度对象系统,指出非线性、大滞后、强耦等特性.并针对强耦合性,提出基于加权模糊解耦机制的注塑机料筒温度单回路控制方案,以及相应的控制策略.这种控制方案将复杂的多输入/多输出系统分解成多个独立的单回路系统,从而减小了控制系统实施多变量控制的复杂度,提高了控制器的实时性.     

声矢量阵远程定向技术(一)--新的协方差矩阵生成方法

MUSIC等子空间类DOA(direction of arrival)估计算法,以其较高的分辨能力和相对较小的计算量而颇受关注．但如果将其简单引用到声矢量阵中,将矢量传感器(AVS)的振速信息仅仅作为独立的阵元来处理,则并没有充分利用AVS 中声压和振速的相干性,以及由此带来的抗各向同性噪声能力．基于AVS中声压和振速的相干性原理,提出了一种新的声矢量阵协方差矩阵牛成方法．该方法完全利用了AVS的平均声强抗噪原理,具有较强的抗各向同性噪声能力,可将子空间类DOA估计方法与声矢量阵技术更为有效地结合起来,实现远程高分辩DOA估计．理论分析和基于湖试数据的仿真实验证明了新方法的有效性．     

A cluster‐chain‐based context transfer mechanism for fast basic service set transition in the centralized wireless LAN architecture

The emergence of centralized WLAN architectures is proposed to solve the problems of large scale deployment of WLANs. In the centralized WLAN, access point (AP) is split into two pieces: wireless termination point (WTP), and access controller (AC). An AC is the centralized controller for a large number of WTPs. A station (STA) has the demand to move from one WTP to another within the same extended service set (ESS). Such behavior is called a basic service set (BSS) transition. In this paper, we propose the cluster‐chain‐based context (C³T) mechanism with a cluster member selection (CMS) algorithm to reduce the BSS transition delay in the centralized WLAN architecture. The proposed mechanism can have lower signaling cost for context transfer and does not have the ping‐pong problem comparing with the existing context transfer schemes in terms of BSS transition, such as the proactive neighbor caching (PNC) scheme, the configuration and provisioning for wireless APs handoff protocol (CAPWAPHP), and so on. Furthermore, since the original 802.11r fast BSS transition does not specify how to work in the centralized WLAN architecture, we incorporate the C³T mechanism into IEEE 802.11r that works in the centralized WLAN architecture. Copyright © 2008 John Wiley & Sons, Ltd.     

Collision‐interference cancellation for space‐based AIS using beam synthesis technology with optimal sparse linear array

A basic problem in the space‐based automatic identification system (AIS) is the low probability of detecting messages because ships' messages arrive at the receiver in the same time slot. In this study, sparse linear array optimal beam synthesis (SLA–OBS) technology is proposed to improve the capture ability of AIS messages by forming a narrow beam pattern that points in the direction of the desired AIS messages. To capture the desired signal within the narrow beam pattern, the directions of arrival (DOA) and the number of sources from ships are first estimated. Then, the ideal narrow beam pattern and minimal number of array elements are achieved synchronously with the CPLEX optimal tool. The simulations show that the message detection probability with the proposed method is greater than 95%, even when the situations are very serious, whereas the number of sparse linear antennas is small (no more than six). Copyright © 2015 John Wiley & Sons, Ltd.     

一种主瓣干扰环境下的雷达目标参数"同维"稀疏估计方法

主瓣干扰对抗一直以来是雷达领域的难题之一，给雷达的探测、跟踪和识别带来了严重威胁.对此，本文提出了一种主瓣干扰环境下的雷达目标参数"同维"稀疏估计方法，可有效抑制主瓣干扰并估计目标距离、角度参数.所提方法首先对接收信号进行阻塞矩阵预处理，可在抑制主瓣干扰的同时保持目标回波在各阵元之间的相位关系，即保留了目标的角度信息；然后对预处理后的数据进行空域波束合成并脉压，可估计目标的距离参数信息；最后，根据得到的目标距离估计，截取预处理数据中目标附近的数据，并对其进行稀疏恢复估计目标角度参数.所提方法即可应用于面阵，也可应用于线阵，其优势在于可以在空域任何一维上抑制主瓣干扰，并同时估计目标在空域两维上的角度.尤其是当目标与干扰的某一维空域角度相同时，所提方法仍然可以同时估计目标的方位、俯仰角.     

一种基于均匀分布型的MIMO OFDM系统最优导频设计

本文提出了一种针对存在虚子载波的MIMO OFDM系统下基于均匀分布型的最优导频设计,该设计通过采用时域最小二乘信道估计(TD-LS-CE),且以数据子载波的频域信道响应的均方误差为准则,在最大化带宽效率的前提下,对各发送天线上均匀分布型的导频子载波进行功率最优化分配,并推导了其闭式解。最后,仿真结果表明该最优导频序列在MSE、BER性能方面均优于传统的移相正交导频序列和等功率分配的交错正交导频序列。     

采用混合核支持向量机的DOA估计

人工神经网络( ANN)进行建模时通常需要准备大量的数据样本,同时网络结构一般都比较复杂;而采用支持向量机( SVM)进行建模时,不同核函数有不同的效果,各有利弊,且选取SVM模型参数的理论支撑尚不完整。为了解决这些问题,提出了一种基于混合核函数的支持向量机来改善来波到达角( DOA)的估计性能,并结合二进制粒子群算法( PSO)来对混合核函数进行参数寻优。该混合核函数由全局核函数和局部核函数构成,提高了SVM的泛化能力和学习能力。首先通过拟合多项式函数,验证了该混合核SVM的有效性。将该方法用于DOA估计建模,在不同信噪比和快拍数下,通过与径向基函数( RBF)神经网络、基于各单一核函数的SVM和MUSIC算法预测结果对比,混合核SVM均方差有所降低,提高了DOA估计的精度且有更好的稳定性。     

Time domain leakage in DFT‐based channel estimation for OFDM systems with guard bands

In this paper, a mathematical analysis of the time domain leakage problem in the discrete Fourier transform (DFT) based channel estimation technique is presented. The time domain leakage is because of the absence of pilots in the guard band. Several solutions to this problem were previously proposed based on reducing the leakage in the frequency domain. These solutions significantly increase the receiver complexity. In this paper, the root cause of the leakage problem is linked to the time domain and a modification is proposed carrying slight additional complexity over the conventional DFT‐based estimator. Performance evaluation is assessed in terms of the bit error rate and the mean square error. The proposed modification significantly decreases the error floor of the conventional DFT‐based channel estimation technique. In addition, its performance is comparable to other more complex techniques recently proposed.Copyright © 2013 John Wiley & Sons, Ltd.     

Adaptive frequency‐hopping schemes for CR‐based multi‐link satellite networks

In this paper, we study two dynamic frequency hopping (DFH)–based interference mitigation approaches for satellite communications. These techniques exploit the sensing capabilities of a cognitive radio to predict future interference on the upcoming frequency hops. We consider a topology where multiple low Earth orbit satellites transmit packets to a common geostationary equatorial orbit satellite. The FH sequence of each low Earth orbit–geostationary equatorial orbit link is adjusted according to the outcome of out‐of‐band proactive sensing scheme, performed by a cognitive radio module in the geostationary equatorial orbit satellite. On the basis of sensing results, new frequency assignments are made for the upcoming slots, taking into account the transmit powers, achievable rates, and overhead of modifying the FH sequences. In addition, we ensure that all satellite links are assigned channels such that their minimum signal‐to‐interference‐plus‐noise ratio requirements are met, if such an assignment is possible. We formulate two multi‐objective optimization problems: DFH‐Power and DFH‐Rate. Discrete‐time Markov chain analysis is used to predict future channel conditions, where the number of states are inferred using k‐means clustering, and the state transition probabilities are computed using maximum likelihood estimation. Finally, simulation results are presented to evaluate the effects of different system parameters on the performance of the proposed designs.     

A probabilistic‐based approach for direction‐of‐arrival estimation and localization of multiple sources

This article contributes to science at two points. The first contribution is at a point of introducing a novel direction‐of‐arrival (DOA) estimation method which based on subspaces methods called Probabilistic Estimation of Several Signals (PRESS). The PRESS method provides higher resolution and DOA accuracy than current models. Second contribution of the article is at a point of localizing the unknown signal source. The process of localization achieved by using DOA information for the first time. The importance of localization exists in a large area of engineering applications. The aim is to determine the location of multiple sources by using PRESS with minimum effort of computation. We used the maximum probabilistic process in this study. Initially, all the signals are collected by the array of sensors and accurately identified using the proposed algorithm. The receiver at the best in test estimates the source location using only the knowledge of the geographical latitude and longitude values of the array of sensors. Several test points with an accurately calculated angle of arrival enable us to draw linear lines towards the transmitter. The transmitter location can be accurately identified with the line of interceptions. Simulation and numerical results show the outstanding performance of both the DOA estimation method and transmitter localization approach compared with many classical and new DOA estimation methods. The PRESS localization method first tested at 19°, 26°, and 35° with an signal‐to‐noise ratio (SNR) value of ‐5 dB. The PRESS method produced results with an extremely low bias of 0 and 0.00080°. The simulation tests are repeated and produced results with zero bias, which give the exact location of the unknown source.     

Tight bounds for the first order Marcum Q‐function

In this paper, we develop new bounds for the first order Marcum Q‐function, which are extremely tight and tighter than any of the existing bounds to the best of our knowledge. The key idea of our approach is to derive refined approximations for the 0th order modified Bessel function in the integration region of the Marcum Q‐function. The new bounds are very tight and can serve as an effective means in bit error rate (BER) performance analysis for non‐coherent demodulation in digital communication. Copyright © 2010 John Wiley & Sons, Ltd.     

OUR: Optimal Update‐based Replacement policy for cache in wireless data access networks with optimal effective hits and bandwidth requirements

In mobile wireless data access networks, remote data access is expensive in terms of bandwidth consumption. An efficient caching scheme can reduce the amount of data transmission, hence, bandwidth consumption. However, an update event makes the associated cached data objects obsolete and useless for many applications. Data access frequency and update play a crucial role in deciding which data objects should be cached. Seemingly, frequently accessed but infrequently updated objects should have higher preference while preserving in the cache. Other objects should have lower preference or be evicted, or should not be cached at all, to accommodate higher‐preference objects. In this paper, we proposed Optimal Update‐based Replacement, a replacement or eviction scheme, for cache management in wireless data networks. To facilitate the replacement scheme, we also presented two enhanced cache access schemes, named Update‐based Poll‐Each‐Read and Update‐based Call‐Back. The proposed cache management schemes were supported with strong theoretical analysis. Both analysis and extensive simulation results were given to demonstrate that the proposed schemes guarantee optimal amount of data transmission by increasing the number of effective hits and outperform the popular Least Frequently Used scheme in terms of both effective hits and communication cost. Copyright © 2011 John Wiley & Sons, Ltd.     

Cluster‐based emergency message dissemination strategy for VANET using V2V communication

Data dissemination in vehicular ad hoc network (VANET) is emerging as a critical area of research. One of the challenges posed by this domain is the reliability of connection, which depends on many parameters, such as the bandwidth consumption, transmission delay, and data quality of service (QoS). Dissemination of emergency messages is very critical since the network topology is changing frequently and rapidly, which leads to data loss. So, it is necessary to develop new protocols and enhance dissemination schemes in VANET to avoid more emergencies and hazards cases. In this regard, we have proposed a new strategy, which consists of data handling before dissemination process as the first step of our scheme. In this phase, the original message is optimized in order to reduce the number of exchanged packets. The second part of this proposition consists of constructing fast and stable clusters to improve the message delivery time and to procure efficient bandwidth consumption. This approach is based on a Fitness function, which takes into account different parameters such as the transmission period, the connectivity degree, the relative velocity, and the link lifetime validity. Since exchanging data in VANET is an important process, routing phase is proposed to perform data exchange among clusters. It is based on a rapid and real‐time heuristic (real‐time adaptive A* [RTAA*]). To evaluate the reliability of the proposed approach, an urban scenario is used with different simulation parameters. The simulation results show that our proposed approach presents a better stability and efficiency performance compared with the discussed approaches. The proposed approach improves the performance of cluster duration (5% ? 25%), delivery rate (2% ? 8%), and the overhead (5% ? 35%) on average compared with the discussed approaches.     

Experiences with SoftToken: a token‐based coordination layer for WLANs

This paper presents our experiences with SoftToken protocol, a new contention‐free medium access control protocol for wireless local area network. This new mechanism adds a token‐passing procedure on top of Institute of Electrical and Electronics Engineers 802.11 for coordinating transmissions and avoiding collisions. With this extension, it becomes possible to offer differentiated services in a deterministic manner. In this paper, we provide a thorough performance evaluation of SoftToken in terms of its scalability, robustness and efficiency in comparison with Institute of Electrical and Electronics Engineers 802.11 and a time division multiple access (TDMA)‐based Wi‐Fi extension called Soft‐TDMA. Our evaluation is based on experiments run on different test beds covering different scenarios in a wired virtual network environment and practical wireless environments supporting different types of traffic. The results show that SoftToken indeed provides better QoS performance in scenarios that require service differentiation (e.g. mixed voice over Internet protocol and best effort traffic scenarios). Copyright © 2013 John Wiley & Sons, Ltd.     

A provably secure biometrics and ECC‐based authentication and key agreement scheme for WSNs

Wireless sensor networks (WSNs) underpin many applications of the Internet of Things (IoT), ranging from smart cities to unmanned surveillance and others. Efficient user authentication in WSNs, particularly in settings with diverse IoT device configurations and specifications (eg, resource‐constrained IoT devices) and difficult physical conditions (eg, physical disaster area and adversarial environment such as battlefields), remains challenging, both in research and in practice. Here, we put forth a user anonymous authentication scheme, relying on both biometrics and elliptic curve cryptography, to establish desired security features like forward and backward secrecy. We then make use of the Random‐or‐Real (RoR) model to prove the security of our scheme. We have implemented the proposed scheme in an environment compatible with WSNs. We show after conducting the comparison of the proposed scheme with some recent and related existent schemes that it satisfies various essential and desirable security attributes of a WSN environment. We conclude that the proposed scheme is suitable for the WSN scenario demanding high security.     

FPS‐MAC: Fuzzy priority scheduling‐based MAC protocol for intelligent monitoring systems

Recent advances in microelectronics have encouraged the implementation of a wireless sensor network (WSN) in intelligent monitoring systems (IMSs). The IMS for time‐critical applications requires timely and reliable data delivery without sacrificing the energy efficiency of the network. This paper proposes FPS‐MAC, a fuzzy priority scheduling‐based medium access control protocol, designed for event critical traffic in hierarchical WSN. The FPS‐MAC allows time‐critical event traffic to opportunistically steal the data slots allocated for periodic data traffic in event‐based situations. Additionally, a fuzzy logic‐based slot scheduling mechanism is introduced to provide guaranteed and timely medium access to emergency traffic load and ensures the quality‐of‐service (QoS) requirements of IMSs. Both analytical and simulation results for data throughput, energy consumption, and transmission delay of FPS‐MAC, TLHA, E‐BMA, and BMA‐RR have been analyzed to demonstrate the superiority of the proposed FPS‐MAC protocol.     

Are transverse phonons important for Γ - X-intervalley scattering?

We employ the rigid pseudo-ion method to calculate the q-dependence of intervalley deformation potentials for GaP from the Γ-point to the X-valley. We find that the fast transverse acoustic phonon (which cannot couple to the symmetry point X) becomes as important along the XW-direction as the longitudinal acoustic phonon (which is allowed at X). We have measured the temperature dependence of the lifetime broadenings of the E₀-gap of GaP with spectroellipsometry in order to obtain an effective intervalley phonon energy from which the relative contributions of the different phonon branches can be determined, but difficulties arise as intervalley and intravalley (Fröhlich) exciton-phonon interaction both contribute to the broadenings.     

SRGH: A secure and robust group‐based handover AKA protocol for MTC in LTE‐A networks

Machine‐type communication (MTC) is defined as an automatic aggregation, processing, and exchange of information among intelligent devices without humans intervention. With the development of immense embedded devices, MTC is emerging as the leading communication technology for a wide range of applications and services in the Internet of Things (IoT). For achieving the reliability and to fulfill the security requirements of IoT‐based applications, researchers have proposed some group‐based handover authentication and key agreement (AKA) protocols for mass MTCDs in LTE‐A networks. However, the realization of secure handover authentication for the group of MTCDs in IoT enabled LTE‐A network is an imminent issue. Whenever mass MTCDs enter into the coverage area of target base‐station simultaneously, the protocols incur high signaling congestion. In addition, the existing group‐based handover protocols suffer from the huge network overhead and numerous identified problems such as lack of key forward/backward secrecy, privacy‐preservation. Moreover, the protocols fail to avoid the key escrow problem and vulnerable to malicious attacks. To overcome these issues, we propose a secure and robust group‐based handover (SRGH) AKA protocol for mass MTCDs in LTE‐A network. The protocol establishes the group key update mechanism with forward/backward secrecy. The formal security proof demonstrates that the protocol achieves all the security properties including session key secrecy and data integrity. Furthermore, the formal verification using the AVISPA tool shows the correctness and informal analysis discusses the resistance from various security problems. The performance evaluation illustrates that the proposed protocol obtains substantial efficiency compared with the existing group‐based handover AKA protocols.