基于连接两段激活模型的IEEE 802.16接纳控制算法

IEEE802.16系统中数据的传输是面向连接的,连接的建立服从两段激活模型。针对系统空闲资源耗尽但还为已接纳而未被激活的业务预留资源这一情况,该文提出了一种适当借用此预留资源去接纳新的立即被激活业务的接纳控制算法,并建立了此算法的3维马尔可夫链模型,进行了理论分析提出了找寻此算法中使用的两个门限的搜索方法。仿真结果表明,该接纳控制算法能显著地降低新业务阻塞率,提高系统的带宽利用率,已接纳业务的激活成功率只有少许下降。     

大型空间遥感器动力学试验

大型空间遥感器结构复杂、重量大,在研制过程中,给地面动力学环境试验工装的设计带来很大的困难.振动工装是振动试验的传力部件,将振动台与遥感器连接起来,其性能直接影响到振动试验的真实程度和可靠程度.本文论述了遥感器振动工装研制及动力学试验过程.正弦振动和随机振动结果表明,振动台的振动输入条件与工装对遥感器的输入条件基本一致...     

无线局域网室外覆盖路径损耗计算分析及规划布局建议

介绍了无线局域网(WLAN)所用IEEE 802.11x标准的技术特点和频率特性,选择修正的COST231 HATA无线信号传播模型对信号路径损耗进行计算,以图表的形式描述了WLAN所在频段(2.4 G-Hz)的空间信道衰落特征.通过计算得出结论:随着传输距离和AP/STA天线高度差的增加,WLAN无线信道路径损耗将迅...     

Inkjet and microcontact printing of functional materials on foil for the fabrication of pixel-like capacitive vapor microsensors

The work presented demonstrates the utilization of micro-contact printing of self-assembled monolayers (SAMs) of gold nanoparticles (NPs) to pattern the porous thin metallic film composing the top electrode of an ultra-fast capacitive relative humidity sensor based on miniaturized parallel-plates electrodes. The rest of the device, which occupies an area of only 0.0314 mm², is fabricated by inkjet printing stacked individual drops of functional materials, namely gold NPs for the bottom electrode and a polymeric humidity sensing layer, on a polymeric foil. Compared to other printing methods, the use of microcontact printing to pattern the top electrode enables the additive transfer of a solvent-free metallic layer that does not interact chemically with the sensing layer, permitting the thinning of the latter without risk of short-circuits between electrodes, and broadening the range of usable sensing materials for detection of other gases. Thinning the sensing layer yields to ultra-fast response devices with high values of capacitance and sensitivity per surface area. The fabrication process is compatible with low heat-resistant polymeric substrates and scalable to large-area and large-scale fabrication, foreseeing the development of low-cost vapor sensing sheets with high space–time resolution, where every sensor would correspond to a pixel of a large array.     

Performance analysis of cooperative spatial multiplexing networks with AF/DF relaying and linear receiver over Rayleigh fading channels

Cooperative spatial multiplexing (CSM) system has played an important role in wireless networks by offering a substantial improvement in multiplexing gain compared with its cooperative diversity counterpart. However, there is a limited number of research works that consider the performance of CSM systems. As such, in this paper, we have derived exact performance of CSM with amplify‐and‐forward and decode‐and‐forward relays in terms of outage capacity and ergodic capacity. We have shown that CSM systems yield a unity diversity order regardless of the number of antennas at the destination and the number of relays in the networks, which is the direct result of diversity and multiplexing gain trade‐off. Our analytical expressions are corroborated by Monte‐Carlo simulations. Copyright © 2013 John Wiley & Sons, Ltd.     

Performance analysis of multiple‐input multiple‐output relay networks based impulse radio ultra‐wideband

In this paper, we study the performance of time hopping pulse position modulation for impulse radio ultra‐wideband. We consider relay network applying decode‐and‐forward protocol. The channels between nodes adopt the IEEE 802.15.4a norms. The bit error rate performance is analyzed considering the effect of interference. Our results show significant improvement due to the diversity gain provided by the relay nodes. However, the performance is limited when multiple access interference (MAI) is present. To combat the MAI effect and further improve the detection reliability, we propose to use antenna selection at the relay. The relay receiver is assumed to be equipped with multiple antennas, and only the best antenna is selected. This is shown to improve the performance in the presence of MAI and improve the diversity gain.Copyright © 2013 John Wiley & Sons, Ltd.     

An altruistic cross‐layer recovering mechanism for ad hoc wireless networks

Video streaming services have restrictive delay and bandwidth constraints. Ad hoc networks represent a hostile environment for this kind of real‐time data transmission. Emerging mesh networks, where a backbone provides more topological stability, do not even assure a high quality of experience. In such scenario, mobility of terminal nodes causes link breakages until a new route is calculated. In the meanwhile, lost packets cause annoying video interruptions to the receiver. This paper proposes a new mechanism of recovering lost packets by means of caching overheard packets in neighbor nodes and retransmit them to destination. Moreover, an optimization is shown, which involves a video‐aware cache in order to recover full frames and prioritize more significant frames. Results show the improvement in reception, increasing the throughput as well as video quality, whereas larger video interruptions are considerably reduced. Copyright © 2014 John Wiley & Sons, Ltd.     

Cooperative Q‐learning techniques for distributed online power allocation in femtocell networks

In this paper, we address the problem of distributed interference management of femtocells that share the same frequency band with macrocells using distributed multi‐agent Q‐learning. We formulate and solve two problems representing two different Q‐learning algorithms, namely, femto‐based distributed and sub‐carrier‐based distributed power controls using Q‐learning (FBDPC‐Q and SBDPC‐Q). FBDPC‐Q is a multi‐agent algorithm that works on a global basis, for example, deals with the aggregate macrocell and femtocell capacities. Its complexity increases exponentially with the number of sub‐carriers in the system. Also, it does not take into consideration the sub‐carrier macrocell capacity as a constraint. To overcome these problems, SBDPC‐Q is proposed, which is a multi‐agent algorithm that works on a sub‐carrier basis, for example, sub‐carrier macrocell and femtocell capacities. Each of FBDPC‐Q and SBDPC‐Q works in three different learning paradigms: independent (IL), cooperative (CL), and weighted cooperative (WCL). IL is considered the simplest form for applying Q‐learning in multi‐agent scenarios, where all the femtocells learn independently. CL and WCL are the proposed schemes in which femtocells share partial information during the learning process in order to strike a balance between practical relevance and performance. We prove the convergence of the CL paradigm when used in the FBDPC‐Q algorithm. We show via simulations that the CL paradigm outperforms the IL paradigm in terms of the aggregate femtocell capacity, especially in networks with large number of femtocells and large number of power levels. In addition, we propose WCL to address the CL limitations. Finally, we evaluate the robustness and scalability of both FBDPC‐Q and SBDPC‐Q, against several typical dynamics of plausible wireless scenarios (fading, path loss, random activity of femtocells, etc.). We show that the CL paradigm is the most scalable to large number of femtocells and robust to the network dynamics compared with the IL and WCL paradigms. Copyright © 2014 John Wiley & Sons, Ltd.     

磁悬浮球系统中光电传感器的研究与设计

主要针对磁悬浮球系统中非接触式位移检测,依据感光器件的光伏效应原理,阐述了非接触式光电传感器的研究与设计,实现了光电信号测量微位移。通过磁悬浮球实验研究表明该传感器的精度(0.01mm)和响应速度(<0.1ms)均达到预期要求,从而给出了一种方便、低成本的位移检测方法。     

具有参数摄动的时滞Hopfield神经网络的鲁棒稳定性分析及吸引域的估计

研究一类具有参数摄动的时滞Hopfield神经网络模型的鲁棒稳定性.应用Lyapunov泛函法,给出了平衡点渐近稳定的充分条件.利用矩阵范数的性质及线性矩阵不等式(LMI)理论,又得到了两个便于计算和验证的推论.提供了一种估计网络渐近稳定平衡点吸引域的方法,并详尽地分析了吸引域对神经网络实现联想记忆的影响.数值例子进一步证明了结论的有效性.