WIRELESS BODY-AREA NETWORKS

The last decade has witnessed the convergence of three giant worlds:electronics,computer science and telecommunications.The next decade should follow this convergence in most of our activities with the generalization of sensor networks.In particular with the progress in medicine,people live longer and the aging of population will push the development of wireless person-     

半封闭压缩机故障分析

分类分析了引起压缩机故障的原因，包括液击、溢流、满液启动、润滑油不足、污染、过热等。     

箱梁大吨位预应力的锚端应力分析

本文以三滩黄河连续刚构件大桥为例 ,比较系统地进行了张拉力为 371 0 7kN锚固区的应力分析。通过对 0 # 、1 1 # 块在纵向预应力 ( 1 91 5j1 5 2 4mm)作用下的大量三维有限元分析 ,研究了混凝土表面与纵向的应力变化规律、局部承压强度及抗裂性能     

低温全封闭滚动转子式和半封闭活塞式制冷压缩机组的性能比较

半封闭活塞式制冷压缩机组和全封闭滚动转子式制冷压缩机组以其各自鲜明的特点得到了广泛的应用。本文分析了某种半封闭活塞式压缩机组和某种全封闭滚动转子式压缩机组的特点,对比了不同蒸发温度下的制冷量和输入功率及COP值,为实际应用打下了基础。     

简析低温地板辐射供暖

从低温地板辐射供暖机理出发,论述了低温地板辐射供暖系统的节能性、舒适性等特点,并对其经济性进行了分析。展望该供暖系统在中国的应用前景,指出低温地板辐射供暖是一种具有发展前途和推广价值的供暖方式。本文所述论点实属作者的见解,欢迎同行共同探讨。     

Energy-Efficient Large-Scale Antenna Systems with Hybrid Digital-Analog Beamforming Structure

A large-scale antenna system(LSAS) with digital beamforming is expected to significantly increase energy efficiency(EE) and spectral efficiency(SE) in a wireless communication system. However, there are many challenging issues related to calibration, energy consumption, and cost in implementing a digital beamforming structure in an LSAS. In a practical LSAS deployment, hybrid digital-analog beamforming structures with active antennas can be used. In this paper, we investigate the optimal antenna configuration in an N × M beamforming structure, where N is the number of transceivers, M is the number of active antennas per transceiver, where analog beamforming is introduced for individual transceivers and digital beamforming is introduced across all N transceivers. We analyze the green point, which is the point of maximum EE on the EE-SE curve, and show that the log-scale EE scales linearly with SE along a slope of-lg2/N. We investigate the effect of M on EE for a given SE value in the case of fixed NM and independent N and M. In both cases, there is a unique optimal M that results in optimal EE. In the case of independent N and M, there is no optimal(N, M) combination for optimizing EE. The results of numerical simulations are provided, and these results support our analysis.     

Matched Filter Based Spectrum Sensing When Primary User Has Multiple Power Levels

In this paper,we investigate the matched filter based spectrum sensing in a more reasonable cognitive radio(CR) scenario when the primary user(PU) has more than one transmit power levels,as regulated in most standards,i.e.,IEEE 802.11 Series,GSM,LTE,LTE-A,etc.This new multiple primary transmit power(MPTP) scenario is specialized by two different targets:detecting the presence of PU and identifying the power level.Compared to the traditional binary sensing where only the presence of PU is checked,SU may attain more information about the primary network(making CR more "intelligent") and design the subsequent optimization strategy.The key technology is the multiple hypothesis testing as opposed to the traditional binary hypothesis testing.We discuss two situations under whether the channel phase is known or not,and we derive the closed form solutions for decision regions and several performance metrics,from which some interesting phenomenons are observed and the related discussions are presented.Numerical examples are provided to corroborate the proposed studies.     

认知超宽带网络的容量分析和最优化

The integration of cognitive radio and Ultra wideband (UWB) networks has attracted lots of research interests. Cognitive UWB networks not only provide very high data rates but also guarantee the uninterrupted communication of primary system operated in the same frequency band. In this work, the problem of the capacity analyses of cognitive UWB networks is investigated. Different from the conventional cognitive spectrum sharing model which can only utilize the idle spectrum hole, the cognitive UWB system can...     

适用于无线通信的动态拓扑感知性P2P网络

 在无线信道环境下，如何解决逻辑拓扑与物理拓扑之间的失配是设计P2P网络的主要挑战之一。本文提出一种适用于无线系统的P2P组网协议。在该协议中，首先，新入网节点从其邻居节点处获得一个数值上相近的节点标号，从而实现网络的瞬时拓扑感知。当节点的位置改变时，它们向中心节点更新自己的位置信息。然后，在中心节点处将节点标号的最优分配转换为旅行商问题，并用模拟退火算法对旅行商问题进行最优化求解，得到优化标号序列。最后，由中心节点向网络广播更新信息，引导节点进行标号和数据交换，从而使无线P2P网络在任何时刻都具有拓扑感知性。仿真结果表明，在基于该协议的无线P2P网络中，文件的定位路径明显缩短，定位延时明显减小。     

基于非线性渐增原理获得抛物线型自相似脉冲的研究

采用理论推导和数值模拟相结合的方法研究了脉冲在指数渐增的非线性渐增光纤(NIF)中的自相似演化。结果表明,与双曲渐减的正色散渐减光纤(ND-DDF)类似,利用指数渐增的NIF也可获得具有严格线性啁啾的抛物线型自相似脉冲。同时深入研究了ND-DDF和NIF两种增益等效方式对自相似演化特性的影响,结果表明:1)等效增益决定了脉冲自相似演化的结果,等效方式决定了脉冲自相似演化进程快慢;2)在具有相等的等效增益条件下,脉冲在指数渐增NIF和双曲渐减ND-DDF中演化为相同的自相似脉冲,但是前者对脉冲的自相似演化更高效,即前者实现自相似演化所需光纤长度更短;3)两种增益等效方式所需光纤长度的关系是使得各自具有相同的光纤有效放大因子。