光学侦察卫星及反侦察技术综述

引述了现代战争采用侦察卫星获取空间情报的关键性,并指出在侦察卫星中照相侦察卫星应用最多,功能最突出;进而叙述了照相侦察卫星的分类及其工作原理,给出了典型侦察卫星图形照片;阐述了光学照相卫星侦察技术发展现状;从另一方面,叙述了反卫星武器分类及其工作原理和反卫星技术发展现状．预示未来战争中,照相侦察卫星将成为重要的作战信息源,为争夺空间优势,反卫星武器的竞赛将愈演愈烈,越来越多的国家将会拥有侦察卫星和发展反卫星武器。     

Complex behavior of the conductance of quantum wires with a long quantum-dot array

We consider electron transport through a quantum wire with an attached quantum-dot array, when the number of dots is large. To this end, we use a noninteracting Anderson Hamiltonian. The conductance at zero temperature shows a complex behavior as a function of the Fermi energy. In particular, two well-defined energy regions are observed. Far from the site-energy of the quantum dots, the conductance depends smoothly on the Fermi energy. On the contrary, at the center of the band the conductance develops an oscillating pattern with resonances and antiresonances due to constructive and destructive interference in the ballistic channel, respectively. We discuss analytically in detail the physical origin of this complex behavior.     

Proper Framework for the Application of Power Management Algorithms

A power aware system can reduce its energy dissipation by dynamically powering off during idle periods and powering on again upon a new service request arrival. We minimize the dissipated energy, by selecting the optimal waiting interval before powering off, under consideration of the expected time of the next arrival. This approach has been already proposed in the past, using the idle times distribution, rather than the interarrival periods captured at the moment of service completion. Algorithms proposed in the literature utilize the history of idle periods or assume a vanishing service time. There has been no clear proposition on how service time affects the time instance of our power off decision; rather, whenever service time has been significant, a “blurred” image of the system’s characteristic and a corresponding approximated optimal policy occurred. We clearly show analytically and experimentally that the idle times distribution should not be used as a primary design input, since it is the product of two separate inputs; the interarrival times and the service times. We give insight to our problem, using a mechanical equivalent established at the moment of service completion of all pending requests and show through analytical examples how service time affects our power-off decision. We explain the paradox of being advantageous to wait for intervals more than the shutdown threshold (which is a system characteristic) and show how the introduction of idle period lengths instead of interarrival periods “blurs” the input distribution, leading to non-optimal decisions. Our contribution is to define and solve the proper problem, solely relying on the interarrival distribution. Further, we examine the problem under the framework of competitive analysis. We show how the interarrival distribution that maximizes the competitive ratio, being an exponential distribution, intervenes with power management; it renders the optimization procedure worthless through its “memoryless property”. Exponential interarrivals, irrespective of the service time pattern, are the marginal case where we cannot obtain energy gains. In all other cases the framework we promote ensures considerable advantages compared to other approaches in the literature. Moreover, it leads to a self contained module, implementable in software or hardware, which is based on an iterative formula and thus reduces power management calculations significantly. Here we exploit all operational features of the problem in proposing an implementation which spreads computations over the whole of the waiting period. We extensively compare our results numerically both against claimed expectations and against previous proposals. The outcome fully supports our framework as the one most appropriate for the application of power management.Part of this work has been supported by the EU IST-2001-34157 project PACKWOMAN (Power Aware Communication for Wireless Optimised Personal Area Networks).     

基于无线传输的智能路灯控制系统设计

针对目前城市道路照明管理系统还是以手动或定时控制为主,既浪费电能,又难以及时维修管理的问题。文中设计了基于GPRS、ZigBee 无线传感网络以及信息管理技术的城市路灯控制系统方案,以实现对路灯的智能控制,其中核心部分主要由信息管理平台、数据库、网络协调器和路灯控制器设计。用户远程监测路灯状态,且可为路灯设置合适的工作模式。通过对系统功能和性能进行测试表明,文中设计的系统与传统定时控制方式相比,在提高管理效率的同时至少还能节省13%的电能。     

Variable length signal detection framework for cognitive radio systems

The cognitive radio (CR) system opportunistically utilizes the frequency bands temporally unoccupied by the primary user. In the CR system, the energy or cyclostationary detector is used to detect the primary user signal. For protecting the primary user tightly, the signal detection time can be very long, which leads to inefficiency in the CR system. Thus, we propose a novel signal detector that greatly reduces the average detection time. The proposed detector periodically decides whether it terminates the detection process or receives more input signal for more information. Therefore, the proposed detector has variable detection time. We will call the proposed detector the variable length signal detector (VLSD). The VLSD is designed by using a partially observable Markov decision process framework for optimal performance. We present the numerical results showing that the VLSD requires much smaller average detection time compared with the traditional fixed length signal detector to achieve a given detection error probability. Copyright © 2012 John Wiley & Sons, Ltd.     

A Modified Method Based on the Discrete Sliding Norm Transform to Reduce the PAPR in OFDM Systems

Orthogonal frequency division multiplexing (OFDM) is a modulation technique that allows the transmission of high data rates over wideband radio channels subject to frequency selective fading by dividing the data into several narrowband and flat fading channels. OFDM has high spectral efficiency and channel robustness. However, a major drawback of OFDM is that the peak‐to‐average power ratio (PAPR) of the transmitted signals is high, which causes nonlinear distortion in the received data and reduces the efficiency of the high power amplifier in the transmitter. The most straightforward method to solve this problem is to use a nonlinear mapping algorithm to transform the signal into a new signal that has a smaller PAPR. One of the latest nonlinear methods proposed to reduce the PAPR is the L₂‐by‐3 algorithm, which is based on the discrete sliding norm transform. In this paper, a new algorithm based on the L₂‐by‐3 method is proposed. The proposed method is very simple and has a low complexity analysis. Simulation results show that the proposed method performs better, has better power spectral density, and is less sensitive to the modulation type and number of subcarriers than L₂‐by‐3.     

Response time and mechanism of Pd modified TiO2 gas sensor

In this work, gas response properties of Pd modified TiO₂ sensing films are discussed when exposed to H₂ and O₂. TiO₂ films are surface modified in PdCl₂-containing solution by the dipping method and treated for different treatment times to get different surface states. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and Kröger–Vink defect theory are used to characterize the sensing films. The gas response properties indicate that the sensor response time which related to the rate of change of sensor resistance is affected by the activation energy (E). In particular, the sensor treated at 900 °C for 2 h exhibits a response time of about 20–240 ms when exposed to H₂ and 40–130 ms when exposed to O₂ at 500–800 °C.     

无线中继协作中LDPC码与网络编码联合设计探讨

在研究无线协作移动通信的基础上,利用LDPC(Low Density Parity Check)码(多层LDPC码或者速率兼容LDPC码),针对多接入协作系统,讨论如何将其与网络编码(线性网络编码、随机网络编码)结合的设计方案,从而提高通信系统性能和吞吐量,具有极高的理论价值和应用前景。