相干接收技术在低速ULH系统中的应用研究

对DP-QPSK(偏振复用正交相移键控)调制和相干接收技术在低速系统中的应用进行了研究,实现了2.67Gbit/s速率的实时传输。实验结果表明,DP-QPSK调制和相干接收技术对无中继ULH(超长跨距)光传输系统的OSNR(光信噪比)容限有优化作用。     

A new segmentation algorithm for videophone applications based onstereo image pairs

The stereo image pair of a speaking person in front of a stationary background taken by two CCD-cameras is used as an input scene for a new segmentation algorithm. The algorithm is based on the phase correlation technique which provides a disparity vector field. A brightness adjustment procedure is performed to provide stereo image pairs suited for the segmentation procedure. Then, a coarse segmentation into background and speaking person is made to achieve a reliable segmentation result. Finally, finer segmentation using a coarse-to-fine control strategy is performed only at the object boundaries. An application is demonstrated by applying a lowpass filter selectively to the background of input sequences for low bit rate image coding algorithms     

Capacity of cordless telephone systems, with discontinuous transmission

The muting of transmitters during periods of silence is shown to increase the voice capacity of a microcellular cordless telephone system. Both average and instantaneous cochannel interference models are considered and used to compare the grade of service of such a technique against that of a continuous transmission system.<>     

Traffic levels supportable by Telepoint systems using current cordless telephone technology

The traffic carrying capability of Telepoint systems utilising CEPT CT1 and CT2/CAI systems is predicted using computer simulation. This shows that a CT2/CAI based Telepoint system is capable of supporting significantly more traffic than a system based on CT1.<>     

Trends in cellular and cordless communications

The evolution of wireless information networks is traced from the present first generation systems to next century's third generation. The third generation is envisioned as a unified wireless access replacing the diverse and incompatible second-generation networks with a single means of wireless access to advanced information services. Four issues are examined: the goal a network is designed to achieve, network architecture, radio transmission technology, and the control channels that make it possible for wireless terminals and the remainder of the network to coordinate their operations. In the framework of these issues, present networks are described; the properties of four second-generation networks, GSM, IS-54, CT2, and DECT, are cited; and early work in progress at the Rutgers WINLAB is described. The latter is a packet-reservation multiple-access scheme that can be viewed as a combination of TDMA and slotted ALOHA     

Transmit antenna selection based strategies in MISO communication systems with low-rate channel state feedback

The performance of multiple-antenna communication systems is known to critically depend on the amount of channel state information (CSI) available at the transmitter. In the low-rate CSI feedback case, an important problem is what kind of information should be submitted to the transmitter in each feedback cycle and what is the optimal transmission strategy in this case. In this paper, we address this problem in the multiple-input single-output (MISO) case by analytically comparing the bit error rate (BER) performance of different low-rate feedback based transmitter strategies involving various combinations of transmit antenna selection, Alamouti's spacetime coding, and adaptive power allocation.     

低速率DDoS攻击的仿真和特征提取

低速率分布式拒绝服务(LDDoS,low-rate distributed denial of service)攻击是一种新型的DDoS攻击方式.LDDoS具有流量小和隐蔽性强的特点,现有的DDoS攻击检测方法不能正确发现LDDoS攻击流量.根据LDDoS攻击流量呈现周期性的特点,采用缓存队列占有率统计的方法,重点研究了受害目标路由器的缓存队列,分别统计分析了正常和攻击流量的占有率,并在NS-2环境中进行了仿真实验,成功提取了LDDoS攻击流量上的2个特征,提高了LDDoS攻击的检测率.     

共享网络和双模无缝网络

GSM/GPRS与WCDMA双模无缝网络是绝大多数GSM运营商推出3G服务时的选择.在双模手机支持下,WCDMA能利用现有GSM/GPRS网络提供全面覆盖和无缝服务.而共享网络则是拥有3G运营证的运营商之间共享部分或全部网络基础设施,同时仍能提供不同业务、应用,保持竞争关系的一种方案.它能节省初期建网投资,加快网络推出速度,加大初期覆盖范围.另一方面,它能在不浪费前期投资的条件下,根据业务发展的需要,逐步过渡到两个完全独立的网络.     

一种双模对讲机的研究与设计

介绍了一种工作在模拟和数字两种模式的对讲机,用于满足对讲机从模拟向数字平缓过渡的需求。系统采用了微控制器与数字信号处理器相结合的方案,具有较好的实用性和可拓展性。着重对系统整体架构,微控制器控制,锁相环电路,发送和接收工作流程进行了介绍。对数字处理进行了阐述。采用TMS320VC5509为核心实现数字部分,不仅可以简化硬件电路,降低成本和功耗,而且可以方便地根据需要选择不同数字处理算法。     

飞机监视应用系统、航迹融合与ADS-B In应用

来自地面、他机和本机的多种航迹数据源为飞机的监视系统带来了新的应用,这些应用在飞行的各个阶段,辅助飞行员更加安全、有效地操作,减轻管制员对每架飞机的负荷。介绍了飞机监视应用系统的架构、组成和作用,讨论了航迹融合的过程以及对多种数据源的整合,总结了建立在ADS-B In基础上的8种应用,梳理了飞机监视应用系统、航迹融合和ADS-B In之间的关系,对飞机监视应用形成了概略的认知。     

Recursive decoding and its performance for low-rate Reed-Muller codes

Recursive decoding techniques are considered for Reed-Muller (RM) codes of growing length n and fixed order r. An algorithm is designed that has complexity of order nlogn and corrects most error patterns of weight up to n(1/2-/spl epsiv/) given that /spl epsiv/ exceeds n/sup -1/2r/. This improves the asymptotic bounds known for decoding RM codes with nonexponential complexity. To evaluate decoding capability, we develop a probabilistic technique that disintegrates decoding into a sequence of recursive steps. Although dependent, subsequent outputs can be tightly evaluated under the assumption that all preceding decodings are correct. In turn, this allows us to employ second-order analysis and find the error weights for which the decoding error probability vanishes on the entire sequence of decoding steps as the code length n grows.     

On-chip pulsed terahertz systems and their applications

The generation and detection of guided wave terahertz (THz) transients in microstrip transmission line systems is demonstrated at both room and cryogenic (～ 4 K) temperatures using thin film low-temperature-grown GaAs (LT-GaAs) switches, excited by a 100 fs, 80 MHz repetition rate pulsed Ti:Sapphire laser. The characterisation of passive filter elements formed in the microstrip line is reported, together with their response to the application of dielectric loads of varying thickness at room temperature.     

Expert systems for power applications

The author briefly discusses expert systems and the incentives for producing them. He then goes on to discuss applications in the power industry including an energy management system for control of power generation, power transmission, and distribution networks. They are also used for power system security, voltage and transient stability, decisionmaking in design, and for planning scenarios. They are also used for process plant control     

Photonic systems for antenna applications

For well over a decade, research groups around the world have been investigating photonic devices for use in antenna, phased-array, and electromagnetic-field-sensor systems. Proposed applications include EMC monitoring, EMP measurements, anechoic-chamber calibration, novel antenna and array designs, remotely located antennas, and smart skins. Photonic antenna links allow immunity from electromagnetic interference, provide an extremely wide working bandwidth, and allow long cable runs with a minimum of loss. Developments in laser technology allow photonic-based links to have very low noise figures and high dynamic range. Opto-electronic devices are now being built in III-V semiconductors (GaAs, InP), which will ultimately lead to opto-electronic integration with MMIC devices. Photonic systems will revolutionize the way in which electromagnetic-measurement and antenna systems will be designed and built in the future. The paper presents an introduction to the types of photonic links and modulator systems available to the antenna engineer     

UWB通信系统简介

UWB(Ultra Wide Band)即超宽带通信,它使用大于0.5GHz或大于中心频率20%的带宽、通过微弱的脉冲信号进行通信,最大数据传输速率可以达到几十Mb/s～几百Mb/s。UWB与现有的无线技术的显著不同是不需要使用载波,而是通过发送纳秒级脉冲来传输数据,而且信号传输时的功耗只有几十μW。UWB在保证了高数据速率传输的同时解决了移动终端的功耗问题。因此它被认为是对目前被炒得沸沸扬扬的无线互联(Wi-Fi)技术最具竞争性的技术。UWB简介UWB技术多年来一直是美国军方使用的作战技术之一,如它可以实现穿墙视物等功能。这项技术在通信领域所具…     

一种双模波导滤波器及应用

基于波导谐振器模式分析理论,文中介绍了一种TM 双模波导谐振器,并采用该谐振器仿真设计了微波滤波器。该滤波器具有体积小、Q 值高、便于调试安装等特点。 滤波器谐振器采用了 TM120 及 TM210 双模设计,谐振器尺寸可以灵活设计,适用于多种需求。 文中采用电磁仿真软件进行了滤波器的设计及优化,并分析了多种物理结构,包括同轴结构输入输出滤波器、高阶滤波器及腔体谐振器平面排列结构的滤波器。 生产加工了一台 Ku 频段的滤波器,测试性能优良,测试数据和仿真数据一致性好。     

A comparative study on flood DoS and low-rate DoS attacks

Denial of service (DoS) attacks is a serious threat for the Internet. DoS attacks can consume memory, Computer processing unit (CPU), and network bandwidths and damage or shut down the operation of the resource under attack. In this paper, based on the taxonomy of DoS attacks, two typical types of DoS—flood DoS (FDoS) and low-rate DoS (LDoS) attacks, are studied on their generation principle, mechanism utilization, signature, impacts, and defense mechanisms. Simulation results illustrate that 1) FDoS is easy to be launched but its signature is easy to be detected. 2) LDoS organizes an average small quantity of traffic and it is stealthier. Comparison of LDoS with FDoS shed light on the emerging new features of DoS attacks and can make the detection and defense mechanisms more efficient.