碰撞冲突下认知无线网络能量效率分析

在认知无线网络的实际应用中,对于一些能量受限的认知用户来说,提高认知无线网络的能量效率尤其重要。该文从最大化认知无线网络能量效率的角度出发,考虑当认知用户在发送数据时突然出现的主用户信号引起碰撞冲突的情况,提出了对感知时间和帧周期进行分别优化和联合优化的单目标最优化问题,并进行理论推导分析。同时,实验仿真验证了理论分析的正确性。结果表明,能量效率分别随感知时间和帧周期的增大而先增大后减小,存在一组最优感知时间和帧周期使能量效率最大化。      

RC4的密钥碰撞

RC4加密算法是密码学家RonRivest在1987年设计的序列密码算法,其密钥长度可变,接受1字节至256字节。RC4在二十世纪八十年代得到了大力发展,广泛应用于商业密码产品中,包括LotusNotes,苹果计算机的AOCE和Oracle安全SQL数据库。RC4的核心部分为可变的S盒。研究了RC4的密钥编制算法,从密钥的碰撞层面研究了RC4的密钥脆弱性,描述了在S盒为256字节时,两组不同密钥KI、K2怎样经过密钥编制算法生成了相同的初始状态,即发生了“密钥碰撞”。     

产生MD5碰撞的新的充分条件集

Wang Xiaoyun等(2005)给出了MD5能产生碰撞的一个充分条件集,并首次成功对MD5进行了碰撞攻击。Yuto Nakano等(2006)指出上述充分条件集中有16个条件是冗余的,并给出了其中14个条件冗余的原因。Liang Jie和Lai Xuejia(2005)指出Wang Xiaoyun等给出的充分条件集并非总能产生碰撞,并增加新的条件使之总能产生碰撞,同时提出了一个新的碰撞攻击算法。本文证明了Yuto Nakano等给出的16个冗余条件中有两个并不冗余,且Liang Jie和Lai Xuejia增加的新条件中有两个是冗余的,指出Liang Jie和Lai Xuejia的碰撞攻击算法在消息修改时忽视了被修改条件之间的制约性,因而未必总能产生碰撞,本文对此进行了修正,给出新的充分条件集,并通过实验验证了该充分条件集总能产生碰撞。     

UHF RFID系统中直接解码碰撞的新方案

通过改造UHF RFID系统中标签的随机码生成器,重新设计随机码模式,并为RFID阅读器添加碰撞解码系统,改善碰撞时隙,使相撞的多个随机码可被直接解码,系统的性能显著提高.在基于GNU无线电和USRP2的实验平台实现此方案以验证其可行性.理论分析和测试平台的实验结果表明,标签读取率较传统方案有显著提高.     

Probabilistic Assessment of Collisions Involving Seagoing Ships

This paper deals with the quantitative study of three major routes-Galveston to the Persian Gulf, New York to Rotterdam, and New York to the Persian Gulf-for ships over 2000 gross tons. An assessment is made of the collision-free traverse over the chosen routes. Estimates are valid for the anticipated life of these ships.     

A New Scheme to Avoid Collisions for Broadcast Packets in Wireless LANs

This paper proposes a new approach to avoiding collisions for broadcast packets in distributed wireless LANs. The basic idea is to use in-band pulses to convey the medium access control information for broadcast packets. The new approach extends the basic functionality of the IEEE 802.11 distributed coordination function (DCF) from the unicast case to the broadcast case and significantly improves the broadcasting efficiency in wireless LANs.     

Practical consideration for bandpass sampling

The uniform bandpass sampling theorem has been modified to cope with sampling frequency instability and carrier frequency variations. Minimum sampling rates for given sampling and carrier frequency variations are derived. A robust bandpass sampling method is proposed which requires the sampling frequency to be such that the carrier frequency is on the 1/4 or -1/4 sampling frequency grid     

实用棱镜耦合器的设计

设计了一种用于 YIG 薄膜光波导输出耦合的装置,该耦合器具有结构简单、制作与使用方便及实用性强等特点。     

Practical algorithms for tornado codes

Tornado codes have been used in the error control of data transmission in IP network. The efficiency of this erasure codes is critically affected by the short cycles in its bipartite graph. To remove this effect, two algorithms are introduced： （1） while generating the graph, the cycle eliminating algorithm is used to reduce the number of the short cycles in it; （2） in the decoding algorithm, cycles that are inevitably in the graph are used to remove decoding efficiency degradation. The simulation results show that they have a better performance than that of general tornado codes.     

实用宽带新技术

简要介绍了三种宽带新技术及其应用，包括替代五类线的VDSL，可解决HFC上行噪音漏斗效应的SCDMA技术以及利用电源线传输高速数据的PLC技术。这些新技术由于具有较高的性能价值比和广阔的应用前景，受到了广泛的关注。     

Practical modeling for circuit simulation

There is much more to modeling for circuit simulation than deriving a set of I(V), and perhaps Q(V), equations and extracting a SPICE MODEL card. Unfortunately, some practical aspects of modeling are often overlooked. This paper details common-sense guidelines for modeling and highlights common modeling problems. Particular emphasis is given on understanding accuracy requirements and numerical requirements, on ensuring that compact models are asymptotically correct, and on highlighting the real goal of modeling for circuit simulation: getting complete models for allowable device layouts working in the CAD system on a designer's desk     

Practical codes for photon communication

In a recent paper, Pierce studied the problems of communicating at optical frequencies using photon-counting techniques, and concluded that "at low temperatures we encounter insuperable problems of encoding long before we approach [channel capacity]." In this paper it is shown that even assuming a noiseless model for photon communication for which capacity (measured in nats/photon) is infinite, it is unlikely that a signaling efficiency of even 10 nats/photon could be achieved practically. On the positive side, it is shown that pulse-position modulation plus Reed-Solomon coding yields practical results in the range of 2 to 3 nats/photon.     

Nonlinear Gain Control of Dispersion-Managed Soliton Amplitude and Collisions

The stabilizing action of nonlinear gain on dispersion-managed soliton transmissions is investigated. By means of a proper combination of nonlinear gain and filtering, the background and amplitude instability introduced by lumped guiding filters can be controlled. Indeed, radiative background that may not be separated from the signal when the average dispersion is close to zero is shown to be suppressed. Taking advantage of the large tolerance with respect to input energy variations, dispersion-managed solitons are found to be stable after collisions among different frequencies when supported by the same nonlinear gain element for all channels. This demonstrates the feasibility of nonlinear gain for wavelength-division-multiplexed transmissions and may open up the possibility of high-speed soliton transmission with large tolerance with respect to power fluctuations and densely packed wavelength channels.     

实用的移动应用接收器

目前市场上大部分接收器在设计上都受到印制电路板的板面空间、材料和成本的限制,移动手机的限制更多.零差接收器虽然外型更为小巧,设计更为简单,但仍有几个实施上的问题必须解决,因此对于系统设计工程师来说,设计零差接收器可说是一大挑战.本文将以美国国家半导体的GSM芯片组作为例子详细分析超外差接收器,以及采用较低中频接收器的蓝牙射频系统.     

实用模拟BIST的基本原则

实用模拟BIST有潜力降低IC测试成本,以及产品上市时间。20多年来,研究人员和半导体制造商一直在试图开发一种针对混合信号IC的实用模拟BIST(内置自检)。这种技术能够用数字测试仪作混合信号IC测试,以及简化的多址测试,从而能减少IC测试成本,以及IC上市时间。其它预期优点还有更快的测试开发,以及系统上的自检等。     

实用的防火墙解决方案

本文介绍适合不同用户需要的几种具体的解决方案。     

Practical microwave circuits for groove waveguides

Groove guides have been known for many years. No practical microwave circuits have yet been described although these types of transmission lines could be used in many cases. This paper discusses the physical realizability of some wide band designs such as matched load, directional coupler, hybrid coupler, bend and phase shifter. Both closed and open groove guides have been investigated. Optical type components seem to be inappropriate for groove guide transmission. The best way to design components for these guides is to adapt those of standard rectangular guides, which perturb only the Rf fields in the vicinity of the narrow walls and to optimize the dimensions of the groove structure as a function of the losses and the symmetry of the induced spurious modes.     

Practical stability criterion for tunnel-diode circuits

A stability criterion for tunnel-diode circuits is described, which requires only plots of modulus of reflection coefficient versus frequency. The criterion is derived intuitively.     

LSIS-II布图设计系统的实用化设计

本文介绍了LSIS-II布图设计系统结合规模生产的要求所进行的实用化设计和发展工作.包括系统采用的功能流、自检流、容错流的结构设计,单层金属布线工艺条件下的高密度布线设计,复合目标组合迭代布局优化设计,多种图形接口和系统稳定性的提高等.该系统已投入规模生产中的实际应用,已设计成功一批实际应用电路,其中包括1000门用户电路(已批量生产55万片)、单片集成度为38k、35k晶体管和8000逻辑等价门的应用电路.     

Practical Channel Transition for Near-VOD Services

Periodic broadcasting is known as an efficient technique to support near Video-on-Demand services for delivering popular videos, since it can reduce the bandwidth requirement for transmitting streaming video to simultaneous viewers. The channel transition problem is an issue to be concerned about the variability of popularity of video. In this paper, we present a novel channel transition scheme based on the fast broadcasting. In most conditions, our proposed scheme has less bandwidth waste than the existing SFB scheme. In addition, no extra startup latency and client buffer are needed in our scheme.