我国内燃机系列型谱“台尔斐”法调查的总结

本文是对我国“八五”～“九五”期内内燃机产品发展纲要和系列型谱进行的二次“台尔斐”法调查总结。文中有15项内容涉及与内燃机系列型谱及部分发展纲要有关的各项重大问题。本文集中反映了内燃机行业专家及有关单位的综合意见和设想。这对于管理部门和企业的规划决策有较大参考价值。     

认知无线电频谱切换技术研究

认知无线电技术是为提高频谱利用率,解决目前无线频谱资源紧缺问题而提出的,准确快速的频谱切换技术是其实现的关键。论文针对认知无线电技术的频谱切换问题,总结频谱切换的关键技术及研究模型,讨论频谱切换技术面临的挑战,以及频谱切换技术的研究方向。     

一种基于直接序列扩频技术的矿井应急通信系统设计及仿真

采用扩频信号进行通信的优越性在于用扩展频谱的方法可以增大带宽来降低信噪比.在阐述扩展频谱通信技术的基本理论和实现方法的基础上,详细介绍了直接序列扩频以及伪随机码m序列原理、产生m序列的条件.继而提出了若干种矿井应急通信系统的具体设计方案,并利用MATLAB/Simulink软件平台对该系统进行了仿真及分析.结果表明,该...     

From Allan Variance to Phase Noise: A New Conversion Approach

A new mathematical method is proposed to convert the oscillator instability parameters from Allan variance to Spectrum Density(SD)of random phase fluctuations,which is the inversion of the classic transformation formula from SD to Allan variance.Due to the fact that Allan variance does not always determine a unique SD function,power-law model of the SD of oscillator phase fluctuations is introduced to the translating algorithm and a constrained maximum likelihood solution is presented.Considering that the inversion is an ill-posed problem,a regularization method is brought forward in the process.Simulation results show that the converted SD of phase fluctuations from Allan variance parameters agrees well with the real SD function.Furthermore,the effects of the selected regularization factors and the input Allan variances are analyzed in detail.     

频谱谐波振动时效在消除旋挖钻机回转平台焊接残余应力中的应用

针对旋挖钻机回转平台在焊接后存在残余应力,以及由于残余应力显现的平台变形问题,采用振动时效进行残余应力消除和均化.通过工艺对比试验,结果表明:基于频谱谐振原理的频谱谐波振动时效处理,能够对回转平台的焊接残余应力起到均化作用,焊接变形得到有效改善,达到设计和使用要求.     

Prediction based channel allocation performance for cognitive radio

The interdependency, in a cognitive radio (CR) network, of spectrum sensing, occupancy modelling, channel switching and secondary user (SU) performance, is investigated. Achievable SU data throughput and primary user (PU) disruption rate have been examined for both theoretical test data as well as data obtained from real-world spectrum measurements done in Pretoria, South Africa. A channel switching simulator was developed to investigate SU performance, where a hidden Markov model (HMM) was employed to model and predict PU behaviour, from which proactive channel allocations could be made. Results show that CR performance may be improved if PU behaviour is accurately modelled, since accurate prediction allows the SU to make proactive channel switching decisions. It is further shown that a trade-off may exist between achievable SU throughput and average PU disruption rate. When using the prediction model, significant performance improvements, particularly under heavy traffic density conditions, of up to double the SU throughput and half the PU disruption rate were observed. Results obtained from a measurement campaign were comparable with those obtained from theoretical occupancy data, with an average similarity score of 95% for prediction accuracy, 90% for SU throughput and 70% for PU disruption rate.     

水声测距技术研究

水声信号相比其它信号在海水中能传得更远和更深,提出了水声测距的技术体制和几种水声信号测距处理方法,分析了海洋环境对水声测距的影响因素,对水声伪随机扩频测距的时间分辨率进行了试验测试,给出了用于同步测距的芯片级原子钟守时性能,对于提升水下高精度导航系统性能有一定参考价值。     

宽带通信中的干扰抑制处理方法研究

综述了DS/FH宽带通信系统中的干扰抑制预滤波处理方法，并侧重时频域的干扰消除技术，基于有关处理算法的适用条件和性能，探讨多系统共存环境下AIC（自适应干扰消除）处理的使用。     

直接序列扩频系统的多次驻留顺序捕获

本文利用矩阵变换方法对多次驻留顺序捕获的平均捕获时间表示式进行了推导,其过程较信号流图法简单。同时还给出了一次、二次及三次驻留顺序捕获系统的平均捕获时间的计算实例。     

超3G研究的最新进展

超3G在ITU—R范围内的各项研究工作还刚刚开始．基本上还处于制定工作计划的阶段。但目前关于对超3G频率需求计算方法的研究．已经有一些国家提出了自己的建议，主要是日本和德国。超3G研究工作。特别是频谱计算、业务预制、新的无线接入和核心网技术方面研究工作的开展，对我国的研究机构、相关公司和高校都是一个继续赶超世界先进通信技术．获取成果的绝好机会。