Time-frequency channel modeling and estimation of multi-carrier spread spectrum communication systems     

Seda ?enay  Luis F. Chaparro 《Journal of The Franklin Institute》2005,342(7):776-792

In wireless communications, the channel is typically modeled as a random, linear, time-varying system that spreads the transmitted signal in both time and frequency due to multi-path propagation and Doppler effects. Estimated channel parameters allow system designers to develop coherent receivers that increase the system performance. In this paper, we show how time-frequency analysis can be used to model and estimate the time-varying channel of a multi-carrier spread spectrum (MCSS) system using a complex quadratic sequence as the spreading code. We will show that for this spreading code, the effects of time delays and Doppler frequency shifts, caused by the mobility of environment objects, can be combined and represented effectively as time shifts. The discrete evolutionary transform (DET), as a time-frequency analysis method, enables us to estimate the effective time shifts via a spreading function and to use them to equalize the channel. Using the effective time shifts, the time-varying channel can be represented simply as linear-time invariant system by embedding the Doppler shifts that characterize the time-varying channel into effective time shifts. The channel parameters are used to estimate the data bit sent. To illustrate the performance of the proposed method we perform several simulations with different levels of channel noise, jammer interference, and Doppler frequency shifts.  相似文献   

中国煤炭消费与影响因素动态关系的实证分析——兼论煤炭消费的非对称价格效应   总被引：4，自引：2，他引：2  

孔宪丽 《资源科学》2010,32(10):1380-1388

本文在建立我国煤炭消费协整方程的基础上,利用状态空间模型技术进一步建立了我国煤炭消费的变参数模型,对1978年-2007年间我国煤炭消费与经济增长及其它影响因素之间的相关关系进行了动态分析,以揭示我国煤炭消费与经济增长相关关系的时变规律。本文在实证分析中不仅考虑了经济增长、产业结构、技术改造、煤炭价格及运输成本对我国煤炭消费的影响,而且还借鉴了Gately(1992)开发的技术,对我国煤炭消费变动的非对称价格效应进行了实证分析。实证分析结果表明经济的持续增长和重工业比重的增加是拉动煤炭消费增长的主要原因,并且经济增长的拉动作用正在逐步减弱,而产业结构特别是工业结构对煤炭消费的影响作用逐步增强。煤炭价格对煤炭消费存在显著的非对称效应,但煤炭消费对煤炭价格变动的敏感性显著弱于运输成本,并且差距呈逐步增加态势。  相似文献   

柴油机活塞-缸套磨损故障振动诊断机理的研究     

胡以怀  刘永长  杨叔子 《上海海事大学学报》1997,(1)

通过对活塞组横向撞击的理论分析和活塞－缸套磨损故障的模拟试验，揭示了机身侧面振动的内部激励源及其与柴油机工况、活塞－缸套磨损间隙的内在联系，讨论了故障诊断中振动特征参量的优化选择问题，提出了一种适用于多种机型柴油机不同工况下活塞－缸套工作间隙的振动监测方法。  相似文献   

一类变时滞离散系统的输出反馈镇定     

陈树伟  郭兴进 《安阳师范学院学报》2008,(2):4-7

本文主要对一类带有时变：状态滞后的离散系统的镇定问题进行研究．给出了该类系统的输出反馈镇定控制器存在的充分条件。进一步将结果推广到不确定系统．给出了鲁棒镇定控制器存在的充分条件？  相似文献