共查询到20条相似文献,搜索用时 62 毫秒
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采用基于软判决和硬判决的方法,对跳时脉冲位置调制(time hopping-pulse position modulation,TH-PPM)和跳时脉冲幅度调制(time hopping-pulse amplitude modulation,TH-PAM)超宽带系统的误比特率性能进行了分析和比较.在加性高斯白噪声(additive white Gausses noise,AWGN)信道下,研究了TH-PPM和TH-PAM超宽带单用户系统接收端信号进行软判决和硬判决时的性能,同时分析比较系统在两种调制方式下采用不同脉冲重复次数时的件能差异.仿真结果表明,在AWGN信道下,TH-PPM和TH-PAM的系统性能均随脉冲重复次数的增加而明显改善,并且后者优于前者.此外,采用软判决时的系统性能优于采用硬判决时的系统性能. 相似文献
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针对UWB信道多址以及加性白噪声这一特点,本文采用高斯二阶脉冲作为发射脉冲,对TH-PAM以及TH-PPM调制解调系统的进行了理论分析,同时给出了这两种调制方式下系统的BER解析公式,并对性能进行了比较。在系统单用户情况下,TH-PAM性能恒优于TH-PPM;在考虑多用户以及系统噪声时,给出了一个仅由用户数目和脉冲波形决定的判决公式,由此可以判断两种系统的性能优劣。 相似文献
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基于多种调制方式的超宽带空时网格编码 总被引:2,自引:2,他引:0
为结合多入多出系统和超宽带的优点来实现高速高效的传输,将空时编码技术应用于超宽带系统中,讨论了基于脉冲位置调制(PPM:Pulse-Position Modulation)、脉冲幅度调制(PAM:Pulse-Amplitude Modulation)以及双正交调制3种不同方式的超宽带空时网格编码方案。考虑在发送和接收端已知信道状态信息,分别建立了3种方案的发射接收模型。仿真结果表明,在高斯信道和IEEE802.15.3a信道条件下,采用PPM的超宽带空时网格编码方案的性能都远优于其他两种方案,当信噪比为8dB时,误码率降低10~100倍。进一步考虑在存在多用户干扰条件下,该系统性能随用户数的增加而下降。 相似文献
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基于混沌脉冲幅度调制的超宽带通信系统 总被引:3,自引:1,他引:2
提出了一种实现超宽带直接混沌通信的混沌脉冲幅度调制(CPAM)算法,给出了CPAM算法原理及其调制解调方案.使用电子电路全功能模拟测试仿真软件(EWB)仿真分析了基于CPAM技术超宽带混沌通信系统的间歇耦合同步.仿真结果表明,收发两端可以精确同步,验证了系统的可实现性.系统误码率仿真显示,其可靠性比传统的正交相移键控(QPSK)等算法差,但混沌信号的引入大大改善了通信的保密性. 相似文献
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娄佳 《重庆邮电大学学报(自然科学版)》2008,20(Z1)
超宽带信号经多径信道传播会产生严重的时间弥散.采用RAKE接收是提高超宽带接收机性能的重要手段.基于IEEE 802.15.3a信道模型,针时脉冲位置调制(PPM)跳时超宽带信号(TH-UWB)系统,对采用RAKE接收机接收时的单用户系统和多用户系统的性能进行了比较分析,并给出了仿真结果. 相似文献
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针对脉冲无线电中跳时-脉冲位置调制的非线性调制方式,采用了一个等效的线性调制模型,提出了一种变形的判决反馈均衡滤波器(decision feedback equalizer,DFE)结构,用来对接收信号进行均衡以减小多径干扰.该变形的DFE增加了一个可调偏移量,反馈来自于根据判决结果而生成的序列,反馈滤波器的抽头间隔小于符号间隔.大量的仿真结果表明,该方法能有效地减小超宽带脉冲无线电通信系统中的多径干扰,降低数据接收的误码率,提高系统的接收性能. 相似文献
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为了改进超宽带通信系统的性能,通过对平衡Gold码的介绍与分析,提出了一种将平衡Gold码用于超宽带的多址接入技术,并对脉位调制(PPM)和脉幅调制(PAM)的超宽带系统进行Matlab仿真.仿真结果表明:该方法产生的跳时序列比传统跳时码序列具有更低的误码率. 相似文献
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QING Hai-ruo 《成都理工大学学报(自然科学版)》2004,31(6)
The discovery of the prolific Ordovician Red River reservoirs in 1995 in southeastern Saskatchewan was the catalyst for extensive exploration activity which resulted in the discovery of more than 15 new Red River pools. The best yields of Red River production to date have been from dolomite reservoirs. Understanding the processes of dolomitization is, therefore, crucial for the prediction of the connectivity, spatial distribution and heterogeneity of dolomite reservoirs.The Red River reservoirs in the Midale area consist of 3~4 thin dolomitized zones, with a total thickness of about 20 m, which occur at the top of the Yeoman Formation. Two types of replacement dolomite were recognized in the Red River reservoir: dolomitized burrow infills and dolomitized host matrix. The spatial distribution of dolomite suggests that burrowing organisms played an important role in facilitating the fluid flow in the backfilled sediments. This resulted in penecontemporaneous dolomitization of burrow infills by normal seawater. The dolomite in the host matrix is interpreted as having occurred at shallow burial by evaporitic seawater during precipitation of Lake Almar anhydrite that immediately overlies the Yeoman Formation. However, the low δ18O values of dolomited burrow infills (-5.9‰~ -7.8‰, PDB) and matrix dolomites (-6.6‰~ -8.1‰, avg. -7.4‰ PDB) compared to the estimated values for the late Ordovician marine dolomite could be attributed to modification and alteration of dolomite at higher temperatures during deeper burial, which could also be responsible for its 87Sr/86Sr ratios (0.7084~0.7088) that are higher than suggested for the late Ordovician seawaters (0.7078~0.7080). The trace amounts of saddle dolomite cement in the Red River carbonates are probably related to "cannibalization" of earlier replacement dolomite during the chemical compaction. 相似文献
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YUJia-shun HEZhen-hua 《成都理工大学学报(自然科学版)》2004,31(6):694-698
AcomputergeneratorforrandomlylayeredstructuresYUJia shun1,2,HEZhen hua2(1.TheInstituteofGeologicalandNuclearSciences,NewZealand;2.StateKeyLaboratoryofOilandGasReservoirGeologyandExploitation,ChengduUniversityofTechnology,China)Abstract:Analgorithmisintrod… 相似文献
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海南岛地体及其毗邻陆缘晚中生代—新生代古地磁研究和构造演化 总被引:9,自引:1,他引:9
本文叙述了对海南岛及其毗邻大陆边缘白垩纪到第四纪地层岩石进行古地磁研究的全部工作过程。通过分析岩石中剩余磁矢量的磁偏角及磁倾角的变化,提出海南岛白垩纪以来经历的构造演化模式如下:早期伴随顺时针旋转而向南迁移,后期伴随逆时针转动并向北运移。联系该地区及邻区的地质、地球物理资料,对海南岛上述的构造地体运动提出以下认识:北部湾内早期有一拉张作用,主要是该作用使湾内地壳显著伸长减薄,形成北部湾盆地。从而导致了海南岛的早期构造运动,而海南岛后期的构造运动则主要是受南海海底扩张的影响。海南地体运动规律的阐明对于了解北部湾油气盆地的形成演化有重要的理论和实际意义。 相似文献
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Yan Yun’an 《华南师范大学学报(自然科学版)》2014,(6):136-137
Various applications relevant to the exciton dynamics,such as the organic solar cell,the large-area organic light-emitting diodes and the thermoelectricity,are operating under temperature gradient.The potential abnormal behavior of the exicton dynamics driven by the temperature difference may affect the efficiency and performance of the corresponding devices.In the above situations,the exciton dynamics under temperature difference is mixed with 相似文献
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Yuriko Aoki 《华南师范大学学报(自然科学版)》2014,46(6):135-135
The elongation method,originally proposed by Imamura was further developed for many years in our group.As a method towards O(N)with high efficiency and high accuracy for any dimensional systems.This treatment designed for one-dimensional(ID)polymers is now available for three-dimensional(3D)systems,but geometry optimization is now possible only for 1D-systems.As an approach toward post-Hartree-Fock,it was also extended to 相似文献
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The explosive growth of the Internet and database applications has driven database to be more scalable and available, and able to support on-line scaling without interrupting service. To support more client's queries without downtime and degrading the response time, more nodes have to be scaled up while the database is running. This paper presents the overview of scalable and available database that satisfies the above characteristics. And we propose a novel on-line scaling method. Our method improves the existing on-line scaling method for fast response time and higher throughputs. Our proposed method reduces unnecessary network use, i.e. , we decrease the number of data copy by reusing the backup data. Also, our on-line scaling operation can be processed parallel by selecting adequate nodes as new node. Our performance study shows that our method results in significant reduction in data copy time. 相似文献
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R-Tree is a good structure for spatial searching. But in this indexing structure,either the sequence of nodes in the same level or sequence of traveling these nodes when queries are made is random. Since the possibility that the object appears in different MBR which have the same parents node is different, if we make the subnode who has the most possibility be traveled first, the time cost will be decreased in most of the cases. In some case, the possibility of a point belong to a rectangle will shows direct proportion with the size of the rectangle. But this conclusion is based on an assumption that the objects are symmetrically distributing in the area and this assumption is not always coming into existence. Now we found a more direct parameter to scale the possibility and made a little change on the structure of R-tree, to increase the possibility of founding the satisfying answer in the front sub trees. We names this structure probability based arranged R-tree (PBAR-tree). 相似文献
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The geographic information service is enabled by the advancements in general Web service technology and the focused efforts of the OGC in defining XML-based Web GIS service. Based on these models, this paper addresses the issue of services chaining,the process of combining or pipelining results from several interoperable GIS Web Services to create a customized solution. This paper presents a mediated chaining architecture in which a specific service takes responsibility for performing the process that describes a service chain. We designed the Spatial Information Process Language (SIPL) for dynamic modeling and describing the service chain, also a prototype of the Spatial Information Process Execution Engine (SIPEE) is implemented for executing processes written in SIPL. Discussion of measures to improve the functionality and performance of such system will be included. 相似文献
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Advances in wireless technologies and positioning technologies and spread of wireless devices, an interest in LBS (Location Based Service) is arising. To provide location based service, tracking data should have been stored in moving object database management system (called MODBMS) with proper policies and managed efficiently. So the methods which acquire the location information at regular time intervals then, store and manage have been studied. In this paper, we suggest tracking data management techniques using topology that is corresponding to the moving path of moving object. In our techniques, we update the MODBMS when moving object arrived at a street intersection or a curved road which is represented as the node in topology and predict the location at past and future with attribute of topology and linear function. In this technique, location data that are corresponding to the node in topology are stored, thus reduce the number of update and amount of data. Also in case predicting the location,because topology are used as well as existing location information, accuracy for prediction is increased than applying linear function or spline function. 相似文献