共查询到19条相似文献,搜索用时 125 毫秒
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PN码捕获技术是DS -CDMA蜂窝移动通信系统的关键技术。这里提出了一种基于能量窗的捕获技术 ,基于能量窗的捕获技术有效地利用了CDMA系统固有的多径分集能力 ,捕获对象是多径信号。研究结果表明对有效多径成分进行捕获有比单径捕获和跟踪更好的性能。 相似文献
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PN码捕获技术是DS-CDMA蜂窝移动通信系统的关键技术.这里提出了一种基于能量窗的捕获技术,基于能量窗的捕获技术有效地利用了CDMA系统固有的多径分集能力,捕获对象是多径信号.研究结果表明对有效多径成分进行捕获有比单径捕获和跟踪更好的性能. 相似文献
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第三代移动通信系统均采用了CDMA技术,因此研究CDMA系统中的同步问题具有十分重要的意义。针对移动通信系统中的时变多径信道,根据WCDMA物理层码同步的要求,提出了基于公共导频PN序列的码同步方法,即在码捕获阶段,采用接收数据与己知PN序列相关,通过大于特定门限值的相关峰值选取多径,实现多径分离和粗同步。仿真结果表明,该码同步方法在减小现有算法运算量和复杂度的情况下,具有良好的性能,便于数字实现。 相似文献
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本文讨论了三种3G通信中最有竞争力的无线通信技术:OFDM、CDMA和MC-CDMA(前面两种技术的结合)。OFDM(OrthogonalFrequencyDivisionMultiplexing)是多载波通信系统的一个特例,它可以有效的对付多径时延带来的符号间的干扰。在频率选择性信道下,采用OFDM技术的高比特速率通信系统也有较好的抗误码性能。CDMA(CodeDivisionMultipleAccess)是3G通信系统中看好的一种技术。它采用PN序列来进行扩展信号频谱,相对于窄带信号来说,它可有效的对付深衰落,提高多用户接入的能力。MC-CDMA是前面两种技术的结合,作者比较了CDMA和MC-CDMA技术,从而给出了MC-CDMA的优点。 相似文献
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基于DMF捕获系统频率选择性信道下捕获性能的分析 总被引:1,自引:0,他引:1
对基于数字匹配滤波器(DMF)捕获系统在频率选择性信道下的捕获性能进行了深入讨论,利用状态转移图推导出单次驻留判决方式时平均捕获时间的表达式,对平均捕获时间与多径分量的关系进行了数字分析。得出的主要结论是:对于多径分量为非衰落信号时,多径分量之间的能量差别越大,系统捕获性能越好,多径分量的能量相等时,系统捕获性能最差,且随着可以分离的多径路数的增加下降;对于多径分量为慢衰落信号时,多径信道的捕获性能好于单径信道(非频率选择性衰落信道),且多径分量之间的能量差别越大,系统捕获性能越差,当多径分量的能量相等时,捕获性能最好,这与非衰落信道的情形相反。因此在频率选择性衰落信道中,采用分集接收可以改善系统的捕获性能。 相似文献
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智能天线和联合检测 总被引:1,自引:0,他引:1
第三代移动通信系统采用宽带码分多址(CDMA)技术为主流技术.智能天线(SA)是移动通信系统中抗多径衰落的关键技术,联合检测(JD)是CDMA通信系统中抗多址干扰的关键技术,智能天线和联合检测技术相结合已成为当前宽带CDMA移动通信应用研究热点之一.本文基于数字通信时空域自适应滤波器的观点讨论单小区单载波CDMA系统基站接收所应用的智能天线和联合检测技术,给出了结合智能天线和联合检测的时空域滤波器结构.我国大唐电信和德国西门子联合开发的TD-SCDMA试验系统已经研发成功,本文在最后结合这一实例,阐述了智能天线和联合检测技术在目前国内TD-SCDMA系统开发中的应用. 相似文献
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CDMA数字蜂窝的优点 1.系统容量大 CDMA技术比其他的蜂窝技术有较强的抗干扰能力,同一射频载波可用在每一个小区及其扇区,从而使系统容量大大提高。相同的频带宽度内,其容量是TACS的8倍,GSM的4~5倍。 2.基站覆盖范围大 CDMA技术很好地解决了多径 相似文献
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采用匹配滤波器(MF)扩频码捕获方案,以恒虚警率(CFAR)准则作为比较器门限设置准则,将平均捕获时间(TMA)作为衡量扩频码捕获性能的主要参数,通过将多径信道与单径信道环境下的TMA特性进行比较,分析了静态多径信道环境对DS/SS系统捕获性能的影响。 相似文献
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多载波CDMA是OFDM和CDMA结合的综合技术,兼有OFDM和CDMA的优点,可以在无线信道中传送高速数据流,在频谱效率、频率分集、抗多径干扰等方面都能获得较大好处。首先介绍了OFDM的基本原理,给出MC-CDMA的系统模型,然后通过仿真,比较了OFDM系统和MC-CDMA系统的误码性能。结果表明,MC-CDMA系统性能优于OFDM系统,说明了OFDM和CDMA技术结合的必要性。 相似文献
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Sangchoon Kim 《Vehicular Technology, IEEE Transactions on》2004,53(5):1354-1369
A multiple-signal-classification (MUSIC) approach of estimating the code timings of a desired user is considered for direct-sequence code-division multiple-access (DS-CDMA) multipath-fading channels when exploiting multiple receive antennas with either spatially uncorrelated or fully correlated fading. The acquisition performance of the conventional MUSIC timing estimator employing a single antenna is not good for the small size of observation windows and low signal-to-noise ratios (SNRs). Multiple antennas allow for rapid acquisition and lowers the range of detectable SNR. An efficient and improved MUSIC algorithm of estimating the multipath timings of a desired user for DS-CDMA systems is presented. In multipath-fading channels, the solution of the proposed algorithm is based on successively optimizing the cost function for increasing numbers of multipath delays, which does not require a multidimensional search for multidelay paths. Furthermore, the estimate of code timing at each path is obtained by finding the zeros of second-order polynomials, which is computationally efficient. The proposed MUSIC algorithm significantly improves the acquisition performance of conventional MUSIC algorithm in the presence of multipath time-varying Rayleigh-fading channels with arbitrary time delays. The acquisition performance of multiple antennas-based MUSIC timing estimators is much better than that of a single-antenna-based timing estimator. The Crame/spl acute/r-Rao bound for the code-timing estimator based on multiple antennas is presented. 相似文献
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基于完全互补码的新型CDMA系统仿真研究 总被引:1,自引:0,他引:1
利用完全互补码的特性 ,分析研究了一种基于完全互补码的新型CDMA系统。这种CDMA系统可以精确估计多径影响 ,实现高速数据传输。且在理论分析的基础上进行了计算机仿真 ,研究了各参数对系统性能的影响特性 相似文献
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Nano Molecular‐Platform: A Protocol to Write Energy Transmission Program Inside a Molecule for Bio‐Inspired Supramolecular Engineering
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Subrata Ghosh Mrinal Dutta Satyajit Sahu Daisuke Fujita Anirban Bandyopadhyay 《Advanced functional materials》2014,24(10):1364-1371
In a coded self‐assembly, a simple code is written in the molecule, which self‐assembles the molecules into a fractal like structure, which acts as a seed for the next step. As the molecule turns into a complex seed, the code transforms into another form and several seeds self‐assemble into another structure, which acts as a seed for the next step. Until now, this technology was considered as a prerogative of nature. Here, a dendritic network is used to write a basic code by synthetically attaching 32 molecular rotors and doping two controller molecules in its cavity. The code live, which is an energy transmission path in the molecule, is imaged. When the energy transmission path or code is triggered, a series of products generate one after another spontaneously. Two examples are: i) dendritic seed (5–6 nm)→paired nanowire (≈12 nm)→nanowire (≈200 nm)→microwire (500 nm)→wire like rod (1–2 μm)→jelly→rectangular sheet (5 μm). ii) dendritic seed→nano‐sphere (20 nm)→micro‐sphere (500 nm)→large balls(1 μm)→oval shape rod (5–10 μm)→Y, L or T shaped rod assembly. The energy level interactions are tracked using spectroscopy how exactly a directed energy transfer code generates multi‐step synthesis from nano to the visible scale. 相似文献
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短波慢跳频系统误码率分析 总被引:1,自引:0,他引:1
本文分析了在慢跳频系统中由于多径效应引起的误码率,并推导了经过自适应均衡后的误码率。模拟分析结果表明:基于平方根卡尔曼算法的判决反馈均衡器的引入大大降低了误码率。 相似文献
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Abdelhafid Jouini Abdelmadjid Maali Mustapha Benssalah Ammar Mesloub Genevieve Baudoin Mhamed Hamadouche 《International Journal of Communication Systems》2021,34(1)
In this paper, a new robust auto‐adaptive approach for pseudo‐noise (PN) code acquisition is proposed. It is applied to the generalized multi‐carrier direct‐sequence code‐division multiple‐access (MC DS‐CDMA) systems communicating over frequency‐selective multipath Rayleigh fading channels. This new approach is based on the constant false alarm rate (CFAR) detection algorithm, referred here as automatic selection partial sum ordered statistics (ASPSOS)‐CFAR. The proposed approach does not require any prior information about the background environment and uses maximum likelihood estimation (MLE) method to detect the interfering signals group in the ranked cells for the full reference window. Once this group is identified and censored, the remaining smaller ranked cells are combined to form an estimate of the background noise level to compute the adaptive threshold. Through simulations, the performance of the proposed detector is analyzed and compared with traditional CFAR detectors based on fixed or automatic censoring algorithms. The obtained results show that the proposed detector eliminates the drawbacks of the previously related detectors and offers a robust detection performance to enhance the acquisition process in heterogeneous background environments. 相似文献
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