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DS—CDMA移动通信系统地址码的正交性 总被引:3,自引:0,他引:3
根据直接序列扩频码分多址(DS-CDMA)系统多址于干扰形成原理,着重分析了m序列,Gold序列,Walsh序列及其正交性,计算机模拟结果表明,同步状态下Walsh序列有理想的正交性,但在非同上状态下正交性不很理想。 相似文献
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本文考虑加性白噪声环境中的同步CDMA通信系统,给出了一种新的线性非相干解调接收机,同时给出了这种抗多址干扰接收机的误码率及渐近效率。结果表明,对于使用Gold码作特征码的CDMA系统,当用户数不大于特征码长度时,这种接收机的最小渐近效率是0.5 相似文献
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CDMA作为一种多址接入技术在无线网络中已广为应用。本文在多码 CDMA和单码 CDMA研究的基础上, 构造了时隙多码CDMA和单码CDMA在无线分组数据网络中的随机多址接入模型,并且分析了两种系统 的吞吐率特性和归一化时延特性。 相似文献
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本文结构3GPP W-CDMA的最新协议,介绍了W-CDMA系统的两次扩频结构,讨论了其中使用的OVSF码与扰码的主要特性及其在W-CDMA系统中的应用,文章的最后讨论了在工程实际中实时产生扩频码的方法。 相似文献
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沃尔什(Walsh)码又称为沃尔什函数,它是一种正交码(序列)。作者通过在多径信道中采用宽带扩频信号舆的理论分析,说明基于宽带信号的正交Walsh码的形式及在CDMA系统正、反向信道中进行我直到原理及应用。 相似文献
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本文简述了CDMA的技术优势,分别介绍了窄带码分多址(N-CDMA)移动通信系统和宽带码多址(W-CDMA)技术的发展情况,最后,提出应加强对W-CDMA技术上和研究并积极参与到第三代移动通信体制标准的制定工作中去 相似文献
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Explosion-insulatedFulOpticalFiberDiferential-presureMeasuringInstrument①ZHENGDezhong,WUChangqi,WANGZhenchen,LIZuofang(Yansha... 相似文献
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The forward link of the 3G code‐division multiple‐access (CDMA) system may become limited under the increasing of the number of users. The conventional channelization code, Walsh code, has not enough sizes for much possible users, therefore, the quasi orthogonal function (QOF), which can process optimal cross‐correlation with Walsh code, is considered. To obtain lower correlations and better performance in 3G CDMA system, we investigate a quasi orthogonal function on Jacket matrices in this paper. Secondly, to simplify the detector and improve the bit error rate (BER) performance, we provide a novel detection scheme for QOF CDMA system. Finally, we give a brief discussion about a simple recursive generation of the bent sequences for QOF mask function. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
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Downlink multicarrier code-division multiple access (MC-CDMA) with maximal ratio combining (MRC) in correlated Rayleigh fading channels is considered. An exact error floor in a closed-form expression is provided based on the characteristic function (CF) and residue calculation method. Numerical results show that orthogonal spreading sequences (Walsh and orthogonal Gold sequences) perform better than nonorthogonal sequences (Gold sequences) and Walsh codes have the best performance. In addition, downlink MC-CDMA is found to benefit from the correlation between subcarriers 相似文献
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A new scheme called ‘Collaborative Spreading’ is proposed for the downlink of CDMA to allow the sharing of the same spreading sequence by more than one user. In particular, it addresses the problem of user overloading and maintain the use of the same set of available orthogonal sequences and simple receiver structure. In this scheme, a total of K users are divided into G groups each containing T users which are collaboratively coded to form uniquely decodable composite codewords. These codewords are spread using a single sequence to perform the CDMA function between the groups. At the receiver, a low complexity maximum likelihood (ML) joint detection and decoding is carried out over a small set of allowed composite codewords to recover the desired user's data. Theoretical and simulation performance analysis of the bit error rate (BER) and user capacity are presented in different channel conditions. It is shown that the proposed collaborative spreading is a simple and very effective means for extending the user capacity at the cost of a modest degradation in BER performance compared with non‐overloaded fully orthogonal CDMA. It can achieve higher signal‐to‐interference plus noise ratio (SINR) and higher overloading ratio compared with Orthogonal CDMA/Orthogonal CDMA schemes and other group orthogonal CDMA schemes. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
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Debolina Chakraborty Milan Kumar Tarafder Abhijit Chandra 《Wireless Personal Communications》2016,88(4):711-729
Present generation mobile communication system employs one of the most popular wireless access technologies called code division multiple access (CDMA). Design of CDMA spreading codes has drawn significant attention amongst the researchers over the last few decades. CDMA code family is generally categorized into purely orthogonal and non-orthogonal (near-orthogonal) members which have established their application in synchronous (downlink) and asynchronous (uplink) CDMA system respectively. Walsh code has been regarded as the most useful spreading code to be used in synchronous link because of its orthogonality property. However, the performance of Walsh code is significantly inferior in asynchronous surroundings. A number of codes have consequently been proposed with an aim to mitigate the shortcomings of Walsh code. This paper makes an innovative attempt to enhance the correlation properties of existing Walsh code through one simple yet powerful algorithm. Proposed code of length ‘N’ has been generated from code sets of length ‘N/4’ and thus makes the code generation algorithm recursive in nature. Performance of the proposed code has subsequently been compared with some existing orthogonal and semi orthogonal codes in terms of various performance metrics and finally the supremacy of our proposition has been established. 相似文献
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一种用于CDMA系统的正交序列调制方法 总被引:2,自引:0,他引:2
在宽带移动通信系统中,经常考虑采用通过FFT实现的多载波调制,如OFDM。本文提出了一种利用FHT实现的CDMA系统的正交序列调制方案。其基本思想为利用Walsh函数作为载波,将Walsh函数分组,从每组中选出一些作为载波,这样不同的载波组合方式本身将包含用户信息。这种方法实现简单,可提高传输效率,并容易与CDMA相结合,能有效地抑制多径干扰。仿真结果表明,该方案在多径衰落信道中能得到很好的性能。 相似文献
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GMW序列和WG序列及WG序列间的互相关特性 总被引:1,自引:0,他引:1
对于奇数n,研究了Gordon-Mills-Welch(GMW)序列与Welch-Gong(WG)序列(及其某一采样序列)间的互相关函数以及WG序列间的互相关函数。研究表明:GMW序列与WG序列(及其某一采样序列)间的互相关函数以及WG序列间的互相关函数最终均与m-序列与其采样序列间的互相关函数相关;并且在一定条件下,WG序列间的互相关函数可为3-值或5-值的。另外,给出了GMW序列与WG序列间互相关函数的最大峰值。 相似文献