共查询到18条相似文献，搜索用时 203 毫秒
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针对复合衰落信道的复杂性,提出了一种简化的信道模型来研究分布式天线系统的误比特率性能.首先,基于阴影Rayleigh衰落信道,在接收端进行最大比合并,并用对数正态分布替代复杂的伽玛-对数正态分布,描述所得信噪比的随机特性.其次,假设发送端已知信道状态信息,推导了分布式天线系统基于天线选择发送的下行误比特率表达式,表达式采用了Gauss-Hermite近似以便于理论计算.最后,仿真结果显示理论值和仿真值能够很好地吻合.因此,可以认为所提出的简化模型是有效的和精确的.同时也表明所推导的解析表达式能够用于精确评估系统的实际性能. 相似文献
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陈晶晶 《宁波职业技术学院学报》2009,13(5):32-33,91
介绍了无线MIMO系统信道容量的计算方法,重点分析和比较了在瑞利衰落信道下,发射端已知或未知,但接收端完全未知的信道状态信息时的独立同分布的多入多出各态历经容量特性。并利用Matlab对其进行仿真。结果表明,在低信噪比时,采用自适应功率分配得到的信道容量特性要优于采用平均功率分配。并且信道容量随收、发天线数目的最小值呈线性增长。 相似文献
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叶卓映 《廊坊师范学院学报(自然科学版)》2014,14(6)
提出一种新的MIMO传输技术,即在发射端(基站)使用最大比发射,接收端使用两根接收天线并采用恒模等增益合并接收,记作MRT/EGC(Maximal-Ratio Transmission/equal gain combiner).利用随机矩阵理论,推导出瑞利衰落信道下MRT/EGC系统多进制相位调制的误符号率的确切表达式.仿真试验验证了理论分析的正确性. 相似文献
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《实验室研究与探索》2016,(6):106-111
针对广义空间调制系统在相关衰落信道下误码率和容量性能严重恶化的问题,提出一种基于距离和范数测度的天线选择方案。该方案中,通过联合考虑信道列空间的距离测度和信道功率增益范数测度,设计了低复杂度的天线选择算法,即从候选发送天线集合中逐个丢弃性能较差的天线,最终获得一个次优的候选天线集合,从而同时改善该系统在空间星座和信号星座部分的误码率和容量性能。仿真表明,该方案能够在复杂度没有明显增加的条件下大大改善系统性能,而且在独立衰落信道下依然能够保持良好性能,展现出其较好的灵活性和可扩展性。 相似文献
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《绵阳师范学院学报》2021,(2):22-27
我国是世界上煤炭开采大国,由于煤炭开采环境的特殊性,矿井下的无线通信环境与地面的无线通信环境相差甚远,若直接将用于广阔空间的无线通信技术应用到煤炭矿井中会产生无线信号的多径衰落等不可预期的问题,严重影响矿井下的无线通信质量.本文首先从理论上分析了煤炭矿井中多径无线信道的复杂性,并采用瑞利多径信道模型对其进行仿真建模.采用无线通信中多输入多输出技术(MIMO)和正交频分复用技术(OFDM),设计了一套基于MIMO-OFDM的矿井无线通信系统,以减少多径衰落现象对无线信号的消极影响.最后通过MATLAB软件对该系统进行仿真分析,实验结果证明本系统具有抗多径衰减的功能. 相似文献
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《实验室研究与探索》2013,(11):82-84
以信道为研究对象,首先分析了加性高斯白噪声信道、瑞利衰落信道和莱斯信道三种信道的数学模型,然后通过仿真比较了三种信道对二进制数字调频系统可靠性的影响。结果表明,加性高斯白噪声信道的性能最好,瑞利衰落信道性能最差,莱斯衰落信道居于两者之间,同时也说明衰落信道对系统可靠性的影响很大,而简单的调频系统不具备抗衰落能力。 相似文献
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刘维周 《南京晓庄学院学报》2006,22(6):7-10
本文介绍了OFDM自适应调制技术的原理、帧格式的设计,给出了调制方式的选取与转换准则;分析了自适应调制系统在瑞利衰落信道下的性能,并对系统进行了仿真.结果表明,在低压电力线信道环境下,自适应调制系统能够获得较高的系统容量,而系统的误比特率也可以保持在较低的水平. 相似文献
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为了满足数据传输的时延约束,提出一种多天线系统的下行帧长优化方案。由于传统的物理层信道模型在评估服务质量方面的局限性,该方案应用有效带宽与有效容量概念从链路层对源数据模式与队列服务动态进行统计特性建模。该链路层模型分别描述了源数据产生过程、信道服务过程与服务质量参数之间的映射关系,将超时违约概率约束转化为数据传输速率限制,将帧长优化问题转换为求解多元联合不等式组。在块衰落信道场景中,求解满足多元联合方程的帧长域下界,得到超时违约概率约束下的最佳系统帧长。理论分析和仿真结果表明,在最佳帧长设置下,用户数据传输的超时违约概率满足要求。 相似文献
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Optimal transmission strategy for spatially correlated MIMO systems with channel statistical information 总被引：1，自引：0，他引：1
ZHAO Zhen-shan XU Guo-zhi 《浙江大学学报(A卷英文版)》2007,8(4):615-619
In real multiple-input multiple-output (MIMO) systems, the perfect channel state information (CSI) may be costly or impossible to acquire. But the channel statistical information can be considered relatively stationary during long-term transmission. The statistical information can be obtained at the receiver and fed back to the transmitter and do not require frequent update. By exploiting channel mean and covariance information at the transmitter simultaneously, this paper investigates the optimal trans- mission strategy for spatially correlated MIMO channels. An upper bound of ergodic capacity is derived and taken as the per- formance criterion. Simulation results are also given to show the performance improvement of the optimal transmission strategy. 相似文献
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Multiple antenna wireless systems can provide larger channel capacity and enable spatial diversity to combat fading. In this paper we conduct an investigation into the design of coded space-time system obtained by serially concatenating channel code module and space-time code module with an interleaver in between. As an example, the system is constructed by employing low decoding complexity turbo-SPC （single parity check） code as outer module and linear complex field space-time code as inner module, which achieves full diversity and lossless equivalent channel capacity. Simulation results prove that our designed system performs well and it only loses 0.8 dB from multiple-input multiple-output （MIMO） capacity at BER = 10^-5 in the case of information bit length 6048. Compared with turbo code-based systems, it also has lower error floor. 相似文献
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Telse Nagler Jan Lonnemann Janosch Linkersdörfer Marcus Hasselhorn Sven Lindberg 《Reading and writing》2014,27(5):841-853
The acceleration phenomenon (AP) is defined by improvements in reading speed and reading comprehension, induced by an artificial text fading procedure corresponding to the previously determined fastest individual reading rate. Recent results, however, indicated that fading that is slower than the self-paced reading rate can produce comparable reading enhancements. As reading performance can be strongly influenced by the reading material, this study aimed at investigating to which extent reading enhancements induced by text fading depend on the reading material’s characteristics. We confronted 39 German third graders with a previously utilized text fading procedure, which was slower than their self-paced reading rate. Included text varied regarding to the lexical accessibility (LA), representing how well information can be accessed from the mental lexicon. Children’s reading rates increased statistically significant due to text fading for all LA levels. However, reading comprehension was sensitive to the text material’s characteristics: Reading comprehension enhancements were observable for easily accessible reading material, but not for material with intermediate or difficult levels of LA. Material that was difficult to retrieve from the mental lexicon even resulted in reduced reading comprehension in the fading condition. Possible influences on immediate lexical access, the impact of working memory capacity and implications for future AP research are discussed. 相似文献
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大容量数字无线通信系统对多径传输引起的传播恶化很敏感，所以抗多径衰落技术是数字通信中研究的重要课题之一。本文分析了几种主要的抗多径衰落技术，并用Matlab仿真了这些技术对通信系统性能改善的情况，由此得出一些结论。这些结论对研究不同衰落下的校正方案、设计最佳均衡器结构等有参考价值。 相似文献
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Pure position permutation image encryption algorithms,commonly used as image encryption investigated in this work are unfortunately frail under known-text attack.In view of the weakness of pure position permutation algorithm,we put forward an effective decryption algorithm for all pure-position permutation algorithms.First,a summary of the pure position permutation image encryption algorithms is given by introducing the concept of ergodic matrices.Then,by using probability theory and algebraic principles,the decryption probability of pure-position permutation algorithms is verified theoretically; and then,by defining the operation system of fuzzy ergodic matrices,we improve a specific decryption algorithm.Finally,some simulation results are shown. 相似文献
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移动通信中的多谱勒频偏估计方法 总被引：1，自引：0，他引：1
针对几种多普勒频偏估计方法,分别为对数包络法、自相关函数法、各阶电平通过率法和均方相位差分法,在理论上分析了瑞利信道中它们的估计原理和估计偏差,说明了这些估计方法各自的适用场合.同时推导了多普勒频偏估计器的CRB (Cramer Rao bound),并且提出了一种新的利用二阶多项式拟合的修正方法以提高多普勒频偏估计精度.算法验证采用门特卡罗计算机仿真,结果表明,相对于原始估计方法,拟合修正后的方法估计性能得到了较大的提高. 相似文献
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在分析多载波码分多址(MC-CDMA)的原理基础上, 提出了一种基于复小波包的MC-CDMA系统. 同时, 研究了该系统分别采用等增益合并和最大比合并时在Nakagami-m衰落信道下的性能; 并推导了相应的误码率表达式. 该系统能克服通常MC-CDMA系统由于插入循环前缀(CP)所带来的频谱效率的下降. 理论分析和仿真结果表明:该系统要优于通常MC-CDMA系统和基于实小波包的MC-CDMA系统, 有着优越的抗多径衰落和多址干扰能力,而且该系统也优于采用CP的通常MC-CDMA系统. 相似文献
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INTRODUCTION Due to the development of communicationtechnology, information security becomes an increasingly important problem. The wide use omultimedia technology and the improvement innetwork transmission gradually enable direct acquisition of information clearly through imagesHence, data security has become a critically important issue. Many encryption algorithms havebeen proposed to protect valuable data from unauthorized parties. The basic methods can be classified into th… 相似文献