排序方式: 共有75条查询结果,搜索用时 15 毫秒
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该文研究一种新型混合通信系统,即基于多载波BPSK调制的相干跳频多址接入(FH/CDMA)系统,接收端采用最大比合并(MRC)分集接收。由于采用相位调制,接收端载波相位恢复的精确度直接影响系统性能。假设载波同步通过一阶锁相环电路(PLL)完成,由于载波恢复环路中存在高斯噪声,当系统达到同步稳态时不可避免地会产生稳态相位误差。该文采用Beaulieu级数方法和特征函数方法,得到理想相干和部分相干(存在稳态相位误差)时FH/CDMA系统误码率性能表达式。仿真结果表明,相对于单用户系统,多用户系统误码率受到相位误差影响较小,误码率性能降低的主要因素是多用户干扰。MRC分集接收能提高系统抵抗相位误差和信道衰落的能力。 相似文献
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《AEUE-International Journal of Electronics and Communications》2014,68(7):616-622
The Daubechies, coiflet and symlet wavelets, with properties of orthogonal wavelets are suitable for multicarrier transmission over band-limited channels. It has been shown that similar wavelets can be constructed by Lagrange approximation interpolation. In this work and using established wavelet design algorithms, it is shown that ideal filters can be approximated to construct new orthogonal wavelets. These new wavelets, in terms of BER, behave slightly better than the wavelets mentioned above, and much better than biorthogonal wavelets, in multipath channels with additive white Gaussian noise (AWGN). It is shown that the construction, which uses a simple simultaneous solution to obtain the wavelet filters from the ideal filters based on established wavelet design algorithms, is simple and can easily be reproduced. The Cramer–Rao lower bound is applied to access the BER performance of the proposed wavelet. 相似文献
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网络负荷的增加,传统依靠人工调整负荷均衡已不能满足优化需求。自动化智能均衡方案通过穷举影响相邻两个小区覆盖性能的天馈、功率、互操作等类别参数,并进行归一化分析,自动输出负荷均衡调整方案。对无法通过覆盖均衡实现负荷均衡的小区,通过引入迭代算法,在优化边界范围内以固定步长自动输出负荷均衡调整建议,这有利于提高LTE网络容量、提高网络资源利用率、也有利于降低传输时延、降低人工和时间成本。 相似文献
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Photovoltaic grid-connected inverters are distributed power generation devices that convert the dc power from solar panels to high-quality ac power at the utility grid interface. Adopting modular design in these systems improves expandability, serviceability, reliability and efficiency. In this paper, the phase-shifted carrier technique, which is normally used in high-power multiconverter schemes, is applied to a modular residential photovoltaic grid-connected inverter to improve the output power quality. First, it is shown, through analysis and simulation, that in the commonly-used grid-connected inverter topology based on the phase-shift modulated full-bridge converter, the well-known rule for the phase-shift between the carrier signals of the adjacent modules is not effective for both odd and even number of modules. Then, a new general rule for the phase-shift is systematically derived and its effectiveness in improving the output power quality for odd and even numbers of modules is verified through simulation. 相似文献
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Deng Ke Yin Qinye Zhang Hong 《电子科学学刊(英文版)》2006,23(1):14-19
Focusing on the space-time coded multiuser mobile communication systems in the frequencyselective fading environment, this paper proposes a Vertical Bell labs LAyered Space-Time (V-BLAST) coded Multicarrier Code-Division Multiple-Access (MC-CDMA) scheme and its blind channel identification algorithm. This algorithm employs an ESPRIT-like method and the singular value decomposition, and the channels between every transmit antenna of every user and every receive antenna of the base station are blindly estimated with a closed-form solution. Based on it, an equivalent Minimum Mean-Squared Error (MMSE) time-domain multiuser detector is derived. Moreover, the proposed scheme exploits the precoding in the transmitter in order to eliminate the constraint of more receive antennas than transmit ones, required by most conventional V-BLAST codec schemes. Computer simulation results demonstrate the validity of this proposed scheme. 相似文献
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多载波CDMA具有更高的灵活性 ,更高的频谱效率 ,简单的检测技术 ,窄带干扰抑制能力等一系列优点 ,引起了研究者的广泛兴趣。文中介绍了三种多载波CDMA技术 ,即MC CDMA (多载波CDMA) ,多载波DS CD MA (直接序列CDMA)和多音CDMA并简单介绍了它们的发射和接收技术。最后还指出多载波CDMA技术所固有的缺陷。 相似文献
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xDSL中的多载波调制技术 总被引:3,自引:0,他引:3
xDSL是一种重要的基于现有的铜线环路的宽带接入网技术,而多载波调制是其中采用的一项重要的信号调制技术。本文分析了在xDSL中使用的2种多载波调制技术,对其性能做了比较,并得出了采用离散小波多音的方式在性能上优于离散多音方式的结论。 相似文献