共查询到20条相似文献,搜索用时 46 毫秒
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对CDMA2000移动台接收机的信道估计单元的算法和实现进行了分析,探讨了如何根据衰落速率对相关长度进行自适应的调整,以使信道估计单元能够对多径系数进行精确估计。 相似文献
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在分析一种多用户OFDM系统中自适应子信道和比特功率分配算法的基础上,根据多径频率选择性衰落信道的瞬时特性,动态地为多用户分配子信道和传输比特数,并服从MA优化准则.并且进一步考虑了系统中有固定速率用户和可变速率用户同时存在的情况:在子信道分配时,先给固定速率的用户分配子信道,再给可变速率用户按照子信道链路增益最大化分配剩余的子信道;在信号发射功率分配上,按照"注水"法则分配,链路增益大的子信道分配的功率大,链路增益小的子信道分配的功率小,则系统的目标函数,总传输速率可以达到最大.仿真证明了此方案优于一般的方案. 相似文献
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在移动通信系统中,由于无线时变衰落信道的特点,使通信过程存在大量的不确定性,自适应方式在信道条件好时提高了传输速率或减小发送功率,在信道条件差时降低了速率或增大功率。通过仿真结果证明,根据信道的优劣情况进行自适应调制的系统在保持较低的误码率性能的同时,能提高了系统的传输速率,从而增强传输的可靠性并可提高频带利用率。 相似文献
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CDMA蜂窝移动通信系统是一种采用多址技术的通信系统,即采用不同的地址码来区分用户、基站和信道.然而由于其在多径衰落信道中的自相关和互相关特性的不理想造成了码道之间的多址干扰.在扩频通信系统中,有效地抵消导频信道引入的多址干扰是进一步改善系统性能和提高系统容量的重要途径. 相似文献
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人机控制与驾驶员模型研究 总被引:7,自引:1,他引:6
基于驾驶员自身控制行为的动态特性分析和驾驶员与飞行控制系统动态特性综合优化设计思想,详述了驾驶员控制模型的发展与应用。并针对驾驶员信息处理能力和特点,应用智能控制神经网络、模糊控制和预测控制方法,建立了新型的基于智能控制理论的驾驶员模型。用以协调驾驶员和被控对象的动态特性,以获得最佳的操纵决策,提高人机闭环系统性能、降低驾驶员工作负担,改善操纵品质。 相似文献
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Pilot two-way CATV systems have been mounted in the United States largely to assess the marketability of various interactive services (e.g., subscriber response) and to assess technical problems over operating CATV systems. Such tests were at their peak in the early 1970's. Twelve systems which have been publicly tested are considered briefly. Three of these, the Theta-Com subscriber response system (SRS), the Coaxial Scientific Telecinema system, and the MITRE MITRIX system, are considered in some detail. 相似文献
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Proposed is a novel technique, hereby referred to as pilot symbol assisted coding (PSAC), where a predetermined fraction of binary pilot symbols is interspersed with the channel-coded bits at the channel coding stage, instead of multiplexing the pilots with the data symbols at the modulation stage, as in classic pilot symbol assisted modulation (PSAM). It is demonstrated that the PSAC succeeds in gleaning more benefits from the pilot overhead investment, than just simply the capability of channel estimation such as in the PSAM technique. 相似文献
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导频设计和信道估计是OFDM系统中重要的研究课题.本文主要介绍了TD-SCDMA在LTE长期演进中的导频设计原则和方案,分别对下行、上行导频的频域和时域结构进行了仿真分析.并对LS和简化的MMSE算法的性能进行了仿真比较和分析. 相似文献
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在多小区大规模多输入多输出(Multiple Input Multiple Output,MIMO)系统中,导频污染(Pilot Co- ntamination,PC)已成为制约整个系统性能的瓶颈。本文从系统级角度出发,提出了一种基于部分导频交替复用(Alternately Fractional Pilot Reuse,AFPR)的导频配置方案,即相邻小区的边缘用户配置相互正交的导频序列,而小区中心用户复用相邻小区边缘用户所配置的导频序列。同时从理论上推导出基于AFPR的导频配置方案上行可达频谱效率(Spectral Efficiency,SE)的关系式。数值仿真结果表明,相比于传统的导频配置方案,无论采用最大比合并(Maximum Ratio Combining,MRC)还是迫零(Zero Forcing,ZF)接收,该方案可显著地提升系统性能增益。 相似文献
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Optimum detectors for pilot symbol assisted modulation (PSAM) signals in Rayleigh and Rician fading channels are derived. Conventional PSAM as used on Rayleigh fading channels is also employed on Rician fading channels. It is shown that the conventional PSAM receiver is optimal for binary phase shift keying in Rayleigh fading but suboptimal for Rician fading and suboptimal for 16-ary quadrature amplitude modulation in Rayleigh fading. The optimum PSAM signal detector uses knowledge of the specular component and also jointly processes the pilot symbols and the data symbol. The performance of the optimum detector is analyzed and compared with that of the conventional detector. It is concluded that substantial gains can be achieved by exploiting knowledge of the specular component while joint processing of the data symbol with the pilot symbols may offer small benefits. 相似文献
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《Spectrum, IEEE》2008,45(9):48-58
Flash back ten years. Apple is a company bleeding money, thought by many to be in a death spiral. Its head of hardware development, a 41?year-old electrical engineer named Jon Rubinstein, is busy cutting projects and people and launching the G3 and iMac computers. He?s living in Palo Alto, Calif., with a cat for companionship, working seven days a week, and subsisting on take-out food at the office. Then came the iPod. 相似文献
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An instrument for the continuous measurement of pre-ejection period (PEP) in the human fetus using Doppler ultrasound is presented. An important feature of the instrument is its ability to track the continuously changing location of the reflections. The design includes a recently developed nonlinear filtering technique that is quite insensitive both to the large amounts of noise of biologic origin and the random dynamic amplitude variations. The efficiency of the scheme is illustrated by simulated and clinical tests. 相似文献