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一种无需导频的适用于差分OFDM系统的符号与采样钟联合同步方法 总被引:1,自引:0,他引:1
该文提出了一种适用于OFDM系统的联合符号和采样钟同步校正方法,其中同步校正是在数字域通过改变对接收过采样信号的插值(interpolation)和抽取(decimation)实现的。这种方法在发送端相邻载波间采用差分QPSK调制,在接收端利用QPSK的差分解调信号获得同步误差信号,从而获得关于OFDM符号同步和采样钟同步调整的算法,其特点是无需专门的同步导频信号。所提出算法的同步性能在高斯白噪声信道和多径衰落信道均得到验证。 相似文献
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物理层网络编码充分利用无线信道的广播特性,能够有效提高网络吞吐量和带宽利用率。但是物理层网络编码的性能受到载波相位、载波频率、时间、采样钟不同步的影响,因此分析同步误差对物理层网络编码性能影响具有重要的研究意义。基于单载波系统,针对使用BPSK调制的无线通信系统,从理论上分析了一定帧长下,载波相位、载波频率、时间及采样时钟同步误差对系统性能的影响。分析结果表明,在载波相位和时间不同步两种情形下,物理层网络编码性能不受帧长影响;而在载波频率和采样时钟不同步两种情形下,系统性能均随帧长的增加而有所下降,其中采样时钟不同步情形受帧长影响最大。 相似文献
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数字电视视频广播的关键技术--OFDM及其同步 总被引:3,自引:2,他引:1
研究数字地面视频广播(DVB-T)OFDM(Orthogonal Frequency Division Multiplex)传输系统接收端的同步.根据DVB-T标准和OFDM原理,在FFT前该方案采用多载波系统时域的保护间隔所携带的冗余信息进行粗符号同步和分数粗频偏估计;在FFT后,利用频域插入的连续导频进行整数倍频偏估计、分数细频偏及采样钟偏移估计,利用散布导频实现精符号同步. 相似文献
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Tayebeh Gholipur Mehdi Mahdavi Abolghasem Zeidaabadi Nezhad 《Wireless Personal Communications》2014,75(2):1547-1571
Resource allocation algorithms play the main role in provisioning high throughput in broad band wireless communications. The previous studies in WiMAX networks have considered either AMC or PUSC techniques for the resource allocation algorithms. In this way, AMC based algorithms have presented high throughput for low speed users. Conversely, PUSC based algorithms have not been affected by users’ speed, whilst the throughput is low. To date, the importance of presenting proportional fair and maintaining the network throughput for the users with different speeds has not been acknowledged yet. This paper presents a novel opportunistic algorithm which is suitable for the users with different mobility speeds. The new algorithm uses two modes of AMC and PUSC simultaneously. The simulation results reveal that in comparison to similar algorithms, the proposed algorithm presents more proportional fair throughput when there are both high and low speed users. 相似文献
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Tayebeh Gholipur Mehdi Mahdavi Abolghasem Zeidaabadi Nezhad 《Wireless Personal Communications》2013,72(2):1203-1228
QoS provisioning and high capacity for high mobility users are considered as the distresses of broadband wireless communications (BWC) and specifically the key technology of WiMAX. Hence, the scheduling and resource allocation algorithms play the main role in this regard. In the research conducted on scheduling algorithms in WiMAX network, two principal methods of AMC and PUSC are used. The high capacity in AMC mode algorithms is achieved by considering the low speed users. Conversely, in PUSC mode algorithms, speed does not affect the network performances; however, the capacity is low. To date, the importance of presenting QoS and maintaining the network capacity for the users with different speeds has not been acknowledged yet. This paper presents novel scheduling algorithms and also new frame partitioning scheme which are proper for the users with different mobility speeds. The new algorithm uses two modes of AMC and PUSC simultaneously to maintain the high capacity of the network. QoS is also provided. The simulation results reveal that our algorithm increases capacity while it presents low packet delay and packet loss rate in the presence of both high and low mobility speed users. 相似文献
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文章主要分析讨论了基于802.16e版本的WiMax用于点对点无线回程传输的头部开销及容量大小。重点分析了信头中FCH(控制帧头)以及下行DL—MAP(下行接入消息)在回程传输中需要的资源大小,再依据这些大小限制进行下行PUSC(部分占用子信道)配置最终估算出容量大小。 相似文献
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《Electron Devices, IEEE Transactions on》1975,22(10):869-880
Starting from Pierce's small-signal TWT equations, a two-wave theory for complicated TWT's and BWO's is developed. Explicit gain expressions for TWT's with severs and velocity tapers are given. A detailed treatment is given of a BWA structure with a single-step velocity taper in the center. The BWO start oscillation current is calculated as a function of the taper strength. The effciency of a step velocity taper as a remedy for backward-wave oscillations in the higher passbands of a TWT is then analyzed. It is shown that a suitable taper can increase the start oscillation current by more than a factor of 10 without adverse effects on the TWT performance if the backward waye coupling impedance is low. A tube with a weak linear taper is analyzed by a perturbation technique and it is found that there is no significant difference between the start oscillation currents for tubes with weak linear or abrupt tapers of comparable strengths. 相似文献
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Internal model control (IMC) is a well-known and effective control scheme. However, when unstable processes are concerned, the original IMC structure cannot be directly used for control system implementation. In this paper, a new scheme called partial internal model control (PIMC) is proposed, which is capable of controlling both stable and unstable processes. In PIMC, a process model is expressed as the sum of the stable and antistable parts and only the stable part of the process model is used as the internal model. The process stable part is canceled by the internal model and the remaining antistable part is stabilized and controlled with a primary controller, which is usually a PID-type regulator when the antistable part is of a low order. Various properties of a PIMC system such as internal stability and robust stability are analyzed. The design of PIMC is discussed in detail. Various simulation examples are included for illustration and a real-time implementation on a motor system is presented 相似文献
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《Lightwave Technology, Journal of》2009,27(11):1448-1453
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《Antennas and Propagation, IEEE Transactions on》2009,57(6):1789-1797
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Whether a computer is in a corporation, government agency, university, small business, or at home, if it is linked to a network, hackers are a risk. The first line of defense against them is a firewall, provided it is set up correctly. Firewall technology is a set of mechanisms that collectively enforce a security policy on communication traffic entering or leaving a guarded network domain. The security policy is the overall plan for protecting the domain. Embodied in hardware, software, or both, a firewall guards and isolates the domain. Broadly, firewalls attempt to maintain privacy and ensure the authenticity of data communications that pass through their domain's boundaries. Whether data is entering or leaving a domain, it is protected from eavesdropping (passive wiretapping) and change (active wiretapping). But only communication traffic entering or leaving a domain comes under the influence of firewall technology 相似文献
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The authors propose a simple structure for a tunable polarization-independent wavelength-selective filter. This successfully fabricated filter consists of a liquid crystal Fabry-Perot interferometer, a γ/4 plate, and a mirror. The input light is divided into a transmitted light and a reflected light. The polarization of this reflected light is rotated 90° by the γ/4 plate and the mirror and then this light is input again into the filter. The bandwidth is 0.48 nm and the tuning range is 50 nm. Fiber-to-fiber loss is approximately 3.9 dB and polarization dependence of the loss is approximately 0.3 dB 相似文献
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Subthreshold leakage loss is a serious problem for GaAs dynamic memory. Since the leakage current in a MESFET is several orders of magnitude higher than that in a MOSFET, it is difficult to retain the charge at dynamic nodes resulting in data storage errors, In order to solve this problem, a novel DRAM architecture is proposed. The design is based on a cell consisting of a MESFET switch and a metal-insulator-metal (MIM) planar capacitor as the storage element. The leakage current is reduced by a level-shift technique and a self-biased transistor is used to maintain the dynamic charge during the sense period. A high performance sense amplifier is used to detect small bit line voltage changes and refresh the stored data. A 1 Kb prototype, fabricated in a 1 μm nonself-aligned GaAs MESFET technology, exhibited a total read/write access time of the order of 3 ns 相似文献