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排序方式: 共有509条查询结果,搜索用时 286 毫秒
31.
A spectrally‐efficient scheme is proposed for orthogonal decode‐and‐forward relaying. By utilizing constellation rotation, the scheme can achieve twice the spectral efficiency as that of the conventional one, with low implementation complexity. It can offer a full diversity order as well, whereas the loss in coding gain is less than 1 dB for practical environments. 相似文献
32.
We systematically investigate the motion of slowly moving
matter--wave gap solitons in a nonlinear potential, produced by the
weak random spatial variation of the atomic scattering length. With
the weak randomness, we construct an effective-particle theory to
study the motion of gap solitons. Based on the effective-particle
theory, the effect of the randomness on gap solitons is obtained, and
the motion of gap solitons is finally solved. Moreover, the analytic
results for the general behaviours of gap soliton motion, such as the
ensemble-average speed and the reflection probability depending on
the weak randomness are obtained. We find that with the increase of
the random strength the ensemble-average speed of gap solitons
decreases slowly where the reduction is proportional to the variance
of the weak randomness, and the reflection probability becomes
larger. The theoretical results are in good agreement with the
numerical simulations based on the Gross--Pitaevskii equation. 相似文献
33.
加热炉炉管的红外热像监测方法研究 总被引:1,自引:1,他引:0
文中所介绍的乃是获奖项目“高温炉管的红外在线监测诊断及评估系统研究”科研成
果的一部分。试验研究结果表明,在进口的如PM350 类焦平面红外热像仪的基础上,合理地选装高温火焰滤片、广角镜头以及红外隔热罩,便可实现通过看火孔对加热炉炉管进行红外热像的在线监测。而通过试验研究所得到的误差修正方法,可以使炉管的红外热像监测结果与接触式的热电偶测试结果相差小于2 %。现场工业试验的结果表明,该方法完全满足了生产装置监测的需要。 相似文献
34.
巧用Word绘制有线电视图纸 总被引:1,自引:0,他引:1
给Word的工具栏中添加“有线电视”专用绘图工具栏,充分开发Word的图文编辑功能,实现有线电视设备或其他元器件单元图形的即点即输,可非常方便地编辑出图文并茂的有线电视专业文稿。 相似文献
35.
This is the second of two papers in which we study real and virtual photon-proton scattering in a nonperturbative framework. In the first paper we have identified the leading contributions to this process at high energies and have derived expressions for them which take into account the renormalisation of the photon-quark-antiquark vertex. In the present paper we investigate the approximations and assumptions that are necessary to obtain the dipole model of high energy scattering from the results derived in the first paper. We discuss the gauge invariance of different contributions to the scattering amplitude and point out some subtleties related to gauge invariance in the correct definition of a perturbative photon wave function. As a phenomenological consequence of the dipole picture we derive a bound on the ratio of the cross sections for longitudinally and transversely polarised photons. This bound is independent of any particular model for the dipole-proton cross section and allows one to test the validity of the assumptions leading to the dipole picture in particular at low photon virtualities. We conclude that the naive dipole model formula should be supplemented by two additional terms which can potentially become large at small photon virtualities. 相似文献
36.
惯性/DGPS精密进场着陆引导系统 总被引:1,自引:0,他引:1
为确保飞机精确直线飞越预定点上空并具备精密进场着陆引导能力 ,研制了机载惯性 /DGPS精密进场着陆引导系统。该系统通过综合技术将惯性导航系统与差分 GPS有效组合 ,不仅定位精度高、工作可靠 ,而且输出信息实时、连续 ;通过着陆引导轨迹及引导画面的精心设计 ,为飞行员提供图形化的、精确安全的进场着陆引导信息 ,引导飞机至决断高处 ,从而解决了飞机全天候尤其是在复杂气象条件的进场着陆引导问题。本文介绍了该系统的方案、组成、系统特点、技术难点以及试飞结果。试飞中飞行员反映该系统精度高 ,引导画面图形直观 ,操作简便 ,能满足复杂气象条件下的进场着陆引导要求 相似文献
37.
Stphane Y. Le Goff 《International Journal of Communication Systems》2002,15(7):621-633
Introduced in 1993, turbo codes can achieve high coding gains close to the Shannon limit. In order to design power and bandwidth‐efficient coding schemes, several approaches have been introduced to combine high coding rate turbo codes with multilevel modulations. The coding systems thus obtained have been shown to display near‐capacity performance over additive white Gaussian noise (AWGN) channels. For communications over fading channels requiring large coding gain and high bandwidth efficiency, it is also interesting to study bit error rate (BER) performance of turbo codes combined with high order rectangular QAM modulations. To this end, we investigate, in this paper, error performance of several bandwidth‐efficient schemes designed using the bit‐interleaved coded modulation approach that has proven potentially very attractive when powerful codes, such as turbo codes, are employed. The structure of these coding schemes, termed ‘bit‐interleaved turbo‐coded modulations’ (BITCMs), is presented in a detailed manner and their BER performance is investigated for spectral efficiencies ranging from 2 to 7 bit/s/Hz. Computer simulation results indicate that BITCMs can achieve near‐capacity performance over Rayleigh fading channels, for all spectral efficiencies considered throughout the paper. It is also shown that the combination of turbo coding and rectangular QAM modulation with Gray mapping constitutes inherently a very powerful association, since coding and modulation functions are both optimized for operation in the same signal‐to‐noise ratio region. This means that no BER improvement is obtainable by employing any other signal constellation in place of the rectangular ones. Finally, the actual influence of the interleaving and mapping functions on error performance of BITCM schemes is discussed. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
38.
Channels' correlation has direct impact to degrade the capacity and reliability of multiple‐input multiple‐output (MIMO) systems considerably. In this paper, new signal constellation designs are investigated to mitigate fading correlation and maximize the capacity and error performance of multiuser MIMO (MU‐MIMO) over correlated channels, which is a major research challenge. Two methods are studied in a novel constellation constrained MU‐MIMO approach, namely, unequal power allocation and rotated constellation. Based on principles of maximizing the minimum Euclidean distance (dmin) of composite received signals, users' data can be recovered using maximum likelihood joint detection irrespective of correlation values. Compared with the identical constellation scenario in conventional MU‐MIMO, it is shown that constellation rearrangement of transmitted signals has direct impact to resolve the detection ambiguity when the channel difference is not sufficient, particularly in moderate to high correlations. Extensive analysis and simulation results demonstrate the superiority of proposed technique to capture most of the promised gains of multiantenna systems and application for future wireless communications. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
39.
真空荧光显示器应用的现状及发展 总被引:2,自引:0,他引:2
本文综述了真空荧光显示器的应用领域,给出了各类VFD的主要技术指标和特点,也介绍了作为打印机光源和象素管的平板荧光器件;并讨论了今后的发展趋势。 相似文献
40.