基于建筑模型的5G Massive MIMO天馈寻优方法研究与应用

当前5G MR/MDT等定位技术尚不成熟且样本过少,本文提出了一种基于建筑物信息的5G Massive MIMO天馈寻优方法,利用5G大规模阵列天线的技术优势,通过Massive MIMO天线波瓣宽度的精确计算,实现了天线覆盖方案的寻优,以最大程度地提升室内覆盖.本方法在降低网络运维成本的同时,提升了资源效能,为后续5...     

四川盆地中二叠统茅口组天然气大面积成藏的地质条件

近年来在四川盆地西北部(川西北)、中部(川中)等地区中二叠统茅口组钻获了一批高产气井,展现出该层系良好的天然气勘探前景,但其能否成为该盆地天然气规模勘探的重要层系,还取决于是否具备天然气大面积成藏的地质条件。为回答上述疑问,从烃源条件、颗粒滩分布、风化壳型岩溶储层分布及成因等3个方面开展了研究。结果表明:(1)茅口组缓坡颗粒滩体在广元—广安—重庆以西地区大面积分布,为储层形成奠定了地质基础;(2)全球海平面下降导致的区域性侵蚀面有利于大面积岩溶型储层的形成;(3)下志留统龙马溪组、茅一段—茅二c层及上二叠统龙潭组等3套主力烃源岩与茅口组风化壳岩溶储层构成"三明治式"源—储成藏组合,是天然气大面积成藏的关键。进而分析了茅口组天然气的富集条件,提出了有利勘探方向与目标。结论认为:(1)该盆地茅口组具备大面积天然气成藏的地质条件;(2)侵蚀微古地貌及后期走滑断裂改造控制了该区大型缝洞体的分布,颗粒滩—风化壳岩溶—走滑断裂"三位一体"控制了该区天然气富集高产的有利区带;(3)川中高石梯—磨溪地区走滑断裂发育,茅口组天然气成藏条件良好,是天然气规模勘探的有利地区。     

Massive Si Phase and Its Growth Mechanism in Al-Si Casting Alloy

Optical microscope and scanning electron microscope were used to observe the microstructure of the AI-11.6%Si and AI-11.6%Si-0.4%Mg alloys and the morphology of the massive silicon particles. It is found that the massive silicon phase, observed in the unfully modified alloys with 0.010%Sr, disappears completely in the alloys fully modified with 0.020%Sr. The serrations and reentrant edges shown in the massive silicon particles with the conventional casting indicate that the TPRE mechanism plays an important role in the growth of the massive silicon phase. The ripples and steps suggest that the "lateral microscopic growth" may be another operating mechanism.     

Energy-Efficient Resource Optimization for Massive MIMO Networks Considering Network Load

This paper investigates the resource optimization problem for a multi-cell massive multiple-input multiple-output (MIMO) network in which each base station (BS) is equipped with a large number of antennas and each base station (BS) adapts the number of antennas to the daily load profile (DLP). This paper takes into consideration user location distribution (ULD) variation and evaluates its impact on the energy efficiency of load adaptive massive MIMO system. ULD variation is modeled by dividing the cell into two coverage areas with different user densities: boundary focused (BF) and center focused (CF) ULD. All cells are assumed identical in terms of BS configurations, cell loading, and ULD variation and each BS is modeled as an M/G/m/m state dependent queue that can serve a maximum number of users at the peak load. Together with energy efficiency (EE) we analyzed deployment and spectrum efficiency in our adaptive massive MIMO system by evaluating the impact of cell size, available bandwidth, output power level of the BS, and maximum output power of the power amplifier (PA) at different cell loading. We also analyzed average energy consumption on an hourly basis per BS for the model proposed for data traffic in Europe and also the model proposed for business, residential, street, and highway areas.     

Quaternion-MUSIC for near-field strictly noncircular sources with large-scale polarization array

In this paper, a novel localization method is proposed for DOA, range and polarization estimation of near-field noncircular sources in massive multiple-input-multiple-output (MIMO) systems. Compared with traditional MUSIC-based algorithms, the proposed algorithms can separate the polarization parameters from the spatial spectrum function, avoiding the four-dimensional (4-D) spectrum search and realizing the fast localization of the near-field source with high accuracy. First, the dimension-reduced MUSIC (DR-MUSIC) algorithm is proposed for DOA and range estimation with low computational complexity, and given a closed-form expression of polarization estimation. Next, based on the quaternion theory, a novel algorithm named quaternion non-circular MUSIC (QNC-MUSIC) is proposed for parameter estimation of non-circular signals with high estimation accuracy. In addition, the analysis of the computational complexity and simulations of the proposed method are provided, showing that the proposed method yields a better performance than DR-MUSIC in massive MIMO systems.     

基于 MOOCs 的高校计算机专业人才培养模式研究

通过调查和数据对比分析发现,计算机专业是我国高校开设数最多的专业,在校人数也领先于其他专业。在分析我国在线教育和大规模在线开放课程MOOCs发展现状的基础上,提出全模式在线教育的思路,并认为在线教育的技术特点是IT技术,若利用专业优势将计算机专业人才培养优先纳入全模式在线教育,将有益于教育与信息技术深度融合的探索。     

The impact of visual design and response formats on data quality in a web survey of MOOC students

The objective of this paper is to gain more evidence regarding how the design of the rating scales and open-ended questions influence data quality in Web surveys of MOOC (Massive Open Online Course) students. We present the results of four full-factorial randomized experiments that investigate the impact of the following factors: 1) order of response options; 2) user interface for rating questions 3) layout of question's options; and 4) size of answer boxes in open-ended questions. We found that responses to scalar questions with ascending (from negative to positive) or descending (from positive to negative) order of response options do not differ substantially. The use of the radio button format allows a reduction in the percentage of respondents who choose the “Don't know” option and makes responding to questions less challenging in comparison with slider and text box interfaces. There are no significant differences in the answers of respondents who completed questionnaires with a vertical or horizontal orientation of the questions' options. In addition, respondents who answer the questions with larger answer boxes are more likely to write longer comments.     

基于改进共轭梯度的大规模多输入多输出预编码

针对大规模多输入多输出（Massive MIMO）系统下行链路预编码实现复杂、线性预编码矩阵求逆困难等问题，提出一种基于对称逐步超松弛预处理共轭梯度法（SSOR-PCG）的低复杂度预编码算法。该算法在共轭梯度（PCG）算法的基础上，采用对称逐步超松弛分裂（SSOR）算法对矩阵进行预处理以降低矩阵的条件数，达到提高预编码算法收敛速度、降低复杂度的目的。仿真结果表明：与PCG算法相比，所提出的SSOR-PCG预编码算法运行时间缩短约88.93%，在信噪比为26 dB时已收敛；与迫零预编码算法相比，所提算法迭代2次即可获得与迫零预编码算法相近的系统容量性能，复杂度降低约一个数量级，误码率降低约49.94%。     

Joint estimation of time delays and directions of arrival using proper set of antenna elements of a high-order antenna array

In this work, we investigate the accuracy and complexity deviation between using all or selected antenna elements of a massive MIMO array for source localization. In addition, we address the problem of highly resolving the propagation time delay, and the angles of arrival (azimuth and elevation) associated with signals in multipath communication channels for many location-based services and three-dimensional (3D) beamforming. The 3D unitary matrix pencil (3D UMP) algorithm is enhanced and applied in a new way to evaluate these parameters simultaneously from the estimated space channel frequency response (S-CFR) using wideband orthogonal multicarrier signals and uniform rectangular array (URA). Furthermore, the 2D UMP is enhanced to estimate the unknown parameters of wideband signals impinging on 8 different array configurations that are structured as combinations of uniform linear arrays (ULAs). It is not necessary to use all antenna elements of a high-order antenna array for source localization. Due to the dependency on mobile unit location, the phase uncertainties and the deviation of received signal strength between array elements, using the proper set of antenna elements can provide a comparable accuracy and a considerable reduction in the computational complexity of the localization algorithm. The computational complexity is further reduced by exploiting real computation and similar eigen-structure property, and using a priori information of wireless positioning. The IEEE 802.11ac system parameters are used in our experiments.