PERFORMANCE OF CODED OFDM VIA VARIABLE GUARD INTERVAL

This letter presents the principles of Coded Orthogonal Frequency Division Multiplexing (COFDM) system and focuses on the effect of the Guard Interval (GI) on the system performance. The role of the GI parameter period to solve the problem of interferences that occur at the receiver is discussed. A new COFDM concept with a Variable GI (VGI) is proposed in order to improve the Bit Error Rate (BER) performance in the presence of multipaths with variable delays. A series of simulations have been carried out on the BER performance as a function of GI, maximum delay spread, and Signal-to-Noise Ratio (SNR), with QPSK as modulation scheme over multipath fading and Additive White Gaussian Noise (AWGN). The results show that the optimum values of the GI parameter approximately equal to the maximum delay spread, and the proposed system with VGI provides a better performance compared with the fixed length GI.     

聚合VGI与GF-2影像的地震救援协助救灾信息获取研究

地震会给人类社会带来巨大损失，在地震发生后及时获得准确有效的地震救援协助救灾信息，为相关部门制定救援方案提供辅助信息，能够最大程度地减少人员伤亡及经济损失，对抢险救灾、应急指挥具有重大意义。地震发生后，为快速获取协助救灾信息，通过Python爬取九寨沟震后微博数据，分类并获取位置信息，聚合地震后自发地理信息（VGI）与遥感影像，进行服务区、最近设施点路径分析，并利用震前震后影像变化提取泥石流滑坡区域。结果表明：震后第一时间对有效数据进行聚合分析，能有效地获取设施点的服务区范围和最优可达路径，形成地理信息互补，在灾害应急等领域发挥出巨大的作用；通过聚合分析VGI与遥感影像数据获取地震协助救灾信息，在应急救援中具有一定可行性。     

VGI集成于中文数字地名词典的研究

提出将自发地理信息（VGI）集成到中文数字地名词典（CDG）的架构。在构建VGI数据爬取模型（VDCM）和地名本体的基础上, 针对从VGI数据中提取地名信息过程中出现的地名geo/geo歧义（多个地理位置对应同一地名）、地名与经纬度匹配错误、多个资源对应同一地名等问题提出相应的解决方案：使用上级行政区划名排歧、参考行政区划本体层次筛除错误地名标签、对同一地名的多个资源进行空间聚类获得唯一的经纬度, 并总结该架构能有效地解决CDG不支持空间推理、数据孤立以及数据维护、更新受限等问题, 提出未来的工作围绕修正错误的地名标签、构建信任模型及将VGI集成于分布式CDG展开。     

Risk perception during urban cycling in volunteered geographic information and in the lab: effects of the vista space’s spatial properties

A wide range of factors affects risk perception during urban cycling. In this research, we investigate a factor so far not addressed: the spatial configuration of the vista space; with the underlying reasoning that more complex or rapidly changing vista spaces are perceived as more dangerous. We present a method to quantify a vista space’s spatial configuration by generating highly precise isovists based on laser scans. We test our assumptions in a lab-based study, where participants rate the perceived risk for cycling in various image sequences displaying complex traffic situations. The tested traffic situations are selected from a project collecting citizens’ reports about urban cycling risks. Our findings support the hypothesis that the spatial configuration of the vista space is a highly relevant factor for risk perception which deserves further investigation. Further analyses imply that volunteered geographic information on subjective topics such as risk perception may be of limited accuracy, but is likely to be representative for a larger population.     

基于多源数据的多维度居住环境主观绿化评价水平与心理健康研究——以上海市里弄为例

既有研究对城市绿地的心理健康效益持有不同观点，原因之一为各研究对绿地的评价方法存在差异。目前评价绿化水平的维度较为单一，且缺乏对城市特殊居住环境和社会空间类型的关注。基于2016年上海市新旧里弄综合调研数据，分析里弄建成环境绿化空间对自评健康与心理健康的影响。研究采用卫星遥感与街景识别等技术，从绿地可达性、绿地面积、社区植被覆盖水平、社区绿视率水平、社区绿化满意度等多个维度和不同尺度，对居住环境主观绿化评价水平进行量化。研究发现：居住区植被覆盖率特征及公园规模与自评健康显著相关，公园规模与心理健康显著相关，未发现绿视率以及居住地到公园距离对健康有显著影响，同时发现主观绿化评价水平对居民健康存在显著的积极作用。     

基于Web2.0的地理信息服务模式研究

Web2.0环境下,地理空间信息领域兴起的新地理（Neogeography）、自发地理信息（VGI）模式带来了地理信息服务新的发展。本文首先介绍Web2.0的概念,然后对Web2.0环境下出现的新地理和自发地理信息模式进行分析,最后详细探讨了基于Web2.0环境的地理信息服务模式。