多天线OFDM(Orthogonal Frequency Division Multiplexing)系统环境下,针对现有全分集全速率空时编码分集复用交换之间的关系问题,在多天线OFDM系统模型下推导了其分集和复用增益交换曲线,进一步证实了FDFR(Full Diversity Full Rate)...多天线OFDM(Orthogonal Frequency Division Multiplexing)系统环境下,针对现有全分集全速率空时编码分集复用交换之间的关系问题,在多天线OFDM系统模型下推导了其分集和复用增益交换曲线,进一步证实了FDFR(Full Diversity Full Rate)空时编码是一种最优的分集复用交换空时编码。给出了实现全分集全速率空时编码的设计方法。理论分析表明,全分集全速率空时编码具有较好的空间链路适应性。在中国未来通用无线环境研究计划(FuTURE:Future Technologies for a Universal Radio Environment)的系统配置条件下,仿真了全分集全速率空时编码的性能并与其他现有最优空时编码的性能进行对比。结果表明,全分集全速率空时编码具有更好的链路适应性和较好的性能。展开更多
生态空间为城市提供所需的生态系统服务,同时也受到城市发展的影响。如何在让生态空间发挥生态价值的同时,平衡人类社会对生态系统提供服务的需求成为近年来城市生态空间规划的重点。生态系统服务可以评估生态和社会价值,顺应其间的协...生态空间为城市提供所需的生态系统服务,同时也受到城市发展的影响。如何在让生态空间发挥生态价值的同时,平衡人类社会对生态系统提供服务的需求成为近年来城市生态空间规划的重点。生态系统服务可以评估生态和社会价值,顺应其间的协同关系并缓解权衡有利于进行兼顾生态和社会目标的生态空间规划。以北京市生态涵养区为例,分析关键性生态系统服务间的权衡协同关系,为不同区域分配优先保护特征,并通过低权衡、低协同和高协同3种情景,以不同灵活程度进行生态系统服务保护目标空间分配。使用Marxan with zones模型得到满足各服务保护目标的管理区划,并比较3个情景的分区结果,验证规划体系对协同权衡作用的影响。得到了3种情景下的管理区分布:低权衡情景布局偏紧凑,实现了生态系统服务间权衡最小化;从低协同到高协同情景,生态系统服务间的协同性增加;从低权衡情景到低、高协同情景,重点保护区的面积逐渐增加,生态缓冲区增加了连接性,控制发展区和集中建设区变化相对稳定,实现了生态空间多层次空间优化。最终得到的更详细的管理区划有助于指导未来生态—社会多目标生态空间规划政策的制定:即对重点保护区严格保护,加强生态缓冲区生态整治和廊道建设,以促进生态效益协同发展。在集中建设区与控制发展区引导城镇节约集约建设,减量增绿,实现社会经济绿色发展。展开更多
在互联网码号资源公钥证书体系(Resource Public Key Infrastructure,RPKI)中,依赖方(Relying Party,RP)负责从资料库同步并验证资源证书和签名对象(ROAs,Manifests,Ghostbusters),而后将有效的ROA处理成用于指导BGP路由的IP地址块和AS...在互联网码号资源公钥证书体系(Resource Public Key Infrastructure,RPKI)中,依赖方(Relying Party,RP)负责从资料库同步并验证资源证书和签名对象(ROAs,Manifests,Ghostbusters),而后将有效的ROA处理成用于指导BGP路由的IP地址块和AS号的真实授权关系.在当前的实现方式中,验证证书模块主要通过数据库查询递归查找待验证证书的父证书从而构建完整的证书链并由OpenSSL完成最终验证.由于RPKI体系中证书量较大,导致基于数据库查询的方法效率不足.结合RPKI运行机制中将计算代价由BGP路由器(用户)迁移到RP服务器(服务器)的特点和"空间换时间"的思想,可以将证书信息读取到内存中从而减少I/O的时间消耗.本文基于上述思想基础,结合哈希表中条目查询的时间复杂度最优为O(1)的特点,设计并实现了基于哈希表的RPKI证书验证优化方法.实验结果表明,在设计的3种实验场景中,平均时间加速比分别为99.03%、98.45%和97.48%,有效的减少了时间的消耗.展开更多
In recent years, MIMO technology has emerged as one of the technical breakthroughs in the field of wireless communications. Two famous MIMO techniques have become investigated thoroughly throughout the literature;Spat...In recent years, MIMO technology has emerged as one of the technical breakthroughs in the field of wireless communications. Two famous MIMO techniques have become investigated thoroughly throughout the literature;Spatial Multiplexing, and Space Time Block Coding. On one hand, Spatial Multiplexing offers high data rates. On the other hand, Space Time Block Coding presents transmission fidelity. This imposes a fundamental tradeoff between capacity and reliability. Adaptive MIMO Switching schemes have been proposed to select the MIMO scheme that best fits the channel conditions. However, the switching schemes presented in the literature directly switch between the MIMO endpoints. In this paper, an adaptive MIMO system that incrementally switches from multiplexing towards diversity is proposed. The proposed scheme is referred to as incremental diversity and can be set to operate in two different modes;Rate-Adaptive, and Energy-Conservative Incremental Diversity. Results indicate that the proposed incremental diversity framework achieves transmission reliability offered by MIMO diversity, while maintaining a gradual increase in spectral efficiency (in the Rate-Adaptive mode) or a reduction in required number of received symbols (in the Energy-Conservative mode) with increase in the SNR.展开更多
文摘多天线OFDM(Orthogonal Frequency Division Multiplexing)系统环境下,针对现有全分集全速率空时编码分集复用交换之间的关系问题,在多天线OFDM系统模型下推导了其分集和复用增益交换曲线,进一步证实了FDFR(Full Diversity Full Rate)空时编码是一种最优的分集复用交换空时编码。给出了实现全分集全速率空时编码的设计方法。理论分析表明,全分集全速率空时编码具有较好的空间链路适应性。在中国未来通用无线环境研究计划(FuTURE:Future Technologies for a Universal Radio Environment)的系统配置条件下,仿真了全分集全速率空时编码的性能并与其他现有最优空时编码的性能进行对比。结果表明,全分集全速率空时编码具有更好的链路适应性和较好的性能。
文摘生态空间为城市提供所需的生态系统服务,同时也受到城市发展的影响。如何在让生态空间发挥生态价值的同时,平衡人类社会对生态系统提供服务的需求成为近年来城市生态空间规划的重点。生态系统服务可以评估生态和社会价值,顺应其间的协同关系并缓解权衡有利于进行兼顾生态和社会目标的生态空间规划。以北京市生态涵养区为例,分析关键性生态系统服务间的权衡协同关系,为不同区域分配优先保护特征,并通过低权衡、低协同和高协同3种情景,以不同灵活程度进行生态系统服务保护目标空间分配。使用Marxan with zones模型得到满足各服务保护目标的管理区划,并比较3个情景的分区结果,验证规划体系对协同权衡作用的影响。得到了3种情景下的管理区分布:低权衡情景布局偏紧凑,实现了生态系统服务间权衡最小化;从低协同到高协同情景,生态系统服务间的协同性增加;从低权衡情景到低、高协同情景,重点保护区的面积逐渐增加,生态缓冲区增加了连接性,控制发展区和集中建设区变化相对稳定,实现了生态空间多层次空间优化。最终得到的更详细的管理区划有助于指导未来生态—社会多目标生态空间规划政策的制定:即对重点保护区严格保护,加强生态缓冲区生态整治和廊道建设,以促进生态效益协同发展。在集中建设区与控制发展区引导城镇节约集约建设,减量增绿,实现社会经济绿色发展。
文摘在互联网码号资源公钥证书体系(Resource Public Key Infrastructure,RPKI)中,依赖方(Relying Party,RP)负责从资料库同步并验证资源证书和签名对象(ROAs,Manifests,Ghostbusters),而后将有效的ROA处理成用于指导BGP路由的IP地址块和AS号的真实授权关系.在当前的实现方式中,验证证书模块主要通过数据库查询递归查找待验证证书的父证书从而构建完整的证书链并由OpenSSL完成最终验证.由于RPKI体系中证书量较大,导致基于数据库查询的方法效率不足.结合RPKI运行机制中将计算代价由BGP路由器(用户)迁移到RP服务器(服务器)的特点和"空间换时间"的思想,可以将证书信息读取到内存中从而减少I/O的时间消耗.本文基于上述思想基础,结合哈希表中条目查询的时间复杂度最优为O(1)的特点,设计并实现了基于哈希表的RPKI证书验证优化方法.实验结果表明,在设计的3种实验场景中,平均时间加速比分别为99.03%、98.45%和97.48%,有效的减少了时间的消耗.
文摘In recent years, MIMO technology has emerged as one of the technical breakthroughs in the field of wireless communications. Two famous MIMO techniques have become investigated thoroughly throughout the literature;Spatial Multiplexing, and Space Time Block Coding. On one hand, Spatial Multiplexing offers high data rates. On the other hand, Space Time Block Coding presents transmission fidelity. This imposes a fundamental tradeoff between capacity and reliability. Adaptive MIMO Switching schemes have been proposed to select the MIMO scheme that best fits the channel conditions. However, the switching schemes presented in the literature directly switch between the MIMO endpoints. In this paper, an adaptive MIMO system that incrementally switches from multiplexing towards diversity is proposed. The proposed scheme is referred to as incremental diversity and can be set to operate in two different modes;Rate-Adaptive, and Energy-Conservative Incremental Diversity. Results indicate that the proposed incremental diversity framework achieves transmission reliability offered by MIMO diversity, while maintaining a gradual increase in spectral efficiency (in the Rate-Adaptive mode) or a reduction in required number of received symbols (in the Energy-Conservative mode) with increase in the SNR.
