Zhu introduced typical analytical models to simulate the 802. 11e EDCF channel access protocol. But our analysis indicates that there are some inaccurate derivations in his presentation. This paper intends to improve ...Zhu introduced typical analytical models to simulate the 802. 11e EDCF channel access protocol. But our analysis indicates that there are some inaccurate derivations in his presentation. This paper intends to improve analytical model with some corrections. Furthermore, for the probability of the channel being busy pb in Zhu＇s model, different points and analysis method are proposed. When the network is under saturation condition, the new results about the probabilities of collision and channel busy, transmission probabilities, successful transmission probabilities, throughput and MAC layer latency are presented.展开更多
[目的]分析雅砻河流域生态系统服务价值的变化,为流域生态文明建设提供科学依据。[方法]基于高精度土地利用数据,运用地形梯度分级、标准差椭圆和地理探测器,探究了近20年流域生态系统服务价值(Ecosystem service value,ESV)的时空演变...[目的]分析雅砻河流域生态系统服务价值的变化,为流域生态文明建设提供科学依据。[方法]基于高精度土地利用数据,运用地形梯度分级、标准差椭圆和地理探测器,探究了近20年流域生态系统服务价值(Ecosystem service value,ESV)的时空演变和地形梯度分异特征。[结果](1)草地是流域主要的土地利用类型,占比达92.45%。研究期内林地、灌木和草地面积有所减少,其他类型有所增加;(2)流域ESV在研究期间增长了0.13%(0.16亿元),ESV在空间上呈现出东南部高西北部低的特征。随着海拔、坡度和地形起伏度的抬升,ESV呈先增后降的分布规律,坡向梯度呈阴坡高于阳坡的特征。(3)流域ESV的标准差椭圆和重心在研究期内逐渐向西南方向移动,并趋于聚集。ESV的空间分异主要受自然和经济因子的影响,其中年均地温是主导因子(q=0.24),任意因子交互均增强了其分异性。[结论]依据雅砻河流域ESV的时空和地形分布特征,采取因地制宜的生态保护措施,促进流域生态环境的可持续发展。展开更多
The object-based scalable coding in MPEG-4 is investigated, and a prioritized transmission scheme of MPEG-4 audio-visual objects （AVOs） over the DiffServ network with the QoS guarantee is proposed. MPEG-4 AVOs are e...The object-based scalable coding in MPEG-4 is investigated, and a prioritized transmission scheme of MPEG-4 audio-visual objects （AVOs） over the DiffServ network with the QoS guarantee is proposed. MPEG-4 AVOs are extracted and classified into different groups according to their priority values and scalable layers （visual importance）. These priority values are mapped to the 1P DiffServ per hop behaviors （PHB）. This scheme can selectively discard packets with low importance, in order to avoid the network congestion. Simulation results show that the quality of received video can gracefully adapt to network state, as compared with the ‘best-effort＇ manner. Also, by allowing the content provider to define prioritization of each audio-visual object, the adaptive transmission of object-based scalable video can be customized based on the content.展开更多
文摘Zhu introduced typical analytical models to simulate the 802. 11e EDCF channel access protocol. But our analysis indicates that there are some inaccurate derivations in his presentation. This paper intends to improve analytical model with some corrections. Furthermore, for the probability of the channel being busy pb in Zhu＇s model, different points and analysis method are proposed. When the network is under saturation condition, the new results about the probabilities of collision and channel busy, transmission probabilities, successful transmission probabilities, throughput and MAC layer latency are presented.
文摘[目的]分析雅砻河流域生态系统服务价值的变化,为流域生态文明建设提供科学依据。[方法]基于高精度土地利用数据,运用地形梯度分级、标准差椭圆和地理探测器,探究了近20年流域生态系统服务价值(Ecosystem service value,ESV)的时空演变和地形梯度分异特征。[结果](1)草地是流域主要的土地利用类型,占比达92.45%。研究期内林地、灌木和草地面积有所减少,其他类型有所增加;(2)流域ESV在研究期间增长了0.13%(0.16亿元),ESV在空间上呈现出东南部高西北部低的特征。随着海拔、坡度和地形起伏度的抬升,ESV呈先增后降的分布规律,坡向梯度呈阴坡高于阳坡的特征。(3)流域ESV的标准差椭圆和重心在研究期内逐渐向西南方向移动,并趋于聚集。ESV的空间分异主要受自然和经济因子的影响,其中年均地温是主导因子(q=0.24),任意因子交互均增强了其分异性。[结论]依据雅砻河流域ESV的时空和地形分布特征,采取因地制宜的生态保护措施,促进流域生态环境的可持续发展。
文摘The object-based scalable coding in MPEG-4 is investigated, and a prioritized transmission scheme of MPEG-4 audio-visual objects （AVOs） over the DiffServ network with the QoS guarantee is proposed. MPEG-4 AVOs are extracted and classified into different groups according to their priority values and scalable layers （visual importance）. These priority values are mapped to the 1P DiffServ per hop behaviors （PHB）. This scheme can selectively discard packets with low importance, in order to avoid the network congestion. Simulation results show that the quality of received video can gracefully adapt to network state, as compared with the ‘best-effort＇ manner. Also, by allowing the content provider to define prioritization of each audio-visual object, the adaptive transmission of object-based scalable video can be customized based on the content.
