In this paper, an Independent Window-Access(IWA) scheme is proposed, and the performance of an input-buffered ATM switching fabric with the IWA scheme is analysed by means of a probability generating function approach...In this paper, an Independent Window-Access(IWA) scheme is proposed, and the performance of an input-buffered ATM switching fabric with the IWA scheme is analysed by means of a probability generating function approach, the closed formulas of the average cell delay and the maximum throughput are given, and results show that the IWA scheme makes the switching fabric have better performances than traditional window-access scheme. The computer simulation results are in good agreement with these analytical results.展开更多
Dynamic spectrum access (DSA) scheme in Cognitive Radio (CR) can solve the current problem of scarce spectrum resource effectively, in which the unlicensed users (i.e. Second Users, SUs) can access the licensed spectr...Dynamic spectrum access (DSA) scheme in Cognitive Radio (CR) can solve the current problem of scarce spectrum resource effectively, in which the unlicensed users (i.e. Second Users, SUs) can access the licensed spectrum in opportunistic ways without interference to the licensed users (i.e. Primary Users, PUs). However, SUs have to vacate the spectrum because of PUs coming, in this case the spectrum switch occurs, and it leads to the increasing of SUs’ delay. In this paper, we proposed a Variable Service Rate (VSR) scheme with the switch buffer as to real-time traffic (such as VoIP, Video), in order to decrease the average switch delay of SUs and improve the other performance. Different from previous studies, the main characteristics of our studying of VSR in this paper as follows: 1) Our study is on the condition of real-time traffic and we establish three-dimension Markov model;2) Using the internal optimization strategy, including switching buffer, optimizing buffer and variable service rate;3) As to the real-time traffic, on the condition of meeting the Quality of Service(QoS) on dropping probability, the average switch delay is decreased as well as improving the other performance. By extensive simulation and numerical analysis, the performance of real-time traffic is improved greatly on the condition of ensuring its dropping probability. The result fully demonstrates the feasibility and effectiveness of the variable service rate scheme.展开更多
IEEE 802.11ax,which is an emerging WLAN standard,aims at providing highly efficient communication in ultra-dense wireless networks.However,due to a large number of stations(STAs)in the ultra-dense device deployment sc...IEEE 802.11ax,which is an emerging WLAN standard,aims at providing highly efficient communication in ultra-dense wireless networks.However,due to a large number of stations(STAs)in the ultra-dense device deployment scenarios,the potentially high packet collision rate significantly decreases the communication efficiency of WLAN.In this paper,we propose an adaptive STA grouping scheme to overcome this dense network challenge in IEEE 802.11ax by using Buffer State Report(BSR)based Two-stage Mechanism(BTM).In order to achieve the optimal efficiency of BSR delivery,we analyze the functional relationship between STA number in group and Resource Unit(RU)efficiency.Based on this analysis results,an adaptive STA grouping algorithm with variable group size is proposed to achieve efficient grouping in BTM.The numerical results demonstrate that the proposed adaptive BTM grouping algorithm significantly improves the BSR delivery efficiency and the throughput of overall system and each STA in the ultra-dense wireless network.展开更多
Bus stop accessibility is a vital component of a successful transportation system. This study aimed at spatially analyzing bus stops to determine their physical accessibility considering the connecting roads surroundi...Bus stop accessibility is a vital component of a successful transportation system. This study aimed at spatially analyzing bus stops to determine their physical accessibility considering the connecting roads surrounding the bus stops. This research used satellite imagery, Global Navigation Satellite System and Kaduna State Traffic and Environment Law Enforcement Authority documents. The spatial analysis covered bus stop accessibility and obtained data of transport routes, bus stop coordinates, bus stop spacing and physical characteristics of bus stops. GIS buffer, network and area analysis was used in measuring bus stop accessibility considering the road network surrounding it. The ratio of ideal access coverage to the actual access coverage of a stop was calculated. Paired sample statistics were used to compare ideal and actual access coverage;the finding revealed a significant difference between the ideal and actual access coverage. A range of 0 - 1.0 was used in the analysis where, a bus stop is less accessible the closer the value is to 0, and more accessible the closer the value is to 1.0. Linear regression statistics was used to determine if the level of accessibility of a bus stop is dependent on the length of roads within the buffer. This revealed that at R = 0.694, a strong degree of correlation exists between the level of accessibility and road length within the buffer. The study concluded that before siting bus stops, surrounding road networks need to be considered in order to make them accessible.展开更多
目的:利用地理信息系统(Geographic information system,GIS)分析预防接种门诊服务可及性,为合理规划预防接种服务模式提供依据。方法:运用平均最邻近方法分析区域内门诊空间分布模式,利用热点分析方法分析以疫苗接种量为权重区域内接...目的:利用地理信息系统(Geographic information system,GIS)分析预防接种门诊服务可及性,为合理规划预防接种服务模式提供依据。方法:运用平均最邻近方法分析区域内门诊空间分布模式,利用热点分析方法分析以疫苗接种量为权重区域内接种人员、接种周期冷链设备和门诊面积的配置和设置情况,缓冲区分析方法分析预防接种门诊服务范围。结果:此研究区域内预防接种门诊空间分布格局呈离散性,门诊接种人员、接种服务时间、冷链设备、门诊服务面积在空间上配置具有差异,并鉴别出资源配置充足的热点区域58个和资源配置薄弱的冷点区域15个,预防接种门诊服务的可及范围为28 666km2。结论:利用距离分析、空间热点分析、缓冲区分析方法分析预防接种门诊服务的空间分布格局、服务资源的配置情况、服务可及范围,可为区域内预防接种门诊服务模式和资源配置提供依据。展开更多
文摘In this paper, an Independent Window-Access(IWA) scheme is proposed, and the performance of an input-buffered ATM switching fabric with the IWA scheme is analysed by means of a probability generating function approach, the closed formulas of the average cell delay and the maximum throughput are given, and results show that the IWA scheme makes the switching fabric have better performances than traditional window-access scheme. The computer simulation results are in good agreement with these analytical results.
文摘Dynamic spectrum access (DSA) scheme in Cognitive Radio (CR) can solve the current problem of scarce spectrum resource effectively, in which the unlicensed users (i.e. Second Users, SUs) can access the licensed spectrum in opportunistic ways without interference to the licensed users (i.e. Primary Users, PUs). However, SUs have to vacate the spectrum because of PUs coming, in this case the spectrum switch occurs, and it leads to the increasing of SUs’ delay. In this paper, we proposed a Variable Service Rate (VSR) scheme with the switch buffer as to real-time traffic (such as VoIP, Video), in order to decrease the average switch delay of SUs and improve the other performance. Different from previous studies, the main characteristics of our studying of VSR in this paper as follows: 1) Our study is on the condition of real-time traffic and we establish three-dimension Markov model;2) Using the internal optimization strategy, including switching buffer, optimizing buffer and variable service rate;3) As to the real-time traffic, on the condition of meeting the Quality of Service(QoS) on dropping probability, the average switch delay is decreased as well as improving the other performance. By extensive simulation and numerical analysis, the performance of real-time traffic is improved greatly on the condition of ensuring its dropping probability. The result fully demonstrates the feasibility and effectiveness of the variable service rate scheme.
文摘IEEE 802.11ax,which is an emerging WLAN standard,aims at providing highly efficient communication in ultra-dense wireless networks.However,due to a large number of stations(STAs)in the ultra-dense device deployment scenarios,the potentially high packet collision rate significantly decreases the communication efficiency of WLAN.In this paper,we propose an adaptive STA grouping scheme to overcome this dense network challenge in IEEE 802.11ax by using Buffer State Report(BSR)based Two-stage Mechanism(BTM).In order to achieve the optimal efficiency of BSR delivery,we analyze the functional relationship between STA number in group and Resource Unit(RU)efficiency.Based on this analysis results,an adaptive STA grouping algorithm with variable group size is proposed to achieve efficient grouping in BTM.The numerical results demonstrate that the proposed adaptive BTM grouping algorithm significantly improves the BSR delivery efficiency and the throughput of overall system and each STA in the ultra-dense wireless network.
文摘Bus stop accessibility is a vital component of a successful transportation system. This study aimed at spatially analyzing bus stops to determine their physical accessibility considering the connecting roads surrounding the bus stops. This research used satellite imagery, Global Navigation Satellite System and Kaduna State Traffic and Environment Law Enforcement Authority documents. The spatial analysis covered bus stop accessibility and obtained data of transport routes, bus stop coordinates, bus stop spacing and physical characteristics of bus stops. GIS buffer, network and area analysis was used in measuring bus stop accessibility considering the road network surrounding it. The ratio of ideal access coverage to the actual access coverage of a stop was calculated. Paired sample statistics were used to compare ideal and actual access coverage;the finding revealed a significant difference between the ideal and actual access coverage. A range of 0 - 1.0 was used in the analysis where, a bus stop is less accessible the closer the value is to 0, and more accessible the closer the value is to 1.0. Linear regression statistics was used to determine if the level of accessibility of a bus stop is dependent on the length of roads within the buffer. This revealed that at R = 0.694, a strong degree of correlation exists between the level of accessibility and road length within the buffer. The study concluded that before siting bus stops, surrounding road networks need to be considered in order to make them accessible.
文摘目的:利用地理信息系统(Geographic information system,GIS)分析预防接种门诊服务可及性,为合理规划预防接种服务模式提供依据。方法:运用平均最邻近方法分析区域内门诊空间分布模式,利用热点分析方法分析以疫苗接种量为权重区域内接种人员、接种周期冷链设备和门诊面积的配置和设置情况,缓冲区分析方法分析预防接种门诊服务范围。结果:此研究区域内预防接种门诊空间分布格局呈离散性,门诊接种人员、接种服务时间、冷链设备、门诊服务面积在空间上配置具有差异,并鉴别出资源配置充足的热点区域58个和资源配置薄弱的冷点区域15个,预防接种门诊服务的可及范围为28 666km2。结论:利用距离分析、空间热点分析、缓冲区分析方法分析预防接种门诊服务的空间分布格局、服务资源的配置情况、服务可及范围,可为区域内预防接种门诊服务模式和资源配置提供依据。
