The encoding and decoding processes of traffic channel in digital trunking system are studied. On the basis of computer simulation, the BER (bit error ratio) with different RCPC decoding step is analyzed. As a result,...The encoding and decoding processes of traffic channel in digital trunking system are studied. On the basis of computer simulation, the BER (bit error ratio) with different RCPC decoding step is analyzed. As a result, the optimal RCPC decoding step is provided, which gives essential theoretical evidences for the implementation of digital trunking system.展开更多
This paper presents a method of determining handover traffic and mean channel occu-pancy time of a traffic model for the LEO(Low Earth Orbit)satellite networks.The mainideas are that the handover traffic is mainly due...This paper presents a method of determining handover traffic and mean channel occu-pancy time of a traffic model for the LEO(Low Earth Orbit)satellite networks.The mainideas are that the handover traffic is mainly due to the movement of the satellite and that thevelocity of the mobile terminals and earth rotation are ignored.The performance level can becalculated according to different handover queuing models.展开更多
As the traffic distribution in China mainland is far from uniform, a new traffic model in China mainland is presented on the basis of per-capita Gross Domestic Product (GDP) and density of population. Based on this ch...As the traffic distribution in China mainland is far from uniform, a new traffic model in China mainland is presented on the basis of per-capita Gross Domestic Product (GDP) and density of population. Based on this characteristic traffic model, a new Traffic Dependent Dynamic Channel Allocation and Reservation (TDDCAR) technique is proposed, the simulation model is built, and the strategies' performance is evaluated through computer simulation. The simulation results show that, compared to the conventional Fixed Channel Allocation (FCA), TDDCAR estimates the traffic conditions in every spot beam and frequently adjusts the traffic according to current traffic conditions. It has achieved a significant improvement in new call blocking probability, handover blocking probability, and fair index, particularly, in heavy traffic conditions. The building of traffic model in China mainland and the analysis of the simulation results has been a key foundation for the study of resource allocation schemes in the future.展开更多
Flyovers are constructed to manage heavy through movement. However, traffic operations underneath a flyover remain unmanaged and often pose a major con- cern in developing countries with non-lane-based hetero- geneous...Flyovers are constructed to manage heavy through movement. However, traffic operations underneath a flyover remain unmanaged and often pose a major con- cern in developing countries with non-lane-based hetero- geneous traffic. This may reduce the overall benefit of a flyover. An alternative intersection layout is proposed to improve traffic operations at the intersection underneath a flyover. The proposed layout segregates the traffic move- ments through effective channelization. A traffic island is also proposed in the middle of the intersection to facilitate concurrent right-turning movements. This layout helps in eliminating a signal phase and cuts down traffic cycle time by 40 %. A microsimulation-based traffic simulation model is developed for the evaluation of the proposed layout. The simulation model demonstrates effectiveness of the proposed layout. Average delay and average queue length are compared to measure the effectiveness. Traffic volume sensitivity analysis is conducted to estimate the capacity of the proposed layout. An intersection underneath a flyover along the Eastern Expressway in Mumbai is considered for the case study. The effectiveness of the proposed layout at the study location for varying flow level is evaluated by comparing average delay, average stop delay, average number of stops per vehicle, average queue length, and maximum queue length.展开更多
A channel allocation scheme for hierarchical wireless networks was proposed in terms of the connection-level quality of service. The channel allocation scheme was analyzed using both horizontal channel borrowing and v...A channel allocation scheme for hierarchical wireless networks was proposed in terms of the connection-level quality of service. The channel allocation scheme was analyzed using both horizontal channel borrowing and vertical traffic overflowing. Pre-emptive priority strategies are used to classify real-time services and non-real-time services, real-time service is given higher priority for it is allowed to pre-empt channels used by non-real-time service. Some channel borrowing thresholds and acceptance ratios are used to avoid channel locking or dynamic power control, which can also be dynamically adjusted according to network load. Simulation results show that the proposed schemes can improve the system performance.展开更多
At intensive winter navigation, the ships should separate under movement on opposite courses or make overtaking of slowly moving cargo vessels in the water areas covered with ice. Under navigation within ice channel, ...At intensive winter navigation, the ships should separate under movement on opposite courses or make overtaking of slowly moving cargo vessels in the water areas covered with ice. Under navigation within ice channel, possibilities for maneuvering are reduced; therefore, danger of collision of ships exists. The ice floes between vessels hulls and outside are the major factors defining values and direction of side force and yawing moment that arise on their hulls during divergence. Ice loads on the ship hull exceed considerably the loads caused by water flow around hull. Performed previously experiments in the ice basin have detected that besides increase of side force and yawing moment modules the change of side force directions occurs during the divergence of vessels in comparison with same maneuvering on water area without ice cover. Article contains the detailed problem definition and mathematical model of ships interaction during opposite passing by or overtaking and technical approach to computation of loads on vessels hulls. As example of strategy application, the simulation of loads on overtaking ship was performed, and main results of computations are presented. Outcomes of investigation are character of variation of side force and yawing moment during passage along overtaken ship and dependence of the peak values of additional ice resistance, side force and yawing moment on beam distance between vessels and thickness that are contained in the article.展开更多
在无中心节点网络中可能存在不同类型的业务,部分高优先级业务具有严格的时延等服务质量(quality of service,QoS)需求。但当网络负载较重时,冲突概率明显提高,使得这些业务的需求难以得到保障,如何设计高效的多址接入协议以保证不同种...在无中心节点网络中可能存在不同类型的业务,部分高优先级业务具有严格的时延等服务质量(quality of service,QoS)需求。但当网络负载较重时,冲突概率明显提高,使得这些业务的需求难以得到保障,如何设计高效的多址接入协议以保证不同种类业务的服务质量是重要的研究方向。信道预约机制是保证QoS的重要方法,但现有信道预约机制对多种业务服务时,通常没有根据服务质量需求和网络状况精细调整预约参数。因此针对以上问题提出了一种面向差异化业务保障的信道预约MAC协议(differentiated service guarantee adaptive reservation mechanism,DSGARM),协议核心思想是针对每种业务的容忍时延需求和网络状况精细提供差异化服务,协议中通过建立的数学模型设计自适应算法,定量计算出满足时延需求的预约参数,能够根据网络状况自适应调整合适的预约参数以保障每一类业务的时延需求。仿真结果说明了提出协议的优势,具有较大的实际意义。展开更多
为科学评价信号交叉口右转渠化岛设置给非机动车过街带来的交通安全风险,实地采集了南昌市5个信号交叉口的视频,并提取了各交叉口右转渠化岛区域机非冲突数据、交叉口几何设计特征、交叉口渠化方式以及交通流特性等数据;采用改进型距离...为科学评价信号交叉口右转渠化岛设置给非机动车过街带来的交通安全风险,实地采集了南昌市5个信号交叉口的视频,并提取了各交叉口右转渠化岛区域机非冲突数据、交叉口几何设计特征、交叉口渠化方式以及交通流特性等数据;采用改进型距离碰撞时间(time to collision,TTC)对交通冲突进行判定,共得到304起冲突事件;基于贝叶斯方法构建了考虑不同交叉口间异质性的随机效应冲突模型,对比了固定效应与随机效应负二项模型的拟合优度并分析了显著影响因素;基于随机效应模型,确定了期望机非冲突数计算公式,绘制了不同交通流情况下信号交叉口渠化岛设置标准曲线并提供了案例说明。研究表明:相比于固定效应模型,随机效应模型对机非冲突有更好的拟合效果;相比于无渠化岛交叉口,软渠化岛和硬渠化岛的设置会导致交通冲突分别增加38%和61.4%;右转机动车交通量、过街非机动车交通量和非机动车违法行驶数量每增加1%,将导致机非冲突分别增加0.85%、0.44%和0.18%;右转机动车平均速度每增加1%,将导致机非冲突减少2.5%。研究成果为定量化分析交通冲突影响要素提供了有效思路,可为右转渠化岛交通设计提供理论支撑。展开更多
文摘The encoding and decoding processes of traffic channel in digital trunking system are studied. On the basis of computer simulation, the BER (bit error ratio) with different RCPC decoding step is analyzed. As a result, the optimal RCPC decoding step is provided, which gives essential theoretical evidences for the implementation of digital trunking system.
文摘This paper presents a method of determining handover traffic and mean channel occu-pancy time of a traffic model for the LEO(Low Earth Orbit)satellite networks.The mainideas are that the handover traffic is mainly due to the movement of the satellite and that thevelocity of the mobile terminals and earth rotation are ignored.The performance level can becalculated according to different handover queuing models.
文摘As the traffic distribution in China mainland is far from uniform, a new traffic model in China mainland is presented on the basis of per-capita Gross Domestic Product (GDP) and density of population. Based on this characteristic traffic model, a new Traffic Dependent Dynamic Channel Allocation and Reservation (TDDCAR) technique is proposed, the simulation model is built, and the strategies' performance is evaluated through computer simulation. The simulation results show that, compared to the conventional Fixed Channel Allocation (FCA), TDDCAR estimates the traffic conditions in every spot beam and frequently adjusts the traffic according to current traffic conditions. It has achieved a significant improvement in new call blocking probability, handover blocking probability, and fair index, particularly, in heavy traffic conditions. The building of traffic model in China mainland and the analysis of the simulation results has been a key foundation for the study of resource allocation schemes in the future.
文摘Flyovers are constructed to manage heavy through movement. However, traffic operations underneath a flyover remain unmanaged and often pose a major con- cern in developing countries with non-lane-based hetero- geneous traffic. This may reduce the overall benefit of a flyover. An alternative intersection layout is proposed to improve traffic operations at the intersection underneath a flyover. The proposed layout segregates the traffic move- ments through effective channelization. A traffic island is also proposed in the middle of the intersection to facilitate concurrent right-turning movements. This layout helps in eliminating a signal phase and cuts down traffic cycle time by 40 %. A microsimulation-based traffic simulation model is developed for the evaluation of the proposed layout. The simulation model demonstrates effectiveness of the proposed layout. Average delay and average queue length are compared to measure the effectiveness. Traffic volume sensitivity analysis is conducted to estimate the capacity of the proposed layout. An intersection underneath a flyover along the Eastern Expressway in Mumbai is considered for the case study. The effectiveness of the proposed layout at the study location for varying flow level is evaluated by comparing average delay, average stop delay, average number of stops per vehicle, average queue length, and maximum queue length.
基金The National Natural Science Foundation of China (No. 60372076)
文摘A channel allocation scheme for hierarchical wireless networks was proposed in terms of the connection-level quality of service. The channel allocation scheme was analyzed using both horizontal channel borrowing and vertical traffic overflowing. Pre-emptive priority strategies are used to classify real-time services and non-real-time services, real-time service is given higher priority for it is allowed to pre-empt channels used by non-real-time service. Some channel borrowing thresholds and acceptance ratios are used to avoid channel locking or dynamic power control, which can also be dynamically adjusted according to network load. Simulation results show that the proposed schemes can improve the system performance.
文摘At intensive winter navigation, the ships should separate under movement on opposite courses or make overtaking of slowly moving cargo vessels in the water areas covered with ice. Under navigation within ice channel, possibilities for maneuvering are reduced; therefore, danger of collision of ships exists. The ice floes between vessels hulls and outside are the major factors defining values and direction of side force and yawing moment that arise on their hulls during divergence. Ice loads on the ship hull exceed considerably the loads caused by water flow around hull. Performed previously experiments in the ice basin have detected that besides increase of side force and yawing moment modules the change of side force directions occurs during the divergence of vessels in comparison with same maneuvering on water area without ice cover. Article contains the detailed problem definition and mathematical model of ships interaction during opposite passing by or overtaking and technical approach to computation of loads on vessels hulls. As example of strategy application, the simulation of loads on overtaking ship was performed, and main results of computations are presented. Outcomes of investigation are character of variation of side force and yawing moment during passage along overtaken ship and dependence of the peak values of additional ice resistance, side force and yawing moment on beam distance between vessels and thickness that are contained in the article.
文摘在无中心节点网络中可能存在不同类型的业务,部分高优先级业务具有严格的时延等服务质量(quality of service,QoS)需求。但当网络负载较重时,冲突概率明显提高,使得这些业务的需求难以得到保障,如何设计高效的多址接入协议以保证不同种类业务的服务质量是重要的研究方向。信道预约机制是保证QoS的重要方法,但现有信道预约机制对多种业务服务时,通常没有根据服务质量需求和网络状况精细调整预约参数。因此针对以上问题提出了一种面向差异化业务保障的信道预约MAC协议(differentiated service guarantee adaptive reservation mechanism,DSGARM),协议核心思想是针对每种业务的容忍时延需求和网络状况精细提供差异化服务,协议中通过建立的数学模型设计自适应算法,定量计算出满足时延需求的预约参数,能够根据网络状况自适应调整合适的预约参数以保障每一类业务的时延需求。仿真结果说明了提出协议的优势,具有较大的实际意义。
文摘为科学评价信号交叉口右转渠化岛设置给非机动车过街带来的交通安全风险,实地采集了南昌市5个信号交叉口的视频,并提取了各交叉口右转渠化岛区域机非冲突数据、交叉口几何设计特征、交叉口渠化方式以及交通流特性等数据;采用改进型距离碰撞时间(time to collision,TTC)对交通冲突进行判定,共得到304起冲突事件;基于贝叶斯方法构建了考虑不同交叉口间异质性的随机效应冲突模型,对比了固定效应与随机效应负二项模型的拟合优度并分析了显著影响因素;基于随机效应模型,确定了期望机非冲突数计算公式,绘制了不同交通流情况下信号交叉口渠化岛设置标准曲线并提供了案例说明。研究表明:相比于固定效应模型,随机效应模型对机非冲突有更好的拟合效果;相比于无渠化岛交叉口,软渠化岛和硬渠化岛的设置会导致交通冲突分别增加38%和61.4%;右转机动车交通量、过街非机动车交通量和非机动车违法行驶数量每增加1%,将导致机非冲突分别增加0.85%、0.44%和0.18%;右转机动车平均速度每增加1%,将导致机非冲突减少2.5%。研究成果为定量化分析交通冲突影响要素提供了有效思路,可为右转渠化岛交通设计提供理论支撑。
