Onboard resources are limited for multibeam satellite communication systems,while differences exist in traffic demands among users.Since conventional multigroup multicast precoding methods do not take traffic demands ...Onboard resources are limited for multibeam satellite communication systems,while differences exist in traffic demands among users.Since conventional multigroup multicast precoding methods do not take traffic demands for users into consideration,it is difficult to flexibly adjust the offered throughput to users’demands.Users with higher demand may obtain lower throughput while users with lower demand may be over-satisfied,which results in the requested-offered throughput mismatch and resource waste.This paper proposes a fair multigroup multicast precoding design based on traffic demands.To obtain the precoding design,the optimization problem aimed at maximizing the minimum throughput satisfaction ratio,which is defined as the ratio of the offered throughput to the traffic demand,is formulated,so as to provide fair service for all users while satisfying per-feed power constraints and traffic demand constraints.To address this problem,an auxiliary variable is first introduced to equivalently simplify it.Then,the semidefinite relaxation and the bisection search strategies are adopted to further handle the problem.Finally,the optimal precoding vectors are obtained by employing eigenvalue decomposition or Gaussian randomization.Simulation results indicate the effectiveness of the proposed precoding algorithm and demonstrate that it can better adapt to the scenarios with different traffic demands.展开更多
Management tactics for urban traffic management are presented.The tactics that underlie traffic demand management (TDM) are preferential development tactics, controlled development tactics,prohibited development tac...Management tactics for urban traffic management are presented.The tactics that underlie traffic demand management (TDM) are preferential development tactics, controlled development tactics,prohibited development tactics and economic lever tactics,and those that underlie traffic system management (TSM) are node traffic management tactics,arterial traffic management tactics and area traffic management tactics.The specific contents and design methods of urban traffic total demand control,urban traffic structure optimization,road traffic movement organization based on TDM and intersection traffic management,road signs and markings management,optimized design of traffic signals and management of parking spaces based on TSM are put forward.The urban traffic management planning scheme design method has already been used in the urban traffic management “Smooth Traffic Project” in China.展开更多
With the rapid development of economy and motorization, the traffic congestion and environmental problems have become more and more serious day by day in Beijing. Therefore, traffic control policies have been graduall...With the rapid development of economy and motorization, the traffic congestion and environmental problems have become more and more serious day by day in Beijing. Therefore, traffic control policies have been gradually adopted by Beijing municipal government since 2008, so as to ease traffic and environmental problems. In this paper, the background and current situation of Beijing to implement traffic control policies are introduced, and also this measure is analyzed and evaluated from traffic effect, environmental effect, motor vehicle development, urban road development, public transport development, and balance between supply and demand, etc. Finally, related conclusions are drawn up as follows: an induced traffic volume will be generated by traffic control policies, and the effect of the traffic control will be erased by the natural growth rate of motor vehicles in three years; public traffic service should be improved for better making traffic control policies; the traffic congestion and environmental problems are alleviated by traffic control policies in the short term, but can't be fundamentally solved in the long run; traffic control policies should cooperate with other traffic demand management policies for reducing demands, and traffic condition should be optimized in both time and space, so that the traffic congestion and environmental problems will be fundamentally solved.展开更多
Based on two main hypotheses of traffic economical equilibrium and the relationship between traffic density and the demand, an evolution equation of traffic cost was proposed to describe the change of cost under decre...Based on two main hypotheses of traffic economical equilibrium and the relationship between traffic density and the demand, an evolution equation of traffic cost was proposed to describe the change of cost under decreasing toll. Economical explanation of the model and a numerical case were given to demonstrate the constraint between the marginal traffic demand and the flow velocity. Key words traffic demand and cost - traffic flow - evolution equation - decreasing toll MSC2000 90B20 - 91B24展开更多
An iterative process,combining a macroscopic simulator and a set of the traffic demand-change estimation models,is developed to estimate the traffic demand at work zones in urban freeway corridors.The process is desig...An iterative process,combining a macroscopic simulator and a set of the traffic demand-change estimation models,is developed to estimate the traffic demand at work zones in urban freeway corridors.The process is designed to capture the interaction between work-zone conditions and traffic diversion in determining the traffic demand approaching the entrance and exit ramps at a given work zone.The proposed models and process were calibrated and tested with the field data from the work zones in the Minnesota metro-freeway network.The test results indicate promising possibilities of the proposed process in terms of the estimation accuracy and transferability of the demand-change estimation models developed in this study.展开更多
The post-earthquake emergency period,which is a sensitive time segment just after an event,mainly focuses on saving life and restoring social order.To improve the seismic resilience of city road networks,a resilience ...The post-earthquake emergency period,which is a sensitive time segment just after an event,mainly focuses on saving life and restoring social order.To improve the seismic resilience of city road networks,a resilience evaluation method used in the post-earthquake emergency period is proposed.The road seismic damage index of a city road network can consider the influence of roads,bridges and buildings along the roads,etc.on road capacity after an earthquake.A function index for a city road network is developed,which reflects the connectivity,redundancy,traffic demand and traffic function of the network.An optimization model for improving the road repair order in the post-earthquake emergency period is also developed according to the resilience evaluation,to enable decision support for city emergency management and achieve the best seismic resilience of the city road network.The optimization model is applied to a city road network and the results illustrate the feasibility of the resilience evaluation and optimization method for a city road network in the post-earthquake emergency period.展开更多
The rapid development and continuous updating of the mega satellite constellation(MSC)have brought new visions for the future 6G coverage extension, where the global seamless signal coverage can realize ubiquitous ser...The rapid development and continuous updating of the mega satellite constellation(MSC)have brought new visions for the future 6G coverage extension, where the global seamless signal coverage can realize ubiquitous services for user terminals. However, global traffic demands present nonuniform characteristics. Therefore, how to ensure the on-demand service coverage for the specific traffic demand, i.e., the ratio of traffic density to service requirement per unit area, is the core issue of 6G wireless coverage extension exploiting the MSC. To this regard, this paper first discusses the open challenges to reveal the future direction of 6G wireless coverage extension from the perspective of key factors affecting service coverage performance, i.e., the network access capacity, space segment capacity and their matchingrelationship. Furthermore, we elaborate on the key factors affecting effective matchings of the aforementioned aspects, thereby improving service coverage capability.展开更多
in order to project a reliable telecommunication network ,we have to measure the call lossrate of present traffic and to predzct the traffic of hajective network. In this paper we point out that afactor of real commun...in order to project a reliable telecommunication network ,we have to measure the call lossrate of present traffic and to predzct the traffic of hajective network. In this paper we point out that afactor of real communication needs for subscrihas should be added in studying the traffic source char-acterization. Generally, the predicted traffic does not equal to the real demends, Considered asubscriber's psychological facter for attempts in busy-hour, a mathematical medel of probable dertva-tive calls from each real communication demand is given,with which the calling-up probabity, andthe repeating attempt probability of original subscribers on line occupation are calculated and the rela-tionship between the traffic and the real cammunication need is predicted.展开更多
Theoretical research often assumes all users arc homogeneous in their route choice decision and will always pick the route with the shortest travel cost,which is not necessarily the case in reality.This paper document...Theoretical research often assumes all users arc homogeneous in their route choice decision and will always pick the route with the shortest travel cost,which is not necessarily the case in reality.This paper documents the research effort in developing a Constrained Time-Dependent K Shortest Paths Algorithm inorder to find K Shortest Paths between two given locations.The goal of this research is to provide sound route options to travelers in order to assist their route choice decision process,during which the overlap and travel time deviation issues between the K paths will be considered.The proposed algorithm balancing overlap and travel time deviation is developed in this research.A numerical analysis is conducted on the Tucson 1-10 network,the outcome of the case study shows that our proposed algorithm is able to find different shortest paths with a reasonable degree of similarity and close travel time,which indicates that the result of the proposed algorithm is satisfactory.展开更多
This paper reports the effects of using an "odd and even" traffic restriction policy in Beijing during the 2008 Olympic Games. Based on data from 529 traffic detectors on the expressway network and some main arteria...This paper reports the effects of using an "odd and even" traffic restriction policy in Beijing during the 2008 Olympic Games. Based on data from 529 traffic detectors on the expressway network and some main arterials in Beijing, China, a comparative analysis has been carried out on the following parameters: the total traffic volume within the expressway network, the total traffic volume on different ring expressways, the traffic volume and speed of a freeway segment, and an arterial street before and after the implementation of the traffic restriction policy. The results show that during the traffic restriction period, although more than 50% of vehicles were forbidden to travel in Beijing, the traffic volume was only reduced by 20%-40% while the travel speed had been increased by 10%-20%. This suggests that such traffic restriction policy may be an effective shortterm management measure in dealing with increased transportation demand and congestion during major events, such as the Olympic Games. Results also indicate that vehicle travel demand does not decrease with the same proportion as the total vehicles forbidden, at least for the expressway and main arterials in a city.展开更多
Traditional trip generation forecasting methods use unified average trip generation rates to determine trip generation volumes in various traffic zones without considering the individual characteristics of each traffi...Traditional trip generation forecasting methods use unified average trip generation rates to determine trip generation volumes in various traffic zones without considering the individual characteristics of each traffic zone. Therefore, the results can have significant errors. To reduce the forecasting error produced by uniform trip generation rates for different traffic zones, the behavior of each traveler was studied instead of the characteristics of the traffic zone. This paper gives a method for calculating the trip efficiency and the effect of traffic zones combined with a destination selection model based on disaggregate theory for trip generation. Beijing data is used with the trip generation method to predict trip volumes. The results show that the disaggregate model in this paper is more accurate than the traditional method. An analysis of the factors influencing traveler behavior and destination selection shows that the attractiveness of the traffic zone strongly affects the trip generation volume.展开更多
Understanding the characteristics of passenger vehicle use is the prerequisite for effective urban management.However,it has been challenging in the existing literature due to the lack of continuously observed data on...Understanding the characteristics of passenger vehicle use is the prerequisite for effective urban management.However,it has been challenging in the existing literature due to the lack of continuously observed data on passenger vehicle use.Thanks to the advances in data collection and processing techniques,multi-day vehicle trajectory data generated from volunteered passenger cars provide new opportunities for examining in depth how people travel in regular patterns.In this paper,based on a week’s operation data of 6600 passenger cars in Shanghai,we develop a systematic approach for identifying trips and travel purposes,and classify vehicles into four categories using a Gaussian-Mixed-Model.A new method is proposed to identify vehicle travel regularities and we use the Z Test to explore differences in travel time and route choices between four types of vehicles.Wefind that commercially used vehicles present high travel intensity in temporal and spatial aspects and the use intensity in elevated roads is higher for household-used commuting vehicles than semi-commercially used vehicles.The methodologies and conclusions of this paper may provide not only theoretical support for future urban traffic prediction,but also guidance for employing customized active traffic demand management measures to alleviate traffic congestion.展开更多
Over the past few decades, urban freeway congestion has been highly recognized as a serious and worsening traffic problem in the world. To relieve freeway congestion, several active traffic and demand management (ATD...Over the past few decades, urban freeway congestion has been highly recognized as a serious and worsening traffic problem in the world. To relieve freeway congestion, several active traffic and demand management (ATDM) methods have been developed. Among them, variable speed limit (VSL) aims at regulating freeway mainline flow upstream to meet existing capacity and to harmonize vehicle speed. However, congestion may still be inevitable even with VSL implemented due to extremely high demand in actual practice. This study modified an existing VSL strategy by adding a new local constraint to suggest an achievable speed limit during the control period. As a queue is a product of the congestion phenomenon in freeway, the incentives of a queue build-up in the applied coordinated VSL control situation were analyzed. Considering a congestion occurrence (a queue build-up) characterized by a sudden and sharp speed drop, speed contours were utilized to demonstrate the congestion distribution over a whole freeway network in various sce- narios. Finally, congestion distributions found in both VSL control and non-VS control situations for various scenarios were investigated to explore the impact of the applied coordinated VSL control on the congestion distribution. An authentic stretch of V^hitemud Drive (I~~ID), an urban freeway corridor in Edmonton, Alberta, Canada, was employed to implement this modified coordinated VSL control strategy; and a calibrated micro-simu- lation VISSIM model (model functions) was applied as the substitute of the real-world traffic system to test the above mentioned performance. The exploration task in this study can lay the groundwork for future research on how to improve the presented VSL control strategy for achieving the congestion mitigation effect on freeway.展开更多
基金the National Key R&D Program of China(No.2020YFB1806800).
文摘Onboard resources are limited for multibeam satellite communication systems,while differences exist in traffic demands among users.Since conventional multigroup multicast precoding methods do not take traffic demands for users into consideration,it is difficult to flexibly adjust the offered throughput to users’demands.Users with higher demand may obtain lower throughput while users with lower demand may be over-satisfied,which results in the requested-offered throughput mismatch and resource waste.This paper proposes a fair multigroup multicast precoding design based on traffic demands.To obtain the precoding design,the optimization problem aimed at maximizing the minimum throughput satisfaction ratio,which is defined as the ratio of the offered throughput to the traffic demand,is formulated,so as to provide fair service for all users while satisfying per-feed power constraints and traffic demand constraints.To address this problem,an auxiliary variable is first introduced to equivalently simplify it.Then,the semidefinite relaxation and the bisection search strategies are adopted to further handle the problem.Finally,the optimal precoding vectors are obtained by employing eigenvalue decomposition or Gaussian randomization.Simulation results indicate the effectiveness of the proposed precoding algorithm and demonstrate that it can better adapt to the scenarios with different traffic demands.
基金The National Natural Science Foundation of China(No.50378016).
文摘Management tactics for urban traffic management are presented.The tactics that underlie traffic demand management (TDM) are preferential development tactics, controlled development tactics,prohibited development tactics and economic lever tactics,and those that underlie traffic system management (TSM) are node traffic management tactics,arterial traffic management tactics and area traffic management tactics.The specific contents and design methods of urban traffic total demand control,urban traffic structure optimization,road traffic movement organization based on TDM and intersection traffic management,road signs and markings management,optimized design of traffic signals and management of parking spaces based on TSM are put forward.The urban traffic management planning scheme design method has already been used in the urban traffic management “Smooth Traffic Project” in China.
基金National Natural Science Foundation of China (Youth Foundation): Study on the Operating Efficiency and Energy Consumption Optimization Methods of the Regional Passenger Transport System (71201006) (Xuesong FENG)
文摘With the rapid development of economy and motorization, the traffic congestion and environmental problems have become more and more serious day by day in Beijing. Therefore, traffic control policies have been gradually adopted by Beijing municipal government since 2008, so as to ease traffic and environmental problems. In this paper, the background and current situation of Beijing to implement traffic control policies are introduced, and also this measure is analyzed and evaluated from traffic effect, environmental effect, motor vehicle development, urban road development, public transport development, and balance between supply and demand, etc. Finally, related conclusions are drawn up as follows: an induced traffic volume will be generated by traffic control policies, and the effect of the traffic control will be erased by the natural growth rate of motor vehicles in three years; public traffic service should be improved for better making traffic control policies; the traffic congestion and environmental problems are alleviated by traffic control policies in the short term, but can't be fundamentally solved in the long run; traffic control policies should cooperate with other traffic demand management policies for reducing demands, and traffic condition should be optimized in both time and space, so that the traffic congestion and environmental problems will be fundamentally solved.
文摘Based on two main hypotheses of traffic economical equilibrium and the relationship between traffic density and the demand, an evolution equation of traffic cost was proposed to describe the change of cost under decreasing toll. Economical explanation of the model and a numerical case were given to demonstrate the constraint between the marginal traffic demand and the flow velocity. Key words traffic demand and cost - traffic flow - evolution equation - decreasing toll MSC2000 90B20 - 91B24
文摘An iterative process,combining a macroscopic simulator and a set of the traffic demand-change estimation models,is developed to estimate the traffic demand at work zones in urban freeway corridors.The process is designed to capture the interaction between work-zone conditions and traffic diversion in determining the traffic demand approaching the entrance and exit ramps at a given work zone.The proposed models and process were calibrated and tested with the field data from the work zones in the Minnesota metro-freeway network.The test results indicate promising possibilities of the proposed process in terms of the estimation accuracy and transferability of the demand-change estimation models developed in this study.
基金National Natural Science Foundation of China under Grant Nos.U1939210 and 51825801。
文摘The post-earthquake emergency period,which is a sensitive time segment just after an event,mainly focuses on saving life and restoring social order.To improve the seismic resilience of city road networks,a resilience evaluation method used in the post-earthquake emergency period is proposed.The road seismic damage index of a city road network can consider the influence of roads,bridges and buildings along the roads,etc.on road capacity after an earthquake.A function index for a city road network is developed,which reflects the connectivity,redundancy,traffic demand and traffic function of the network.An optimization model for improving the road repair order in the post-earthquake emergency period is also developed according to the resilience evaluation,to enable decision support for city emergency management and achieve the best seismic resilience of the city road network.The optimization model is applied to a city road network and the results illustrate the feasibility of the resilience evaluation and optimization method for a city road network in the post-earthquake emergency period.
基金supported in part by the National Key R&D Program of China under Grant 2020YFB1806100in part by the Natural Science Foundation of China under Grants U19B2025, 62121001, 62001347, and 61801361。
文摘The rapid development and continuous updating of the mega satellite constellation(MSC)have brought new visions for the future 6G coverage extension, where the global seamless signal coverage can realize ubiquitous services for user terminals. However, global traffic demands present nonuniform characteristics. Therefore, how to ensure the on-demand service coverage for the specific traffic demand, i.e., the ratio of traffic density to service requirement per unit area, is the core issue of 6G wireless coverage extension exploiting the MSC. To this regard, this paper first discusses the open challenges to reveal the future direction of 6G wireless coverage extension from the perspective of key factors affecting service coverage performance, i.e., the network access capacity, space segment capacity and their matchingrelationship. Furthermore, we elaborate on the key factors affecting effective matchings of the aforementioned aspects, thereby improving service coverage capability.
文摘in order to project a reliable telecommunication network ,we have to measure the call lossrate of present traffic and to predzct the traffic of hajective network. In this paper we point out that afactor of real communication needs for subscrihas should be added in studying the traffic source char-acterization. Generally, the predicted traffic does not equal to the real demends, Considered asubscriber's psychological facter for attempts in busy-hour, a mathematical medel of probable dertva-tive calls from each real communication demand is given,with which the calling-up probabity, andthe repeating attempt probability of original subscribers on line occupation are calculated and the rela-tionship between the traffic and the real cammunication need is predicted.
文摘Theoretical research often assumes all users arc homogeneous in their route choice decision and will always pick the route with the shortest travel cost,which is not necessarily the case in reality.This paper documents the research effort in developing a Constrained Time-Dependent K Shortest Paths Algorithm inorder to find K Shortest Paths between two given locations.The goal of this research is to provide sound route options to travelers in order to assist their route choice decision process,during which the overlap and travel time deviation issues between the K paths will be considered.The proposed algorithm balancing overlap and travel time deviation is developed in this research.A numerical analysis is conducted on the Tucson 1-10 network,the outcome of the case study shows that our proposed algorithm is able to find different shortest paths with a reasonable degree of similarity and close travel time,which indicates that the result of the proposed algorithm is satisfactory.
基金supported by National Key Technology R&D Program(No.2012 BAJ05B04)Hang Lung Center for Real Estate,Tsinghua UniversityCollaborative Innovation Center for Capital World City's Smooth Traffic Construction
文摘This paper reports the effects of using an "odd and even" traffic restriction policy in Beijing during the 2008 Olympic Games. Based on data from 529 traffic detectors on the expressway network and some main arterials in Beijing, China, a comparative analysis has been carried out on the following parameters: the total traffic volume within the expressway network, the total traffic volume on different ring expressways, the traffic volume and speed of a freeway segment, and an arterial street before and after the implementation of the traffic restriction policy. The results show that during the traffic restriction period, although more than 50% of vehicles were forbidden to travel in Beijing, the traffic volume was only reduced by 20%-40% while the travel speed had been increased by 10%-20%. This suggests that such traffic restriction policy may be an effective shortterm management measure in dealing with increased transportation demand and congestion during major events, such as the Olympic Games. Results also indicate that vehicle travel demand does not decrease with the same proportion as the total vehicles forbidden, at least for the expressway and main arterials in a city.
基金the National Natural Science Foundation of China (No. 50478041)the Natural Science Foundation of Beijing (No. 8053019)
文摘Traditional trip generation forecasting methods use unified average trip generation rates to determine trip generation volumes in various traffic zones without considering the individual characteristics of each traffic zone. Therefore, the results can have significant errors. To reduce the forecasting error produced by uniform trip generation rates for different traffic zones, the behavior of each traveler was studied instead of the characteristics of the traffic zone. This paper gives a method for calculating the trip efficiency and the effect of traffic zones combined with a destination selection model based on disaggregate theory for trip generation. Beijing data is used with the trip generation method to predict trip volumes. The results show that the disaggregate model in this paper is more accurate than the traditional method. An analysis of the factors influencing traveler behavior and destination selection shows that the attractiveness of the traffic zone strongly affects the trip generation volume.
基金supported by the project of the National Natural Science Foundation of China(No.71734004)。
文摘Understanding the characteristics of passenger vehicle use is the prerequisite for effective urban management.However,it has been challenging in the existing literature due to the lack of continuously observed data on passenger vehicle use.Thanks to the advances in data collection and processing techniques,multi-day vehicle trajectory data generated from volunteered passenger cars provide new opportunities for examining in depth how people travel in regular patterns.In this paper,based on a week’s operation data of 6600 passenger cars in Shanghai,we develop a systematic approach for identifying trips and travel purposes,and classify vehicles into four categories using a Gaussian-Mixed-Model.A new method is proposed to identify vehicle travel regularities and we use the Z Test to explore differences in travel time and route choices between four types of vehicles.Wefind that commercially used vehicles present high travel intensity in temporal and spatial aspects and the use intensity in elevated roads is higher for household-used commuting vehicles than semi-commercially used vehicles.The methodologies and conclusions of this paper may provide not only theoretical support for future urban traffic prediction,but also guidance for employing customized active traffic demand management measures to alleviate traffic congestion.
基金supported by the Natural Sciences and Engineering Research Council(NSERC) of Canada, City of Edmonton,and Transport Canadasupported by the National Natural Science Foundation of China(No.51208052,51308058)the Science and Technology Research and Development Program of Shaanxi Province,China(No.2013K13-04-02)
文摘Over the past few decades, urban freeway congestion has been highly recognized as a serious and worsening traffic problem in the world. To relieve freeway congestion, several active traffic and demand management (ATDM) methods have been developed. Among them, variable speed limit (VSL) aims at regulating freeway mainline flow upstream to meet existing capacity and to harmonize vehicle speed. However, congestion may still be inevitable even with VSL implemented due to extremely high demand in actual practice. This study modified an existing VSL strategy by adding a new local constraint to suggest an achievable speed limit during the control period. As a queue is a product of the congestion phenomenon in freeway, the incentives of a queue build-up in the applied coordinated VSL control situation were analyzed. Considering a congestion occurrence (a queue build-up) characterized by a sudden and sharp speed drop, speed contours were utilized to demonstrate the congestion distribution over a whole freeway network in various sce- narios. Finally, congestion distributions found in both VSL control and non-VS control situations for various scenarios were investigated to explore the impact of the applied coordinated VSL control on the congestion distribution. An authentic stretch of V^hitemud Drive (I~~ID), an urban freeway corridor in Edmonton, Alberta, Canada, was employed to implement this modified coordinated VSL control strategy; and a calibrated micro-simu- lation VISSIM model (model functions) was applied as the substitute of the real-world traffic system to test the above mentioned performance. The exploration task in this study can lay the groundwork for future research on how to improve the presented VSL control strategy for achieving the congestion mitigation effect on freeway.