Cooperative Adaptive Cruise Control Using Delay-Based Spacing Policy:A Robust Adaptive Non-Singular Terminal Sliding Mode Approach

This study proposes two speed controllers based on a robust adaptive non-singular terminal sliding mode control approach for the cooperative adaptive cruise control problem in a connected and automated vehicular platoon.The delay-based spacing policy is adopted to guarantee that all vehicles in the platoon track the same target velocity profile at the same position while maintaining a predefined time gap.Factors such as nonlinear vehicle longitudinal dynamics,engine dynamics with time delay,undulating road profiles,parameter uncertainties,and external disturbances are considered in the system modeling and controller design.Different control objectives are assigned to the leading and following vehicles.Then,controllers consisting of a sliding mode controller with parameter adaptive laws based on the ego vehicle’s state deviation and linear coupled state errors,and a Smith predictor for time delay compensation are designed.Both inner stability and strong string stability are guaranteed in the case of nonlinear sliding manifolds.Finally,the effectiveness of the proposed controllers and the benefits of 44.73%shorter stabilization time,11.20%less speed overshoot,and virtually zero steady-state inner vehicle distance deviation are illustrated in a simulation study of a seven-vehicle platoon cooperative adaptive cruise control and comparison experiments with a coupled sliding mode control approach.

Integrated Spacing Policy Considering Micro- and Macroscopic Characteristics

An appropriate spacing policy improves traffic flow and traffic efficiency while reducing commuting time and energy con-sumption.In this paper,the integrated spacing policy that combines the benefits of the constant time headway(CTH)and safety distance(SD)spacing policies is proposed in an attempt to improve traffic flow and efficiency.Firstly,the performance of the CTH and SD spacing policies is analyzed from the perspective of the microscopic characteristics of human-vehicle and the macroscopic characteristics of traffic flow.The switching law between CTH and SD spacing policies and the integrated spacing policy are then proposed to increase traffic efficiency according to the traffic conditions,and the critical speed for the proposed integrated spacing policy is derived.Using the proposed switching law,the integrated spacing policy utilizes the safety redundancy difference between the CTH and SD spacing policies in a flexible manner.Simulation tests demon-strate that the proposed integrated spacing policy increases traffic flow and that the traffic flow maintains string stability in a wider range of traffic flow density.

Evolution of National Space Policy as Predominantly Implicit Policy: India, an Intrinsic Case Study

India,despite being a leading space-faring nation,and operating one of the six largest space programmes in the world,has developed little in terms of expressly documented national space policy over its 58-year history of space activity-besides two standalone policy documents primarily designed to address some operational policy issues pertaining to satellite communication services and use of remote sensing data.However,the Indian space programme,given its phenomenal technological advancements and operational maturity achieved over the decades,clearly exhibits evidence of having been continually and consistently guided,since its very inception,by a cohesive and consistent policy so far as its directional and strategic policy aspects are concerned.In other words,there does exist an apparent undeclared policy embedded in the Indian space establishment that has continued to inform and guide its strategic decisions and actions.The objective of the present case-study is to systematically describe the evolution of the national space policy of India,predominantly as implicit policy,as reflected by the key decisions and actions of the Indian national space establishment since beginning of the Indian space programme.This analysis strives to identify the directional and the strategic elements of policy as reflected by the decisions and actions of the space establishment,and the socio-economic,technological,political and institutional factors that have influenced such policies.

On String Stable Control of Platoon of Automated Vehicles with Predecessor-successor Information Framework

For the constant distance spacing policy,the existing researches of the string stability focus on the single-predecessor information framework（SPIF） and predecessor-successor information framework（PSIF）.The research results demonstrated that the string stability could not be guaranteed with the SPIF,and then the PSIF was proposed to resolve this string instability.But the issue,whether the string stability can be guaranteed when applying the PSIF,is still controversial.Meanwhile,most of the previous researches on the string stability were conducted without consideration of the parasitic time delays and lags.In this paper,the practical longitudinal vehicle dynamics model is built with consideration of the parasitic time delays and lags existing in the actuators,sensors or the communication systems.Secondly,the detailed theoretical analysis of string stability in frequency domain is conducted to demonstrate that the classical linear control laws can not ensure the string stability when applying both the symmetrical PSIF（SPSIF） and asymmetrical PSIF（APSIF）.Thirdly,a control law,which adds the position and velocity information of the leading vehicle,is proposed to guarantee string stability for small/medium platoon,and the other control law,which adds the acceleration information of the controlled vehicle,is proposed to guarantee string stability for large platoon as well as small/medium platoon.Finally,the comparative simulation is conducted to confirm the conducted analysis and the proposed control laws.The conducted research completes the means to analyze the string stability in frequency domain,provides the parameters＇ reference for the design and implementation of the practical automatic following controllers,and improves the reliability and stability of the platoon of automatic vehicles.

国际商业航天市场与政策分析

At present,in the world the development of space is undergoing profound changes brought by commercial space,from the traditional government-driven development to the joint government and market promotion.This paper analyzes the current status of both foreign and domestic commercial space markets and policies,and then put forward the ideas and inspirations for the development of China’s commercial space market.

A Study on the Trend of China＇s Space Legislation

The slow progress and lack of fundamental breakthroughs in legislative practices are an important subject for China's space legislation. Oriented by the idea to formulate China's space law as soon as possible, it is necessary to solve five key issues. In the national policy, it is needful not only to implement China's space policy and promote the development of the space industry in depth, but also to advance the deep integration of military and civil application in space field. In terms of legal orientation, three features should be reflected upon, including the functional integration of public and private laws, the balance of regulation by substantive and procedural laws, and the effective coordination of domestic and international laws. To this end, both top-level design and implementation should be paid close attention to in order to achieve significant progress in China's space legislation.

The Role of Planning in National Innovative City Development: On the Evolution and Implementation Effect of Shenzhen Industry Layout Planning

From the two perspectives of urban development and industrial development, this paper presents and explains the stage characteristics of the evolution process of Shenzhen to build a national innovative city, on which both the urban and the industrial policies produce remarkable influences. By analyzing three cases of industry layout planning of Shenzhen, in particular the evolution of planning thoughts and the implementation effect of the plans, this paper argues that an effective industry layout planning should focus on studying the spatial requirements of industries and creating the suitable physical environment for industrial development instead of directly arranging the layout of various industries. Moreover, the implementation of the latest planning policy in Shenzhen proves that the industry space policies issued by the local government should be problem-oriented and be aimed to solve the practical difficulties in the innovative development.

Markov decision processes associated with two threshold probability criteria

This paper deals with Markov decision processes with a target set for nonpositive rewards. Two types of threshold probability criteria are discussed. The first criterion is a probability that a total reward is not greater than a given initial threshold value, and the second is a probability that the total reward is less than it. Our first （resp. second） optimizing problem is to minimize the first （resp. second） threshold probability. These problems suggest that the threshold value is a permissible level of the total reward to reach a goal （the target set）, that is, we would reach this set over the level, if possible. For the both problems, we show that 1） the optimal threshold probability is a unique solution to an optimality equation, 2） there exists an optimal deterministic stationary policy, and 3） a value iteration and a policy space iteration are given. In addition, we prove that the first （resp. second） optimal threshold probability is a monotone increasing and right （resp. left） continuous function of the initial threshold value and propose a method to obtain an optimal policy and the optimal threshold probability in the first problem by using them in the second problem.