Xingshe Zhou

Delay analysis and study of IEEE 802.11p based DSRC safety communication in a highway environment

As a key enabling technology for the next generation inter-vehicle safety communications, The IEEE 802.11p protocol is currently attracting much attention. Many inter-vehicle safety communications have stringent real-time requirements on broadcast messages to ensure drivers have enough reaction time toward emergencies. Most existing studies only focus on the average delay performance of IEEE 802.11p, which only contains very limited information of the real capacity for inter-vehicle communication. In this paper, we propose an analytical model, showing the performance of broadcast under IEEE 802.11p in terms of the mean, deviation and probability distribution of the MAC access delay. Comparison with the NS-2 simulations validates the accuracy of the proposed analytical model. In addition, we show that the exponential distribution is a good approximation to the MAC access delay distribution. Numerical analysis indicates that the QoS support in IEEE 802.11p can provide relatively good performance guarantee for higher priority messages while fails to meet the real-time requirements of the lower priority messages.

LORA: Loss Differentiation Rate Adaptation Scheme for Vehicle-to-Vehicle Safety Communications

The existing study shows that safety applications supported by vehicle-to-vehicle (V2V) communications have the potential to address 80% of all road crash issues. IEEE 802.11p is a key enabling technology to support V2V safety applications. To meet the stringent delay and reliability requirements of these applications, rate adaptation (RA) approaches have been proposed to determine the optimal data transmission rate, according to the channel conditions such as packet losses. However, existing RA solutions cannot be directly applied to V2V safety communications in highway scenarios, which exhibit lots of dynamics and severe packet losses. Moreover, physical (PHY)-layer channel fading and medium-access-control (MAC)-layer interference contribute differently to the packet losses and, thus, should be treated separately. To address these issues, in this paper, we propose a LOss differentiation RA (LORA) scheme. LORA can estimate the average packet loss rate (PLR) for each sender and differentiate the fading losses from the interference losses. Extensive evaluation results demonstrate that LORA can provide reliability guarantees for V2V safety applications, as well as a response to environment changes in a real-time manner.

Intelligent joint spatio-temporal management of electric vehicle charging and data center power consumption

A data center is designed to have the capacity matching spike workload from a geographical region. This design concept comes with a significant waste of expense on power peak charged by the electrical grid, since workload fluctuations cause large variations in data center power demand. On the other hand, electric vehicles (EVs) have been emerging as major electricity consumers due to their large power demand for battery charging. In this paper, we propose a ValleyFill method that explores EVs to fill power valleys of geographically distributed data centers without increasing their power peaks. Leveraging geographical diversities of workload processing and temporal flexibilities of EV charging, this method determines routing scheme for workload and charging schedule for EVs to improve cost efficiency on the peak charge. We evaluate the proposed method with real-world workload traces and EV arrival patterns. The result shows that our method significantly improves the cost efficiency and saves up to 6% on total electricity bills. We observe that a data center with larger gap between its power peak and valley leads to less charging time for EVs and less workload migration.

Architecture for Distributed Embedded Systems Based on Workflow and Distributed Resource Management

Distributed embedded computing differs itself from traditional computing by its great heterogeneous, dynamic and non-standardized nature. This requires more powerful technologies that enable us to develop systems with more flexible architectures. Workflow technology achieves this by managing collaborations between system elements explicitly. However, in distributed embedded environment, current workflow systems could not be used directly for the reason of very different supporting platforms. Distributed resource management technology could bridge this gap. In this paper, we classify distributed embedded systems into fundamental types of elements representing both basic structural components and relationship between them. Then we present an architecture based on the integration of workflow and DRM systems according to our classification and analyze important coordination mechanisms among workflow, DRM systems and other elements. Ideas, such as utilizing function model to customize and optimize the design of systems, also reflect important principles to design distributed embedded systems.

Density-Aware Rate Adaptation for Vehicle Safety Communications in the Highway Environment

In this letter, we propose a density-aware rate adaptation (DARA) protocol to ensure reliable vehicle safety communication in a highway broadcast environment. DARA significantly improves system reliability by addressing the challenges of estimating channel conditions caused by various dynamics due to factors, including channel fading, interference, and varying traffic density. One salient advantage of DARA is that it can estimate the average packet loss rate for each sender locally without the use of any control frames (such as ACK and RTS/CTS). DARA can also distinguish the interference losses from the fading losses based on an empirical model. It adjusts the bit rate only in response to the packet loss due to channel fading and the change of the traffic density. Simulation results demonstrate that DARA can provide reliability guarantees for vehicle safety communication.

Agent Based Adaptive Cooperative Models and Mechanisms of Multiple Autonomous Cyber-Physical Systems

Networked cooperation is one primarily problem for autonomous Cyber-Physical Systems(CPS) that feature cyber-physical fusion, and smart behavior. After analyzing current contributions, a three-level task model, with which missions can be recognized and mapped to tasks, is studied firstly in this paper. And then, based on a designed uniform model of the surroundings, external missions and internal computational resources, two hybrid models, which are autonomously cooperative and real-time reactive by taking advantages of agent and adaptive control, are illuminated respectively. Further, a hierarchal cooperation mechanism of CPS fleet is put forward. With this mechanism, the dynamic topologies of a fleet will be more flexible and dependable, and by adopting an intelligent algorithm, all tasks mapped from a mission can be autonomously assigned to suitable members under decentralized consultation or centralized allocation mode. In this paper, an optimized genetic algorithm is employed to illustrate the process of proposed mechanisms.

An Adaptive Performance Management Method for Failure Detection

Failure detection is an essential part to build high dependable distributed real-time embedded systems. However, the performance degradation of production work due to the execution of failure detection cannot be omitted. We present an adaptive performance management method for failure detection based on feedback control theory. This method is autonomous and thus allows the system to self-manage the CPU resources allocated for failure detection, with only the high-level policy input. Therefore, it limits the performance impact due to the execution of failure detection, even in the dynamic environment.

IBP: an index-based XML parser model

With XML widely used in distributed system, the existing parser models, DOM and SAX, are inefficient and resource intensive for applications with large XML documents. This paper presents an index-based parser model (IBP), which contains validation and non-validation modes, supports nearly all the XML characteristics. IBP has the characters of speediness, robustness and low resource requirement, which is more suitable for mass information parsing. We presents the application of IBP in a real-time distributed monitoring prototype system, the results have shown IBP effective.

A Flexible Multi-Channel Coordination MAC Protocol for Vehicular Ad Hoc Networks

The IEEE 802.11p/1609.4 standard supports both safety applications and non-safety services for vehicular ad hoc networks (VANETs) via multi-channel operations. In this letter, we establish an analytical model to calculate the optimal bandwidth resource allocation and propose a flexible multi-channel coordination MAC (FMC-MAC) protocol for VANETs. The FMC-MAC protocol allows safety messages broadcasted on service channel and non-safety data transmitted on control channel in a flexible way. It does not only guarantee the reliability of safety applications, but also improve the throughput of non-safety services. The simulation results validate the analytical model and the proposed FMC-MAC protocol.

Application of a self-organizing fuzzy neural network controller with group-based genetic algorithm to greenhouse

As a complex nonlinear system, greenhouse can not be controlled perfectly by traditional control strategies. This paper proposes a self-organizing fuzzy neural network controller (SOFNNC) with group-based genetic algorithm (GGA) to drive the internal climate of the greenhouse. SOFFNNC is a hybrid control strategy which combines fuzzy control and neural network organically. It generates or prunes neurons automatically by the structure learning algorithm, which can adaptively strike a balance between the rule number and the desired performance. In other to avoid the shortage of the original learning algorithm to SOFNNC, we come up with an improved structure learning method and a new parameter learning method with GGA. Based on a greenhouse model established by an Elman neural network (ENN), we test the performance of SOFNNC. Simulation and comparison results prove that SOFNNC can achieve outstanding control effect with high efficiency.