Current Issue : January - March Volume : 2012 Issue Number : 1 Articles : 5 Articles
As the environmental pollution and energy crises are getting more and more remarkable, hybrid electric vehicles (HEVs) have taken on an accelerated pace in the world. A comprehensive overview of HEVs is presented in this paper, with the emphasis on configurations, main issues, and energy management strategies. Conclusions are discussed finally....
The problem of resource allocation for the downlink of wireless systems operating over a frequency-selective channel is investigated. It is assumed that both the Base Station (BS) and each user are equipped with a single antenna (Single Input Single Output-SISO case), and Orthogonal Frequency Division Multiple Access (OFDMA) is used as a multiple access scheme. The aim is to maximize the sum of the users' data rates subject to constraints on total available power and proportional fairness among users' data rates. Achieving the optimal solution has a high computational cost thereby the use of suboptimal techniques is necessary. A suboptimal, but efficient, scheme is devised, and it is shown, via simulation, that not only the proposed resource allocation scheme achieve higher sum of the users' data rates than other existing schemes but also the sum data rate is distributed fairly and flexibly among users. In addition, the proposed scheme is complexity effective and can be applied to latest-generation wireless systems that provide Quality-of-Service (QoS) guarantees....
A Hybrid Pneumatic Power System (HPPS) has been developed for several years with the major aim of reducing the vehicle fuel consumption, environment pollution and enhancing the vehicle performance as well. Comparing with the conventional hybrid system, HPPS replaces the battery's electrochemical energy with a high-pressure air storage tank and enables the internal combustion engine (ICE) to function at its sweet spot. Besides, the HPPS, which effectively merges both the high-pressure air flow from the storage tank and the recycled exhaust flow from the ICE, thereby increases the thermal efficiency of the ICE and transforms the merged flow energy into mechanical energy using a high-efficiency turbine. This paper focuses on the major research process into HPPSs, including overall dynamic simulation and experimental validation. By using the simulation tool ITI-Sim, this research demonstrates an experiment which can be operated precisely according to the requirements of various driving conditions under which a car actually runs on the road in accordance with the regulated running vehicle test mode. HPPS is expected to increase the performance of the entire system from 15% to 39%, and is likely to replace the traditional system in the coming years....
Just as wireless communications develop further to achieve higher performance, new application areas emerge to challenge the limits. Vehicular ad hoc networks are one of these areas, and emergency situation warning is one of their most popular applications since traffic safety is a concern for everyone. Due to the life-critical nature of emergency applications, however, it is extremely important to ensure the solutions proposed meet the standards required, such as reliable and timely delivery of the safety warning in a situation like car collision avoidance. In order to put the candidate solutions to the test and evaluate their feasibility, we adopt the approach of computer simulation. We implement four different selective broadcast algorithms used for information dissemination in vehicular ad hoc networks, and compare their performance under identical realistic simulation conditions. Our goal is to provide an evaluation focussing on the performance with respect to safety, rather than to network aspects like throughput, loss, and delay. We define four new performance criteria to address the effectiveness, efficiency, timeliness, and overhead of the broadcast algorithms in safety warning delivery. The results we obtain using these criteria help us to understand better the design requirements of a high-performance selective broadcast algorithm....
The FlexRay Transport Protocol (FrTp) is designed to support reliable and efficient communication between various computers embedded in vehicles. It uses a standardised FlexRay communication bus and introduces a go-back-N style retransmission algorithm. A formal modelling language, Coloured Petri nets (CPN), has been applied to verify the protocol design. Separate CPN models of the FrTp service and protocol are developed and with state space analysis-used to prove for selected configurations that FrTp is deadlock-free and conforms to the service specification when transferring a single-protocol data unit from sender to receiver. In addition, closed-form solutions relating the state space size, retransmission limit, and number of segments are found, giving increased confidence that FrTp is error-free, even for configurations where the state explosion problem arises....
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