Current Issue : July - September Volume : 2015 Issue Number : 3 Articles : 5 Articles
In 4G cellular networks, call admission control (CAC) has a direct impact on quality of service (QoS) for individual\nconnections and overall system efficiency. Reservation-based CAC schemes have been previously proposed for\ncellular networks where a certain amount of system bandwidth is reserved for high-priority calls, e.g., hand-off calls\nand real-time new calls. Traditional reservation-based schemes are not efficient for 4G vehicular networks, as the\nreserved bandwidth may not be utilized effectively in low hand-off rates. We propose a channel borrowing approach\nin which new best effort (BE) calls can borrow the reserved bandwidth for high-priority calls. Later, if a hand-off call\narrives and all the channels are busy, it will pre-empt the service of a borrower BE call if there exists any. The\npre-empted BE calls are kept in a queue and resume their service whenever a channel becomes available. The\nanalytical model for this scheme is a mixed loss-queueing system for which it is difficult to calculate call blocking\nprobability (CBP) and call dropping probability (CDP). Our focus in this paper is on the system modeling and\nperformance evaluation of the proposed scheme. We present two system models that approximate the operation of\nthe proposed scheme. For these models, we derive the CBP and CDP analytically. It is shown that our analytical results\nare very close to the ones obtained from simulations. Furthermore, it is observed that our channel borrowing\napproach decreases the CBP considerably while increases the CDP slightly over a large range of hand-off rates....
Vehicular networks have attracted increasing attention from both the academy and industry. Applications of vehicular\nnetworks require efficient data communications between vehicles, whose performance is concerned with delivery\nratio, delivery delay, and routing cost. The most previous work of routing in vehicular networks assumes oversimplified\nnode mobility when evaluating the performance of vehicular networks, e.g., random mobility or artificial movement\ntraces, which fails to reflect the inherent complexity of real vehicular networks. To understand the achievable\nperformance of vehicular networks under real and complex environments, we first comprehensively analyze the\naffecting factors that may influence the performance of vehicular networks and then introduce four representative\nrouting algorithms of vehicular networks, i.e., Epidemic, AODV, GPSR, and MaxProp. Next, we develop an NS-2\nsimulation framework incorporating a large dataset of real taxi GPS traces collected from around 2,600 taxis in\nShanghai, China. With this framework, we have implemented the four routing protocols. Extensive trace-driven\nsimulations have been performed to explore the achievable performance of real vehicular networks. The impact of\nthe controllable affecting factors is investigated, such as number of nodes, traffic load, packet TTL, transmission range,\nand propagation model. Simulation results show that a real vehicular network has surprisingly poor data delivery\nperformance under a wide range of network configurations for all the routing protocols. This strongly suggests that\nthe challenging characteristics of vehicular networks, such as unique node mobility, constraints of road topology,\nneed further exploration....
Tracking the channel impulse response in systems based on the IEEE 802.11p standard, the most widely accepted standard for the\nphysical layer in vehicular area networks (VANETs), is still an open research topic. In this paper we aim to improve previously\nproposed channel estimators by utilizing data aided algorithm that includes the channel decoding to enhance the quality of\nthe estimated data. Moreover we propose a novel technique that exploits information provided by external sensors like GPS or\nspeedometer, usually present in vehicles. The algorithm proposed so far has been analyzed in non-line-of-sight link conditions; in\nthis paper we present an analysis of performances in the line-of-sight condition as well. Simulations show that both proposals give\nconsiderable improvements in terms of packet error rate and channel estimation error in the highway scenario which is surely the\nmost stressing environment for the channel response tracker....
This paper reports on a real-world wireless channel measurement campaign for in-vehicle scenarios in the UWB\nfrequency range of 3 to 11 GHz. The effects of antenna placement in the vehicle�s passenger compartment as well as\nthe effects due to the presence of passengers are studied. The measurements have been carried out in the frequency\ndomain, and the corresponding channel impulse responses (CIRs) have been estimated by inverse Fourier transform.\nThe influence of a specific band group selection within the whole UWB range is also given. Statistical analysis of the\nmeasured channel transfer functions gives a description of the wireless channel statistics in the form of a generalized\nextreme value process. The corresponding parameter sets are estimated and documented for all permutations of\nantenna placement and occupancy patterns inside the vehicle�s passenger compartment. Further, we have carried\nout a feasibility study of an in-vehicle UWB-based localization system based on the TOA. The positioning performance\nis evaluated in terms of average error and standard deviation....
With the gradual development of economy, the scale of transportation industry continues to expand. The problem of\noverload or overrun in the vehicle transport has emerged. Therefore, how simply and conveniently to know the vehicle\nload and how to effectively limit overload has become a key issue. This paper demonstrates the feasibility of vehicle\nload control system from the above problems. Through the pressure sensors installed in the vehicle suspension, the\nsingle-chip microprocessor receives the information transmitted by the pressure sensors, and calculates the total weight\nof the vehicle load; if overweight, the single-chip microprocessor will send commands to the ignition system, to stop the\nignition system working. Its purpose is to improve vehicle safety and effectively reduce heavy workload of the vehicle\ndetection station to improve their work efficiency....
Loading....