Time synchronization method among VANET devices
01 Mar 2017-
TL;DR: The proposed approach reduces synchronization error to that of less than 0.3 ms, which meets the accuracy requirement of VANET specification and can greatly reduce the frequency of handover performed by the high speed OBUs.
Abstract: Vehicular Ad hoc Network (VANET) is still a very attractive technology by which the construction of an Intelligent Transportation System (ITS) will be realized. The communication devices of VANET, i.e., OBUs and RSUs, are only allowed to transmit data in an assigned channel time and the channel switch will take place in about every 50 ms according to the standards of IEEE 802.11p and IEEE 1609.4. On the other hand, in the case of a large scale VANET, e.g., in the scenario of a traffic rush hour, available transmission time interval would be a few of milliseconds or even much less. Therefore, it is essential to achieve a precise time synchronization among the embedded devices. In this paper, we put forward a new specific time synchronization method among VANET devices. In our method, OBU can synchronize to other OBU or RSU initiatively. In the case that there is no center node in BSS (Basic Service Set), the proposed approach reduces synchronization error to that of less than 0.3 ms, which meets the accuracy requirement of VANET specification. In addition, we achieved time synchronization among RSUs. This can greatly reduce the frequency of handover performed by the high speed OBUs.
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TL;DR: The key role of real-time traffic signal control technology in managing congestion at road junctions within smart cities is explored and the benefits of synchronizing the traffic signals on various busy routes for the smooth flow of traffic at intersections are examined.
Abstract: The effective control and management of traffic at intersections is a challenging issue in the transportation system. Various traffic signal management systems have been developed to improve the real-time traffic flow at junctions, but none of them have resulted in a smooth and continuous traffic flow for dealing with congestion at road intersections. Notwithstanding, the procedure of synchronizing traffic signals at nearby intersections is complicated due to numerous borders. In traditional systems, the direction of movement of vehicles, the variation in automobile traffic over time, accidents, the passing of emergency vehicles, and pedestrian crossings are not considered. Therefore, synchronizing the signals over the specific route cannot be addressed. This article explores the key role of real-time traffic signal control (TSC) technology in managing congestion at road junctions within smart cities. In addition, this article provides an insightful discussion on several traffic light synchronization research papers to highlight the practicability of networking of traffic signals of an area. It examines the benefits of synchronizing the traffic signals on various busy routes for the smooth flow of traffic at intersections.
12 citations
TL;DR: An intelligent channel access algorithm empowered by cooperative Reinforcement Learning (RL), in which vehicles coordinate the channel access in a fully-decentralized manner is proposed, which satisfies the low latency requirement of VANET safety applications as well as both short-term and long-term communication fairness.
Abstract: Vehicular Ad-hoc Network (VANET) is an emerging technique dedicated to wireless vehicular communication to improve transportation safety by exchanging driving information between vehicles. For safety purposes, vehicles periodically broadcast a safety packet via Vehicle-to-Vehicle (V2V) communication. Accordingly, VANET safety applications demand a reliable exchange of the safety packet with high Packet Delivery Ratio (PDR), acceptable latency, and communication fairness. However, the communication performance significantly degrades due to numerous packet collisions when a large number of vehicles simultaneously access limited channel resources for the safety broadcast. In particular, the problem grows more severe in congested VANETs absent infrastructures since vehicles must control channel access using a self-adaptive scheme without external assistance. Thus, a robust and decentralized channel access protocol for VANETs is required to achieve road safety. In this paper, we propose an intelligent channel access algorithm empowered by cooperative Reinforcement Learning (RL), in which vehicles coordinate the channel access in a fully-decentralized manner. We also consider a proper interaction scheme between vehicles for enhancing the V2V safety broadcast in infrastructure-less congested VANETs. We provide evaluation results with extensive simulations according to various levels of traffic congestion. Simulations confirm the superior performance of the algorithm: the algorithm has a 20% increase in PDR compared to the latest RL-based channel access scheme. Furthermore, the algorithm satisfies the low latency requirement of VANET safety applications as well as both short-term and long-term communication fairness.
11 citations
Cites background from "Time synchronization method among V..."
...control the channel access of vehicles, which requires synchronization and connection among vehicles controlled by infrastructures [7]....
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TL;DR: Simulation results obtained show that Sync-free RadChat is able to mitigate interference without degrading the radar performance, and relies on using the relative time for radar coordination, eliminating the dependency on the absolute time provided by GPS.
Abstract: Automotive radar interference mitigation is expected to be inherent in all future ADAS and AD vehicles. Joint radar communications is a candidate technology for removing this interference by coordinating radar sensing through communication. Coordination of radars requires strict time synchronization among vehicles, and our formerly proposed protocol (RadChat) achieves this by a precise absolute time, provided by GPS clocks of vehicles. However, interference might appear if synchronization among vehicles is lost in case GPS is spoofed, satellites are blocked over short intervals, or GPS is restarted/updated. Here we present a synchronization-free version of RadChat (Sync-free RadChat), which relies on using the relative time for radar coordination, eliminating the dependency on the absolute time provided by GPS. Simulation results obtained for various use cases show that Sync-free RadChat is able to mitigate interference without degrading the radar performance.
1 citations
References
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TL;DR: This article investigates the surveillance dimensions of “intelligent transportation systems” in the United States, with a particular focus on the mediation of data by engineers in transportation control centers.
Abstract: This article investigates the surveillance dimensions of “intelligent transportation systems” in the United States, with a particular focus on the mediation of data by engineers in transportation control centers. These communication systems lend themselves to surveillance by means of “function creep” beyond their primary intended purposes and through the everyday collection and manipulation of data to manage mobilities. In the U.S., dominant system protocols privilege vehicular throughput and discipline those who deviate from that norm.
65 citations
"Time synchronization method among V..." refers background in this paper
...The VANET (Vehicular Ad hoc Network) is a key component of ITS....
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...ITS, VANET, WAVE, IEEE 802.11p, IEEE 1609.4, time synchronization....
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...The author of [1] proposed a Distributed Time Synchronization Mechanism (DTS) for VANET....
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...Promoting traffic safety is the main purpose of ITS [1], as well; it can provide information and entertainment applications for both drivers and passengers [2], [3]....
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26 Apr 2004
TL;DR: A modification to a known interval-based synchronization algorithm is proposed; the new algorithm obtains substantially better results in sensor-network scenarios by taking advantage of the typical drift diversity of the nodes' clocks.
Abstract: Interval-based synchronization provides the nodes of a distributed system with guaranteed bounds on a common time. This is a crucial piece of infrastructure in many distributed sensing and actuating systems. In this paper, we propose a modification to a known interval-based synchronization algorithm; our new algorithm obtains substantially better results in sensor-network scenarios by taking advantage of the typical drift diversity of the nodes' clocks. We propose a model for synchronization in ad-hoc, sporadic-communication scenarios. The model allows us to identify the worst and the best case in terms of achievable time uncertainty and to show the worst-case optimality of the discussed algorithms. Simulations show that in the average case, our modification significantly reduces the time uncertainty.
62 citations
"Time synchronization method among V..." refers background in this paper
...We define the deviation of the absolute rate as the clock frequency drift h(t) [11], [12]:...
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30 Jul 2007
TL;DR: In the protocol, the clock offset is corrected continuously avoiding the time discontinuity which is a prevalent drawback of existing synchronization protocols and the bound-drift clock model is extended by considering both the absolute drift and the relative drift.
Abstract: Time synchronization is an essential problem for WSNs. The synchronization performance is mainly affected by two factors: the uncertainty in the message delay, and the clock drift. Most solutions on time synchronization in WSNs have concentrated on one of the two factors, and neglected the other. In this paper, we consider both of them and propose a novel time synchronization protocol for WSNs. In the protocol, we model the variation of the clock drift and develop algorithms to estimate and compensate the drift. Meanwhile, the clock offset is corrected continuously avoiding the time discontinuity which is a prevalent drawback of existing synchronization protocols. Additionally, we extend the bound-drift clock model by considering both the absolute drift and the relative drift. Mathematical analyses and simulations are presented in this paper, and verify the effectiveness of our synchronization protocol.
4 citations