| 1. |
- Balador, Ali, et al.
(författare)
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A Reliable Token-Based MAC Protocol for Delay Sensitive Platooning Applications
- 2015
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Ingår i: 2015 IEEE 82nd Vehicular Technology Conference (VTC2015-Fall). - [S.l.] : IEEE. - 9781479980918 - 9781479980901
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Konferensbidrag (refereegranskat)abstract
- Platooning is both a challenging and rewarding application. Challenging since strict timing and reliability requirements are imposed by the distributed control system required to operate the platoon. Rewarding since considerable fuel reductions are possible. As platooning takes place in a vehicular ad hoc network, the use of IEEE 802.11p is close to mandatory. However, the 802.11p medium access method suffers from packet collisions and random delays. Most ongoing research suggests using TDMA on top of 802.11p as a potential remedy. However, TDMA requires synchronization and is not very flexible if the beacon frequency needs to be updated, the number of platoon members changes, or if retransmissions for increased reliability are required. We therefore suggest a token-passing medium access method where the next token holder is selected based on beacon data age. This has the advantage of allowing beacons to be re-broadcasted in each beacon interval whenever time and bandwidth are available. We show that our token-based method is able to reduce the data age and considerably increase reliability compared to pure 802.11p. © 2015 IEEE.
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| 2. |
- Balador, Ali, et al.
(författare)
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An Efficient MAC Protocol for vehicle platooning in automated highway systems
- 2015
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Ingår i: Jornadas Sarteco 2015 JS 2015. - Cordoba, Spain.
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Konferensbidrag (refereegranskat)abstract
- Lately, all the top truck manufacturers are investing considerable resources in the research and development of platooning systems which would allow vehicles to save fuel and improve safety by travelling in a close-following manner. The platooning system requires frequent and reliable vehicle-to-vehicle communications. As platooning takes place in a vehicular ad hoc network, the use of IEEE 802.11p is close to mandatory. However, the 802.11p medium access method suffers from packet collisions and random delays. Most ongoing research suggests using TDMA on top of 802.11p as a potential remedy. However, TDMA requires synchronization and is not very flexible if the beacon frequency needs to be updated, the number of platoon members changes, or if re-transmissions for increased reliability are required. We therefore suggest a token-passing medium access method where the next token holder is selected based on beacon data age. This has the advantage of allowing beacons to be re-broadcasted in each beacon interval whenever time and bandwidth are available. We show that our token-based method is able to reduce the data age and considerably increase reliability considerably compared to pure 802.11p.
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| 3. |
- Bengtsson, Henrik, et al.
(författare)
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Protocol for wireless real-time systems
- 1999
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Ingår i: Proceedings of the 11th Euromicro Conference on Real-Time Systems, 1999. - Los Alamitos, CA : IEEE Computer Society. - 0769502407 ; , s. 168-174
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Konferensbidrag (refereegranskat)abstract
- A protocol and a communication mechanism intended for time and safety critical applications using a radio channel for information transport are considered jointly. The protocol is based on a scheme of retransmissions done on demand within a given time window. Each retransmission is coded with a varying number of redundant symbols. The set of blocks used for retransmission is controlled by two quality-of-service parameters: deadline for the transmission and the probability that the correct decoded message will reach the recipient before this deadline. Analysis of a protocol model indicates that it is possible to transmit time critical information in a mobile wireless system with very low error probabilities in an industrial environment.
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| 4. |
- Bilstrup, Katrin, et al.
(författare)
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Evaluation of the IEEE 802.11p MAC method for vehicle-to-vehicle communication
- 2008
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Ingår i: 68th IEEE Vehicular Technology Conference, 2008. VTC 2008-Fall. - Piscataway, N.J. : IEEE Press. - 9781424417216 ; , s. 1-5
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Konferensbidrag (refereegranskat)abstract
- In this paper the medium access control (MAC) method of the upcoming vehicular communication standard IEEE 802.11p has been simulated in a highway scenario with periodic broadcast of time-critical packets (so-called heartbeat messages) in a vehicle-to-vehicle situation. The 802.11p MAC method is based on carrier sense multiple access (CSMA) where nodes listen to the wireless channel before sending. If the channel is busy, the node must defer its access and during high utilization periods this could lead to unbounded delays. This well-known property of CSMA is undesirable for time critical communications. The simulation results reveal that a specific node/vehicle is forced to drop over 80% of its heartbeat messages because no channel access was possible before the next message was generated. To overcome this problem, we propose to use self-organizing time division multiple access (STDMA) for real-time data traffic between vehicles. This MAC method is already successfully applied in commercial surveillance applications for ships (AIS) and airplanes (VDL mode 4). Our initial results indicate that STDMA outperforms CSMA for time-critical traffic safety applications in ad hoc vehicular networks.
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| 5. |
- Bilstrup, Katrin, et al.
(författare)
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Medium access control in vehicular networks based on the upcoming IEEE 802.11p standard
- 2008
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Ingår i: 15th World Congress on Intelligent Transport Systems and ITS America Annual Meeting 2008. - : World Congress on ITS. - 9781615677566 ; , s. 4155-4167, s. 12-
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Konferensbidrag (refereegranskat)abstract
- In this paper, initial simulations are presented showing that the upcoming IEEE 802.11p standard is not suitable for traffic safety applications requiring reliable, low delay communication between vehicles. The medium access control procedure is one of the most important parts in the design of delay-constrained communication systems, and emerging vehicle safety applications put new stringent demands on timely and reliable delivery of data packets. The medium access procedure used in 802.11p is carrier sense multiple access, which is inherently unsuitable for time-critical data traffic since it is contention-based and cannot provide a finite upper bound on the time to channel access. The simulation results indicate that with IEEE 802.11p, channel access cannot be granted in a manner that is sufficiently predictable to support reliable, low-delay communications between vehicles on a highway.
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| 6. |
- Bilstrup, Katrin, et al.
(författare)
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On the ability of the 802.11p MAC method and STDMA to support real-time vehicle-to-vehicle communications
- 2009
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Ingår i: EURASIP Journal on Wireless Communications and Networking. - New York : Hindawi Publishing Corporation. - 1687-1472 .- 1687-1499. ; 2009:902414, s. 1-14
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Tidskriftsartikel (refereegranskat)abstract
- Traffic safety applications using vehicle-to-vehicle (V2V) communication is an emerging and promising area within the intelligent transportation systems (ITS) sphere. Many of these new applications require real-time communication with high reliability, meaning that packets must be successfully delivered before a certain deadline. Applications with early deadlines are expected to require direct V2V communications, and the only standard currently supporting this is the upcoming IEEE 802.11p, included in the wireless access in vehicular environment (WAVE) stack. To meet a real-time deadline, timely and predictable access to the channel is paramount. However, the medium access method used in 802.11p, carrier sense multiple access with collision avoidance (CSMA/CA), does not guarantee channel access before a finite deadline. In this paper, we analyze the communication requirements introduced by traffic safety applications, namely, low delay, reliable, real-time communications.We show by simulation of a simple, but realistic, highway scenario, that vehicles using CSMA/CA can experience unacceptable channel access delays and, therefore, 802.11p does not support real-time communications. In addition, we present a potential remedy for this problem, namely, the use of self-organizing time division multiple access (STDMA). The real-time properties of STDMA are investigated by means of the same highway simulation scenario, with promising results.
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| 7. |
- Bilstrup, Katrin, 1972, et al.
(författare)
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On the ability of the IEEE 802.11p and STDMA to provide predictable channel access
- 2009
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Ingår i: Proceedings of the 16<sup>th</sup> World Congress on Intelligent Transport Systems (ITS). ; , s. 10-
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Konferensbidrag (refereegranskat)abstract
- Emerging traffic safety applications requiring low delay communications will need vehicle ad-hoc networks. The only communication standard currently supporting this is IEEE 802.11p. However, 802.11p uses the medium access method CSMA/CA, which has a major drawback: unbounded worst case channel access delay. We therefore propose an algorithm already in commercial use in the shipping industry: STDMA. With STDMA, nodes always get predictable channel access regardless of the number of competing nodes and the maximum delay is deterministic. In this paper we elaborated with different parameter settings for the two protocols with the aim of improving performance without altering the standards.
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| 8. |
- Bilstrup, Katrin, et al.
(författare)
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Report on the Collaboration between CVIS and CERES in the Project Vehicle Alert System (VAS)
- 2009
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In March 2007, an agreement was made for interchange of experiences between CVIS and the Centre for Research on Embedded Systems (CERES) at Halmstad University in Sweden. The majority of the work relating to this collaboration has been conducted within the CERES project Vehicle Alert System (VAS), aiming to use vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) communications to provide different types of warning messages. The main focus of the VAS project is on communication and in particular the lower layers of the communication stack are investigated. VAS involves academic researchers from Halmstad University as well as researchers from Volvo Technology, SP Technical Research Institute of Sweden and the company Free2move. This report presents the results of the VAS project, its publications, and other issues of interest both to the CVIS consortium as well as a broader scope.
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| 9. |
- Böhm, Annette, et al.
(författare)
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Adaptive Cooperative Awareness Messaging for Enhanced Overtaking Assistance on Rural Roads
- 2011
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Ingår i: IEEE Vehicular Technology Conference (VTC Fall 2011). - Piscataway, N.J. : IEEE Press. - 9781424483280 ; , s. Article number 609316211-
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Konferensbidrag (refereegranskat)abstract
- Cooperative traffic safety applications such as lane change or overtaking assistance have the potential to reduce the number of road fatalities. Many emerging traffic safety applications are based on IEEE 802.11p and periodic position messages, so-called cooperative awareness messages (CAM) being broadcasted by all vehicles. In Europe, ETSI defines a periodic report rate of 2 Hz for CAMs. Although a high report rate is the key to early hazard detection, the 2 Hz rate has been chosen to avoid congestion in settings where the vehicle density is high, e.g., on major highways and in urban scenarios. However, on rural roads with a limited number of communicating vehicles, a report rate of 2 Hz leads to unnecessary delay in cooperative awareness. By adapting the CAM report rate depending on the specific application and road traffic density, and by making use of the priority levels provided by the 802.11p quality of service mechanism, we show that hazards can be detected earlier and the available bandwidth is used more efficiently, while not overexploiting the network resources.
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| 10. |
- Böhm, Annette, et al.
(författare)
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Co-existing periodic beaconing and hazard warnings in IEEE 802.11p-based platooning applications
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- A platoon of trucks driving at the same, mutually agreed speed while keeping a minimum inter-vehicle distance will reduce fuel consumption, enhance transport efficiency as well as improve the safety of other adjacent road users. The European profile of IEEE 802.11p for inter-vehicle communications uses a single 10 MHz control channel dedicated to safety-critical data, shared by periodic status updates, CAM (Cooperative Awareness Message), and event-triggered warnings, DENM (Decentralized Environmental Notification Message). Coupled with the random access delay inherent to the 802.11p medium access method, the strict timing and reliability requirements of platoon applications are not easily met. To this end, we evaluate by simulation the effect of IEEE 802.11p-compliant send rate adaptations and message type prioritizations and the choice of warning dissemination strategy on CAM transmissions and DENM dissemination in a platooning scenario. Simulation studies of a platoon of 10-20 vehicles in a busy highway scenario show that the context-aware choice of send rate, priority class and dissemination strategy not only reduce the dissemination delay of DENMs but even has a significant effect on the throughput of CAMs exchanged by platoon members.
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