| 1. |
- Balador, Ali, et al.
(författare)
-
A Density-Based Contention Window Control Scheme for Unicast Communications in Vehicular Ad Hoc Networks
- 2015
-
Ingår i: International Journal of Ad Hoc and Ubiquitous Computing. - 1743-8225 .- 1743-8233. ; 24, s. 65-75
-
Tidskriftsartikel (refereegranskat)abstract
- Achieving a well-designed medium access control MAC protocol is a challenging issue to improve communications efficiency due to the dynamic nature of vehicular ad hoc networks VANETs. IEEE 802.11p standard was selected as the best choice for vehicular environments considering its availability, maturity, and cost. The common problem in all IEEE 802.11 based protocols is scalability, exhibiting performance degradation in highly variable network scenarios. Experimental results for the IEEE 802.11-based MAC protocol show the importance of contention window adjustment on communications performance; however the vehicular communications community has not yet addressed this issue in unicast communication environments. This paper proposes a novel contention window control scheme for VANET environments based on estimating the network density, which is then used to dynamically adapt the CW size. Analysis and simulation results show that our proposal provides better overall performance compared with previous proposals, even in high network density scenarios.
|
|
| 2. |
- Balador, Ali, et al.
(författare)
-
An Efficient MAC Protocol for vehicle platooning in automated highway systems
- 2015
-
Ingår i: Jornadas Sarteco 2015 JS 2015. - Cordoba, Spain.
-
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.
|
|
| 3. |
- Balador, Ali, et al.
(författare)
-
DTB-MAC : Dynamic Token-Based MAC Protocol for Reliable and Efficient Beacon Broadcasting in VANETs
- 2016
-
Ingår i: The 13th Annual IEEE Consumer Communications & Networking Conference CCNC 2016. - 9781479963904 ; , s. 109-114
-
Konferensbidrag (refereegranskat)abstract
- Most applications developed for vehicular environments rely on broadcasting as the main mechanism to disseminate their messages. However, in IEEE 802.11p, which is the most widely accepted Medium Access Control (MAC) protocol for vehicular communications, all transmissions remain unacknowledged if broadcasting is used. Furthermore, safety message transmission requires a strict delay limit and a high reliability, which is an issue for random access MAC protocols like IEEE 802.11p. Therefore, transmission reliability becomes the most important issue for broadcast-based services in vehicular environments. In this paper, we propose a hybrid MAC protocol, referred as Dynamic Token-Based MAC Protocol (DTB-MAC). DTB-MAC uses both a token passing mechanism and a random access MAC protocol to prevent channel contention as much as possible, and to improve the reliability of safety message transmissions. Our proposed protocol tries to select the best neighbouring node as the next transmitter, and when it is not possible, or when it causes a high overhead, the random access MAC protocol is used instead. Based on simulation experiments, we show that the DTB-MAC protocol can achieve better performance compared with IEEE 802.11p in terms of channel utilization and beacon delivery ratio.
|
|
| 4. |
|
|
