IEEE 802.11p Enhancements for Unicast V2V and V2I Communication

In this study, we propose a novel, intelligent medium access control (MAC) mechanism for vehicular ad hoc networks, by adapting the contention window (CW) parameter value. Specifically, a simple, effective, and efficient nonlinear control law is built, based on fuzzy logic control principles, which can be easily adopted in different network environments (e.g. V2V and V2Ι communication).

Moreover, this work has been enhanced by having the minimum and maximum CW parameters dynamically tuned based on network observations, concerning all applications’ access categories. Thus, the proposed fuzzy logic based MAC framework is designed to maintain the adaptation of the back-off/CW parameter value, but at the same time to dynamically adjust the minimum and maximum CW parameter values; this allows it to react better to the dynamic network conditions. It can be easily adapted for V2V and V2I communication.

It is demonstrated, via simulative evaluation, that the proposed fuzzy control methodology offers inherent robustness with effective control of the system under dense and dynamic conditions, without the need to (re)tune any controller parameters. The proposed approach offers distinct differentiation among differently prioritized traffic types, thus providing adequate Quality of Service (QoS) in terms of throughput, losses, delay performance, in contrast with the IEEE 802.11p MAC protocol we compared it against.

IEEE 802.11p Enhancements for Broadcast Communication

The work described above assumed unicast V2V and V2I communication. Therefore, we further show the need for providing an intelligent controller offering decision support in vehicular networks in terms of broadcast communication channel access.

In broadcast communication, as it is the case of the active road safety and control applications, along with the use of beacons for cooperative awareness among vehicles, there is a further need to improve the performance of the MAC protocol. This is due to the fact that because of the lack of acknowledgements when performing broadcast beaconing and other active road safety/control messages, the CW MAC parameter is never increased. Thus, despite a possible increase of the traffic load and consequently a severe congestion on the communication channel, the MAC protocol does not respond appropriately.  This behavior badly influences the communication between the vehicles, especially when safety applications are run, like vehicles collision avoidance, etc.

Therefore, we exploit fuzzy logic control, derived from its reported strength of using linguistic information to control nonlinear systems, to build an adaptive, intelligent controller, based on the traffic density, that aid vehicles to decide when to access the broadcast communication channel.  This supports the cooperative awareness that is essential among vehicles, from which many applications can be depicted, under the active road safety and control applications. The results clearly show that the proposed fuzzy logic-based adaptive decision support solution outperforms the original 802.11p solution, in all the important performance metrics.

Adaptation of Beaconing Generation Rate and Transmission Power

Many challenges in the broadcast communication channel access decision support remain open. For example, based on the dynamics of the vehicular environment, the transmission power level can be adjusted, as well as the beacon generation rate, so as to provide the necessary decision support. Thus, a comprehensive study is depicted to include not only the contention window adaptation, but the adaptation of other important network parameters (such as transmission power and message generation rate, as indicated above). With this approach, the influence of such parameters in the decision support in vehicular networks can be demonstrated. Fuzzy logic is particularly well suited to incorporate multiple inputs.

Intelligent Re-broadcasting for Information Dissemination of Safety Messages

The challenge to avoid the flooding problem, which occurs in the re-broadcast procedure of safety messages in VANETS, is still open. An intelligent, robust approach is needed to handle the trade-off between maximizing the number of vehicles that receive the safety messages and minimizing the number of vehicles that re-broadcast the messages. At the same time, the latency and losses/collisions should be kept at nominal values. An initial design for such a mechanism has been developed, and computer simulations will be used to evaluate and prove its efficiency.

Efficient Use of Multiple Channels by Single-Receiver Clients

Relevant to the broadcasting challenges mentioned above, is the investigation on the efficient use of multiple channels by single-receiver clients in wireless data broadcasting.