Cooperative protocols for wireless vehicular communication Good afternoon ladies and gentelmen My name is Fatma Hrizi, I am a phd student at EURECOM and I’m working with Jerome Haerri and Christian bonnet My talk is concerned with cooperation in wireless vehicular networks and I am going to talk particularly about challenges and visions in this field. Fatma Hrizi, Jerome Haerri and Christian Bonnet EURECOM, Mobile communications department

Vehicular networks: The Challenges Applications Safety Efficiency Entertainment, Internet access Key concept Provide appropriate information to the driver/vehicle Large amount of data to exchange Local scope information: Awareness (GPS data) Global scope information: Emergency, traffic and road information… The emergence of wireless vehicular networks is related to the development of a new set of intelligent traffic applications that could enhance traffic safety and efficiency. Basically, there are three classes of applications, first the traffic safety applications such as the post crash warning applications where a vehicle detecting an accident has to send the information to others. The second one is traffic efficiency applications like traffic congestion detection and finally entertainment applications. We are focusing mainly on the first and vital category : safety applications. The key concept of/behind such applications is to provide relevant information to the driver. Moreover, due to the diversity of applications, a large amount of data is expected to be exchanged among vehicles. It consists of local scope information related to awareness provided by GPS receiver And secondly global information scope such as emergency, traffic and road information 4/16/2017 EURECOM, Mobile communications department

Cooperation in vehicular networks (1/2) Safety applications requirements Short delay and high reliability Awareness: Broadcast – need to reach all neighboring nodes Periodic – need to update position information Shared medium limitation Congestion at medium access Collision at reception Channel capacity exceeded! On the other hand, safety applications require very short delay and high reliability in information reception and to fit these requirements periodic broadcast communication has to be used. For example for the local scope information: the awareness, we need that all one-hop neighbors receive an updated position information. However, the problem here is that we do have only one shared medium which may result in a severe channel congestion problem when the channel capacity is exceeded. Moreover there is still an issue with the collisions at reception that increase with the increase of number of vehicles and could be present even when the channel capacity is not exceeded. So we do need to regulate the channel load in order to alleviate the problem of congestion at medium access which is the main focus in this presentation. Load on channel Need to regulate the channel load 4/16/2017 EURECOM, Mobile communications department

Cooperation in vehicular networks (2/2) Does not impact channel load at A Best relay to be selected A B A C B If B does not retransmit => reduce channel load at A Reduce channel load at B No need for B retransmission Congestion control policy of a node benefits others Need for cooperative and common congestion control policy One hop transmission Transmission rate control Transmission power control Multi-hop transmission Select best relay So to regulate the channel load, a vehicle can for example reduce his transmission rate of periodic message (e.g. awareness). For example, when all vehicles transmit at the same rate all of them utilize the maximum channel capacity. However, if vehicle A reduce his rate, it does not impact his channel load but the others’ so here we notice the decrease of channel load at B. Another example is related to the emergency information transmission, in this scenario, A will be selected as the best relay to forward the information, If B sends as well he will overload the channel at A. On the other hand, C is covered by A and does not need B transmission. So, we observe that a vehicle cannot benefit from its own congestion control policy but from that of its neighbors. Therefore, we do need an efficient and common cooperative congestion control policy. For one-hop transmission, mainly there are the transmission rate and power control and in this presentation we focus in the transmission rate control scheme And for multi-hop the main issue concerns the selection of best relay. 4/16/2017 EURECOM, Mobile communications department

EURECOM, Mobile communications department Talk outline Cooperative congestion control strategies Multi-hop communication Bi-Zone Broadcast protocol (BZB) One-hop communication Transmission rate control Conclusion and perspectives I propose to present our research activities related cooperative congestion control strategies as follows First, an overview of a proposed multihop broadcast protocol: Bi-zone broadcast protocol, then an analysis of our proposed transmission rate control policy. Finally, we conclusion and perspectives 4/16/2017 EURECOM, Mobile communications department

Multi-hop communication: BZB Disseminate broadcast information reliably and in brief delay Distance-based contention scheme Select the best relay according to the distance: the furthest Minimize the waiting time of distant node Tx Range Dth Dth: Distance threshold C C A Right, to start BZB is a broadcast protocol aiming at ensuring reliability and short delay in data reception. It consists in a distance-based contention scheme. So, the main idea behind distance-based approaches is to select the relay according to the distance from the source. Moreover/Furthermore, in order to decrease the delay, BzB manages to minimize the waiting time of distant node. By fixing a distance threshold beyond it vehicles have more priority to forward the packet quickly/in short delay. We have been investigating also the impact of RSU in the message dissemination and how to give more priority to RSUs in forwarding since they are equipped with high antennas ensuring more coverage and are wired connected as well. B D D B t A sends B sends C cancels D cancels Impact of RSU in dissemination 4/16/2017 EURECOM, Mobile communications department

BZB: Performance Evaluation Here I am going to present some simulation results of BzB: We compared BzB to a simple distance-based strategy where the waiting time is inversely proportional to the distance from the source. We have measured the Average information reception delay regarding the distance from the source and varying the distance threshold. We have SDP in green curves and other color regards BZB with different dth values. The first plot considers sparse network and the second dense network. As you can see, for close distances (lower than 100m) both protocols show the same results since all nodes in this distance can receive the message from the originator node directly. For further distances, BZB outperforms SDP in terms of delay for both dense and sparse networks. SDP: Simple distance based protocol 50 nodes 500 nodes 4/16/2017 EURECOM, Mobile communications department

One-hop communication: Transmission rate control Approach: Tune rate to avoid congestion Rely on position information prediction Transmit only when Mobility not predictable: Sudden mobility change Topology not predictable: Announce its presence Intersection collision warning Transmission I moved from predicted position! Now, we move to the second part, I am going to present ongoing research topic related to the transmission rate control in one-hop transmission. The main aim is to avoid congestion by tuning the transmission rate and by limiting the one-hop message’s channel capacity to leave more bandwidth to other type of messages. Therefore, we propose to consider position data prediction and to transmit only when it is needed by other neighbors. When the mobility is not predictable when a sudden mobility change occur. For example, the real position of this vehicle deviates from the predicted one and it can not be predicted by others. So he has to send his position to update the information of his neighbors. Another possibility of transmission is when the topology is not predictable and particularly when the applications require it. For instance, in intersection collision warning application a vehicle may need to announce its presence to new neighbors so it has to send the packet even though its position can be predicted. A part from that, to ensure a high minimum level of accuracy, we have fixed a maximum transmission period in which a vehicle should transmit anyway. Predicted position Real position Transmission! Transmission Application requirement! Tmax: Maximum Tx period t Tmax Tmax 4/16/2017 EURECOM, Mobile communications department

Transmission rate control: Architecture GPS data V2X data Map data Decision Mobility Prediction system Cooperative Decision maker Predicted data Real Position data Error Transmit position? Application Requirements Network density Kalman Filter Neural Network Genetic algorithm Particle Filter Kalman Filter Simplistic assumptions: linear problem with Guassian noise Neural Network Learning phase Genetic algorithm Processing time No guarantee for convergence Particle Filter Degeneracy problem 4/16/2017 EURECOM, Mobile communications department

Conclusion and perspectives So far.. Congestion-aware approach for multi-hop and one-hop communications BZB protocol Transmission rate control Some issues have not yet been fully investigated Mobility prediction schemes Channel-aware mechanisms for congestion control strategies Cooperation between multiple applications and protocols 4/16/2017 EURECOM, Mobile communications department

Conclusion and perspectives Multiple applications Satisfy different applications requirements Multiple protocols Consider the various congestion control policies and resources limitation (1) Intersection collision warning (ICW)! Which decision I take? (2) Lane change warning (LCW)! Applications ICW LCW … Appn Facilities Networking & Transport CP1 CP2 CPn Access Technologies Which congestion control scheme I use? ICW: Intersection collision warning LCW: Lane change warning CP: Congestion control policy 4/16/2017 EURECOM, Mobile communications department

Thank you for your attention Contact : Fatma Hrizi Mobile Communications Department EURECOM 2229 Route des Crêtes - BP 193 F-06904 Sophia Antipolis Cedex FRANCE Tel: +33-493.00.82 68 Fax: +33-493.00.82 00 Email : fatma.hrizi@eurecom.fr 4/16/2017 EURECOM, Mobile communications department

Multi-hop communication: BZB V2V dissemination Contention-based scheme Minimise the waiting time of distant node Tx Range Dth 4/16/2017 EURECOM, Mobile communications department

Multi-hop communication: I-BZB V2V/V2I dissemination: Impact of infrastructure in message dissemination RSUs are equipped with high antennas ensuring more coverage and are wiredly connected to the TOC More priority to RSU considering density 4/16/2017 EURECOM, Mobile communications department