Simulation of Car-to-X Communication Networks Braunschweiger Verkehrskolloquium DLR, 03.02.2011 02 2011 Henrik Schumacher, IKT
Introduction VANET = Vehicular Ad hoc NETwork Originally used to emphasize ad hoc nature of vehicular networks Nowadays generally describes Car-to-X Communication based on wireless local area networking Car-to-X Communication consists of Vehicle-to-Vehicle (Car-to-Car) and Vehicle-to-Roadside (Car-to-Infrastructure) Communication Source: ETSI ITS 2
Motivation: Safety in Road Traffic Road accidents EU-25 in 2005 (ca.): 41.300 fatalities 1.3 million accidents involving ing injury Costs: 160*10 9 per year or 1.5% of EU GDP 1.8 million injuries (Source: C2C-CC, EU: SafetyNet Annual Statistical Report 2008) Accident reasons: 86% involve drivers Too fast or too close: 31% Driver mistakes concerning right of way, entering exits, turnings: 26% Wrong lane, wrong overtaking: 13% Others (esp. alcohol): 30% (Source: C2C-CC, CC, Verkehr in Zahlen 2003, Dt. Verkehrs-Verlag) Verlag) EU target: Reduce number of road fatalities by 50% until 2010 compared to 2001 3
Car-to-X Use Cases Some Examples Safety use cases Cooperative Forward Collision Warning Intersection Collision Warning Emergency Electronic Brake Lights Hazardous Location V2V Notification Traffic Efficiency Enhanced Route Guidance and Navigation Green Light Optimal Speed Advisory V2V Merging Assistance Infotainment t and Others Internet Access in Vehicle Point of Interest Notification Remote Diagnostics 4
European ITS Protocol Stack Basic Profile of European ITS Protocol Stack: Cooperative Awareness Research Focus ITS = Intelligent Transportation Systems 5
What is ITS-G5? ETSI ES 202 663: European profile standard for PHY and MAC layer of 5 GHz Intelligent Transport Systems (ITS) Defines ITS-G5 mode of operation for IEEE 802.11-2007 Uses 10 MHz profile of IEEE 802.11a PHY Dedicated frequency band for ITS applications at 5.9 GHz 1 Control Channel (CCH) and 4 (+2) Service Channels (SCHs), 5855 5,855-5,905 (5,925) GHz, 10 MHz per channel Exclusively for ITS safety and non-safety applications Operation outside the context of a BSS No association, no authentication 6
Cooperative Awareness Basic Service Goal: Provide cooperative awareness to neighboring nodes Distribution of Cooperative Awareness Messages (CAMs) within the ITS-G5 VANET Each vehicle periodically sends CAMs containing status data Vehicle position, speed and heading, basic sensor information One-hop broadcast Part of the ITS Facilities Layer Used for several ITS use cases Mandatory for all ITS stations 7
Challenges in VANETs Accuracy of cooperative awareness information has significant impact on traffic safety Vehicles that can broadcast their status data successfully can become a danger for others Reliability is necessary Requirement: All nodes need to access the channel successfully in regular intervals VANETs present adverse conditions for reliable communication Path loss, shadowing, fading No acknowledgments and no RTS-CTS in broadcast mode Collisions can not be detected through missing ACKs Hidden node problems can not be alleviated by RTS-CTS exchange Highly variable node densities 8
Hidden Station Problem 9
Network Simulation Network simulation based on OMNeT++ Discrete event-controlled network simulator implemented in C++ Open source availability INET extension Elaborate implementation of 802.11 MAC layer Implementations of IPv4, IPv6, TCP, UDP, application models etc. Protocol development for Car-to-X based on INET's 802.11 implementation ti Car-to-car and car-to-infrastructure scenarios Optimization i of protocol performance Simulation of Car-to-X Communication Networks Braunschweiger Verkehrskolloquium, February 2011 10
Road Traffic Simulation Accurate modeling of vehicle movement is indispensable for simulation of car-to-x communication scenarios SUMO (Simulation of Urban MObility) Open source road traffic simulation package Microscopic i traffic model: each vehicle is modeled explicitly Easy import of digital maps Connection with other tools is possible Simulation of Car-to-X Communication Networks Braunschweiger Verkehrskolloquium, February 2011 11
Simulation environment: Coupling of simulators TraCI = Traffic Control Interface SUMO = Simulation of Urban MObility 12
Baseline simulations: scenario setup Vehicles equipped with ITS-G5A Interfaces TxPower 1 W (30 dbm), data rate = 6 Mbps, Physical Layer Capturing (PLC) enabled OCB-Mode, AC = AC_BK, AIFSN = 9, CW = 15 (const.) All vehicles generate Cooperative Awareness Messages (CAMs) Message size = 400 Bytes, Generation interval = 100 ms Single hop broadcast Highway scenario: 10 km, 2 lanes per direction Vehicle arrivals: Poisson process, speed limit 120 km/h Varying traffic densities 15 vehicles / km: 30 vehicles / km: 60 vehicles / km: 13
Evaluation metrics Probability of successful carrier sensing (sensing probability) P(RxPower Sensitivity) Corresponds to probability of successful frame reception in absence of interference (no collisions) Probability of successful frame reception (reception probability) P(RxPower Sensitivity) AND P(SNIRmin SNIR Threshold ) Collisions considered: Collision occurs if SNIR decreases below SNIR Threshold (caused by interference) during frame reception Recording data for 10 s / 20 s / 40 s per simulation run 20 simulation runs per configuration 14
Sensing Probability TxPower = 1 W (30 dbm), Sensitivity = -85 dbm 15
Sensing Probability vs. Reception Probability TxPower = 1 W (30 dbm), Sensitivity = -85 dbm, SNIR Threshold = Capturing Threshold = 4 db 16
Simulating VANETs in Urban Environments In urban environments, path loss is strongly influenced by shadowing and multipath reflections Simple propagation models that only consider TxRx distance not appropriate Integration of radio channel simulator based on raytracing into the simulation environment in cooperation with IfN (TU BS) 17
Scenario Realistic scenario of Braunschweig has been developed Urban area of 1500 m x 1500 m incl. university campus Residential zones, small industrial areas and parks Different street types included One-way and two-way streets, varying numbers of lanes Speed limits of 30 and 50 km/h Braunschweig scenario contains different types of data: Street data Traffic flow data Building and elevation data 18
Scenario Street data based on Tele Atlas MultiNet Traffic data Incoming and outgoing traffic on main streets based on traffic counts Traffic on side roads and phases of traffic lights estimated by isolated studies Turning ratios 3D building and elevation data acquired from city administration Simulation of Car-to-X Communication Networks Braunschweiger Verkehrskolloquium, February 2011 19
Radio Channel Simulation Simple propagation models not suitable to describe complex multipath situations Frequency-selective and time-variant character of the propagation channel Particularly in dense urban environments Radio channel simulator based on 3D ray tracing using image method developed by IfN Provides power delay profile incl. attenuation and time delay of rays Simulation of Car-to-X Communication Networks Braunschweiger Verkehrskolloquium, February 2011
Architecture of simulator coupling Coupling of simulators motivated by weaknesses regarding Radio channel simulation Mobility models Simulation of Car-to-X Communication Networks Braunschweiger Verkehrskolloquium, February 2011 21
Proof-of-concept of scenario Simulation of Car-to-X Communication Networks Braunschweiger Verkehrskolloquium, February 2011 22
Conclusions and further work VANETs offer a huge set of possible applications Traffic safety, efficiency and infotainment Scalability is a serious problem in VANETs Dynamic adaptation of transmission parameters is necessary to control channel load Mechanisms and optimized parameter sets have to be investigated Accurate modeling is necessary regarding Protocols: network simulation Mobility: road traffic simulation Radio propagation: propagation models or channel simulation Simulation of scalability effects in urban VANETs is still an open issue Appropriate models have to be derived d from raytracing results 23
C3World Connected Cars in a Connected World Funded by the Ministry of Science and Culture of Lower Saxony Partners: 24