Vehicle Networks. V2X communication protocols. Univ.-Prof. Dr. Thomas Strang, Dipl.-Inform. Matthias Röckl

Transcription

1 Vehicle Networks V2X communication protocols Univ.-Prof. Dr. Thomas Strang, Dipl.-Inform. Matthias Röckl

2 Outline Wireless Access for Vehicular Environments (WAVE) IEEE p IEEE SAE 2735 Car-2-Car Communication Consortium & ETSI TC ITS

3 Wireless Access for Vehicular Environments Rationale What was the motivation behind a vehicle specific WLAN? What prevented the existing IEEE family from being adopted as is? [Source: Daimler/C2C-CC]

4 Wireless Access for Vehicular Environments (WAVE) IEEE p x + SAE 2735

5 Wireless Access for Vehicular Environments Overview SAE J2735 No. of layer ISO/OSI ref model Data Plane Management Plane Higher Layers Network Services Lower Layers IEEE IEEE IEEE IEEE IEEE p 7 Application e.g. HTTP 4 Transport TCP/UDP 3 Network IPv6 2b 2a 1b 1a Data Link Physical Resource Manager Security Services Networking Services Multi-channel operations LLC WAVE MAC WAVE Application (Resource Manager) WSMP WAVE Physical Layer Convergence Protocol (PLCP) WAVE Physical Medium Dependent (PMD) MAC Management PHY Management Management WAVE WAVE Station Station Management Entity Entity WSME WSME

6 IEEE p Requirements Changes in baseline standards are required to: support longer ranges of operation (up to ~1000 meters), the high speed of the vehicles (up ~500 km/h relative velocities), the extreme multipath environment (many reflections with long delays (up to ~5 μs max excess)), the need for multiple overlapping ad-hoc networks to operate with extremely high quality of service, and the nature of the automotive applications (e.g. reliable broadcast) to be supported. Based on: IEEE p & Tan (2008): Measurement and Analysis of Wireless Channel Impairments in DSRC Vehicular Communications

7 IEEE p Overview IEEE p is based on: IEEE a PHY: OFDM modulation IEEE MAC: CSMA/CA IEEE e MAC enhancement: message prioritization

8 IEEE p Communication entities Communication between: roadside units and mobile radio units (Vehicle-2-Infrastructure), mobile units (Vehicle-2-Vehicle), or portable units and mobile units (Vehicle-2-Pedestrian) Infrastructure: Roadside Units (RSUs) Gantries (e.g. tolling gantries) Poles, traffic lights, etc. Mobile/Portable equipment: On-board Unit (OBU) Denso DSRC platform Based on IEEE p

9 IEEE p Vehicle-2-Pedestrian [Source:

10 IEEE p Pedestrian? IEEE p DSRC module GPS receiver Regular GSM phone

11 V2X frequency bands

12 IEEE p Frequency band U.S. FCC allocated 75 MHz band in 1999 for ITS Power Limit Power Limit Power Limit Shared Public Safety/Private Control Medium Rng Short Rng Service Service dbm dbm Uplink Downlink Public Public Public Public Public Public Safety Control Safety Safety/ Safety/ Safety/ Safety/ Intersections Channel Veh-Veh Private Private Private Private Ch 172 Ch 174 Ch 176 Ch 178 Ch 180 Ch 182 Ch Dedicated Public Safety High Availability Intersections 40 dbm 23 dbm Based on B. Cash (2008): North American 5.9 GHz DSRC Operational Concept / Band Plan

13 IEEE p Multi-channel Control Channel (CCH): Broadcast communication Dedicated to short, high-priority, data and management frames: Safety-critical communication with low latencies Initialization of two-way communication on SCH Service Channel (SCH): Two-way communication between RSU and OBU or between OBUs For specific applications, e.g. tolling, internet access Different kinds of applications can be executed in parallel on different service channels Requires the setup of a WAVE Basic Service Set (WBSS Ad-hoc group ) prior to usage of the SCH

14 IEEE p Operation modes Operation modes Without WAVE Basic Service Set (WBSS) Safety-critical, low latency messages and control messages Mainly broadcast Only on CCH With WAVE Basic Service Set (WBSS) Two-way transactions (e.g. tolling, internet access) Required to use a SCH Requires initiation on CCH In contrast to the Independent Basic Service Set (IBSS), WBSS does not require authentication and association procedures

15 IEEE p PHY OFDM-based modulation similar to IEEE a Halved channel bandwidth of IEEE a: 10 MHz channels half data rate: 3-27 Mbps doubled symbol duration: 8.0 μs 10 MHz khz

16 IEEE p PHY: Comparison to IEEE a Data rate 6, 9, 12, 18, 24, 36, 48, 54 Mbps Modulation Error Correction Coding IEEE a IEEE p BPSK OFDM QPSK OFDM 16-QAM OFDM 64-QAM OFDM Convolutional Coding with K=7 3, 4.5, 6, 9, 12, 18, 24, 27 Mbps BPSK OFDM QPSK OFDM 16-QAM OFDM 64-QAM OFDM Convolutional Coding with K=7 Coding Rate 1/2, 2/3, 3/4 1/2, 2/3, 3/4 # of subcarriers 52 net 52 net OFDM Symbol Duration 4.0 μs 8.0 μs Guard Period 0.8 μs 1.6 μs Occupied bandwidth 20 MHz 10 MHz Frequency 5 GHz ISM band GHz Longer guard period Less Inter-symbol Interference Better resistance against multipath error Re-order of sub-carriers Better multipath mitigation Dedicated frequency band Less Co-Channel Interference

17 IEEE p MAC Based on Distributed Control Function (DCF) with CSMA/CA MAC-level acknowledgements for unicast communication, but no acknowledgements for broadcast communication unreliable broadcast communication RTS/CTS is only used on SCH Because of higher range, slot time and SIFS should be longer Addressing: RSUs have a fixed 48-bit MAC address OBUs generate a random MAC address upon start-up of the device If a MAC address collision occurs the OBU automatically changes its MAC address Prioritization based on IEEE e EDCA (Enhanced Distributed Channel Access), defined in IEEE IEEE a IEEE p Slot time 9 μs 13 μs SIFS time 16 μs 32 μs CW min CW max SIFS Short Inter-Frame Space

18 IEEE Extension for multi-channel coordination IEEE is a functional extension to IEEE e MAC to enable multi-channel coordination Functions: Channel routing Data buffers (queues) Prioritization Channel coordination

19 IEEE Channel Coordination Each Universal Time Coordinated (UTC) second is split into 10 Sync Intervals Every Sync Interval is composed of alternating: CCH Intervals: Every node monitors the CCH and SCH Intervals: Nodes can monitor one of the SCHs All WAVE devices have to monitor the CCH during the CCH Interval During the SCH Interval nodes may switch to a SCH (RX or TX) At the start of each UTC second the first Sync Interval begins Synchronization is performed via GPS

20 IEEE Networking Services IP-based communication: IPv6-based with optional: Mobile IPv6 (MIPv6) and Network Mobility (NEMO) enhancements UDP or TCP on transport layer Transmission on SCH only Non-IP-based communication: Based on WAVE Short Message Protocol (WSMP) Transmission on CCH or SCH No. of Data Plane layer 4 TCP/UDP WSMP 3 IPv6 2b 2a 1b 1a SCH LLC WAVE MAC WAVE PLCP WAVE PMD CCH/SCH

21 IEEE WAVE Short Message Protocol (WSMP) Networking protocol specifically designed for V2X communications WAVE Short Message (WSM) structure: WSMP can use CCH and SCH During the SCH Interval low priority messages can be transmitted on CCH for stations that do not switch to a SCH, high priority frames and WAVE Announcement frames shall be transmitted during the CCH Interval In order to access a SCH, the nodes have to be member of the WBSS WBSS roles: Provider: Initiates a WBSS by sending a WAVE Announcement User: Joins a WBSS based on the receipt of the WAVE Announcement

22 SAE J2735 Message Dispatcher Implementation specific common Implementation specific Based on: Robinson et al. (2006): Efficient Coordination and Transmission of Data for Cooperative Vehicular Safety Applications

23 SAE J2735 Basic message set definition SAE J2735: Dedicated Short Range Communication (DSRC) Message Set Dictionary ASN.1 representation of message structures Hierarchical definition of messages and substructures Basic message set is not so basic any more, i.e. comprehensive: 16 different message frames, which use 54 different data frames, which are parametrized through 162 different data elements

24 Car-2-Car Communication Consortium (C2C-CC) & ETSI TC ITS

25 Car-to-Car Communication Consortium Partners Partners Associate Members Dev. Members

26 Car-2-Car Communication Consortium Protocol stack

27 Car-to-Car Communication Consortium Objectives of the First Demonstration (October 2008) Objectives Demonstrate the functionality of CAR 2 CAR Communication Consortium system with 5 selected use cases Warning of road works Emergency vehicle Broken down vehicle Motorcycle use case / intersection scenario Situation Monitor interoperability between different communication platforms 9 vehicle manufacturers (Opel, BMW, Daimler, Volvo, Renault, Fiat, Volkswagen, Audi, Honda, ) 4 communication supplies (NEC, Hitachi / Renesas, Delphi, Denso) 1 after market supplier (Alpine) impact of vehicle-to-x communication [Slide by M. Kranz]

28 Demonstration self-restricted to just two message types: CAM and DEN Demonstration of technology although not fully specified yet. Thus, as compromise, mask layer 3..6 (i.e. APP on top of LLC) Cooperative Awareness Message (CAM) Type of Vehicle, Position, Speed, Heading Broadcasted by all vehicles with 1 Hz Decentralized Environment Notification Message (DEN) Type of Event, Region of Event Broadcasted by RSU or Vehicle No. of layer b 2a 1b 1a Data Plane Demo-APP LLC WAVE MAC WAVE PLCP WAVE PMD

29 Use Cases Warning of Road Works Use Case 1 Construction sites and temporary maintenance working areas are accident black spots: Changed traffic flow More traffic signs Lane width changes, lane merging, stress, and other factors The CAR 2 CAR system informs the driver on the details of the situation well before entering the potentially dangerous area Geographic extent and affected area Duration of road works Reason of road works [Slide by M. Kranz]

30 Use Cases Emergency Vehicle (EV) Use Case 2 When it comes to situations affecting the safety of lives every minute and every second is crucial. Road users are obliged to make way for Emergency vehicles (EVs) like ambulances or police cars. Potential problems are: Source of siren Crossing emergency vehicles at green lights Destination of emergency vehicle The CAR 2 CAR system informs the driver about the location of the source of the siren where the emergency vehicle is heading on what lane the emergency vehicle will be overtaking only if the emergency vehicle is expected to cross his route [Slide by M. Kranz]

31 Use Cases Broken Down Vehicle / Post Crash Warning Use Case 3 Accidents and break downs are dangerous for any involved or assisting person as well as for approaching vehicles. Problems are: Line of sight obstruction, e.g. behind a curve or hill top or due to weather conditions Timely warning of affected traffic participants If a vehicle detects a incident based on emergency flasher status, crash sensors, or onboard diagnosis, it can use the CAR 2 CAR system to inform about the type and location of the incident raise awareness and alertness to the traffic situation act as modern warning vest [Slide by M. Kranz]

32 Use Cases Motorcycle Warning / Intersection Assistance Use Case 4 European In-depth motorcycle accident analyses highlights that human error, and more specifically not seeing the motorcycle coming or misinterpreting distance and speed is the primary cause of accidents involving motorcycles. Reasons are: Motorcycles have a smaller silhouette and are easier to overlook Motorcycles do not have a crumble zone The CAR 2 CAR system informs the drivers of the involved vehicles about the presence of other traffic participants by sending a respective warning message if a crash is predicted [Slide by M. Kranz]

33 Car-2-Car Communication Consortium Focus and on-going discussions Focus on vehicle-to-vehicle communication (well, focus get s blurred more and more ) Multi-hop Geo-based addressing and routing Dual-receiver concept: Parallel reception on 2 channels Optional: dual-transmitter Simulation scenarios and scalability If you are looking for an interesting thesis topic in this area, contact me!

34 Car-2-Car Communication Consortium / ETSI TC ITS Relationship European industrial development of V2X communication by C2C-CC Created the European derivative of IEEE p Standardization by the European Telecommunications Standards Institute (ETSI) Technical Committee ITS ETSI is the relevant European standardization body for telecommunication protocols Transferring the standardization process from C2C-CC to ETSI TC ITS C2C-CC WGs act as preparatory platforms & discussion fora for ETSI TC ITS WGs. One critical issue with the transfer of standardization to ETSI are the ETSI voting rules, which may add a strong bias to the whole process