Intelligent Transportation Systems. Wireless Access for Vehicular Environments (WAVE) Engin Karabulut Kocaeli Üniversitesi,2014

Transcription

1 Intelligent Transportation Systems Wireless Access for Vehicular Environments (WAVE) Engin Karabulut Kocaeli Üniversitesi,2014

2 Outline Wireless Access for Vehicular Environments (WAVE) IEEE p IEEE SAE 2735

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?

4 IEEE in C2C Requirements to be used for C2C 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)), 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.

5 IEEE in C2C VANET communication entities not only cars 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) Based on IEEE p DSRC platform

6 Vehicle to Pedestrian

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

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

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

10 V2X frequency bands

11 IEEE p Frequency band U.S. FCC allocated 75 MHz band in 1999 for ITS Shared Public Safety/Private Control Medium Rng Service Short Rng Service Dedicated Public Safety High Availability Intersections Power Limit 44.8 dbm 40 dbm Po w er Limit 33 dbm Pow er Lim it Uplink Downlink 23 dbm Public Safety Veh-Veh Ch 172 Public Safety/ Private Ch 174 Public Safety/ Private Control Channel Ch 176 Ch 178 Public Safety/ Private Ch 180 Public Public Safety Safety/ Intersections Private Ch 182 Ch 184 Based on B. Cash (2008): North American 5.9 GHz DSRC Operational Concept / Band Plan

12 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

13 ITS non-safety applications (ITS-G5B) ITS road safety (ITS-G5A) Future ITS applications IEEE p Frequency band European ITS-G5 Frequency Allocation

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 PHY: p Comparison to IEEE a Data rate 6, 9, 12, 18, 24, 36, 48, 54 Mbps Modulation IEEE a IEEE p BPSK OFDM QPSK OFDM 16-QAM OFDM 64-QAM OFDM Error Correction Coding 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 SIFS Short Inter-Frame Space IEEE p Slot time 9 μs 13 μs SIFS time 16 μs CW min μs CW max

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 Priorization

20 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 time base

21 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 No. of Data Plane layer 4 TCP/UDP 3 IPv6 WSMP 2b 2a 1b 1a LLC WAVE MAC WAVE PLCP WAVE PMD Non-IP-based communication: Based on WAVE Short Message Protocol (WSMP) Transmission on CCH or SCH SCH CCH/SCH

22 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

23 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

24 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