Intelligent transportation systems


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Intelligent transportation systems

  1. 1. Intelligent Transportation Systems Wireless Access for Vehicular Environments (WAVE) Engin Karabulut Kocaeli Üniversitesi,2014
  2. 2. Outline Wireless Access for Vehicular Environments (WAVE) IEEE 802.11p IEEE 1609.1-4 SAE 2735
  3. 3. Wireless Access for Vehicular Environments Rationale What was the motivation behind a vehicle specific WLAN? What prevented the existing IEEE 802.11-family from being adopted as is?
  4. 4. IEEE 802.11 in C2C Requirements to be used for C2C Changes in baseline 802.11 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. 5. IEEE 802.11 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 802.11p DSRC platform
  6. 6. Vehicle to Pedestrian
  7. 7. Wireless Access for Vehicular Environments (WAVE) IEEE 802.11p + 1609.x + SAE 2735
  8. 8. Wireless Access for Vehicular Environments Overview Higher Layers SAE J2735 IEEE 1609.1 No. of ISO/OSI layer ref model 7 Application Data Plane e.g. HTTP WAVE Application (Resource Manager) TCP/UDP Network Services WSMP IEEE 1609.2 IEEE 1609.3 IEEE 802.11p IEEE 1609.4 IEEE 802.11p 3 Network IPv6 802.2 LLC 2b Data Link WAVE MAC 2a 1b Physical 1a 1609.1 Resource Manager 1609.2 Security Services 1609.3 Networking Services 1609.4 Multi-channel operations WAVE Physical Layer Convergence Protocol (PLCP) WAVE Physical Medium Dependent (PMD) W A VE WAVE Station Management Entity WSME Transport WAVE Station 4 Lower Layers Management Plane Station WSME MAC MAC Management Managem Management ent PHY Management PHY Management Entity
  9. 9. IEEE 802.11p Overview IEEE 802.11p is based on: IEEE 802.11a PHY: OFDM modulation IEEE 802.11 MAC: CSMA/CA IEEE 802.11e MAC enhancement: message prioritization
  10. 10. V2X frequency bands
  11. 11. IEEE 802.11p Frequency band U.S. FCC allocated 75 MHz band in 1999 for ITS Shared Public Safety/Private Short Rng Control Medium Rng Service Service Power Limit Dedicated Public Safety InterHigh Availability sections 44.8 dBm Power Limit 40 dBm 33 dBm Power Lim it 23 dBm Uplink Based on B. Cash (2008): North American 5.9 GHz DSRC Operational Concept / Band Plan 5.925 5.920 5.915 5.910 5.905 5.900 Public Public Safety Safety/ Intersections Private Ch 182 Ch 184 5.895 Public Control Safety/ Channel Private Ch 178 Ch 180 5.890 5.880 Public Safety/ Private Ch 176 5.875 5.870 Public Safety/ Private Ch 174 5.865 5.860 5.855 5.850 5.845 5.835 5.830 5.825 Public Safety V eh eh-V Ch 172 5.885 Downlink
  12. 12. IEEE 802.11p 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. 13. IEEE 802.11p Frequency band 5500 5550 5600 5650 5700 5750 5800 5850 Future ITS applications ITS road safety (ITS-G5A) ITS non-safety applications (ITS-G5B) European ITS-G5 Frequency Allocation 5900
  14. 14. IEEE 802.11p Operation modes Operation modes Without W VE Basic A Service Set (WBSS) Safety-critical, low latency messages and control messages Mainly broadcast Only on CCH With W VE Basic A 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. 15. IEEE 802.11p PHY OFDM-based modulation similar to IEEE 802.11a Halved channel bandwidth of IEEE 802.11a:  10 MHz channels  half data rate: 3-27 Mbps  doubled symbol duration: 8.0 μs 156.25 kHz 10 MHz
  16. 16. IEEE 802.11p PHY: Comparison to IEEE 802.11a IEEE 802.11a IEEE 802.11p Data rate 6, 9, 12, 18, 24, 36, 48, 54 Mbps 3, 4.5, 6, 9, 12, 18, 24, 27 Mbps Modulation BPSK OFDM QPSK OFDM 16-QAM OFDM 64-QAM OFDM BPSK OFDM QPSK OFDM 16-QAM OFDM 64-QAM OFDM Error Correction Coding Convolutional Coding with K=7 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 5.850-5.925 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. 17. IEEE 802.11p 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: IEEE IEEE RSUs have a fixed 48-bit MAC address 802.11a 802.11p OBUs generate a random MAC address Slot time 9 μs 13 μs upon start-up of the device SIFS time 16 μs 32 μs If a MAC address collision occurs the CW min 15 15 OBU automatically changes its MAC CW max address 1023 1023 Prioritization based on IEEE 802.11e EDCA SIFS – Short Inter-Frame Space (Enhanced Distributed Channel Access), defined in IEEE 1609.4
  18. 18. IEEE 1609.4 Extension for multi-channel coordination IEEE 1609.4 is a functional extension to IEEE 802.11e MAC to enable multi-channel coordination Functions:  Channel routing  Data buffers (queues)  Prioritization  Channel coordination
  19. 19. Priorization
  20. 20. IEEE 1609.4 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. 21. IEEE 1609.3 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 layer 4 TCP/UDP 3 IPv6 Data Plane WSMP 2b 802.2 LLC 2a WAVE MAC 1b WAVE PLCP 1a WAVE PMD SCH CCH/SCH
  22. 22. IEEE 1609.3 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. 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. 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