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Aspects of Vehicular WLAN Implementation

Aspects of Vehicular WLAN Implementation. Roger Berg Vice President - Technology and Product Development DENSO INTERNATIONAL AMERICA, INC. LA Laboratories. Contents. Identify Use cases Application Requirements Necessary Technology Innovate Technology Solutions Prioritization

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Aspects of Vehicular WLAN Implementation

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  1. Aspects of Vehicular WLAN Implementation Roger Berg Vice President - Technology and Product Development DENSO INTERNATIONAL AMERICA, INC. LA Laboratories

  2. Contents • Identify • Use cases • Application Requirements • Necessary Technology • Innovate • Technology Solutions • Prioritization • Channelization • Synchronization • Latency • Implement • Simulation • Feasibility Platform HW & SW • Insure • Test and Evaluation • Comparison to analytical and simulated results

  3. Identify: United States Vehicle Safety Scenarios autonomous sensors limited sensor range Cooperative sensors sensor range extension Motor vehicle crashes are the leading cause of death for every age from 2 to 33 years old. However, US vehicle crash related death rates have flattened. The trend and focus must move from crash mitigation to crash prevention. Safety improvements have come from crash mitigation. Goal for 2010: < 1.0 fatalities / 100 M VMT

  4. Identify: VSC in the USA Safety Mobility Reduce US Transportation inefficiency 3.6 Billion hours of vehicle delay / yr 5.7 Billion gallons of wasted fuel Reduce highway fatalities US DOT #1 priority $230B/yr $70B/yr February 2004 FCC authorized 75 MHz in the 5.9 GHz band for exclusive use of ITS. DSRC is proposed as the critical communications link US DOT envisions DSRC units in every new motor vehicle for life saving communications capability DSRC WAVE WIRELESS ACCESS FOR VEHICULAR ENVIRONMENTS For interoperability nation wide… Specification Feasibility a public standard of operation must be created Development 1998 2006 2009 Government wants to have standard capable for both V2V and V2R communications.

  5. Identify: Applications & Requirements SAE VSCC ISO TC204 WG16 WAVE IEEE 1556 ICDN NAWG ITS OTHER Latency, range, mobility, security, … Focus: requirements of groups of applications (range of required values)

  6. Identify: Vehicular applications requirements • Top 7 Vehicle Safety Applications • Intersection Collision Warning and Avoidance (Vehicle-to-Roadside-to-Vehicle) • Left Turn Assistance (Vehicle-to-Vehicle) • Cooperative Forward Collision Warnings (Vehicle-to-Vehicle) • Pre-crash sensing (Vehicle-to-Vehicle) • Emergency Electronic Brake light Signaling (Vehicle-to-Vehicle) • Curve Speed/Rollover Warnings (Vehicle-to-Roadside-to-Vehicle) • Pre-crash Sensing (Vehicle-to-Vehicle) • Preliminary Common Communications System Requirements • 50 - 100 ms access latency and update rates • 250+ km/hr mobility • Scalable on the basis of vehicle traffic density • Dynamic message routing • 10 - 500 m radio link range • Shared communication channel • Message payload 2 - 5 kbytes • Data rates 2 - 12 Mbps

  7. Identify: Technology improvement Channelization Scheme for Vehicle/Public Safety & Private Applications Control Channel Service Channel Service Channel Service Channel Service Channel Service Channel Service Channel High Priority Vehicle Safety CH 172 5860 MHz CH 174 5870 MHz CH 176 5880 MHz CH 178 5890 MHz CH 180 5900 MHz CH 182 5910 MHz CH 184 5920 MHz • Channelization solution to: • provide priority to vehicle/public safety message traffic • provide guaranteed and configurable message latency • allow channel capacity to be adaptively allocated

  8. Innovate: i-Channel Main Goals • Prioritization • Public/Vehicle Safety is guaranteed highest priority • Channelization latency is predictable and configurable • Synchronization • RSU not necessary for synchronization • Messaging is organized into Safety/Non-Safety time slots • Provides synchronization in overlapping RSU communication zones • No restrictions EXCEPT channel switching priority based on i-Channel rules • Non-Safety operation is flexible as long as i-Channel rules are followed • Adaptive Channel Access • Allows available system capacity to be allocated to Non-Safety when Public Safety is not needed • Allows full system capacity to be allocated to Public Safety when necessary Main Features: Prioritizes Safety, reduces latency, supports non-RSU communications.

  9. Innovate: Safety & Non-Safety Systems SAFETY (ADAPTIVE) NON-SAFETY (FIXED) • Safety Slot: • An adaptive time slot. • High-Priority Safety Messages transmitted only during Safety time slot. • Lower Priority Safety Messages may also be transmitted during the Safety time slot. • 802.11e QoS ensures highest priority messages get first access to RF medium. • OBUs and RSUs monitor the Safety Channel during the Safety time slot. • All devices stay on Safety Channel until High-Priority Safety Messages have not been transmitted or received for a predetermined period of time. • Once this predetermined time expires, Safety time slot ends, Non-Safety time slot begins. • Non-Safety Slot: • A fixed time slot. Guarantees return to Safety Channel to meet latency requirements. • OBUs and RSUs may change channels at will. • High-Priority Safety Messages may not be transmitted, even if tuned to the Safety Channel. Separate the Safety and Non-Safety operations.

  10. Innovate: Architectural Concept Focus: Specification of control mechanism for channel/system isolation.

  11. Innovate: i-Channel Parameters First HP Last HP First LP or NS Last LP or NS TNS TIDLE TTUNE TTUNE TNS-TX Tc = One Adaptive I-Channel Cycle TNS-TX Time left over for Non-Safety Communication. This time period is fixed to TNS – (2 x TTUNE). TIDLE Idle time that follows the last High Priority Safety Message (TX or RX). TTUNE Time allocated for receiver settling after a channel change. TNS Time allocated for Low Priority Non-Safety Communication. This time period is fixed.

  12. Tune to Safety Channel; Complete all pending High-Priority Safety (HP S); While verifying all High-Priority Safety has been completed, exchange Low-Priority Safety (LP S); HP S HP S HP S HP S HP S LP S LP S LP S LP S LP S Tune Back to Non-Safety Channel. DSRC Band Safety Channel Time Non-Safety Channel(s) Paused Paused Paused HP S HP S LP S LP S HP S HP S LP S LP S Adaptive Duration for HP Safety Fixed Duration for Non-Safety Fixed Duration for LP Innovate: i-Channel Cycle >> x2 Zoom Out

  13. 1) T idle Init Safety Channel Non-Safety Channel(s) 0 Legend HP Safety Message from Radio 0 HP Safety Message from Radio 1 LP Safety Message from Radio 1 Innovate: i-Channel Timing Channel Switch timing is derived solely from HP Safety Messages. (1) Idle Timeris initialized upon entering the Safety Slot. Idle Timer [ms]

  14. T idle = 1.5 Legend HP Safety Message from Radio 0 HP Safety Message from Radio 1 LP Safety Message from Radio 1 Innovate: i-Channel Timing Channel Switch timing is derived solely from HP Safety Messages. (1) Idle Timeris initialized upon entering the Safety Slot. Idle Timer [ms] 1.5

  15. 2) HP Radio 0 Radio 0 HP 0 Legend HP Safety Message from Radio 0 HP Safety Message from Radio 1 LP Safety Message from Radio 1 Innovate: i-Channel Timing Channel Switch timing is derived solely from HP Safety Messages. (1) Idle Timeris initialized upon entering the Safety Slot. (2) Idle Timeris reset every time aHP Safety messageis received OR transmitted by any OBU or RSU in the network. Idle Timer [ms]

  16. T idle = 1.0 Radio 0 HP 1.0 Legend HP Safety Message from Radio 0 HP Safety Message from Radio 1 LP Safety Message from Radio 1 Innovate: i-Channel Timing Channel Switch timing is derived solely from HP Safety Messages. (1) Idle Timeris initialized upon entering the Safety Slot. (2) Idle Timeris reset every time aHP Safety messageis received OR transmitted by any OBU or RSU in the network. Idle Timer [ms]

  17. HP Radio 1 Radio 0 HP Radio 1 HP 0 Legend HP Safety Message from Radio 0 HP Safety Message from Radio 1 LP Safety Message from Radio 1 Innovate: i-Channel Timing Channel Switch timing is derived solely from HP Safety Messages. (1) Idle Timeris initialized upon entering the Safety Slot. (2) Idle Timeris reset every time aHP Safety messageis received OR transmitted by any OBU or RSU in the network. Idle Timer [ms]

  18. T idle = 3.5 Radio 1 LP Radio 0 HP Radio 1 HP 3.5 Legend HP Safety Message from Radio 0 HP Safety Message from Radio 1 LP Safety Message from Radio 1 Innovate: i-Channel Timing Channel Switch timing is derived solely from HP Safety Messages. (1) Idle Timeris initialized upon entering the Safety Slot. (2) Idle Timeris reset every time aHP Safety messageis received OR transmitted by any OBU or RSU in the network. Idle Timer [ms]

  19. T idle Timeout Radio 1 LP Radio 0 HP Radio 1 HP Timeout Legend HP Safety Message from Radio 0 HP Safety Message from Radio 1 LP Safety Message from Radio 1 Innovate: i-Channel Timing Channel Switch timing is derived solely from HP Safety Messages. (1) Idle Timeris initialized upon entering the Safety Slot. (2) Idle Timeris reset every time aHP Safety messageis received OR transmitted by any OBU or RSU in the network. (3)The Idle Timertimes out when it reached a predetermined value. Then, the radio MAY tune away from safety. (4) Even if the radio does not tune away during the fixed non-safety period, HP Safety messagesSHALL NOT be sent during that time. Idle Timer [ms]

  20. Innovate: How do nodes and networks synchronize? Nodes enter High Awareness mode (HA) periodically Nodes enter HA, e.g. every 1 or 2 seconds, and stay on the safety channel during the next NS period looking for other nodes within communication distance. Nodes in a network enter High Awareness mode at different times Node 0 HP LP NS HP LP NS HP LP NS HP LP NS HP LP NS HP LP HA HP LP NS HP LP NS Node 1 HP LP NS HP LP NS HP LP NS HP LP NS HP LP NS HP LP NS HP LP NS HP LP HA Node 2 HP LP NS HP LP NS HP LP HA HP LP NS HP LP NS HP LP NS HP LP NS HP LP NS Node 3 HP LP NS HP LP NS HP LP NS HP LP NS HP LP HA HP LP NS HP LP NS HP LP NS t0 tf High Awareness = Stay on Safety Channel during Non-Safety period.

  21. Innovate: Follow the Leader Last HP Last HP Follow Me! LEADER TIDLE TNS = TSRCH TIDLE Go to High Awareness In High Awareness “Follow Me” Returning THA Timeout Other Network Detected HP TX Last HP FOLLOWERS TIDLE TIDLE Following Searching RX Follow Me Packet “Follow the Leader” allows two clusters to join very quickly.

  22. HP S HP S HP S HP S HP S HP S HP S HP S HP S HP S HP S HP S HP S HP S HP S HP S LP S LP S LP S LP S LP S LP S LP S LP S LP S LP S LP S LP S LP S LP S LP S LP S HP S LP S High-Awareness (instead of NS) HP S LP S HP S LP S HP S HP S LP S LP S HP S HP S HP S LP S LP S Innovate: i-Channel Multiple Networks Radios in different networks (i.e. unsynchronized) Radios in the same network (i.e. synchronized) i-Channel High-Awareness Mode Radio 0 RX F Radio 1 TX F Acquire Radio 0 Network Networks Merged

  23. Innovate: High Awareness Equal Size Clusters Unequal Size Clusters Equal Size Clusters Unequal Size Clusters THA = 1.0 THA = 1.0 Simulation data shows switching times independent of network size and mobility

  24. Implement: Channelization Latency Problem • All channel switching causes delays, • unless a radio is camped on a channel continuously. • All 802.11 systems have delays for medium access. • CSMA/CA access and back-off and • impacts of hidden nodes, interference, propagation delay, … • 802.11 packet latency depends on circumstances, environment, number of nodes, dynamics, loading, … • How can we isolate these impacts to determine the performance of a given channel switching method? How can we effectively compare channel switching methods?

  25. Implement: Useful Measure of Latency • DEFINITION: Channelization latency is the component of packet latency attributable to delays caused by the multi-channel management system. • Time delay between: • Packet arrival in MAC transmit queue from upper layer, and • Radio tuned to channel corresponding to that MAC queue. • Thus, Packet Latency = • Channelization latency • + Queue delay • + Access delay • + Propagation delay • + Process delay in receiver Channelization Latency is a measure of the efficiency of the channel switching.

  26. Implement: Expected Latency (analytic) Expected Latency for HP and LP Safety and Non-Safety ___ HP Safety ___ LP Safety ___ Non-Safety T_IDLE = 0.005 T_NS = 0.050 T_TUNE = 0.002 • Computation of expected value of channelization latency according to: • Probability of packet arrival relative to channel switching system time; • Probability of channel change latency given load.

  27. Implement: Measured Latency (simulations) T_IDLE = 0.005 T_NS = 0.050 T_TUNE = 0.002 • Measured actual channelization latency from ns2 simulations with varying degrees of high priority safety load.

  28. Implement: feasibility platform ITS / DSRC prototyping

  29. Implement: Tools for prototype 10 / 20 MHz Band Width Selection Adjustable TX Pout (1dB incremental) WAVE Frequency Channel Selection Variable Data Rate t-ns T-ns setting T-idle setting T-High Awareness setting WAVE Prototype Communications Module Support Tool

  30. Insure: Expected vs. Measured Latency (prototype) T_IDLE = 0.005 T_NS = 0.100 T_TUNE = 0.002 • Measured packet latency from WRM prototypes with very low loading and few units: • low loading approximates zero queue delay; • few units approximates zero access delay; • thus, packet latency approximates channelization latency. Measurements using radio module prototype confirm Analytical & Simulation analysis.

  31. Insure: Other Evaluation Tools Automatic data plotting

  32. Insure: Other Evaluation Tools

  33. Conclusion • Identified • Application requirements are the center point • Analyze technology deficiencies • Innovated solutions • Prioritize, channelize, synchronize with low latency • Implemented • Simulation and feasibility HW & SW • Insured • Match theory/simulation to implementation results • Test tools validate innovative implementation

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