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Cooperative Collision Warning Using Dedicated Short Range Wireless Communications

Cooperative Collision Warning Using Dedicated Short Range Wireless Communications. Performance Evaluation of Safety Applications over DSRC Vehicular Ad Hoc Networks. J. Yin, T. Elbatt G.Yeung, B. Ryu HRL Laboratories, LLC. S. Habermas, H. Krishnan T. Talty General Motors Corporation.

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Cooperative Collision Warning Using Dedicated Short Range Wireless Communications

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  1. Cooperative Collision Warning UsingDedicated Short Range Wireless Communications Performance Evaluation of Safety Applications over DSRC Vehicular Ad Hoc Networks J. Yin, T. Elbatt G.Yeung, B. Ryu HRL Laboratories, LLC S. Habermas, H. Krishnan T. Talty General Motors Corporation T. ElBatt, S.K. Goel G. Holland HRL Laboratories, LLC H. Krishnan, J. Parikh General Motors Corporation Presented by Ray K. Lam Slides adapted from authors’ presentation at VANET’06 CS 598-JH Advanced Topics in Wireless Networking

  2. 6 5 8 4 7 3 2 1 Vehicle Safety TRADITIONAL SENSORS • Vehicle safety research is focusing oncollision avoidance • Cons for using sensors • Limited range (sense immediate vehicles) • Limited Field of View (FOV) • Expensive • What about using wireless communication? COOPERATIVE COLLISION WARNING (CCW) “360 Degrees Driver Situation Awareness” using wireless comm.

  3. Forward Collision Warning (FCW) Host Vehicle (HV) utilizes messages from the immediate Forward Vehicle in the same lane to avoid forward collisions Lane Change Assistance (LCA) HV utilizes messages from the Adjacent Vehicle in a neighboring lane to assess unsafe lane changes Electronic Emergency Brake Light (EEBL) HV utilizes messages to determine if one, or more, leading vehicles in the same lane are braking Requirements: Wireless Platform GPS device with ~1-1.5m resolution to associate vehicles with lanes Examples of CCW Applications Host Vehicle Forward Vehicle Next Forward Vehicle Adjacent Vehicle We focus on Forward Collision Warning

  4. Outline • Paper 1 • Dedicated Short Range Communications (DSRC) Standard • Bit Error Rate (BER) of DSRC Links • Paper 2 • Performance Evaluation of Forward Collision Warning Applications

  5. Dedicated Short Range Communications (DSRC) • Similar to IEEE 802.11a with some major differences • Frequency band • Licensed spectrum in 5.9 GHz band • Free from interference of other devices • Environment • Outdoor high-speed vehicle • Large multi-path delay spread • Doppler effects

  6. Dedicated Short Range Communications (DSRC) • MAC layer • 7 channels • 1 channel for priority safety applications • Follows 802.11 MAC and 802.11e QoS • Physical layer • Bandwidth of each channel: 10 MHz • Max data rate supported: 27 Mbps • OFDM-based

  7. DSRC Channel Needs Special Treatment • DSRC channel exhibits different characteristics • RMS multi-path delay spread up to 400 ns at intersections • Doppler effect by vehicles moving at 120 mph • Dramatic impact on bit error rate • BER-based physical layer modeling more realistic • Successful decoding based on • Packet length • Bit error rate given SINR • MATLAB simulations on physical layer • Map BER with SINR • Used in network simulations in paper 1

  8. 16-QAM modulation (12 Mbps) BER sensitive to vehicle speed Error floor even at high SINR Channel characteristics change within a packet duration Training sequence at the beginning of packet insufficient BER versus SINR Results

  9. All vehicles periodically broadcast small messagescontaining location, velocity Application Model Single-hop broadcasts over UDP Broadcast rate: 10 packets/sec Packet size = 100 Bytes payload Measure the quality of reception at a random HV for messages transmitted by the FV Latency Packet delivery probability Forward Collision Warning Host Vehicle Forward Vehicle

  10. What dominates the latency of periodic broadcast applications? • Packet-level Metric: • Per-packet Latency (PPL) • Time between generating a packet at the application of the sender and successfully receiving the same packet at the application of the receiver • Gathered only for successful packets • Does not capture impact of packet losses Problem:Not the latency perceived by applications • Application-level Metric: • Packet Inter-Reception Time (IRT) • Time between two successful reception of packets from a specific transmitter • Reflects the impact of packet losses on safety applications Strong need for performance metrics that bridge the gap between the networking and automotive communities

  11. Simulation Setup • Simulation Tool: QualNetTM • Protocol Stack: • PHY/MAC: DSRC @ 6 Mbps data rate, single-channel operation • Transport: UDP • Application: single-hop broadcast @ 10 packets/sec broadcast rate • Wireless Channel Model: • Exponential decay with distance • Path loss = 2.15 by measurements • BER vs. SNR performance by measurements • Transmission Power:16.18 dBm (range ~150 meters) • Mobility: straight freeway

  12. High Density Scenario: (1920 vehicles) One Side of the freeway Stationary vehicles (simulates congestion) Vehicle separation = 5m On the other side: Avg vehicle speed = 25 mph Avg vehicle separation ~10m Freeway Mobility Scenarios 1 mile • Low Density Scenario: (208 vehicles) • Avg vehicle speed = 65 mph • Avg vehicle separation ~61m

  13. FCW performance for a chosen pair of vehicles (High Density) • Cumulative Packet Reception: • ~ 46 packets lost out of 290 sent • But, Max. # consecutive packet losses is only 3 • Inter-Reception Time (IRT): • Max. ~400 msec, Min. ~100 msec • Per-packet Latency (PPL): • Max. ~17 msec, Min. ~0.321 msec • Max IRT stats over 20 runs: Mean = 372.1 ms, SD = 66.3 ms • IRT and PPL vary over vastly different ranges (due to consecutive pkt losses)

  14. FCW performance for a chosen pair of vehicles (Low Density) • Cumulative Packet Reception: • Only 7 packets lost in total • No consecutive packet losses • Max. Inter-Reception Time (IRT): • Max. = 200 msec, Min. = 100 msec • Per Packet Latency (PPL): • Max. ~1 msec, Min. ~0.321 msec • Max IRT stats over 20 runs: Mean = 238 ms, SD = 74.4 ms • Performance gap between extreme densities is small • High density performance could be improved by broadcast enhancement techniques

  15. FCW Broadcast Rate Adaptation • Motivation: balance the factors contributing to the packet inter-reception time (IRT) • Low broadcast rates, fewer packet losses • High broadcast rates, smaller inter-broadcast interval • High density scenario, 150 m range, 100 Bytes payload • Examine different Broadcast intervals: • 50, 100, 200, …, 700 msec Conjecture: There is an optimal broadcast interval that minimizes IRT

  16. Motivation: Reduce interference using short Tx range Examine different Tx ranges: 50 m, 100 m, …, 300 m Observations: FCW IRT increases with the Tx range due to higher number of successive packet collisions 50 m range improves IRT by 4-fold over 300 m range Application may require minimum Tx range though FCW Transmission Range Adaptation Dynamic Power Control considerably improves FCW performance

  17. Objective: Characterize the behavior of packet success probability with increasing distance from the Host Vehicle For applications such as EEBL Transmission range is fixed All vehicles are stationary Measured at a randomly chosen Host Vehicle 150m comm. range is divided into 10 concentric bins at 15m, 30m, 45m, …. DSRC Performance Trends with Distance Host Vehicle

  18. Packet Success Probability at the Host Vehicle • Success probability varies considerably with distance • Good reception from nearby vehicles • Even at the edge of the reception range (150m), success probability ~ 38% Quality of reception at HV strongly depends on the distance to the relevant sender

  19. Comments on VANET Research • Attention • DSRC channel needs special treatment • Realistic mobility model required • Future directions • More study on application-level metrics • Theoretical analysis • Tuning of broadcast rate, Tx power, … • Distributed algorithm for dynamic tuning of control knobs

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