OKI Project - Phase 2. Simulator Development Overview. Department of Electrical and Computer Engineering The Ohio State University August 2004. Topics. Overview Wireless simulator Physical layer modeling Traffic and driver behavior simulator Next steps Demonstration. Overview.
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OKI Project - Phase 2 Simulator Development Overview Department of Electrical and Computer Engineering The Ohio State University August 2004
Topics • Overview • Wireless simulator • Physical layer modeling • Traffic and driver behavior simulator • Next steps • Demonstration
Overview Advance the simulators developed for OKI phase 1 Incorporate new features/considerations Wireless simulator [Alberto Avila] Multiple transmissions, retransmission interval, repeater Real-time interface with vehicle traffic simulator Physical model [Heelim Teh] Incorporate modulation, reflection, blockages, and shadowing Intelligent transportation system (ITS) [Yiting Liu] Real-time interface vehicle traffic simulator with wireless simulator Collision warning system implementation Driver behavior model implementation
Offline Wireless Simulator • Objective: • Accurate representation of broadcast medium performance • Based on protocol and physical specifications • Incorporate physical layer to determine path loss and frame error rate • Flexibility on scenario parameters: • MAC protocol [Dolphin; 802.11 a;b;a R/A] • Building location • Repeater presence • Initial data transmission distance • Transmission interval • Maximum number of retransmissions • Retransmission interval
Offline Wireless Simulator Data update interval Transmission intervals Repeater [single retransmission] Retransmission attempts Initial data update • Dolphin protocol (CSMA) [Phase 1] • Multiple transmissions within area • Retransmissions within interval  • Physical specification [Phase 1] • Transmit power [10 dBm] • Receiver sensitivity [-82 dB] • Repeater • Single retransmission
Offline Wireless Simulator • Input Parameters: • - Vehicle density • Vehicle throughput • Transmission interval Offline Wireless Simulator Vehicle Traffic Simulator • Trace files: • Vehicle information • Vehicle position • - Vehicle velocity Physical layer model • Statistical information: • Packet collision probability • Vehicle density • Frame error rate • Latency • Statistical information: • Packet collision probability • Vehicle density • Frame error rate • Latency • Statistical information: • Packet collision probability • Vehicle density • Frame error rate • Latency Multiple scenarios with different input parameters
Offline Wireless Simulator • Simulation data available: • Vehicle packet collision rate • Base station packet collision rate • Vehicle density • Out of range average • Frame error rate • Coverage rate • Delivery rate
Online Wireless Simulator • Objective: • Provide packet transmission success determination • Low latency • Incorporate physical layer to determine path loss and frame error rate • Why? • Offline simulator is computation, memory intensive • CSIM is event driven, virtual time scale
Online Wireless Simulator • Functionality: • Estimate collision rate probability for specific scenario parameters and vehicle conditions • Low latency response (< 200 msec) • Encapsulate data from offline wireless simulator • Handle a variety of simulation scenarios: • Intersection type (signal/no signal) • Repeater • Building • Transmission interval; retransmissions
Online Wireless Simulator Online Wireless Simulator Physical layer model Offline simulator data • Density • Distance • Interval • .... Communication protocol Protocol parameters Scenario parameters Vehicle density Vehicle positions Vehicle sources Packet Generator Vehicle Traffic Simulator Collision Warning System Driver Behavior Receiver vehicle Source vehicle Reception time • Allows real-time feedback to the vehicle traffic simulator. This, in turn, enables driver behavior to be affected by information received from other vehicles through the online wireless simulator.
Wireless Simulation Results No signal, low throughput Signal, med/high throughput
Online Wireless Simulator Physical layer model Offline simulator data • Density • Distance • Interval • .... Physical Layer Offline Wireless Simulator Physical layer model • Leveraged by both offline and online wireless simulators
Physical Layer • Objective: • Provide a simple and accurate channel model for the Dedicated Short Range Communications (DSRC) in an urban environment • Determine path loss, frame error rate • Functionality: • Flexibility for different physical environments and conditions: • Buildings • Repeater • Vehicle types
Scenario Setup Building TX Building Sidewalk Sidewalk RX3 RX2 RX1 Sidewalk Sidewalk Building Building RX4
Possibilities • Line-of-sight communication: • - TX↔RX2, TX↔RX3 • No-line-of-sight communication: • Shadowing caused by other vehicles on the street: • - TX↔RX4 • Blockage caused by building at the corners: • - TX↔RX1
Line-of-sight Communication I can see you! I can see you, too! Line-of-Sight • When the source and the destination vehicle have a clear, unobstructed communication. • For example, between TX and RX2, RX3.
Two-ray Model Virtual reflection surface Direct path rt ht hr Reflection path rr h0 Distance: r • When there is line-of-sight, the received power is mainly contributed by the direct path and the reflection.
Two-ray Model • Path Loss rt: distance between TX ant. and RX ant. = rr: reflection path length from TX ant. to RX ant. = R: reflection coefficient. k: wave number. ht: TX antenna height. hr: RX antenna height. h0: virtual reflection surface height. : Y. Oda, K. Tsunekawa and H. Hata, “Advanced LOS path loss model in microcellular mobile communications”, IEEE Trans. Vehicular Technology, vol. 49, (6) pp.2121-2125, Nov. 2000
Virtual Reflection Surface [h0] • Due to different traffic densities and street characteristics, reflected ray does not necessarily come from the ground. • Each h0 corresponds to a specific traffic density and street characteristic. • To get h0: • Collect field test results. • Compute the free space propagation path loss. • Use the difference between the above two and the two-ray path loss equation to computer h0.
No-line-of-sight Communication Where are you? ??? Obstacle • When there are large obstacles between the source and the destination vehicles, the line-of-sight communication is obstructed. • Communications between TX and RX1, RX4.
Knife Edge Model TX d1 h d2 α RX2 RX4 • For modeling shadowing effect. Ex., TX ↔ RX4 • Fresnel integral:  where the Fresnel-Kirchoff parameter ν =  T. S. Rappaport, Wireless Communications. New Jersey: Prentice Hall, 2002
Ld(ν) = ν ≤ -1 -1 ≤ ν ≤ 0 0 ≤ ν ≤ 1 1 ≤ ν ≤ 2.4 ν > 2.4 Knife Edge Model
Virtual Source Model TX x Building Building rs ws r VS RX1 Building Building • Finding a virtual source located in the line-of-sight with both the transmitter and receiver.
Virtual Source Model • Path loss (dB): , r ≤ rb , where , r > rb
ITS Components • Vehicle traffic simulator (VTS): • Simulates traffic network and intersection behavior • Message generator • Sends messages when vehicles cross specific borders • Collision warning system • Generates warning message based on received information • Driver behavior module • Simulates individual vehicle’s response to various warning messages Message Generator Vehicle Traffic Simulator Collision Warning System Driver Behavior
Vehicle Traffic Simulator Traffic Flow Characteristic Input Vehicle Management Traffic Light Management Road Scenario Input
Scenario Input Traffic Flow Characteristic Input Simulation Setup Screen
Vehicle Management • Driver information: • Its own speed • Its own position data from DGPS • Turning direction • Other vehicles in Line-of-sight and the estimated distance and speed • Status of traffic lights Vehicle Management Turning Vehicle Following Normal Driving
Scenario Input Cycling Time Direction Status Traffic Light Management Cycling Time ( Two Phase):G=25sec; Y=5sec
Message Generator • Predefined Transmission Set: • Initial data update • Data update interval • Retransmission times Send messages when vehicle crosses data update interval borders Data update interval Initial data update Retransmissions Retransmissions
Collision Warning System • Three level warning system: • Warning level 1-- ELEVATED Danger ahead; Need to decelerate • Warning level 2-- HIGH Moderate danger ahead; Decelerate immediately • Warning level 3--SEVERE Critical situation; Severe danger ahead Stop immediately Collision probability
R: relative distance : : relative velocity li : Vehicle i’s length along the route contention Collision Warning System • Time-to-collision (TTC): • The time required for two vehicles to collide if they continue at their present speed and on the same path • The lower the TTC, the higher the collision risk • Time-to-avoidance (TTA): • The required stopping distance time • : Speed reduction parameter • If 1, then full stop • μ: Friction coefficient
Collision Warning System • Get communication data • Compute route contention • If no route contention • No warning • Else • Compute TTC and TTA • If TTC >= TTA+ driver’s response time (1.93 s -2.53 s) • If deceleration>=TTA deceleration • No warning • Else if deceleration < TTA deceleration • Warning level 1 • Else if no acceleration • Warning level 2 • Else (acceleration) • Warning level 3 • Else • No warning
Effects of Collision Warning System Animation of Intersection warning system Intersection Collision Scenario
Driver Response Module • Aggressive driver: • Only response to warning level 3 • Initial accelerator release only • Normal driver: • Response to both warning level 3 and level 2 • Braking to warning level 3 • Decelerate slowly to warning level 2 • Conservative driver: • Response to all the warnings • Braking to warning level 3 and warning level 2 • Decelerate quickly to warning level 1
Next Steps General Evaluate QoS for collision avoidance application Wireless simulator Improve correlation of scenario and traffic conditions to collision rate probability Incorporate different types of traffic for multiple intersection applications Physical layer Incorporate configurable modulation type Handle various obstacle types Traffic simulator Improve collision warning system Provide a more detailed driver model