Coordinated Vehicle Control and Communication

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Coordinated Vehicle Control and Communication

• Professor Karl Hedrick
• Yu-Han Chen Sonia Mahal
• Vehicle Dynamics Laboratory
• U.C. Berkeley

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Overview

• Background and Motivation
• String Stability Criteria
• Types of Communication Delays
• Effects of Communication Delays on String
  Stability
• Analytical work in progress
• Simulation Results
• Future Research and Conclusion

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Background Motivation

• Platoon consists of tightly spaced vehicles
  traveling at relatively high speeds.
• To safely maintain constant spacing between
  vehicles, controllers have to guarantee string
  stability.
• To analyze the effects of communication
  delays/packet losses on string stability

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String Stability Definition

• Spacing errors between the vehicles must be
  attenuated as they propagate upstream, thus
  eliminating the slinky effect

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String Stability

• G(s) spacing error transfer function
• ei-1(t) is the input spacing error
• ei(t) is the output spacing error
• g(t) is the inverse Laplace transform of G(s)
• Necessary and sufficient condition for spacing
  error attenuation

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String Stability

• from linear control theory
• where

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• If the impulse response g(t) remains positive
  then the inequality becomes an equality giving
  us
• Note If impulse response is not positive, the
  condition above can not guarantee string
  stability.

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String Stability Results

• semi-autonomous mode
• preceding and lead acceleration
• velocity information
• additional lead vehicle position

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Communication Architecture

• token-bus architecture (TDMA)
• lead vehicle broadcasts message to all followers
• each vehicle sends a message to the vehicle
  immediately behind it

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Types of Communication Delays

• Periodic
• delay caused by time selected to send updated
  data
• Intermittent
• delay due to packet losses
• Radio failure
• Note Communication packets are received with no
  errors. The control law will use the most recent
  information received.

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Model of Communication Delays

• Pure time delay
• Sample and Hold

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Constant Spacing Control Using Lead Preceding
Vehicle Information

• vehicle (plant) model
• define sliding surface
• in order to make we define a
  synthetic control law

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Without Communication Delays

• Model of Actuator Lag
• Transfer function G(s)

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Effects of Communication Delays

• Lead Vehicle Information Modeled with Pure Time
  Delay

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Using the following information
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Transfer function dependent on the communication
delay of lead vehicle informationwhere
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Simulation Results

• Assumed control law module is triggered when
  vehicle receives new data from its predecessor
• lead vehicle information time delay
• assume the preceding vehicle information
  transmission delay is negligible
• Modeled communication delay as a pure time delay
• Vehicle modeled as a double integrator

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Desired Lead Vehicle Trajectory
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Simulation Results
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Simulation Results
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Future Research

• Numerically show time delay versus platoon size
  that will guarantee string stability
• Similar analysis for communication delay of
  preceding vehicle information
• Model the time delay as sample and hold instead
  of a pure time delay
• Model a lossy communication channel
• Compare results with simulation results obtained
  using CombSim using a realistic vehicle model