Increasing Realism in Auto Radar Drive
Scenario Simulation with Multipath,Diffuse Scattering, and Micro-Doppler
Presenter: Greg Skidmore
European Microwave Week 2021
Virtual Validation of Automotive Sensors

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Introduction: Requirements and Challenges for
Auto Radar Drive Scenario Simulation
Drive scenario simulation can offer significant benefits for early testing of sensor designs and as acomplement to operational road tests.
Focusing on mmWave radar sensors, there are several challenges to simulation of a realistic
automotive scenario:• Near-field conditions that invalidate traditional RCS concepts• Densely-faceted vehicle models; complex for traditional “propagation” ray-tracers• Complex multipath from roadside structures (guard rails, signs, parked vehicles, etc.)• Dynamic scenarios with multiple vehicles in motion, potentially with moving parts

This presentation uses Remcom’s WaveFarer® Radar Simulation Software to describe
challenges, solutions, and recent R&D to address key aspects of the problem, including target
scattering, multipath and clutter, and micro-Doppler from motion such as the moving limbs of awalking pedestrian.

© Remcom Inc. All rights reserved.

WaveFarer Radar Simulator
High fidelity radar simulator• Designed for close-ranges withincluttered multipath environments

Key capabilities• Scattering from complex models ofvehicles, structures and people• Multipath with the environment• mmWave propagation• Detailed 3D path, polarization, phasedata to support Doppler analysis

Applications• Automotive radar• Indoor sensors• Far-field radar cross section (RCS)© Remcom Inc. All rights reserved.

Innovative Ray-Tracing Enhancements
Targeted ray-casting• Launches rays directly at target facets,and extends multipath hits
• Unlike standard SBR, ensures fullillumination for surface integration

Exact path correction• Accurate magnitude, phase, polarization,and time of arrival

Spherical wave incidence to eliminate
far-field assumptions
Multipath on way to and fromscattering objects© Remcom Inc. All rights reserved.

Electromagnetic Methods
Physical Optics (PO) for backscatter• Surface integration technique accurately predicts backscatter from highly faceted vehicle
models in full, 4-π steradians• Does not make far-field assumptions, allowing for spherical wave incidence

Method of Equivalent Currents (MEC) for edge effects• Specially derived for Remcom’s PO technique to find electric and magnetic line currents• Included as line integrals to supplement PO surface integral

Geometric Optics and Uniform Theory of Diffraction (GO/UTD)• Used to propagate to scattering surfaces to provide incident electric and magnetic fields forsurface integration• Used to propagate back to ensure reciprocity© Remcom Inc. All rights reserved.

Clutter from Diffuse Scattering
Rough surfaces on roads, walls, andother structures can contributesignificant clutter to radar returns
Diffuse scattering models offer a way
to capture these effects
Remcom extended traditional methods
to retain relative phase between chirps• Initial phases are random, but consistent
between scenarios and positions• Predictable phase shifts allow inclusion
in Doppler calculations

Clutter from Diffuse Scatter(additional returns fromdiffuse backscatter)© Remcom Inc. All rights reserved.

Drive Scenario Modeling
Drive scenarios typically include
roadside clutter, other structures• Examples: guard rails, street sign
• Maybe buildings, walls, poles

Complex impulse response (CIR)shows mag and phase of returns vs.
time of arrival• Figure compares (a) car alone vs. (b) carwith ground and clutter• Ground bounce affects car return, while
guard rail posts and sign add numerous
secondary returns© Remcom Inc. All rights reserved.

Chirped Waveforms
WaveFarer’s script-driven utilities tosimulate and process linear chirps

Sequence of Chirps in a Frame• Define and simulate linear chirp frames• Post-process to calculate I&Q, rangeDoppler

Key Optimization• Extract detailed path data, mapping
shifting interactions between chirps• Adjust paths to generate impulse
response for each sample point of eachchirp• Minimizes required simulations while
retaining accuracy via detailed path data

Result: orders of magnitude faster thansimulating every sample point of everychirp

Request a demonstration of WaveFarer here.

© Remcom Inc. All rights reserved.

Range-Doppler Post-processing
Range-Doppler post-processing steps• Extract detailed path data and map
between simulations bounding frames• Adjust path mag and phase to calculate
CIR for each sample point of each chirp• Calculate I&Q at sample points• Perform 2D FFT to generate rangeDoppler

Key Assumptions:• Motion short during frame (~few ms), sopaths between sensor and geometry
can be captured with just a few
bounding sims
• Frequency dispersion is driven mostly
by phase shift due to path length

Complex Impulse
ResponseI&Q

Range-Doppler• Phase shifts from interactions(reflection, diffraction, scattering)assumed constant over band

© Remcom Inc. All rights reserved.

Range-Doppler Results
FFT of I&Q from One Chirp:
Power vs. Range (from BeatFrequencies)

FFT across Chirps in Frame:
Range-Doppler (from Phase Shifts)

Vehicle(roadside clutter)
VehicleGuard
RailPosts© Remcom Inc. All rights reserved.

Validation: Theory and Full-Wave Sim
Example 1: Sphere (vs. Theory)

Example 2: Corner Reflector at 24
GHz (vs. FDTD simulation)• Far-zone RCS at 77 GHz• Theory: -21.05 dBsm
• WaveFarer: -20.94 dBsm

Corner Reflector RCS from H-Polarized Plane Wave,
Theta=90deg• RCS vs Range• Theory: RCS + radar range equation

20100PEC Sphere

Received Power vs. Range: 77 GHz
Received Power (dBm)-110.0-120.0 020406080-10100-130.020406080 100 120 140 160 180 200 220 240 260 280 300 320 340 360-20-30-140.0-150.0Far-zone Theory-160.0WF, 5K Sphere-170.0-180.0-190.00-40-50-60

Distance (meters)

CoPol, dBsm

XF CoPol, dBsm

© Remcom Inc. All rights reserved.1Validation vs. NHTSA Measurements
Compared high-range resolution (complex impulse response) RCS• 94 GHz with 8 GHz bandwidth• Good agreement for key RCS peaks~7 dBsm~10 dBsm~4.5dBsm~6.5dBsm~-6 dBsm~-10 dBsm~-7.8 dBsm~-12 dBsm~-22 dBsm~-23 dBsm

Chevrolet Suburban (2009) returns at 0.0o in elevation from [1] Figure 25(a)1. Buller, W., et al., “Radar Measurements of NHTSA’s Surrogate Vehicle SS_V,”
National Highway Traffic Safety Administration (NHTSA), U.S. Dept. ofTransportation Report DOT HS 811 817, August 2013.
© Remcom Inc. All rights reserved.

Path Data Pinpoints Potential Sources of Key Returns
1. Tow-hitch and area around
license plate

2. Cross bar under front
passenger area

~10 dBsm~6.5dBsm~-12 dBsm~-22 dBsm~-7.8 dBsm

3. Rear axles© Remcom Inc. All rights reserved.

Automotive Radar Example: Vehicle Crossing Scenario
Scenario• Intersection of local road with two-lane
highway• Large truck in opposite lane obscurescrossing car (hatchback), acceleratingfrom full stop at stop sign
TABLE I. DRIVE SCENARIO PARAMETERS

Category
Simulated Time
Host Vehicle
Oncoming Truck
Accelerating Vehicle

Parameter
TimeVelocity
Velocity
Initial Velocity
Acceleration

Value
5 Seconds
15 m/s
15 m/s0 m/s
4 m/s2

CLICK to see video clip
© Remcom Inc. All rights reserved.

Simulating Linear Chirp
Auto Radar System Parameters

Chirp Waveform and Sampling Parameters• Power: 10 dBm (24.9 dBmi EIRP)• Frequency: 77 GHz, 540 MHz BW• Nominal parameters based on data fromITU, vendors, etc.
• Adjusted for mid-range radar scenario
TABLE II. CHIRP PARAMETERS

Category
Chirp Waveform

Chirp Sampling
Parameters

Parameter
Frequency
Modulation
Chirp Duration
Reset Time
Chirps / FrameFirst Sample
Sample Spacing# SamplesValue
77 – 77.54 GHz
Sawtooth
25 us
2 us
128
40 ns40 ns500© Remcom Inc. All rights reserved.

Range–Doppler at 1-Second Snapshots

CLICK to seevideo clip

© Remcom Inc. All rights reserved.

Diffuse Scattering
Roughness of road and ground add
clutter to radar returns
Diffuse scattering model can be used
to simulate these effects
Result:• Significant clutter across field of view,
particularly at shorter ranges© Remcom Inc. All rights reserved.

Diffuse Scattering: Path Comparison
PO Scatter and UTD interactions only

With Diffuse Scatter© Remcom Inc. All rights reserved.

Diffuse Scattering: Range-Doppler(Clutter fromDiffuse Scatter)© Remcom Inc. All rights reserved.

Range–Doppler at 1-Second Snapshots(with Diffuse Scatter)

CLICK to seevideo clip

© Remcom Inc. All rights reserved.

Micro-Doppler from Pedestrians
Many objects in an auto radar scene
have moving parts
These can result in micro-Doppler thatvaries about the Doppler of the objectPedestrian• Torso motion is somewhat sinusoidal
during walking• Arms and legs swing forward and back• Interactions between limbs and body cancause sudden phase shifts• Resultant micro-Doppler can vary
several meters-per-second about theoverall velocity (see next slide)

Sources of Micro-Doppler

Request a demonstration of WaveFarer here.
© Remcom Inc. All rights reserved.

Micro-Doppler from Walking
To evaluate pedestrian micro-Doppler,
obtained a rigged CAD model withspecified walking motion
As pedestrian cycles through steps at
1.4 m/s velocity:•Doppler spread periodically extends out tobetween 0 and 4.5 m/s•

Peak Doppler fluctuates between 0.6 m/s and2.8 m/s

Variations due to micro-Doppler causedby:• Swinging arms and legs
• Sinusoidal motion of torso while walking

CLICK to see video clip
© Remcom Inc. All rights reserved.

Pedestrian Crossing Scenario
Crossing Scenario• Pedestrian crosses intersection• At first partially obscured by stopped
vehicle before coming into full view• Calculate range-Doppler as vehicle andpedestrian progress

TABLE I. DRIVE SCENARIO PARAMETERSCategory
Simulated Time
Host Vehicle
Pedestrian
Oncoming truck
Parked Vehicle

ParameterTime
Velocity
Velocity
Velocity
VelocityValue
3 Seconds
15 m/s
1.4 m/s
12 m/s
0 m/s (parked)

CLICK to see video clip
© Remcom Inc. All rights reserved.

Pedestrian Scenario: Propagation Paths
Dominant paths show interactions with vehicle, pedestrian, and stop signs••

When pedestrian partially shadowed, paths primarily from above and below parkedcar
Once in full line-of-sight, radar returns are from full bodyPedestrian partially obscured (0.5 s)

Pedestrian in full line-of-sight (2.5 s)© Remcom Inc. All rights reserved.

Pedestrian Scenario: Range-Doppler
Pedestrian partially obscured (0.5 s)

Pedestrian(shadowed)
Parked car

Pedestrian in full line-of-sight (2.5 s)

Truck
Pedestrian(LOS)

Truck

Parked car© Remcom Inc. All rights reserved.

Concept for Virtual Drive TestingSensor Array,
Antenna Gain
Scenario Library
S1. Vehicle Braking
S2. Vehicle Crossing
S3. Pedestrian
Crosswalk
N. Scenario N

Drive Scenario
Simulation

Simulation
Outputs
Complex
ImpulseResponseI&Q

Signal
Processor

Pass/Fail?

(HW or SW in the loop)© Remcom Inc. All rights reserved.

SummaryIn this talk, we reviewed some of the challenges for mmWave radar drive
scenario simulation and an approach based on ray-tracing and Physical Optics
developed to address them.
Results from simulated scenarios show value that predictive simulation can bringto assessment of performance for potential drive scenarios• Insight into sources of radar returns, impacts of environment, etc.
• Simulated returns, I&Q or range-Doppler for input into testing• Ability to capture clutter from diffuse scattering and micro-Doppler

For best accuracy, may require detailed CAD model (e.g., undercarriage details)
or motion (e.g., pedestrian micro-Doppler)• But perhaps there can be a tradeoff between fidelity and run-time

Remcom is interested in collaborating with partners in the industry and academia
to determine how we can continue to improve these capabilities and integratewith design processes to assist with virtual validation.
© Remcom Inc. All rights reserved.

Contact

Request a demonstration of WaveFarer here.

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