Simulator/intel/radar/metrology_suite/RARD_CFAR_Guide.md

RARDCFAR_guide.md

C-Shenron Radar Metrology Debugging & Correction Guide

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1. System Architecture (Your Implementation)

Signal Chain

LiDAR → Physics Engine → Raw ADC → Range FFT → Doppler FFT → Angle FFT → CFAR → Point Cloud

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Your Actual Implementation (Code Verified)

Range FFT

fft(data * rangeWin * velWin, axis=0)

Doppler FFT

fftshift(fft(rangeProfile, axis=1), axis=1)

RD Heatmap

avgDopplerProfile = np.mean(dopplerProfile, axis=2)
rd_heatmap = |avgDopplerProfile|^2

RA Heatmap

ra_heatmap_raw = np.mean(dopplerProfile, axis=1)
ra_heatmap = |FFT(ra_heatmap_raw)|^2

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2. Current Observations (From Your Output)

✅ Correct

• Range axis correct
• RD vertical column at V=0
• CFAR pipeline working
• FFT chain structurally valid

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❌ Issues

Component	Issue
RD	No Doppler spread
RA	Horizontal banding + no angular separation
CFAR	Over-detecting static clutter
RA	Phase cancellation artifacts

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3. ROOT CAUSE ANALYSIS (CODE LEVEL)

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❌ ISSUE 1 — RA Banding (CRITICAL)

Problem Line:

ra_heatmap_raw = np.mean(dopplerProfile, axis=1)

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Why This is WRONG

You are doing:

Coherent integration across Doppler (complex mean)

This causes:

🔴 Phase cancellation

For moving targets:

[ \sum e^{j\phi_k} ≈ 0 ]

→ Signal disappears

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Result:

• Horizontal banding
• Missing targets
• Weak angular structure

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✅ FIX (MANDATORY)

Replace with:

ra_heatmap_raw = np.sum(np.abs(dopplerProfile), axis=1)

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Why This Works

• Preserves energy
• Removes phase sensitivity
• Matches real radar power integration

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❌ ISSUE 2 — Missing Window on Angle FFT

Current:

fft(pointSel, axis=1)

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Problem:

• No spatial window → sidelobes
• Poor angular resolution
• Leakage → smearing

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✅ FIX

Apply Hann window:

window = np.hanning(N_antennas)
pointSel_windowed = pointSel * window

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Then:

fft(pointSel_windowed, axis=1)

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❌ ISSUE 3 — Doppler Collapse

Problem Location:

avgDopplerProfile = np.mean(dopplerProfile, axis=2)

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Why This is WRONG

• Averaging complex signals across antennas
• Phase misalignment → cancellation

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Result:

• Everything collapses to V=0
• No velocity separation

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✅ FIX

Use power summation:

rd_heatmap = np.sum(np.abs(dopplerProfile)**2, axis=2)

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Why:

• Preserves Doppler energy
• Matches real radar processing

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❌ ISSUE 4 — CFAR Too Permissive

Config:

threshold: 20
win_param: [9, 9, 3, 3]

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Problem:

• Large window → over-smoothing
• Static clutter dominates noise estimate

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Symptoms:

• Entire vertical column detected
• Poor selectivity

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✅ FIX

Adjust:

win_param: [6, 6, 2, 2]
threshold: 25–35

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Optional Upgrade:

Switch to:

• OS-CFAR (better robustness)
• Or adaptive threshold per range band

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❌ ISSUE 5 — Velocity Axis Compression

Code:

velAxis = ...

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Problem:

• Likely too wide range
• Real velocities compressed near zero

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✅ FIX

Limit:

vel_min = -20 m/s
vel_max = +20 m/s

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❌ ISSUE 6 — RA Formation Order

Current Flow:

Doppler → mean → angle FFT

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Correct Flow:

Doppler → magnitude → sum → angle FFT

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4. CORRECTED PIPELINE

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RD Generation

rd_heatmap = np.sum(np.abs(dopplerProfile)**2, axis=2)

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RA Generation

ra_heatmap_raw = np.sum(np.abs(dopplerProfile), axis=1)

window = np.hanning(N_ant)
ra_heatmap_raw *= window

ra_heatmap = np.abs(fftshift(fft(ra_heatmap_raw, axis=1)))**2

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Angle Estimation

aoaProfile = fft(pointSel * window, axis=1)

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5. VALIDATION CHECKLIST

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RD

• Static → vertical line
• Moving → offset blobs
• No collapse to center

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RA

• Left/right separation
• Matches LiDAR geometry
• No horizontal banding

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CFAR

• Sparse detections
• Peaks only
• No full-column activation

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6. KEY INSIGHT (IMPORTANT)

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Your Current System

FFT pipeline is correct BUT integration strategy is wrong

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Core Problem

You are doing:

Coherent integration where incoherent is required

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Radar Rule

Stage	Integration Type
FFT	Coherent
Power	Incoherent

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7. Shenron vs Your System

Component	Shenron	Your Current
Integration	Incoherent	❌ Coherent
RA	Energy field	❌ Phase-sensitive
RD	Power-based	⚠️ Mixed
CFAR	Tuned	⚠️ Over-permissive

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8. Expected Outcome After Fix

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RD

• Clear moving targets
• Velocity separation visible

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RA

• Clean blobs
• Angular localization restored

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CFAR

• Sparse detections
• True target extraction

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9. Next Steps

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Immediate

1. Fix RD power calculation
2. Fix RA incoherent integration
3. Add Hann window

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Then

4. Tune CFAR
5. Validate against LiDAR

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Optional (Advanced)

• Add antenna array geometry
• Add beam pattern
• Add noise model

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10. Offer

If you want:

👉 I can rewrite your RadarProcessor into a correct, production-grade version 👉 Or debug further edge cases (multipath, clutter, velocity aliasing)

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FINAL TAKEAWAY

Your system is architecturally correct But one fundamental mistake (coherent averaging) is breaking RA and RD fidelity.

Fix that → your system will jump to near Shenron-quality radar output.

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End of Document