61 lines
3.1 KiB
Markdown
61 lines
3.1 KiB
Markdown
# Tick 11 — 2026-05-22 06:01 UTC
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**Thread:** R13 (contactless BP) — **NEGATIVE RESULT**
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**Verdict:** Don't pursue contactless BP from CSI as a primary product feature. The physics floors make it provably worse than a $20 arm cuff at every dimension.
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## What shipped
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- `examples/research-sota/r13_bp_physics_floor.py` — pure-numpy quantification of four physics floors that defeat the published CSI-BP approach.
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- `examples/research-sota/r13_bp_results.json` — machine-readable predictions.
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- `docs/research/sota-2026-05-22/R13-contactless-bp-negative.md` — explicit negative-result scrutiny note.
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## Four floors quantified
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| Floor | Need | Have | Gap |
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|---|---|---|---|
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| PTT temporal resolution | 0.5 ms (for 1 mmHg) | 10 ms typical, 1 ms max | typical ESP32 deployment cannot do <20 mmHg |
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| Spatial separation of two body sites | 55 cm | 40 cm Fresnel at 5 m link | sites CANNOT be resolved by single link |
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| Pulse-contour SNR | +25 dB | +20 dB after bandpass | **5 dB short** |
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| Vs $20 arm cuff | ±2 mmHg | best published ±10 mmHg | **5× worse** |
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The cleanest result: pulse signal motion at the chest is **0.3 mm**, breathing is **8 mm** — 27× larger. After bandpass we recover rate (we already ship this) but cannot recover waveform shape, which is what BP estimation needs.
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## Why this is the most valuable kind of tick
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A research loop that only publishes successes biases toward overclaiming. Two negative results this loop:
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1. **R12 eigenshift** — naive SVD-spectrum approach fails because signal doesn't dominate drift floor
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2. **R13 contactless BP** — published approaches require unrealistic SNR and spatial resolution
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Both follow the same pattern: a plausible-sounding ML approach fails because the underlying signal doesn't dominate the noise. Both have explicit follow-up paths if anyone wants to revisit (R12 → PABS over Fresnel basis from R6; R13 → bed-instrumented `cog-bedside` niche, multistatic PWV with 6+ anchors).
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## Confirms R14's design choice
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R14 (empathic appliances) explicitly assumed BP would *not* be available — its V1/V2/V3 sketches depend only on breathing + HR rate + motion intensity. R13 confirms that assumption is right.
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## What's still open in the negative space
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Three niche scenarios where BP-from-CSI *might* close some day:
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1. Single-subject **trend** monitoring (relative not absolute)
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2. Bed-instrumented controlled-still subject (25+ dB SNR achievable)
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3. Multistatic PWV with 6+ anchors + per-installation calibration
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The general "BP from a $9 ESP32 in the corner" claim does not close.
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## Composes with prior threads
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- **R1** (CRLB) — confirms temporal-resolution floor for PTT
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- **R6** (Fresnel) — provides the spatial floor that defeats two-site PTT
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- **R5** (saliency) — band-spread occupancy explains why the whole chest is observed but the 0.3 mm pulse isn't
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- **R12** — loop's other negative result; same failure pattern
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## Coordination
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`ticks/tick-11.md`. No PROGRESS.md edit. Branch `research/sota-r13-contactless-bp-negative`.
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## Remaining threads
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R3 (cross-room re-ID), R4 (federated learning), R15 (RF biometric across rooms).
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~6.0h to cron stop. 11 threads landed (2 explicit negative results).
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