wifi-densepose/docs/research/sota-2026-05-22/ticks/tick-11.md

Tick 11 — 2026-05-22 06:01 UTC

Thread: R13 (contactless BP) — NEGATIVE RESULT 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.

What shipped

• examples/research-sota/r13_bp_physics_floor.py — pure-numpy quantification of four physics floors that defeat the published CSI-BP approach.
• examples/research-sota/r13_bp_results.json — machine-readable predictions.
• docs/research/sota-2026-05-22/R13-contactless-bp-negative.md — explicit negative-result scrutiny note.

Four floors quantified

Floor	Need	Have	Gap
PTT temporal resolution	0.5 ms (for 1 mmHg)	10 ms typical, 1 ms max	typical ESP32 deployment cannot do <20 mmHg
Spatial separation of two body sites	55 cm	40 cm Fresnel at 5 m link	sites CANNOT be resolved by single link
Pulse-contour SNR	+25 dB	+20 dB after bandpass	5 dB short
Vs $20 arm cuff	±2 mmHg	best published ±10 mmHg	5× worse

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.

Why this is the most valuable kind of tick

A research loop that only publishes successes biases toward overclaiming. Two negative results this loop:

1. R12 eigenshift — naive SVD-spectrum approach fails because signal doesn't dominate drift floor
2. R13 contactless BP — published approaches require unrealistic SNR and spatial resolution

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).

Confirms R14's design choice

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.

What's still open in the negative space

Three niche scenarios where BP-from-CSI might close some day:

1. Single-subject trend monitoring (relative not absolute)
2. Bed-instrumented controlled-still subject (25+ dB SNR achievable)
3. Multistatic PWV with 6+ anchors + per-installation calibration

The general "BP from a $9 ESP32 in the corner" claim does not close.

Composes with prior threads

• R1 (CRLB) — confirms temporal-resolution floor for PTT
• R6 (Fresnel) — provides the spatial floor that defeats two-site PTT
• R5 (saliency) — band-spread occupancy explains why the whole chest is observed but the 0.3 mm pulse isn't
• R12 — loop's other negative result; same failure pattern

Coordination

ticks/tick-11.md. No PROGRESS.md edit. Branch research/sota-r13-contactless-bp-negative.

Remaining threads

R3 (cross-room re-ID), R4 (federated learning), R15 (RF biometric across rooms).

~6.0h to cron stop. 11 threads landed (2 explicit negative results).