Tick 21 — 2026-05-22 08:10 UTC

Thread: R6.2.1 (3D antenna placement extension) Verdict: Counter-intuitive finding — ceiling-only mounting gives 0% coverage. Mixed-height (one low, one high) gives the best result.

What shipped

• examples/research-sota/r6_2_1_3d_placement.py — pure-numpy 3D Fresnel ellipsoid placement search.
• examples/research-sota/r6_2_1_3d_results.json — strategy comparison.
• docs/research/sota-2026-05-22/R6_2_1-3d-placement.md — research note.

Headline strategy comparison

3D room (5×5×2.5 m), three 3D target zones (bed at z=0.3-0.6, chair at z=0.5-1.2, standing at z=1.0-1.7):

Strategy	Coverage
Desk-height (0.8 m walls)	22.2%
Wall-mount (1.5 m walls)	17.4%
Ceiling-only (2.5 m grid)	0.0%
Mixed walls + ceiling	25.7% ← best

The physics

Ceiling-only fails because both antennas at 2.5 m create a Fresnel ellipsoid sitting at ceiling height (2.1-2.9 m vertically). Target zones at 0.3-1.7 m are below the envelope by 0.4-2.0 m. The 39 cm transverse radius is symmetric around LOS, so a flat horizontal link at any height misses targets at any other height.

This is the 3D version of R6.1's on-LOS-degeneracy finding. A horizontal link at any single height has its envelope concentrated at that height.

Why mixed wins

Best placement: Tx at (5.0, 4.0, 0.8) desk-height + Rx at (0.0, 4.0, 1.5) wall-mount. The diagonal-in-z link tilts the ellipsoid through multiple elevations. Covers chair AND standing AND bed simultaneously.

Vertical link diversity is the 3D insight 2D analysis missed.

Installation-guide updates

Use case	Recipe
Single Tx-Rx pair	One low (0.8 m), one high (1.5 m), opposite walls
4-anchor R6.2.2	2× low corners + 2× high opposite corners
5-anchor knee	Mix 0.8 / 1.5 / one ceiling (2.5) for top-down
Bed-only sleep monitoring	Both LOW (0.5-0.8 m), opposite sides of bed
Standing-only (gym, kitchen)	Both HIGH (1.5 m)
NEVER	Both ceiling without low anchor

Why coverage numbers are lower than R6.2's 51%

3D target zones are volumes, not 2D areas. A point must be inside the ellipsoid in all 3 axes. Volumetric coverage is inherently lower; the 22-26% range is honest 3D physics.

Composes with prior threads

• R6.2 (2D) — incomplete; height matters as much as horizontal
• R6.2.2 (N-anchor) — N=5 knee should distribute across heights
• R6.1 multi-scatterer — needs 3D body model (head/chest/legs at different z) for proper composition
• R14 V1/V2/V3 — each vertical needs height-recipe specific to its sensing zone
• ADR-029 — anchor placement is (x, y, z), not (x, y)
• R12 PABS — sensitivity to intruders inherits the coverage; mixed-height detects standing/sitting/lying intruders alike

Honest scope

• 3-zone discrete approximation of continuous human occupancy
• Single-pair only; multi-anchor 3D = R6.2.2.1 (next)
• No furniture occlusion
• 0.1 m resolution
• Greedy single-pair search (brute-force feasible at this scale)

Coordination

ticks/tick-21.md. No PROGRESS.md edit. Branch research/sota-r6.2.1-3d-placement.

Remaining work

• R6.2.2.1: 3D N-anchor union coverage
• R6.2.3: chest-centric zones (per R6.1 chest = 27.6% of signal)
• R12.1: pose-PABS closed loop
• ADR-107: cross-installation federation

~3.8h to cron stop. 21 ticks landed. Loop covered R1-R15 + 2 ADRs + 6 deferred follow-ups + 3 negative-result categorisations.