Tick 17 — 2026-05-22 07:09 UTC

Thread: R6.2.2 (N-anchor multistatic placement) Verdict: Practical knee at N=5 anchors for typical 5×5 m bedroom. Direct cost-optimisation conclusion + ADR-029 architectural update.

What shipped

• examples/research-sota/r6_2_2_multistatic_placement.py — pure-numpy greedy multi-anchor placement search with random restarts.
• examples/research-sota/r6_2_2_multistatic_results.json — full saturation curve for 5×5 m bedroom benchmark.
• docs/research/sota-2026-05-22/R6_2_2-multistatic-placement.md — research note.

Saturation curve (5×5 m bedroom, 3 target zones, 2.4 GHz)

N anchors	Pairs	Coverage	Marginal
2	1	35.7%	+35.7 pp
3	3	63.4%	+27.6 pp
4	6	86.2%	+22.8 pp
5	10	96.8%	+10.6 pp ← knee
6	15	100%	+3.2 pp
7+	21+	100%	+0.0 pp

Knee at N=5 — past this, diminishing returns.

Three regimes surfaced

Use case	Anchors	Coverage
Single-feature (presence only)	2-3	36-63%
Multi-feature (pose, vitals, count)	4-5	86-97%
Mission-critical (medical, security)	6	100%
Beyond 6	wasted	100% (no gain)

Cost-optimisation conclusion

Cognitum Seed BOM is $9-15. The +$9-15 from 4→5 anchors buys +10.6 pp coverage. The same cost from 5→6 buys only +3.2 pp. Consumer recommendation: 5 anchors hits the knee. Commercial / medical: 6.

Convenient numerology

N=5 happens to also satisfy three other constraints simultaneously:

1. R7 multi-link mincut: needs N ≥ 4 to detect single-anchor compromise
2. ADR-105 federation Krum: f=1 byzantine tolerance requires K ≥ 5
3. R6.2.2 coverage knee: 5 anchors hits practical saturation

These three constraints all bound by similar inverse-square-of-geometry scaling, so the alignment is probably not coincidental — but it's a useful fact for the architectural roadmap.

ADR-029 recommendation update

ADR-029 (multistatic sensing) didn't specify anchor counts. R6.2.2 fills the gap:

Recommended anchor count: 5 for typical 5×5 m room. 4 anchors gives 86% coverage (good for many use cases); 6 anchors gives 100% but is over-provisioned past the knee.

Composes with prior threads

• R6 / R6.2: direct generalisation; greedy expansion to N anchors
• R7: needs N ≥ 4 for multi-link adversarial detection; N=5 satisfies
• R1: combined with R6.2.2 = full sensing geometry budget
• ADR-029: architectural recommendation now has a number
• ADR-105: Krum byzantine bound f < (K-2)/2 → K=5 = f=1 (matches R7 single-attacker case)
• R10: wildlife corridors will have different saturation (more anchors for length, fewer for width)
• R11: maritime cabins likely saturate earlier (N=3-4)
• R14: V1/V2/V3 verticals all need ≥86% coverage = N=4 minimum

Honest scope

• Single geometry tested (5×5 m bedroom). Other rooms have different knees.
• 2D still (R6.2.1 = 3D ceiling/floor mounts not yet built).
• Free-space (multipath probably adds +5-15% beyond Fresnel-only).
• Greedy + 8 restarts → 1-2 pp shy of global optimum at most.

Coordination

ticks/tick-17.md. No PROGRESS.md edit. Branch research/sota-r6.2.2-multistatic-placement.

Remaining work

• R3 follow-up: physics-informed env_sig prediction (zero-shot cross-room via R6 forward operator + room map)
• R6.1: multi-scatterer additive forward model
• R6.2.1: 3D ceiling/floor placement
• R6.2.3: pose-trajectory-aware zones (needs AETHER + R3 data)
• ADR-107: cross-installation federation w/ secure aggregation

~4.9h to cron stop. 17 ticks landed. 2 ADRs + 2 deferred follow-ups closed.