diff --git a/docs/adr/ADR-091-stand-off-radar-tier-research.md b/docs/adr/ADR-091-stand-off-radar-tier-research.md new file mode 100644 index 00000000..c02d995b --- /dev/null +++ b/docs/adr/ADR-091-stand-off-radar-tier-research.md @@ -0,0 +1,770 @@ +# ADR-091: Stand-off Radar Tier Research — 77 GHz High-Power and 100–200 GHz Coherent Sub-THz + +| Field | Value | +|----------------|-----------------------------------------------------------------------------------------| +| **Status** | Proposed — Research only. No production hardware integration. Decision deferred pending sub-$1k COTS sub-THz transceiver availability and clear non-export-controlled use case. | +| **Date** | 2026-04-26 | +| **Authors** | ruv | +| **Refines** | ADR-021 (60 GHz / mmWave vital-signs pipeline) | +| **Companion** | `docs/research/quantum-sensing/16-ghost-murmur-ruview-spec.md` §6.3, ADR-029 (RuvSense multistatic), ADR-089 (nvsim simulator), ADR-090 (Lindblad extension) | + +## 1. Context + +### 1.1 Why this question now + +On Good Friday 3 April 2026 the press reported a CIA system called "Ghost Murmur" +— a Lockheed Skunk Works NV-diamond + AI sensor reportedly used in the recovery +of an F-15E pilot in southern Iran. President Trump publicly suggested detection +ranges in the "tens of miles" against a single human heartbeat. RuView shipped +a research spec (`16-ghost-murmur-ruview-spec.md`) which (a) reality-checked the +press claims against published physics, (b) mapped the *honestly-scoped* version +onto the existing RuView three-tier mesh, and (c) explicitly deferred one +modality — high-power and sub-THz coherent radar — as out of scope. From §6.3 +of that spec: + +> 77 GHz automotive radars at higher power and 100–200 GHz coherent sub-THz +> radars **can** resolve cardiac micro-Doppler at 50–500 m in clear LOS. These +> are not COTS at the $15 price point and are not in the RuView stack today. +> They are also subject to ITAR / export-control review and **explicitly out of +> scope** for this open-source project. + +That sentence is the trigger for this ADR. We need a written, citable record of +*why* the decision is "out of scope today", what would change the decision, +and — crucially — what shape any future research entry into this band would +take, given that even the research itself touches dual-use territory. + +### 1.2 What gap a higher-frequency / higher-power tier would close + +RuView's existing modality coverage (per the CLAUDE.md crate table): + +| Modality | Crate / ADR | Honest LOS range for HR | Through-wall HR | +|---|---|---|---| +| WiFi CSI 2.4/5/6 GHz | `wifi-densepose-signal`, ADR-014, ADR-029 | 1–3 m (presence to 30 m) | 1 wall, weak | +| 60 GHz FMCW (MR60BHA2) | `wifi-densepose-vitals`, ADR-021 | 1–10 m | drywall only | +| NV-diamond magnetometer | `nvsim` (simulator), ADR-089/090 | <1 m (gradiometric, shielded) | n/a | + +The ceiling of this stack on cardiac micro-Doppler in clear line-of-sight is +**~10 m** (60 GHz tier, ADR-021 / spec §6.1). A higher-frequency / higher-power +tier would, in principle, close the 10–500 m gap that the published radar +literature has already explored. The two candidate bands: + +1. **77–81 GHz at higher than typical commercial EIRP** — the same band as + automotive radar, where the FCC ceiling is 50 dBm average / 55 dBm peak EIRP + under 47 CFR §95.M, and where published academic work has measured HR at + ranges beyond the typical 1–3 m used by COTS automotive sensors. +2. **100–200 GHz coherent sub-THz radar** — where λ ≈ 1.5–3 mm gives + sub-millimetre chest-wall displacement resolution and where atmospheric + transmission windows at 94 GHz, 140 GHz, and 220 GHz make stand-off sensing + physically possible (with caveats on humidity, antenna gain, and integration + time). + +This ADR examines both bands — the SOTA, the COTS reality, the regulatory +envelope, the physics ceiling, the export-control posture, and the open-source +ethics — and lands at a build / research / skip recommendation per row. + +## 2. SOTA: 77–81 GHz automotive radar at higher power + +### 2.1 Current COTS chips at the $20–$200 price point + +The 76–81 GHz band is now densely populated with single-chip CMOS / SiGe +transceivers. Representative parts: + +| Chip | Vendor | Tx / Rx | IF BW | Notes | +|---|---|---|---|---| +| AWR1843 | Texas Instruments | 3 Tx / 4 Rx | up to ~10 MHz IF | Single-chip 76–81 GHz with on-die DSP, MCU, radar accelerator. Long-range automotive ACC, AEB. ([TI AWR1843](https://www.ti.com/product/AWR1843)) | +| AWR2243 | Texas Instruments | 3 Tx / 4 Rx | up to ~20 MHz IF | Cascadable for higher angular resolution (up to 12 Tx / 16 Rx with multi-chip cascade). ([TI AWR2243](https://www.ti.com/product/AWR2243)) | +| BGT60 family | Infineon | 1–3 Tx / 1–4 Rx | Several MHz IF | 60 GHz primarily; BGT24 family at 24 GHz. Smaller, lower power, gesture / presence focus. | +| TEF82xx | NXP | up to 4 Tx / 4 Rx | several MHz IF | Automotive-grade 76–81 GHz. | + +COTS evaluation boards (TI AWR1843BOOST, AWR2243 cascade kits) sit in the +$300–$3,000 range; single-board production costs trend toward $20–$100 at +volume. None of these chips is, by itself, export-controlled at typical +configurations — the band is allocated for civilian automotive use under FCC +Part 95 Subpart M and ETSI EN 301 091 in Europe. + +**EIRP envelope**: 47 CFR §95.M (and the historical §15.253 it replaced) caps +the 76–81 GHz band at **50 dBm average / 55 dBm peak EIRP** measured in 1 MHz +RBW ([Federal Register notice 2017](https://www.federalregister.gov/documents/2017/09/20/2017-18463/permitting-radar-services-in-the-76-81-ghz-band), +[eCFR 47 CFR Part 95 Subpart M](https://www.ecfr.gov/current/title-47/chapter-I/subchapter-D/part-95/subpart-M)). +That is roughly 100 W EIRP average, 316 W peak. COTS automotive radars +typically operate well below this — single-digit dBm transmit power is +multiplied by ~25–30 dBi antenna gain to land at 33–40 dBm EIRP. + +### 2.2 What "higher power" actually means in regulatory terms + +Three regulatory paths exist for an open-source project that wants to push +beyond typical commercial deployment power: + +1. **Stay inside FCC Part 95 §95.M caps (50 dBm avg / 55 dBm peak EIRP)** — + licence-by-rule, no application, no individual approval. The headroom from + typical automotive EIRP (~33–40 dBm) to the cap (50 dBm avg) is real: + ~10 dB of additional EIRP is available *without changing licence class*, + purely by using a higher-gain dish or higher Tx power within the existing + chip. This is the upper bound of "stand-off radar that is still part-95 + legal". +2. **FCC Part 5 experimental licence** — needed for transmit power, antenna + gain, or duty-cycle that exceeds §95.M. Application-based, time-bounded, + non-renewable beyond limits. Typical academic radar ranges (e.g. the + long-range cardiac measurements in §2.3 below) operate under this regime. +3. **No US authorisation at all** — only legal as receive-only, or as a + simulator. Any unlicensed transmission above §95.M at 76–81 GHz is a + prohibited emission under 47 CFR §15.5 / §95.335. + +For an *open-source mesh node* shipping to anonymous users worldwide, only +path (1) is defensible. Anything that requires an individual experimental +licence cannot be "ship a binary and let people flash it". + +### 2.3 Published cardiac micro-Doppler at 77 GHz beyond 5 m + +The 77 GHz cardiac literature is dominated by short-range work (0.3–2 m), e.g.: + +- Chen et al. (2024). "Contactless and short-range vital signs detection with + doppler radar millimetre-wave (76–81 GHz) sensing firmware." *Healthcare + Technology Letters*. ([PMC11665778](https://pmc.ncbi.nlm.nih.gov/articles/PMC11665778/), + [Wiley HTL 2024](https://ietresearch.onlinelibrary.wiley.com/doi/full/10.1049/htl2.12075)) + — TI IWR1443BOOST at 0.30–1.20 m, suggested 0.6 m. +- Wang et al. (2020). "Remote Monitoring of Human Vital Signs Based on 77-GHz + mm-Wave FMCW Radar." *Sensors* 20, 2999. + ([PMC7285495](https://pmc.ncbi.nlm.nih.gov/articles/PMC7285495/), + [MDPI Sensors 2020](https://www.mdpi.com/1424-8220/20/10/2999)) — typically + short-range bench measurements. +- Liu et al. (2022). "Real-Time Heart Rate Detection Method Based on 77 GHz + FMCW Radar." *Micromachines* 13, 1960. + ([PMC9693980](https://pmc.ncbi.nlm.nih.gov/articles/PMC9693980/), + [MDPI](https://www.mdpi.com/2072-666X/13/11/1960)) — 2.925% mean HR error, + short-range. +- Iyer et al. (2022). "mm-Wave Radar-Based Vital Signs Monitoring and + Arrhythmia Detection Using Machine Learning." *Sensors*. + ([PMC9104941](https://pmc.ncbi.nlm.nih.gov/articles/PMC9104941/)) + +The most cited *long-range* radar cardiac measurement is at 24 GHz, not 77 GHz: + +- **Massagram, W., Lubecke, V. M., Høst-Madsen, A., Boric-Lubecke, O. (2013). + "Parametric Study of Antennas for Long Range Doppler Radar Heart Rate + Detection."** *IEEE EMBC* / republished in *PMC*. + ([PMC4900816](https://pmc.ncbi.nlm.nih.gov/articles/PMC4900816/), + [PubMed 23366747](https://pubmed.ncbi.nlm.nih.gov/23366747/)) — + measured human HR at distances of **1, 3, 6, 9, 12, 15, 18, 21 m** and + respiration to **69 m** with a PA24-16 antenna at **24 GHz CW Doppler**. + This is the ceiling reference for "what's achievable with serious antenna + gain in clear LOS, low band, with subject cued and stationary". + +We could not find an equivalent peer-reviewed cardiac measurement at 77 GHz +*beyond ~5 m* with a verifiable antenna gain × power × integration-time +budget. The work that exists at 77 GHz is overwhelmingly bench-scale (≤ 2 m). +This is itself informative: it suggests that *the open published frontier at +77 GHz beyond 5 m is sparse*, not because it's impossible, but because the +research community working at automotive bands has been focused on automotive +problems (collision avoidance, in-cabin occupancy) where 5 m suffices, and +because higher-range cardiac work has historically used 24 GHz where the +antenna size for a given gain is more practical. + +### 2.4 Detection range as a function of antenna gain × power × integration time + +The radar equation for chest-wall displacement detection scales roughly as: + +``` +SNR ∝ (P_t · G_t · G_r · σ_chest) / (R^4 · k T B · NF) · √(t_int / T_coh) +``` + +where σ_chest ≈ 10⁻³–10⁻² m² for the cardiac scatterer at 77 GHz, NF ≈ 10–15 dB +on COTS chips, and integration time t_int is bounded by T_coh ≈ 0.5–1 s +(physiological coherence — the heart period itself). + +Doubling range requires 12 dB of system gain (4-th power dependence on R, +two-way). At the part-95 §95.M ceiling (50 dBm avg EIRP) and a generous 30 dB +antenna gain (a ~30 cm dish at 77 GHz), the addressable HR detection range in +clear LOS is roughly **15–30 m for a stationary cued subject**, dropping to +3–10 m for an uncued subject in light clutter. Pushing to 100 m+ in an open +field would require either (a) a much larger antenna (60+ cm dish), (b) +out-of-band EIRP beyond §95.M (experimental licence territory), or (c) much +longer integration (incompatible with cardiac coherence times). + +The 2013 Massagram paper achieves 21 m at 24 GHz with a high-gain antenna +under tightly controlled conditions. Pushing the same setup to 77 GHz with +the same antenna *aperture* would actually help (smaller beamwidth, same +free-space path loss), but the chest-wall RCS at 77 GHz is comparable, and +clutter / multipath are much harsher. We have **no public reference** for a +77 GHz cardiac measurement at 21 m that we could find with the same rigour. + +### 2.5 Cost ceiling for an open-source mesh node + +An open-source mesh node spec implies "ships in a kit, does not require +individual licensing, fits the existing PoE / mini-PC edge model". That +implies: + +- Single-chip transceiver at $20–$100 BOM. +- Antenna assembly at $50–$200 (high-gain dish or printed array). +- Mini-PC or Pi 5 host at $80. +- Total under $500 to be plausible. + +The chip cost is already met by COTS. The antenna and host are met. The +bottleneck is *not* hardware cost — it is regulatory exposure, dual-use +ethics, and the fact that the addressable range at part-95 ceilings (15–30 m) +is *only marginally beyond* what the existing 60 GHz tier already does for +$15. The marginal *technical* benefit of jumping to 77 GHz at the part-95 +ceiling, for a civilian opt-in mesh, does not clear the marginal *governance* +cost. + +## 3. SOTA: 100–200 GHz coherent sub-THz radar + +### 3.1 Why sub-THz + +At 140 GHz, λ ≈ 2.14 mm. A coherent radar with this wavelength can resolve +chest-wall displacement at the **sub-millimetre** level by direct phase +tracking, which makes the cardiac micro-Doppler signal-to-clutter ratio +fundamentally better than at 60 or 77 GHz for the same integration time. +Atmospheric *windows* at 94 GHz, 140 GHz, and 220 GHz — between the strong +oxygen absorption peaks at 60 GHz and 119 GHz and the water vapour peaks at +22, 183, and 325 GHz — make stand-off operation physically possible per +**ITU-R Recommendation P.676** ([ITU-R P.676-11](https://www.itu.int/dms_pubrec/itu-r/rec/p/R-REC-P.676-11-201609-I!!PDF-E.pdf), +[ITU-R P.676-9](https://www.itu.int/dms_pubrec/itu-r/rec/p/R-REC-P.676-9-201202-S!!PDF-E.pdf)). + +### 3.2 Atmospheric attenuation table (clear-air, ITU-R P.676) + +Order-of-magnitude values for one-way attenuation through standard atmosphere +at sea level, taken from ITU-R P.676-11 Annex 1 / 2 figures (approximate +values; consult the recommendation for precise numbers at any (T, P, ρ)): + +| Frequency | Dry air, dB/km | 7.5 g/m³ humid, dB/km | Notes | +|---|---|---|---| +| 60 GHz | ~14 | ~14.5 | O₂ absorption peak — terrible for stand-off | +| 77 GHz | ~0.4 | ~0.5 | Allocated for automotive radar | +| 94 GHz | ~0.4 | ~0.7 | First major window above 60 GHz | +| 119 GHz | ~2.5 | ~3 | O₂ subsidiary peak | +| 140 GHz | ~0.5 | ~1.5 | Second major window | +| 183 GHz | ~30+ | ~100+ | H₂O peak — unusable for outdoor stand-off | +| 220 GHz | ~2 | ~5 | Third window | +| 325 GHz | ~10+ | ~50+ | H₂O peak | +| 380 GHz | ~3 | ~20 | Imaging-band window, very humidity-sensitive | + +For a 100 m one-way clear-LOS link at 140 GHz in 7.5 g/m³ humidity, atmospheric +attenuation alone is ~0.15 dB — negligible compared to free-space path loss +(~115 dB at 100 m) and target RCS. The atmosphere is *not* the limiting factor +for sub-THz cardiac sensing inside ~100 m. **Beyond ~1 km in humid conditions, +atmospheric absorption dominates** and the budget breaks down quickly, +especially at 220 GHz and above. + +### 3.3 COTS chipsets and academic platforms + +The sub-THz commercial landscape in 2026 is sparse and expensive: + +- **Analog Devices HMC8108** — 76–81 GHz transceiver. Not sub-THz; named here + only to anchor "the most COTS-friendly mmWave part Analog Devices ships". +- **Virginia Diodes WR-* multipliers and mixers** — the dominant lab-grade + source for 140–500 GHz work. Module prices are $5,000–$50,000 each; + building a coherent transceiver typically requires $30,000–$150,000 of VDI + hardware plus a stable phase reference and an external RF source. +- **Wasa Millimeter Wave imagers** — passive imagers around 90 / 220 / 380 GHz. + Receive-only. +- **imec 140 GHz FMCW transceiver in 28 nm CMOS** — reported at IEEE ISSCC and + in *Microwave Journal* (2019), centred at 145 GHz with 13 GHz RF bandwidth + giving 11 mm range resolution, on-chip antennas, integrated Tx / Rx in 28 nm + bulk CMOS. ([Microwave Journal 2019](https://www.microwavejournal.com/articles/32446-integrated-140-ghz-fmcw-radar-for-vital-sign-monitoring-and-gesture-recognition), + [imec magazine May 2019](https://www.imec-int.com/en/imec-magazine/imec-magazine-may-2019/a-compact-140ghz-radar-chip-for-detecting-small-movements-such-as-heartbeats)) + This is the most COTS-relevant sub-THz cardiac chip published to date, + but it is **not** a buyable part — it is a research demo. +- **Academic platforms** at Tampere University, FAU Erlangen-Nürnberg, Bell Labs + / Nokia, MIT Lincoln Lab, and the various US NSF / DARPA-funded sub-THz + programmes have produced sub-THz radars in the 100–300 GHz band. None of + these is a ship-it part. + +### 3.4 Coherent vs. incoherent + +A *coherent* sub-THz radar maintains phase reference between Tx and Rx (and +ideally across multiple Tx / Rx channels for MIMO or multistatic operation). +Coherent processing buys: + +- **Matched-filter SNR scaling**: SNR improves linearly with integration + time t (vs. √t for incoherent), bounded by the cardiac coherence + time T_coh. +- **Phase-based displacement extraction**: chest-wall displacement at the + micrometre level becomes directly observable as Δφ = 4π·Δd / λ. +- **MIMO / multistatic phase coherence**: multiple Tx / Rx phase-coherent + channels enable beamforming gain that scales as N_Tx × N_Rx instead of + √(N_Tx × N_Rx). + +It costs: + +- **Sub-picosecond clock distribution** between channels at sub-THz frequencies + (a 1 ps clock skew at 140 GHz is 50° of phase error). +- **Phase-locked LO distribution** — the LO must be coherent across the + array; this is non-trivial at 140 GHz (typical solution: distribute a low + GHz reference and multiply locally, with cm-precision cable matching). +- **Calibration burden** — phase-coherent arrays need per-channel calibration + drift correction. + +For a single-aperture monostatic radar (one Tx, one Rx, one chip), coherence +is nearly free (the LO is shared on-die). For a *mesh* of coherent sub-THz +nodes, the engineering cost is significant — and would require RuView to +develop sub-ns mesh clock-synchronisation it does not have today. + +### 3.5 Published cardiac micro-Doppler at sub-THz + +The published peer-reviewed cardiac literature at 100–300 GHz is sparse but +not empty: + +- **Mostafanezhad & Boric-Lubecke (2014).** "Benefits of coherent low-IF for + vital signs monitoring." *IEEE Microw. Wireless Compon. Lett.* 24. — anchor + for *coherent* CW vital-signs radar; not specifically sub-THz, but + establishes the coherent-IF advantage. +- **imec (2019) — 140 GHz FMCW transceiver demonstration.** Reported real-time + measurement of micro-skin motion reflecting respiration and heartbeat at + short range using an integrated 28 nm CMOS transceiver with on-chip antennas. + Cited above; engineering demo, not a published systematic range study. + ([Microwave Journal 2019](https://www.microwavejournal.com/articles/32446-integrated-140-ghz-fmcw-radar-for-vital-sign-monitoring-and-gesture-recognition)) +- **Yamagishi et al. (2022).** "A new principle of pulse detection based on + terahertz wave plethysmography." *Scientific Reports* 12, 2022. + ([Nature SREP](https://www.nature.com/articles/s41598-022-09801-w)) — + THz-band plethysmography demonstrator, contactless pulse detection at very + short range using THz transmission/reflection through skin. Not a stand-off + radar paper, but the only widely-cited THz-cardiac primary source. +- **Zhang et al. (2021).** "Non-Contact Monitoring of Human Vital Signs Using + FMCW Millimeter Wave Radar in the 120 GHz Band." *Sensors* 21. + ([PMC8070581](https://pmc.ncbi.nlm.nih.gov/articles/PMC8070581/)) — 120 GHz + band, FMCW, short-range cardiac extraction. + +**Honest assessment**: published primary work on cardiac micro-Doppler at +*beyond a few meters* in the 100–300 GHz band is limited. The +imec / EU-funded demonstrators have shown that the chip exists; the systematic +range studies that exist for 24 GHz (Massagram 2013) and 60–77 GHz +(Adib / Wang / Liu) do not yet have published sub-THz analogues. Some of this +work may exist in the classified or US-Government / EU defence-funded +literature; it is **not** in the open record at the level of detail required +for a build decision. + +## 4. Physics ceiling for RuView's heartbeat-mesh use case + +### 4.1 Cardiac signal vs. distance, multi-band comparison + +For a stationary, cued, line-of-sight subject with chest-wall displacement +~0.2 mm at the heart fundamental and ~5 mm at the breathing fundamental, +order-of-magnitude HR-detection range estimates at three bands (compiled from +the radar equation, Massagram 2013, ITU-R P.676, and standard chest-RCS +estimates): + +| Band | λ | Required Δφ for HR | Free-space loss @ 30 m | Atm loss @ 30 m | Estimated HR range (cued LOS, COTS Tx + 30 dBi antenna, part-95) | +|---|---|---|---|---|---| +| 24 GHz CW | 12.5 mm | 0.36° | 89 dB | <0.01 dB | 21 m measured (Massagram 2013) | +| 60 GHz FMCW | 5.0 mm | 0.9° | 97 dB | 0.4 dB | 5–10 m (ADR-021 / spec §6.1) | +| 77 GHz FMCW | 3.9 mm | 1.2° | 99 dB | 0.01 dB | ~15–30 m (estimated, no rigorous public ref beyond 5 m) | +| 140 GHz FMCW | 2.1 mm | 2.2° | 105 dB | 0.04 dB | ~30–100 m (estimated, sparse open lit) | +| 220 GHz FMCW | 1.4 mm | 3.3° | 109 dB | 0.15 dB | ~30–100 m (estimated, sparse open lit, humidity-sensitive) | + +The phase-displacement resolution *improves* with frequency (Δφ for the same +displacement scales as 1/λ), but the link budget *degrades* (R⁻⁴ in +two-way path loss, plus atmospheric absorption, plus higher noise figure on +sub-THz LNAs). The two effects partially cancel; the net result is that +**every doubling in frequency above 60 GHz buys roughly a factor of 2–4× in +plausible HR range when antenna aperture is held constant** — but only if +the system noise figure and Tx power can be maintained at levels comparable +to the lower-band part. Sub-THz CMOS NF is typically 10 dB worse than 77 GHz +CMOS, which eats much of the apparent gain. + +### 4.2 Two-way path loss + atmospheric absorption + +| Range | 77 GHz total loss | 140 GHz total loss | 220 GHz total loss | +|---|---|---|---| +| 1 m | 70 dB + 0 | 76 dB + 0 | 80 dB + 0 | +| 10 m | 90 dB + 0.01 | 96 dB + 0.03 | 100 dB + 0.1 | +| 100 m | 110 dB + 0.1 | 116 dB + 0.3 | 120 dB + 1 | +| 1 km | 130 dB + 1 | 136 dB + 3 | 140 dB + 10 | +| 10 km | 150 dB + 10 | 156 dB + 30 | 160 dB + 100 | +| 65 km (40 mi) | 168 dB + 65 | 174 dB + 200+ | 178 dB + impossible | + +**Observations**: + +- At 1 km, 220 GHz loses 9 dB more to atmosphere than 77 GHz; at 10 km it + loses 90 dB more. Sub-THz is fundamentally a sub-1-km modality in humid air. +- At 65 km (the "40 miles" in the press), atmospheric absorption alone makes + 220 GHz cardiac detection physically impossible at any plausible Tx power. + 140 GHz needs 200+ dB of antenna gain on each end to close the link in + humid air — far beyond any deployable antenna. +- **77 GHz is the only band where 1 km cardiac sensing is physically plausible + in the open air.** It is also the band that is closest to civilian COTS. + +### 4.3 Required antenna gain × power × integration time + +Holding integration time at 0.5 s (half a cardiac cycle, the rough coherence +limit), and assuming a 10 dB SNR target at 0.2 mm displacement, the required +EIRP × antenna-gain product to detect HR at various ranges in clear LOS at +77 GHz: + +| Range | Required EIRP × G_r (one-way) | Achievable under FCC §95.M? | +|---|---|---| +| 1 m | 25 dBm + 20 dBi | Yes (commercial COTS) | +| 10 m | 45 dBm + 30 dBi | Yes (high-end COTS, 30 cm dish) | +| 30 m | 55 dBm + 35 dBi | Marginal — at the §95.M peak ceiling | +| 100 m | 70 dBm + 45 dBi | No — above §95.M, experimental-licence territory | +| 500 m | 90 dBm + 55 dBi | No — military / experimental only | +| 1 km | 100 dBm + 60 dBi | No — military only | +| 10+ km | beyond physical antenna realisability for civilian use | No | + +**Bottom line**: 30 m is the honest ceiling for cardiac sensing inside FCC +§95.M power limits with a 30 cm dish at 77 GHz. Anything beyond ~30 m is +either experimental-licence territory or military. + +### 4.4 Fold-over with the Ghost Murmur "tens of miles" claim + +The press claim of HR detection at "40 miles" (65 km) corresponds to a one-way +path loss at 77 GHz of roughly 168 dB (free space) plus ~65 dB of atmospheric +absorption (humid). Closing this link to detect a 0.2 mm chest-wall +displacement would require: + +- **Required EIRP**: roughly 200 dBm (10²⁰ W) in the simplest analysis. For + context, the entire global average solar flux is ~1.4 kW/m². A 65 km + radar would need to deliver more transmit power, focused onto a single + human chest, than the sun delivers to that chest by daylight. +- **Required antenna**: even with 100 dB of combined two-way antenna gain + (a 6 m dish at 77 GHz), the EIRP requirement is unphysical. +- **Required atmospheric conditions**: dry, stable, no rain, no fog, no + intervening terrain. + +The honest reading: **HR detection at "tens of miles" against a single +heartbeat is not consistent with any physically realisable open-air radar +system at any band the laws of physics allow**. The claim either refers to +*cued* detection (i.e., a survival beacon or IR thermal already pinpointed +the target, the radar is just confirming "alive"), or it is press-release +hyperbole. RuView is not in a position to either confirm or contest the +operational reality; we are in a position to say that the *modality alone* — +"detect a heartbeat at 40 miles with a radar" — is not what closed the loop. + +This is consistent with the Ghost Murmur spec's analysis (§4 of doc 16) and +with `nvsim`'s magnetic-field falloff calculations (1/r³ — even more brutal +than radar's 1/r⁴). + +## 5. Regulatory + ethics + +### 5.1 FCC envelope summary + +| Use | FCC path | Practical for open source? | +|---|---|---| +| 60 GHz unlicensed (existing tier) | Part 15.255 (57–71 GHz) | Yes — current tier | +| 76–81 GHz at COTS automotive EIRP | Part 95 Subpart M (50/55 dBm) | Yes — research-allowed | +| 76–81 GHz pushing toward §95.M ceiling | Part 95 Subpart M | Yes — single-installation | +| 76–81 GHz beyond §95.M | Part 5 experimental licence | **No** for shipping firmware | +| 90–300 GHz coherent radar | Mostly experimental-only | **No** for shipping firmware | +| 300+ GHz transmitters | Almost all unallocated for civilian active use | **No** for shipping firmware | + +For an *open-source civilian project*, only the unlicensed and part-95 +licensed-by-rule categories are defensible. The moment a node would need an +individual experimental-licence application to operate legally, it cannot be +"flash and ship". + +### 5.2 ITAR / EAR posture + +- **ECCN 6A008** controls radar systems and components under the EAR + ([BIS Commerce Control List Cat. 6](https://www.bis.doc.gov/index.php/documents/regulations-docs/2340-ccl9-4/file)). + The general radar control sub-paragraph 6A008.e covers "radar systems, + having any of the following characteristics" — including high power, + specific frequency / coherence properties, and certain processing + capabilities. The exact thresholds change from revision to revision; the + current authoritative source is the [BIS Interactive Commerce Control + List](https://www.bis.gov/regulations/ear/interactive-commerce-control-list). +- **USML Category XI(c)** (ITAR) covers radar that is specifically designed + or modified for military application. Sub-THz coherent radar with the + combination of frequency, coherence, and antenna gain that would matter + for stand-off cardiac sensing tends to fall in or near this category. +- **EAR99 / no-licence-required** thresholds for low-power 60–77 GHz + automotive radar are clear. Sub-THz coherent radar above certain + thresholds (ECCN 6A008) requires an export licence for many destinations. + Some open-source firmware that *implements* such a radar may be subject + to "publicly available" exemptions; some may not. +- **Open-source publication.** EAR §734.7 / §734.8 ("publicly available + information") exempts most code that has been or will be published openly. + However, this exemption has limits — particularly for "specially designed" + technology supporting controlled commodities, and for encryption / certain + munitions categories. The line for radar firmware is not fully clear, and + the safe path for an open-source project is: **do not publish firmware + whose primary purpose is to push a controlled-radar configuration**. + +The correct posture for RuView is: **assume the worst case**. If RuView +*shipped* firmware that drove a 140 GHz coherent sub-THz cardiac mesh, even +without the hardware in the workspace, that firmware *itself* could fall +within ECCN 6A008 / USML XI(c), particularly if it implemented the +matched-filter / coherent-array signal processing that distinguishes +controlled radars from uncontrolled ones. We do not ship that firmware. + +### 5.3 Open-source ethics and dual-use risk + +The Ghost Murmur spec (§9) is explicit about RuView's civilian-only ethics +framing: + +1. Civilian, opt-in deployments only. +2. No directional pursuit. +3. Data minimisation. +4. PII detection on the wire. +5. Adversarial-signal detection. +6. **No export-controlled hardware.** + +Stand-off radar at 77 GHz with §95.M-ceiling EIRP and a 30 cm dish *can* be +used for through-wall surveillance, biometric tracking, target acquisition. +Sub-THz coherent radar can do the same with finer resolution. Even *research* +into these modalities — building a simulator, publishing range / sensitivity +analyses, contributing to the open literature — pushes the open-source +ecosystem closer to capabilities that the press already (correctly, in the +sense of "physically possible") associates with covert military intelligence. + +Two specific dual-use risks if RuView research were to ship anything beyond +this ADR: + +- **Through-wall surveillance**: high-power 77 GHz radar with a wide-band + FMCW chirp can resolve human presence and coarse pose through interior + drywall at tens of meters. This is the literal Ghost Murmur use case at + short range. RuView already discloses this capability for the existing + 60 GHz tier; pushing it to 77 GHz at higher power expands the addressable + surveillance distance. +- **Biometric tracking at distance**: cardiac and respiratory micro-Doppler + signatures are individually identifying enough for re-identification + across short occlusions (this is part of the AETHER / re-ID work in + ADR-024). Combining higher-power radar with re-ID at 30+ m is + surveillance at distance. +- **Target acquisition**: this is the use case RuView explicitly does not + build for. Period. + +## 6. Build / Research / Skip decision matrix + +| Tier | Build now | Research only | Skip permanently | Notes | +|---|---|---|---|---| +| 77 GHz commercial COTS (already shipping at low EIRP via the 60 GHz tier; mentioned for completeness) | — | — | — | Already covered by 60 GHz tier ADR-021. No action. | +| 77 GHz higher-power experimental (≤ §95.M ceiling) | — | **✓ Research only** (passive simulator + range analysis) | — | The technical gap to the 60 GHz tier is small; the marginal range gain (30 m vs 10 m) does not justify the marginal regulatory + ethics cost for a *shipped* civilian mesh. Research / simulation only. | +| 77 GHz beyond §95.M (Part 5 experimental) | — | — | **✓ Skip permanently** | Cannot ship as open-source firmware. Individual experimental licences are not delegatable. | +| 100 GHz coherent mesh | — | **✓ Research only** | — | Document the physics, the COTS gap (no sub-$1k transceiver), the regulatory gap (no civilian allocation for active sensing in the 90–110 GHz band). Build only if all three conditions in §7.4 below trigger. | +| 140 GHz coherent stand-off | — | **✓ Research only (simulator only)** | — | The imec 2019 demonstrator shows the chip is realisable at 28 nm CMOS; nothing buyable today at sub-$1k. ECCN 6A008 risk is real. Simulator OK; firmware no. | +| 220 GHz coherent stand-off | — | — | **✓ Skip permanently for hardware** (research the physics only) | Atmospheric humidity sensitivity makes outdoor deployment fragile; ECCN 6A008 / ITAR Cat XI(c) risk is highest at this band; no buyable COTS chip at sub-$10k. The marginal sensing benefit over 140 GHz does not justify the regulatory and ethics escalation. | +| 380+ GHz imaging | — | — | **✓ Skip permanently** | Imaging-band, not radar; humidity destroys outdoor link; export-controlled at any meaningful aperture. Not RuView's modality at any plausible build. | + +The recommendation density is intentional: **most of the matrix lands on +"skip" or "research only"**. Only one row (77 GHz at the §95.M ceiling) sits +near a build decision, and even that one is gated on a use case that does not +exist in RuView today. + +## 7. If we research: what does RuView ship? + +### 7.1 Mirror the `nvsim` pattern + +ADR-089 / 090 established the precedent: when a sensing modality is +*physically interesting but not buildable today*, RuView ships a deterministic +forward simulator, not hardware. The simulator becomes the design tool for +fusion algorithms, the sanity check for press-release physics, and the +honest answer to "what would you actually need to build this?" + +Applied to this ADR, the corresponding artifact would be **a sub-THz radar +forward simulator crate**, working name `subthz-radar-sim`. Scope: + +- Forward-model the 77 GHz / 140 GHz / 220 GHz radar equation including + ITU-R P.676 atmospheric attenuation, free-space path loss, antenna gain + patterns, and chest-RCS models. +- Simulate cardiac micro-Doppler displacement → received-signal phase + modulation in the FMCW or CW-Doppler regime. +- Add deterministic noise (thermal + 1/f LO phase noise + chest-RCS + fluctuation) seeded from `rand_chacha` for byte-identical outputs across + runs. +- Emit `RadarFrame`-shaped output with magic distinct from + `0xC51A_6E70` (`nvsim`'s `MagFrame`) and `0xC511_0001` (CSI frames). +- SHA-256 witness for end-to-end determinism, mirroring `nvsim::Pipeline::run_with_witness`. + +### 7.2 Hard constraints on what the crate can ship + +- **No firmware.** Not for ESP32, not for any SDR, not for any FPGA. The crate + is host-side only. No executable binary capable of *driving* a sub-THz + transmitter is published. +- **No matched-filter / coherent-array signal processing that exceeds + ECCN 6A008 thresholds.** The crate documents the physics and simulates the + forward path. It does not implement the inverse / processing pipeline at + the level that would constitute a controlled radar processor. +- **No beamforming primitives for actively-steered phased arrays.** Simulating + a fixed-pattern dish is fine; simulating a steerable phased array used for + targeted person-of-interest tracking is not. +- **No re-identification across the simulated radar stream.** AETHER-style + re-ID exists in `ruvector/viewpoint/`; it must not be wired to the sub-THz + radar simulator's output. +- **Documented dual-use posture.** The crate's README starts with a section + titled "What this crate is not for", linking to this ADR. + +### 7.3 What the simulator answers + +The same questions `nvsim` answers for NV-diamond, the sub-THz simulator +would answer for radar: + +- "If a 140 GHz transceiver has noise figure 12 dB and Tx power 0 dBm with a + 35 dBi antenna, what's the joint posterior P(human alive at (x, y)) + given my CSI + 60 GHz + 77 GHz + 140 GHz radar evidence at 5 m, 30 m, + 100 m?" +- "What sensitivity does my hypothetical 220 GHz radar need to add useful + information beyond the 60 GHz tier at 10 m? And does the answer change + in 7.5 g/m³ humidity vs. 1 g/m³ dry air?" +- "What does my published witness change if I swap the receiver noise figure + from 8 dB to 15 dB? From 15 dB to 25 dB?" + +These are pre-build sanity checks. They cost CI time, not export-control +exposure, not dual-use risk, not regulatory exposure. + +### 7.4 Conditional triggers (mirror ADR-090's pattern) + +Promotion of any "research only" row in §6 to "build" requires *all three* +of: + +1. **A COTS sub-THz transceiver drops below $1k** at the chip level, with + datasheet-confirmed phase coherence and an evaluation board buildable on + open hardware. (Today: nothing.) +2. **A clear non-export-controlled application emerges** — most plausibly + *medical*: contactless vital-sign monitoring at clinical bedside or + ambulatory ranges (1–3 m), regulated by the FDA as a medical device, with + the commercial / regulatory path paved by another vendor. RuView would + then be one of many open-source contributors to a medical sensing modality + already cleared for civilian use. +3. **RuView core team agrees by RFC**, with explicit sign-off on the dual-use + review and the ethics framing in §5.3. + +If *any one* of those three is missing, this ADR remains Proposed indefinitely +and the modality stays in the simulator-only tier. + +If only condition (1) fires — sub-$1k chip with no medical clearance and no +RFC sign-off — RuView still does not ship. The simulator might be expanded; +no firmware ships. + +## 8. Related work / cross-references + +### 8.1 ADRs + +- **ADR-021** — Vital-sign detection via 60 GHz mmWave + WiFi CSI. The tier + immediately below this ADR; defines the 1–10 m HR ceiling that a stand-off + tier would extend. +- **ADR-029** — RuvSense multistatic sensing mode. Defines the cross-viewpoint + fusion that any future radar tier would feed. The mathematical framework + for combining radar + CSI + NV evidence is already in `ruvector/viewpoint/`. +- **ADR-089** — `nvsim` NV-diamond pipeline simulator. The architectural + precedent: ship a deterministic forward simulator when the modality is + interesting but not buildable. Same proof / witness pattern applies here. +- **ADR-090** — `nvsim` Lindblad / Hamiltonian extension. Same "Proposed + conditional" pattern with explicit trigger conditions and a deferred build. + This ADR follows the same shape. +- **ADR-040** — PII detection gates. Any future stand-off radar output stream + would need to flow through PII gates before crossing the local mesh + boundary, identical to existing CSI / vitals streams. +- **ADR-024** — AETHER contrastive embedding. Cross-references the + re-identification work that *must not* be combined with stand-off radar. +- **ADR-028** — ESP32 capability audit + witness verification. The + deterministic-witness pattern applies to any new simulator crate. + +### 8.2 Research docs + +- `docs/research/quantum-sensing/16-ghost-murmur-ruview-spec.md` — the + Ghost Murmur reality-check spec. §6.3 is the explicit boundary that + triggered this ADR. §7–§9 establish the architecture, ethics, and legal + framework that this ADR inherits. + +### 8.3 Primary literature (radar at 24 / 77 / 120–140 GHz) + +- **Massagram, W., Lubecke, V. M., Høst-Madsen, A., Boric-Lubecke, O. + (2013).** "Parametric Study of Antennas for Long Range Doppler Radar + Heart Rate Detection." *IEEE EMBC* 2013. + ([PMC4900816](https://pmc.ncbi.nlm.nih.gov/articles/PMC4900816/)) + — HR @ 21 m, respiration @ 69 m at 24 GHz CW. +- **Mostafanezhad, I., Boric-Lubecke, O. (2014).** "Benefits of Coherent + Low-IF for Vital Signs Monitoring." *IEEE Microw. Wireless Compon. Lett.* + 24(10), 711–713. +- **Adib, F. et al. (2015).** "Smart Homes that Monitor Breathing and Heart + Rate." *Proc. CHI 2015*. Short-range through-wall. +- **Wang, G. et al. (2020).** "Remote Monitoring of Human Vital Signs Based + on 77-GHz mm-Wave FMCW Radar." *Sensors* 20(10), 2999. + ([PMC7285495](https://pmc.ncbi.nlm.nih.gov/articles/PMC7285495/)) +- **Liu, J. et al. (2022).** "Real-Time Heart Rate Detection Method Based on + 77 GHz FMCW Radar." *Micromachines* 13(11), 1960. + ([PMC9693980](https://pmc.ncbi.nlm.nih.gov/articles/PMC9693980/)) +- **Chen, J. et al. (2024).** "Contactless and Short-Range Vital Signs + Detection with Doppler Radar Millimetre-Wave (76–81 GHz) Sensing Firmware." + *Healthcare Technology Letters* 11. + ([Wiley HTL](https://ietresearch.onlinelibrary.wiley.com/doi/full/10.1049/htl2.12075)) +- **Iyer, S. et al. (2022).** "mm-Wave Radar-Based Vital Signs Monitoring + and Arrhythmia Detection Using Machine Learning." *Sensors*. + ([PMC9104941](https://pmc.ncbi.nlm.nih.gov/articles/PMC9104941/)) + +### 8.4 Primary literature (sub-THz) + +- **imec / Peeters et al. (2019).** Integrated 140 GHz FMCW Radar + Transceiver in 28 nm CMOS for Vital Sign Monitoring and Gesture + Recognition. *Microwave Journal* 2019-06-09; imec magazine May 2019. + ([Microwave Journal](https://www.microwavejournal.com/articles/32446-integrated-140-ghz-fmcw-radar-for-vital-sign-monitoring-and-gesture-recognition), + [imec magazine](https://www.imec-int.com/en/imec-magazine/imec-magazine-may-2019/a-compact-140ghz-radar-chip-for-detecting-small-movements-such-as-heartbeats)) +- **Zhang, Q. et al. (2021).** "Non-Contact Monitoring of Human Vital + Signs Using FMCW Millimeter Wave Radar in the 120 GHz Band." *Sensors* + 21. ([PMC8070581](https://pmc.ncbi.nlm.nih.gov/articles/PMC8070581/)) +- **Yamagishi, H. et al. (2022).** "A new principle of pulse detection + based on terahertz wave plethysmography." *Scientific Reports* 12, + 2022. ([Nature SREP](https://www.nature.com/articles/s41598-022-09801-w)) +- ITU-R Recommendation **P.676-11** (2016). "Attenuation by atmospheric + gases." International Telecommunication Union. + ([P.676-11 PDF](https://www.itu.int/dms_pubrec/itu-r/rec/p/R-REC-P.676-11-201609-I!!PDF-E.pdf)) +- 47 CFR Part 95 Subpart M — The 76–81 GHz Band Radar Service. + ([eCFR](https://www.ecfr.gov/current/title-47/chapter-I/subchapter-D/part-95/subpart-M)) +- US Department of Commerce, Bureau of Industry and Security. **Commerce + Control List Category 6 — Sensors and Lasers**, ECCN 6A008. + ([BIS CCL Cat. 6](https://www.bis.doc.gov/index.php/documents/regulations-docs/2340-ccl9-4/file)) + +### 8.5 Reviews + +- **Li, C. et al. (2024).** "Radar-Based Heart Cardiac Activity Measurements: + A Review." *Sensors*. ([PMC11645089](https://pmc.ncbi.nlm.nih.gov/articles/PMC11645089/)) +- **Frontiers in Physiology (2022).** "Radar-based remote physiological + sensing: Progress, challenges, and opportunities." + ([Frontiers](https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2022.955208/full)) + +## 9. Open questions + +These are the questions that, if answered differently, could move a row of +the §6 decision matrix: + +1. **Does a published, peer-reviewed cardiac micro-Doppler measurement at + 77 GHz beyond 5 m exist that we missed?** A rigorous Massagram-style + parametric study at 77 GHz with explicit antenna-gain × Tx-power × + integration-time budgets would change the picture for the "77 GHz higher + power" row from "research only" toward "build (simulator + reference + implementation)". +2. **Does a sub-$1k 140 GHz coherent transceiver chip exist or appear in the + next 12 months?** The imec 28 nm CMOS demo from 2019 has not yet led to + a buyable part; it is unclear whether this is an engineering / yield issue + or a market issue. If a part appears, condition (1) of §7.4 fires. +3. **Is there a clear medical FDA-cleared application for sub-THz cardiac + sensing?** This is the single most important gating condition. If a + commercial vendor clears a 140 GHz contactless vital-sign monitor as a + Class II medical device, the entire ethical framing of "open-source + contribution to a medical sensing modality" opens up. Without that + clearance, RuView remains in the simulator-only tier. +4. **Are there current ECCN 6A008 thresholds we should be more concerned + about for the *simulator itself* than the §5.2 analysis suggests?** The + simulator is forward-only and emits IQ samples and a SHA-256 witness. + It does not implement matched-filter / coherent-array processing that + would be characteristic of controlled radars. We believe this is on the + right side of the line; a formal export-control review by counsel would + confirm. +5. **Should RuView contribute the sub-THz simulator to a neutral upstream** + (e.g., an open-source academic group's repository) rather than shipping + it in the wifi-densepose workspace? Decoupling the simulator from RuView + reduces the risk that future RuView capability work is interpreted as + building toward a stand-off cardiac mesh. +6. **What's the right venue for the deterministic-proof bundle for the + sub-THz simulator?** Same question that ADR-089 left open. Probably + the same answer: in-tree fixture + tagged release artifact. + +## 10. Decision summary + +This ADR is **Proposed — Research only**. The decision matrix in §6 lands on: + +- **Skip permanently**: 77 GHz beyond §95.M, 220 GHz coherent stand-off + hardware, 380+ GHz imaging. +- **Research only (simulator-class artifact)**: 77 GHz higher-power + experimental (≤ §95.M ceiling), 100 GHz coherent mesh, 140 GHz coherent + stand-off. +- **Build now**: nothing. + +If RuView builds anything in this space, it builds a sub-THz forward +simulator (`subthz-radar-sim`) following the `nvsim` pattern: deterministic, +host-side, witness-verified, with explicit "what this is not for" framing +and no firmware. The simulator does not ship until conditions §7.4 (1)–(3) +all fire; the hardware does not ship under any conditions current as of +2026-04-26. + +The ADR's job is to make these decisions citable, defensible, and +reversible only via explicit RFC. It is not a build commitment.