Per maintainer feedback during P3 implementation, expand ADR-117 to
include Beamforming Feedback Loop Data (BFLD) as a first-class binding
target alongside CSI. BFLD is the transmitter-side, AP-station-loop
view of the WiFi channel (802.11ac/ax/be compressed beamforming feedback
frames) — complementary to receiver-side CSI, with three properties
that make it strategically important for the pip wheel:
1. **Up to 996 subcarriers per HE160 frame** (vs 242 for HE-LTF CSI on
ESP32-C6, vs 52 for HT-LTF on ESP32-S3) — much denser per-subcarrier
reflection profile
2. **Works on stock 802.11ac+ hardware** — no Nexmon patch, no ESP32
monitor mode, no firmware drift. Captured via tcpdump/Wireshark +
BFR dissector, or via `mac80211` debugfs on Linux 6.10+
3. **Direct input for the soul-signature spec** (`docs/research/soul/`)
— the seven-channel biometric needs dense subcarrier reflection;
BFLD provides it without specialized hardware
## Three additions to ADR-117
### §5.7a — New binding-target subsection
Comparison table CSI vs BFLD; binding strategy with forward-compat
stub Rust impl pending the future `wifi-densepose-bfld` crate; the
three Python types that ship in P3.5:
- `BfldFrame` (frozen) — one compressed feedback matrix snapshot
- `BfldReport` (frozen) — aggregator over a 60-s scan window
- `BfldKind` enum — `CompressedHE20/40/80/160`, `UncompressedHT20/40`
### §6 P3.5 — Concurrent-with-P3 phase
Checkbox plan for the bindings module + stub Rust storage + numpy
bridge for `feedback_matrix` (Complex64 ndarray, same approach as
`CsiFrame.amplitude` from P3). Lands in the same wheel as P3, no
schedule cushion needed.
### §11.11/12 — Two new open questions
- **§11.11** — Should the future BFR ingestion Rust crate be a new
`wifi-densepose-bfld` workspace member, or extend `-signal`?
*Tentative: new dedicated crate. Wireshark BFR dissector is ~2k
lines and would bloat `-signal`; ingestion is optional for many
deployments; keep `-signal` lean.*
- **§11.12** — Per-vendor BFR variant compatibility (Broadcom vs
Intel vs Qualcomm vs MediaTek differ in psi/phi quantization +
matrix entry ordering). How much normalisation in the Python
binding vs. the future Rust crate? *Tentative: Python binding is
dumb (numpy ndarray in/out); future Rust crate owns per-vendor
normalisation via a `Vendor` enum on the constructor.*
### §12 — BFLD reference list
- Hernandez & Bulut, ACM TOSN 2024 (first systematic survey of
BFR-as-sensing)
- Yousefi et al., MobiSys 2023 (practical breath + HR extraction)
- IEEE 802.11ax-2021 §27.3.10 (frame format)
- Wireshark `packet-ieee80211.c` dissector
- AX210 Linux mac80211 debugfs path (kernel 6.10+)
ADR line count: 644 → 807 (+163). Refs #785 (tracking issue).
The implementation work for P3.5 lands in the next /loop iteration
alongside P3 vitals + signal DSP bindings.
Co-Authored-By: claude-flow <ruv@ruv.net>
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