docs/bench: on-air TX throughput vs wfb-ng (svpcom) + SDR duty tool

[josephnef]

What

An SDR-measured on-air TX throughput benchmark for the Jaguar family — per-chip, and devourer (userspace libusb) vs wfb-ng (the svpcom/rtl8812au driver + wfb_tx) — plus a ceiling-free measurement tool and a writeup of the most efficient wfb-ng config.

devourer vs wfb-ng (USRP B210 channel-occupancy, clean 5 GHz ch149, 1500 B)

Config	devourer	wfb-ng (svpcom + wfb_tx)
MCS1 / 20 MHz	94.6 % → 12.3 Mbps	94.5 % → 12.3 Mbps
MCS7 / 20 MHz	80.1 % → 52.1 Mbps	79.8 % → 51.9 Mbps
MCS7 / 40 MHz	62.7 % → ~85 Mbps	—

Both deliver the same on-air injection throughput. After FEC (k/n=8/12): MCS1 ≈ 8 Mbps, MCS7 ≈ 35 Mbps — consistent with wfb-ng's ~7 Mbps default and OpenIPC's 52-total/36-video figures.

Per-chip on-air throughput (README hardware table)

HT MCS7 / 20 MHz, USRP-measured. 8812AU is the fully-benchmarked reference (56 / 52 / 52 Mbps at 2.4 GHz / UNII-1 / UNII-3). 8821AU does 54 / 32 / 28. 8814AU saturates 2.4 GHz (65) and reaches ~32 Mbps at 5 GHz on a powered port.

USB-power caveat: 5 GHz TX is current-hungry and browns out through deep bus-powered hub chains — frames submit fine but on-air power collapses, intermittently, while 2.4 GHz keeps working. Figures marked † in the README are bench-power-bound, not chip limits. A new CLAUDE.md USB Vbus sag gotcha documents the symptom, the uhubctl recovery, and the powered-hub fix (plus how to avoid mis-diagnosing it as a per-chip/EFUSE/gate bug).

Other findings

• The kernel injection rate is the driver: svpcom ~52 Mbps vs in-tree rtw88 ~6 Mbps.
• svpcom builds on the host 6.18 kernel (and the VM's 5.15) — bare-metal wfb-ng on a modern host works.
• No VM-passthrough penalty: same svpcom + injector, bare-metal 80.5 % vs qemu-xhci passthrough 80.4 %.

Changes

• tests/sdr_duty.py — USRP energy/duty-cycle on-air throughput (ceiling-free; a Wi-Fi monitor sniffer caps ~2900 fps and undercounts).
• tests/bench_onair.py — per-chip per-band on-air throughput sweep (drives the README table).
• txdemo DEVOURER_TX_PAYLOAD_BYTES — pad PSDU to N (3993 = wfb-ng max frame).
• inject_beacon.py --size + --max-rate AF_PACKET blaster.
• docs/wfb-ng-tuning.md — optimal wfb-ng config (svpcom driver, MCS/40 MHz/short-GI/LDPC/STBC, tx-pwr override, clean 5 GHz) + the comparison + methodology + reproduce steps.
• README.md — per-chip on-air TX throughput in the hardware-landscape table.
• CLAUDE.md — USB Vbus-sag hardware gotcha.

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