IFF architecture

Summary¶

libdrone's IFF architecture is a layered system of five implementation levels, each addressing different operational scenarios and observer capabilities. The IR strobe (L1) is the most resilient — it works when everything else fails and requires no infrastructure. Remote ID (L2) satisfies regulatory compliance and civilian airspace management. ATAK/CoT integration (L3/L4) provides tactical network presence visible to allied forces. A reserved hardware interface (L6) positions libdrone for future allied IFF standards. The ESP32-S3 companion board is the IFF intelligence layer: it bridges the flight controller's internal protocol to the external tactical network, making IFF capability a firmware function rather than a hardware redesign.

Concept¶

Why layers and not a single system¶

No single IFF technology covers all operational scenarios. IR strobe works in daylight and darkness for NVG-equipped observers but produces no machine-readable identification. Remote ID is machine-readable but limited in range and broadcasts to anyone in range, including adversaries. CoT provides precision tactical network integration but requires IP connectivity. Classified military IFF provides the strongest identification but is inaccessible to civilian operators.

Each layer adds coverage in the scenario where the layers above it fail. The correct deployment is the maximum applicable layers for the operational context, not a single chosen solution.

The ESP32-S3 as the IFF intelligence layer¶

The flight controller (Matek H7A3-SLIM) generates all the data needed for IFF: GPS position, attitude, battery state, flight mode, armed status. But it has no WiFi, no TCP/IP stack, and no CPU headroom for application-layer protocol translation. The ELRS radio link is a control channel, not a data network.

Only the ESP32-S3 sits at the intersection of the FC data bus and the IP world. It receives MSP (Betaflight) or MAVLink (ArduPilot) from the FC via companion UART, translates it to CoT XML, and multicasts via WiFi to the tactical network. It simultaneously manages Remote ID broadcast and sensor payload data upload. This is why ESP32-S3 is mandatory on Pro, Bandit, Ghost, and Wing — without it, IFF capability above L2 does not exist.

ArduPilot vs Betaflight IFF capability¶

ArduPilot (Bandit, Ghost): natural ATAK advantage. MAVLink is a full telemetry standard. ArduPilot streams HEARTBEAT, GLOBAL_POSITION_INT, and ATTITUDE messages continuously. Any TAK server with a MAVLink plugin, or an ESP32-S3 MAVLink → CoT bridge, consumes this directly. Mission state (waypoints, auto modes) is visible to the GCS. Position quality is high (EKF-fused GPS).

Betaflight (Pro, Core): architecturally constrained. MSP is a Betaflight-specific binary protocol with no GCS standard. An ESP32-S3 MSP → CoT bridge polls MSP_RAW_GPS, MSP_ATTITUDE, MSP_ANALOG, and MSP_STATUS_EX to construct CoT events. Position fidelity is lower than ArduPilot (no EKF). Mission state is not available. The gap is real but closeable for situational awareness use cases: position and status arrive in ATAK as a blue rotary-wing track.

Reference¶

IFF layer implementation status¶

CoT event format (ESP32-S3 output)¶

xml <event version="2.0" uid="LIBDRONE-PRO-001" type="a-f-A-M-F-Q" time="2026-04-13T10:00:00Z" start="..." stale="..."> <point lat="50.0755" lon="14.4378" hae="350.0" ce="10" le="15"/> <detail> <contact callsign="LIBDRONE-PRO-001"/> <track speed="8.2" course="270"/> <remarks>BAT: 22.1V / 840mAh / Mode: ANGLE</remarks> </detail> </event>

CoT type a-f-A-M-F-Q: Atom / Friendly / Air / Military / Fixed-Wing / Quadrotor. Appears in ATAK as a blue rotary-wing icon. Multicast address: 239.2.3.1:6969, UDP.

Reserved IFF module interface (L6)¶

GX12-7 Connector B GPIO pins 3 and 4 are reserved for future IFF module: - Physical: standard payload mast mount, ≤ 50 g - Electrical: Connector B GPIO pins 3/4 for digital challenge/response - Power: 3.3V or 5V from Connector B

When an allied civilian IFF standard emerges, the libdrone response is an ESP32-S3 firmware update plus a new GX12 payload module — not a platform redesign.

Procedure¶

Enabling ATAK CoT on Pro (Betaflight)¶

1. Ensure ESP32-S3 companion board is fitted and functional (OSD working).
2. Flash updated ESP32-S3 firmware with MSP → CoT bridge function enabled.
3. Configure in lcm1_config.json:
4. callsign: unique identifier for this drone
5. tak_server_ip: TAK server address or multicast (239.2.3.1)
6. tak_server_port: 6969 (multicast) or assigned port
7. cot_update_rate_hz: 1–2 (adequate for blue force tracking)
8. Power on drone outdoors. Verify GPS fix.
9. On ATAK tablet: confirm blue rotary-wing icon appears with drone's callsign.
10. Verify position tracks correctly as drone moves.
11. Confirm stale timeout: icon should disappear within 60 seconds if drone powers off.

Enabling ATAK CoT on Bandit (ArduPilot)¶

1. Configure ArduPilot to stream MAVLink on UART6 at 57,600 baud.
2. Flash ESP32-S3 with MAVLink → CoT bridge firmware.
3. Configure callsign and TAK server as above.
4. Verify in ATAK — same procedure as Pro.

Rationale¶

Why the CoT bridge is firmware and not a separate hardware device¶

A separate hardware device adds mass, cost, connector complexity, and a failure mode. The ESP32-S3 is already present on the platform, already connected to the FC via companion UART, already managing WiFi. Adding CoT output is a software function on existing hardware — the architecture that exists already is the correct architecture for IFF integration. This is the benefit of making ESP32-S3 mandatory across the platform family.

Why the Core is excluded from the ESP32-S3 mandate¶

Core is a training platform. Adding IFF complexity to the education pathway increases the configuration surface area without improving the training outcome. The IFF mandate applies to operational platforms (Pro, Bandit, Ghost, Wing) where deployment in security-sensitive environments is a use case. The Core's use case is pilot and builder training — this is not compromised by omitting IFF capability.

Connections¶

requires: - threat-assessment - iff-layers - emissions-control related: - remote-id-compliance - lcm1-spec - payload-software-protocol - flight-controller-hardware - esp32-s3-companion leads_to: - operational-security - platform-selection - esp32-s3-companion