MeshInt

MeshInt is a passive radio-frequency sensing system for unmanned aircraft. It measures transmissions in complex baseband, reports what can be observed about them, and, when several aircraft hear the same emission, places that emission in an area. A detection is a measurement and a confidence. A controller on the ground keeps the picture, manages the airborne probes, and can contribute detection reports to a wider SAPIENT sensor system.

flowchart LR
  mesh["Mesh node"] --> probe["Probe on the airframe"]

  subgraph ground["Ground"]
    administrator["Administrator"] --> dashboard["Dashboard / console"]
    dashboard --- controller["Controller"]
  end

  probe --> controller
  controller --> sapient["SAPIENT"]

Guides

• Installing the controller
• Installing the probe
• Administering the controller
• Using the dashboard
• Administering a probe

The purpose

Small unmanned aircraft often carry a mesh radio so that they can stay in contact with one another and with a ground party. Those transmissions are of interest as a physical fact: something is on the air, at a time, at a frequency, with a measurable width and strength, and it may be consistent with a particular kind of waveform. MeshInt answers that from the measurement, and says where the source may lie.

The longer-term interest is mesh radios associated with unmanned aircraft. Public descriptions of that class of radio point to an OFDM waveform, time-division duplex, and frequency agility. MeshInt is built toward those observable traits. Wi-Fi recordings are a convenient public test signal.

The questions MeshInt is for are these:

1. Is a transmission present?
2. Where is it in time and frequency?
3. What are its measurable radio-frequency features?
4. Are those features consistent with an OFDM-type waveform?
5. Given the aircraft that heard it, in what area might the source lie?

A detection is a measurement and a confidence. Features such as occupied bandwidth, burst timing, and any later observation of time-division or frequency-agile behaviour stay as separate observations, so that a later judgement can use each one on its own.

What is deployed

MeshInt is split between the aircraft and the ground.

Each aircraft carries a probe. The probe receives a dwell of complex baseband — the signal after a receiver has already produced it — and turns that dwell into detection events. A scanner that tunes the receiver and waits for it to settle can supply that dwell. MeshInt also works from recordings and from dwells supplied to it.

The samples stay on the aircraft. What leaves the aircraft is the detection: that an emission was measured, what was measured about it, and where the aircraft was at the time.

A controller on the ground receives those events from probes it has accepted. It associates reports that belong to the same emission, estimates the area in which the source may lie, and shows the probes, their coverage, and that area to an administrator. It also tells accepted probes how they are to be used: which part of the spectrum to walk, and how each antenna should be understood. It can describe the aircraft they fly on. Any suggestion that an aircraft move, so that the area might be improved, is advice to the platform.

Probes are managed. An unknown aircraft is visible to the administrator. Once accepted, it contributes detections and keeps its identity, and further probes that report the same aircraft name are treated as the same airframe. Several probes may share one aircraft. Each remains its own sensor.

The wider picture

The controller can emit its detection reports as SAPIENT messages, so that MeshInt can sit beside other sensors in a common picture. An administrator enables that emission. The report describes a detection and an area. The samples remain on the aircraft.

An administrator can see which probes are in contact, which of them are reporting detections, and how recent that contact is. The console is for the people operating the controller.

What a detection reports

A detection reports the measurements of the signal in front of the probe: whether energy is present, where it sits in time and frequency, and whether those features are consistent with an OFDM-type waveform. That consistency is a measurement about the signal. It can be withdrawn, and it can be left undecided.

MeshInt starts from complex baseband.

A result from generated data, and a result from noise added to a recording, each carries its own condition, so that a published figure says what it was measured on.

Present scope

The first use of MeshInt is recorded complex baseband, including public Wi-Fi and OFDM recordings as a surrogate, together with a controller that can enrol probes, draw the resulting picture, and emit SAPIENT when asked. Live input from a software-defined radio is a later step. The processing already consumes a dwell, so a live receiver can be added and a detection keeps the same meaning.

The software that measures a recording on a workstation answers the same four questions about presence, time, frequency, and waveform. The airborne probe and the ground controller are what turn those measurements into a managed, localised picture.