SigMF: The Signal Metadata Format

Welcome to the SigMF project! The SigMF specifications can be viewed here or downloaded as a PDF. Below we discuss why and how you might use SigMF in your projects.

Introduction

Sharing sets of recorded signal data is an important part of science and engineering. It enables multiple parties to collaborate, is often a necessary part of reproducing scientific results (a requirement of scientific rigor), and enables sharing data with those who do not have direct access to the equipment required to capture it.

Unfortunately, these datasets have historically not been very portable, and there is not an agreed upon method of sharing metadata descriptions of the recorded data itself. This is the problem that SigMF solves.

By providing a standard way to describe data recordings, SigMF facilitates the sharing of data, prevents the "bitrot" of datasets wherein details of the capture are lost over time, and makes it possible for different tools to operate on the same dataset, thus enabling data portability between tools and workflows.

SigMF signal recordings typically involve a data file (e.g., a binary file of IQ or RF samples) and a metadata file containing plain text that describes the data. Together these files represent one recording, such as example.sigmf-data and example.sigmf-meta. Here is a minimal example of a SigMF .sigmf-meta file:

{
    "global": {
        "core:datatype": "cf32_le",
        "core:sample_rate": 1000000,
        "core:hw": "PlutoSDR with 915 MHz whip antenna",
        "core:author": "Art Vandelay",
        "core:version": "1.2.0"
    },
    "captures": [
        {
            "core:sample_start": 0,
            "core:frequency": 915000000
        }
    ],
    "annotations": []
}

Using SigMF

There are at least four ways you can use SigMF today, thanks to the community-supported projects:

Within Python, using the official SigMF Python package sigmf available from pip: pip install sigmf.
Within C++ using the header-only C++ library libsigmf.
Within GNU Radio using the built-in SigMF source & sink blocks.
Manually, using our examples and the spec itself, even if it's simply editing a text file.

Contributing

The SigMF standards effort is organized entirely within this Github repository. Questions, suggestions, bug reports, etc., are discussed in the issue tracker, feel free to create a new issue and provide your input, even if it's not a traditional issue. Changes to the specification only occur through Pull Requests. This ensures that the history and background of all discussions and changes are maintained for posterity.

There is also a SigMF chat room on GNU Radio's Matrix chat server where you can ask SigMF-related questions, or participate in various discussions. Lastly, there are monthly SigMF calls covering a variety of topics, on the third Monday of each month at 11:30AM Eastern/New York Time, please email marc@gnuradio.org for an invite and Zoom link.

Anyone is welcome to get involved - indeed, the more people involved in the discussions, the more useful the standard is likely to be!

Extensions

The "Core" SigMF standard is intentionally kept limited in scope, additional metadata fields can be added through SigMF Extensions. For example, the signal extension provides a standard way to specify modulation schemes and other attributes of wireless comms signals. Several general purpose canonical extensions live within this repository directly in the extensions directory, while others are maintained by third parties. Below are some popular sources for SigMF extensions. To have your extension reviewed for inclusion on this list, please open a PR adding the repository to the list below:

In general, extension publication pull requests should go into the Community Extension repository. Occasionally there is an extension that is so general purpose that it may be warranted to include in the core SigMF Repository extensions directory. Opening an issue in this repository for discussion (or noting this in a pull request in the Community Extension repository), or discussing on the SigMF Matrix Chat room is the best way to make that happen.

Software that seeks to perform validation on metadata can open a metafile, parse which extensions are used (if any), then pull the core JSON schema plus the JSON schemas for each extension being used (and optionally, an application-specific schema), then merge the global/captures/annotations objects between all schemas, and disable additionalProperties for all three so that typos can be detected.

PDF Generation of Specifications Document

The main pdf is generated using the following content:

sigmf-schema.json - global/captures/annotations tables and descriptions, as well as the Abstract
collection-schema.json - Collection object documentation
additional_content.md - mix of plaintext/markdown/latex for the remaining sections of the document

The script docs-generator.py uses Python, PyLaTeX, Pandoc, and Inkscape to create the specifications document in PDF and HTML formats.

Frequently Asked Questions

Is this a GNU Radio effort?

No, this is not a GNU Radio specific effort. This effort first emerged from a group of GNU Radio core developers, but the goal of the project is to provide a standard that will be useful to anyone and everyone, regardless of tool or workflow.

Is this specific to wireless communications?

No, similar to the response, above, the goal is to create something that is generally applicable to signal processing, regardless of whether or not the application is RF or communications related.

It seems like some issues take a long time to resolve?

Yes, and in most cases this is by design. Since the goal of this project is create a broadly useful standards document, it is in our best interest to make sure we gather and consider as many opinions as possible, and produce the clearest and most exact language possible. This necessarily requires extreme attention to detail and diligence.