RIFP radio image sender and receiver

The Radio Image Framing Protocol (RIFP) 1.0 is an experimental, extensible standard for sending images over low-rate radio links.

The default rifp-cpfsk-4800 profile uses binary continuous-phase FSK and can be deployed around 433.92 MHz where local regulation permits it. RIFP itself is not tied to 433 MHz or to FSK.

The implementation is not an analogue WEFAX receiver. The group3 and group4 codecs nevertheless use real CCITT Group 3/4 TIFF facsimile compression.

Protocol properties

RIFP 1.0 provides:

• a 28-byte versioned base header;
• 64-bit random session identifiers;
• 32-bit sequence and chunk-count fields;
• advisory and critical flags;
• extensible 16-bit type/length/value header fields;
• mandatory fixed 56-byte OBJECT_DESCRIPTOR plus DATA, END and CANCEL frames;
• optional extended JSON MANIFEST frames with namespaced extension data;
• CRC-32 on every frame;
• CRC-32 and SHA-256 verification of the complete encoded image;
• out-of-order delivery, repetition and duplicate detection;
• explicit media types and content-encoding names; and
• named radio profiles that are independent of the framing protocol.

Unknown advisory extensions are ignored. Unknown critical extensions cause the individual frame to be rejected, allowing future features such as encryption, signatures, FEC and repair requests to be introduced safely.

Potential Use Cases

RIFP is intended for the local distribution of visual information to nearby electronic displays, particularly in environments where Internet connectivity is unavailable, unreliable, undesirable, or unnecessarily complex.

Potential use cases include:

• Local information and alert displays: Distributing menus, schedules, operational notices, safety instructions, and alerts to nearby electronic displays. One example is displaying a restaurant menu on a ferry where Internet connectivity is unavailable or unreliable.

• Visitor information: Providing practical information to visitors when they arrive at a location, such as opening hours, maps, instructions, local rules, event schedules, or contact details.

• Low-impact public information and advertising: Displaying temporary information, announcements, or advertisements without permanently altering or visually cluttering the public space with printed posters, stickers, or signs.

• Museums, galleries, and art exhibitions: Associating descriptions, contextual information, translations, or multimedia references with artworks without attaching visually intrusive paper labels next to each work.

• Electronic price labels: Updating product prices, promotions, stock information, origin details, or other commercial information on electronic shelf labels.

• Emergency and disaster communications: Broadcasting maps, evacuation instructions, shelter information, medical guidance, or status updates to battery-powered displays when mobile and Internet infrastructure is unavailable.

• Public transport information: Updating departure times, route changes, platform information, disruptions, and passenger instructions at stops, stations, ferries, or temporary boarding points.

• Temporary events and exhibitions: Distributing programmes, room assignments, speaker information, schedules, and wayfinding information during conferences, festivals, fairs, and community events.

• Tourism and cultural heritage sites: Providing historical information, walking-route guidance, translations, accessibility information, and temporary notices at monuments, archaeological sites, nature trails, and remote attractions.

• Hotels, campsites, and accommodation facilities: Updating breakfast times, activity schedules, weather warnings, check-out instructions, transport information, and local recommendations.

• Schools, universities, and campuses: Distributing room changes, timetables, examination notices, emergency instructions, and event information to local displays.

• Industrial and operational environments: Displaying equipment status, maintenance instructions, safety notices, work orders, and production information in warehouses, workshops, ports, and construction sites.

• Healthcare and care facilities: Providing room information, queue status, visiting instructions, hygiene notices, or non-sensitive guidance without requiring each display to maintain an Internet connection.

• Remote and off-grid locations: Updating information boards in mountain shelters, islands, rural areas, nature reserves, temporary camps, or other locations with limited infrastructure.

• Mobile or rapidly deployed installations: Supplying information to displays installed in temporary shelters, field hospitals, emergency coordination centres, pop-up shops, mobile exhibitions, or humanitarian operations.

• Community noticeboards: Distributing local announcements, municipal information, event notices, and public-service messages to low-power electronic noticeboards.

• Personal and domestic displays: Updating household dashboards, shared calendars, reminders, weather information, or home-automation status on low-power displays without giving every device direct Internet access.

Dependencies

python3 -m pip install -r requirements_radiofax.txt

For live RF, install SoapySDR, its Python bindings and the hardware module for your SDR. Transmission requires TX-capable hardware such as a HackRF, LimeSDR, PlutoSDR or USRP. Many RTL-SDR devices are receive-only but can run the receiver.

Offline conformance loopback

Run the commands from the directory containing all three Python files:

python3 radiofax_sender.py example.png \
  --preset small --codec group4 --bits 1 \
  --packet-repeats 1 --manifest-repeats 1 \
  --extended-manifest \
  --sender-id CIRCL \
  --content-hint "scheduled weather image" \
  --manifest-extension 'org.example.source={"camera":"north"}' \
  --duty-cycle 1 --iq-output example.cf32

python3 radiofax_receiver.py \
  --iq-input example.cf32 \
  --output-dir received-radiofax

Both sides must use the same sample and symbol rates. Defaults are 96 ksample/s and 4,800 symbols/s. IQ-file mode uses --iq-gap and does not add long silence representing regulatory duty-cycle pacing.

Manifest extensions use NAMESPACE=JSON. The namespace must contain a dot or colon, for example org.example.feature={"enabled":true}.

Live recurring transmission

python3 radiofax_sender.py images/ \
  --recursive \
  --device driver=hackrf \
  --frequency 433.92M \
  --preset small \
  --codec auto \
  --bits 1 \
  --cycles 0 \
  --interval 900 \
  --packet-repeats 2 \
  --manifest-repeats 3 \
  --manifest-every 8 \
  --duty-cycle 0.10

--cycles 0 repeats the set indefinitely. Directories are rescanned at the start of each cycle, so newly added images are included. --shuffle changes the order for every cycle.

Fixed-frequency reception

python3 radiofax_receiver.py \
  --device driver=rtlsdr \
  --frequency 433.92M \
  --gain 25 \
  --output-dir received-radiofax

Wideband discovery

python3 radiofax_receiver.py \
  --device driver=rtlsdr \
  --discover \
  --scan-center 434.0M \
  --scan-span 1.9M \
  --scan-sample-rate 2.4M \
  --gain 25

Discovery performs energy detection and then retunes to the strongest candidate. Identification still requires a valid RIFP synchronization word, header and CRC.

Encoding profiles

Line art or text, lossless and normally smallest:

--preset tiny --bits 1 --codec group4 --packet-repeats 1

Photographs, lossy and much smaller:

--preset small --bits 8 --codec jpeg --jpeg-quality 35 --packet-repeats 1

Grayscale diagrams, lossless:

--preset small --bits 4 --codec zlib --packet-repeats 1

--codec auto selects the smallest successful lossless encoding. Add --allow-lossy-auto to include JPEG in the comparison.

Tests

python3 -m unittest -v test_rifp_protocol.py

The implementation has also been exercised with offline IQ loopbacks for Group 3, Group 4, PNG, JPEG, raw raster, RLE, ZLIB and automatic codec selection. A repeated-frame transfer was reconstructed after adding synthetic noise and a +2.5 kHz carrier offset.

Internet-Draft

The Radio Image Framing Protocol (RIFP) draft-dulaunoy-rifp-00 defines the base header, TLV extension model, compact descriptor and optional manifest schemas, fragmentation rules, CRC algorithm, CPFSK profile, security considerations, test vector and proposed IANA registries.

Radio and regulatory notes

Use a shielded setup, attenuators, a dummy load or very low output power during development. Confirm permitted frequency, effective radiated power, occupied bandwidth, duty cycle, equipment requirements and licensing conditions before connecting an antenna. --duty-cycle only paces software bursts; it does not certify compliance or measure radiated emissions.

Open-Source License

The software is open-source under a BSD 2-Clause License. RIFP is free of patent or specific restriction on the standard.

BSD 2-Clause License

Copyright (c) 2026, Alexandre Dulaunoy

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