# mfsk-core
[](https://github.com/jl1nie/mfsk-core/actions/workflows/ci.yml)
[](https://crates.io/crates/mfsk-core)
[](https://docs.rs/mfsk-core)
[](LICENSE)
Pure-Rust library for **WSJT-family digital amateur-radio modes** — a
single crate that implements FT8, FT4, FST4, WSPR, JT9, JT65 and
Q65-30A decode / encode / synthesis on top of a small set of shared
primitives (DSP, sync correlation, LLR, LDPC / convolutional /
Reed-Solomon / QRA FEC, message codecs).
## Why this exists
[WSJT-X](https://sourceforge.net/projects/wsjt/) is the reference
implementation of these modes and will stay that way — it is
battle-tested on the desktop, heavily optimised, and the source of
truth for every protocol constant you will find in this crate. But
it is also a mixed Fortran / C / Qt application built around a
specific desktop workflow. That makes it a poor fit whenever you
want to run the decoders *somewhere else*:
- in a **browser** as a WASM PWA,
- on **Android or iOS** for portable operation, where linking a
Fortran runtime is a non-starter,
- in a **headless Rust application** (skimmer, monitoring station,
remote SDR front end),
- or as the core of a **new protocol experiment** that reuses FT8's
LDPC and sync machinery for a different modulation / FEC /
message recipe.
The seven protocols share roughly 80 % of their signal path. In the
Fortran codebase that commonality is expressed by copy-and-paste
between per-mode source files; here it is expressed by traits.
## The abstraction
```text
┌────────────────────────────────────────────────────────┐
│ ft8 ft4 fst4 wspr jt9 jt65 q65 │ per-protocol ZSTs
│ (each implements Protocol + FrameLayout) │ (feature-gated)
└─────────────┬─────────────────┬────────────────────────┘
│ │
┌────────▼─────────┐ ┌────▼─────────┐
│ msg │ │ fec │ shared codecs
│ Wsjt77 · Jt72 │ │ LDPC · RS │ behind traits
│ Wspr50 · Q65 │ │ ConvFano·QRA │
│ · Hash table │ │ │
└────────┬─────────┘ └────┬─────────┘
│ │
┌───▼─────────────────▼───┐
│ core │ Protocol trait, DSP
│ sync · llr · equalize · │ (resample / GFSK /
│ pipeline · tx · dsp │ downsample / subtract)
└─────────────────────────┘
```
Each protocol declares its slot length, tone count, Gray map, Costas
/ sync pattern, FEC codec and message codec at compile time via the
`Protocol` trait. The generic code in `core` — coarse sync, fine
sync, LLR computation, LDPC / RS / convolutional decode, GFSK
synthesis — works for any type that satisfies the trait. Dispatch is
monomorphised, so the machine code is byte-identical to a hand-
written per-protocol decoder.
Adding a new protocol is a trait impl on a ZST, not a cross-cutting
refactor: FST4-60A joined the crate post-hoc without changing any
shared pipeline code.
```toml
[dependencies]
mfsk-core = { version = "0.3", features = ["ft8", "ft4"] }
```
## Attribution
Every algorithm in this crate is derived from
[WSJT-X](https://sourceforge.net/projects/wsjt/) (Joe Taylor K1JT and
collaborators). Source files cite the corresponding upstream
`lib/ft8/*`, `lib/ft4/*`, `lib/fst4/*`, `lib/wsprd/*`, `lib/jt65_*`,
`lib/jt9_*`, `lib/packjt.f90`, etc. that they port from. This is a
Rust re-implementation aimed at broadening the set of platforms
(browser / WASM, Android, embedded) that can host the decoders —
**not** a replacement for WSJT-X itself, which remains the reference
implementation.
License matches upstream: **GPL-3.0-or-later**.
## Protocols
| FT8 | 15 s | LDPC(174, 91) + CRC-14 | 77 bit | 3 × Costas-7 | `ft8` |
| FT4 | 7.5 s | LDPC(174, 91) + CRC-14 | 77 bit | 4 × Costas-4 | `ft4` |
| FST4-60A | 60 s | LDPC(240, 101) + CRC-24 | 77 bit | 5 × Costas-8 | `fst4` |
| WSPR | 120 s | Convolutional r=½ K=32 + Fano | 50 bit | Per-symbol LSB (npr3) | `wspr` |
| JT9 | 60 s | Convolutional r=½ K=32 + Fano | 72 bit | 16 distributed slots | `jt9` |
| JT65 | 60 s | Reed-Solomon(63, 12) GF(2⁶) | 72 bit | 63 distributed slots | `jt65` |
| Q65-30A | 30 s | QRA(15, 65) GF(2⁶) + CRC-12 | 77 bit | 22 distributed slots | `q65` |
| Q65-60A‥E | 60 s | (same QRA codec) | 77 bit | (same sync layout) | `q65` |
### Applied example: `uvpacket`
The `uvpacket` module (`--features uvpacket`, off by default) is
an in-tree example of how the trait abstractions handle a
non-WSJT mode: a single-carrier π/4-DQPSK packet protocol with
LMS equaliser and dedicated header LDPC block, fitted to the
3 kHz audio passband of NFM / SSB voice channels. It reuses the
shared `Ldpc240_101` codec but otherwise has its own modulation,
sync (4-variant 127-chip preamble), framing, and byte-pipe API.
uvpacket is a hobbyist application included as documentation of
how the abstractions extend beyond WSJT-X. **Its public API may
change within the 0.4.x line** — pin to an exact version if you
depend on it. See
[`docs/UVPACKET.md`](https://github.com/jl1nie/mfsk-core/blob/main/docs/UVPACKET.md)
([日本語](https://github.com/jl1nie/mfsk-core/blob/main/docs/UVPACKET.ja.md))
for the full design narrative and per-mode performance
characterisation.
## Modules
- `mfsk_core::core` — protocol traits, DSP (resample / downsample /
GFSK / subtract), sync, LLR, equaliser, pipeline driver.
- `mfsk_core::fec` — `Ldpc174_91` / `Ldpc240_101` / `ConvFano` /
`ConvFano232` / `Rs63_12` / `qra::Q65Codec` (with the
`qra15_65_64::QRA15_65_64_IRR_E23` code instance) for Q65.
- `mfsk_core::msg` — 77-bit (`Wsjt77Message`), 72-bit (`Jt72Codec`),
50-bit (`Wspr50Message`) and Q65 (`Q65Message`, 77-bit ↔ 13-symbol
packing helpers) message codecs; callsign hash table.
- `mfsk_core::{ft8, ft4, fst4, wspr, jt9, jt65, q65}` — per-protocol
ZSTs, decoders and synthesisers (each feature-gated). The `q65`
module exposes one ZST per wired sub-mode — `Q65a30` for
terrestrial work, plus `Q65a60` / `Q65b60` / `Q65c60` / `Q65d60` /
`Q65e60` for EME at 6 m through 10 GHz+ — with generic
`synthesize_standard_for<P>` / `decode_at_for<P>` / `decode_scan_for<P>`
helpers that pick the right NSPS and tone spacing from the type
parameter.
## Features
| `ft8` | ✓ | FT8 decode / synth |
| `ft4` | ✓ | FT4 decode / synth |
| `fst4` | | FST4-60A decode / synth |
| `wspr` | | WSPR decode / synth |
| `jt9` | | JT9 decode / synth |
| `jt65` | | JT65 decode / synth (+ erasure-aware RS) |
| `q65` | | Q65-30A decode / synth (QRA soft-decision) |
| `uvpacket` | | Applied example: NFM voice-channel packet protocol (QPSK + LDPC), reuses `Ldpc240_101` |
| `full` | | Aggregate of all seven WSJT protocols + uvpacket + packet-bytes |
| `parallel` | ✓ | Rayon-parallel candidate processing |
| `osd-deep` | | OSD-3 fallback on AP decodes (extra CPU) |
| `eq-fallback` | | Non-EQ fallback inside `EqMode::Adaptive` |
## Quick example
```rust
use mfsk_core::ft8::{
decode::{decode_frame, DecodeDepth},
wave_gen::{message_to_tones, tones_to_i16},
};
use mfsk_core::msg::wsjt77::{pack77, unpack77};
// 1. Synthesise an FT8 frame and pad it into a 15-second slot.
let msg77 = pack77("CQ", "JA1ABC", "PM95").unwrap();
let tones = message_to_tones(&msg77);
let frame = tones_to_i16(&tones, /* freq */ 1500.0, /* amp */ 20_000);
let mut audio = vec![0i16; 180_000]; // 15 s @ 12 kHz
let start = (0.5 * 12_000.0) as usize;
for (i, &s) in frame.iter().enumerate() {
if start + i < audio.len() { audio[start + i] = s; }
}
// 2. Decode it back.
for r in decode_frame(&audio, 100.0, 3_000.0, 1.0, None, DecodeDepth::BpAllOsd, 50) {
if let Some(text) = unpack77(&r.message77) {
println!("{:7.1} Hz dt={:+.2} s SNR={:+.0} dB {}",
r.freq_hz, r.dt_sec, r.snr_db, text);
}
}
```
Each protocol module documents its top-level entry points and
carries its own Quick example:
- [`mfsk_core::ft8`](https://docs.rs/mfsk-core/latest/mfsk_core/ft8/)
— `decode_frame` + `decode_sniper_ap` (narrow-band "sniper" mode)
- [`mfsk_core::ft4`](https://docs.rs/mfsk-core/latest/mfsk_core/ft4/)
— `decode_frame`
- [`mfsk_core::fst4`](https://docs.rs/mfsk-core/latest/mfsk_core/fst4/)
— FST4-60A `decode_frame`
- [`mfsk_core::wspr`](https://docs.rs/mfsk-core/latest/mfsk_core/wspr/)
— `decode::decode_scan_default`
- [`mfsk_core::jt9`](https://docs.rs/mfsk-core/latest/mfsk_core/jt9/)
— `decode_scan_default`
- [`mfsk_core::jt65`](https://docs.rs/mfsk-core/latest/mfsk_core/jt65/)
— `decode_scan_default` + `decode_at_with_erasures` (for low SNR)
- [`mfsk_core::q65`](https://docs.rs/mfsk-core/latest/mfsk_core/q65/)
— `decode_scan_default` (Q65-30A); generic `decode_scan_for<P>`
for any wired sub-mode including the Q65-60A‥E EME variants;
`decode_scan_with_ap` / `decode_scan_with_ap_for<P>` for AP-biased
decoding (~2 dB threshold gain when call signs are known); and
`decode_scan_fading_for<P>` for the fast-fading metric (Gaussian
/ Lorentzian channel models) that recovers 5–8 dB on Doppler-spread
channels — required for microwave EME at 5.7 / 10 / 24 GHz; and
`decode_scan_with_ap_list_for<P>` (paired with `standard_qso_codewords`)
for BP-free template matching against the full WSJT-X "AP list"
of standard exchanges (~3 dB threshold gain when the callsign pair
is known up-front)
## C / C++ / Kotlin
The `mfsk-ffi` sibling crate in this repository builds a
`libmfsk.{so,a,dylib}` + `mfsk.h` (via `cbindgen`) that exposes the
same decoder and synthesiser surface through an opaque-handle C ABI.
It is not published to crates.io — consumers clone this repo and run:
```
cargo build -p mfsk-ffi --release
```
See `mfsk-ffi/examples/cpp_smoke/` for an end-to-end driver test
(including multi-threaded usage) and `mfsk-ffi/examples/kotlin_jni/`
for an Android/JNI skeleton.
## Architecture & ABI reference
For a deeper look at the design — trait hierarchy with worked
examples, shared DSP / sync / LLR / pipeline primitives, the C ABI
memory model, Kotlin/Android scaffolding — see the library
reference:
- **English:** [`docs/LIBRARY.md`](https://github.com/jl1nie/mfsk-core/blob/main/docs/LIBRARY.md)
- **日本語:** [`docs/LIBRARY.ja.md`](https://github.com/jl1nie/mfsk-core/blob/main/docs/LIBRARY.ja.md)
## Status
`0.3.x` — API is deliberately not frozen. Breaking changes follow
cargo-style minor bumps (`0.3 → 0.4`). Algorithm correctness is
covered by ~330 tests across the workspace, including end-to-end
synth → decode roundtrips for every protocol, an AWGN sensitivity
sweep that confirms Q65-30A hits its WSJT-X-published −24 dB
threshold, an AP-vs-plain comparison that shows the expected ~2 dB
gain from a-priori call sign information, an AP-list (template
matching) comparison that decodes 6/6 frames at SNR −25 dB where
plain BP fails 0/6, a real 6 m EME recording (W7GJ exchanges from
the WSJT-X reference set), and a real 10 GHz EME recording that
the fast-fading metric is required to decode. The trait surface
itself is pinned by `tests/protocol_invariants.rs` — a single
generic `<P: Protocol>` checker run across every wired ZST so a
new protocol gets structural validation without bespoke glue.