GNSSDecoder.jl

Decodes various GNSS satellite signals from soft symbols (Float32: sign = bit decision, magnitude = confidence) as produced by a tracking loop such as Tracking.jl (feed get_soft_bits). By convention positive ⇒ bit 0 and negative ⇒ bit 1, but this is only a convention: the decoder resolves the 180° polarity ambiguity itself, so the opposite sign decodes the same data, and the magnitudes need not be normalized.

Currently implemented:

• GPS L1 C/A (LNAV)
• GPS L1C-D (CNAV-2)
• GPS L2C (CNAV)
• GPS L5I (CNAV)
• Galileo E1B (I/NAV), including the BOC(1,1) approximation
• Galileo E5b (I/NAV)
• Galileo E5a (F/NAV)
• Galileo E6B (C/NAV — the High Accuracy Service corrections)
• BeiDou B1I (D1/D2 NAV)
• BeiDou B3I (D1/D2 NAV)
• BeiDou B1C (B-CNAV1)
• BeiDou B2a (B-CNAV2)
• BeiDou B2b (B-CNAV3)

Installation

julia> ]
pkg> add GNSSDecoder

Usage

using GNSSDecoder

state = GPSL1CADecoderState(25)   # every buffer is allocated here, once
for chunk in soft_symbol_chunks   # e.g. `get_soft_bits` from Tracking.jl
    state = decode!(state, chunk, length(chunk))
end
is_decoding_completed_for_positioning(state) && is_sat_healthy(state)

decode! allocates nothing: it overwrites the buffers the decoder state was constructed with (soft-symbol buffer, FEC scratch, the almanac stores and other containers behind state.raw_data and state.data). Always continue with the state it returns and do not keep using the old one — take a copy(state) if you need a snapshot.

Standalone executables (juliac --trim)

On Julia 1.12 and later every decoder compiles under JuliaC's --trim=safe, so you can build a small standalone binary around it. test/trim/main.jl is a working example, and CI builds it on every change:

julia -e 'using Pkg; Pkg.Apps.add("JuliaC")'
julia --project=test/trim -e 'using Pkg; Pkg.instantiate()'
juliac --output-exe gnssdecoder_trim --bundle build --trim=safe --experimental \
    --project test/trim test/trim/main.jl
build/bin/gnssdecoder_trim

The LDPC parity-check matrices (GPS L1C-D, BeiDou B1C/B2a/B2b) are embedded in the package image, so the bundled binary does not need the source tree.

Documentation

For usage examples and API reference, see the documentation.

License

This project is licensed under the MIT License - see the LICENSE file for details.