API Reference

struct GNSSDecoderState{D<:GNSSDecoder.AbstractGNSSData, C<:GNSSDecoder.AbstractGNSSConstants, CA<:GNSSDecoder.AbstractGNSSCache, B<:Unsigned}

Generic decoder state for GNSS signal decoding. This parametric struct holds all state required for decoding navigation messages from GNSS satellites.

Type Parameters

• D<:AbstractGNSSData: The data type holding decoded navigation message fields
• C<:AbstractGNSSConstants: Constants specific to the GNSS system (e.g., preamble, timing)
• CA<:AbstractGNSSCache: Cache for intermediate decoding state
• B<:Unsigned: Buffer type for storing raw bits (sized for the specific GNSS system)

Fields

• prn::Int64: Pseudo-Random Noise code identifier for the satellite

• raw_buffer::Unsigned: Raw bit buffer before phase correction

• buffer::Unsigned: Bit buffer after phase correction

• raw_data::GNSSDecoder.AbstractGNSSData: Partially decoded navigation data (not yet validated)

• data::GNSSDecoder.AbstractGNSSData: Validated navigation data ready for use

• constants::GNSSDecoder.AbstractGNSSConstants: System-specific constants (preamble, timing parameters)

• cache::GNSSDecoder.AbstractGNSSCache: Cache for intermediate decoding state

• num_bits_buffered::Int64: Number of bits currently stored in buffer

• num_bits_after_valid_syncro_sequence::Union{Nothing, Int64}: Number of bits received after last valid synchronization sequence, or nothing if not yet synchronized

• is_shifted_by_180_degrees::Any: Whether the signal phase is inverted by 180 degrees

See Also

• GPSL1DecoderState: Constructor for GPS L1 C/A decoder state
• GalileoE1BDecoderState: Constructor for Galileo E1B decoder state
• decode: Main function to decode bits using this state
• reset_decoder_state: Reset decoder state after signal loss

GPSL1DecoderState(
    prn
) -> GNSSDecoderState{GNSSDecoder.GPSL1Data, GNSSDecoder.GPSL1Constants, GNSSDecoder.GPSL1Cache, GNSSDecoder.UInt320}

Create a decoder state for GPS L1 C/A navigation messages.

Initializes a GNSSDecoderState configured for decoding GPS L1 C/A (Coarse/Acquisition) civil navigation messages. The decoder extracts ephemeris, clock correction, and health data from the 50 bps LNAV data stream.

Arguments

• prn::Int: Pseudo-Random Noise code identifier (1-32 for GPS satellites)

Returns

• GNSSDecoderState{GPSL1Data}: Initialized decoder state for GPS L1

Example

state = GPSL1DecoderState(1)  # Create decoder for PRN 1
state = decode(state, bits, num_bits)
if is_sat_healthy(state)
    # Use state.data for positioning
end

See Also

• GNSSDecoderState: The underlying state structure
• decode: Decode bits using this state
• reset_decoder_state: Reset after signal loss
• is_sat_healthy: Check satellite health status

GalileoE1BDecoderState(
    prn
) -> GNSSDecoderState{GNSSDecoder.GalileoE1BData, GNSSDecoder.GalileoE1BConstants, GNSSDecoder.GalileoE1BCache, GNSSDecoder.UInt288}

Create a decoder state for Galileo E1B I/NAV navigation messages.

Initializes a GNSSDecoderState configured for decoding Galileo E1B (Open Service) navigation messages. The decoder extracts ephemeris, clock correction, ionospheric parameters, and health data from the 250 bps I/NAV data stream using Viterbi decoding.

Arguments

• prn::Int: Pseudo-Random Noise code identifier (1-36 for Galileo satellites)

Returns

• GNSSDecoderState{GalileoE1BData}: Initialized decoder state for Galileo E1B

Example

state = GalileoE1BDecoderState(1)  # Create decoder for PRN 1
state = decode(state, bits, num_bits)
if is_sat_healthy(state)
    # Use state.data for positioning
end

See Also

• GNSSDecoderState: The underlying state structure
• decode: Decode bits using this state
• reset_decoder_state: Reset after signal loss
• is_sat_healthy: Check satellite health status

decode(
    state::GNSSDecoderState,
    bits::Unsigned,
    num_bits::Int64;
    decode_once
) -> GNSSDecoderState

Decode GNSS navigation message bits and update the decoder state.

Processes incoming bits from a GNSS signal, detecting preambles and decoding synchronization sequences to extract navigation data. The function handles both normal and 180-degree phase-shifted signals automatically.

Arguments

• state::GNSSDecoderState: Current decoder state
• bits::T: Unsigned integer containing the bits to decode (MSB first)
• num_bits::Int: Number of valid bits in bits to process

Keywords

• decode_once::Bool=false: If true, stops decoding after all required positioning data has been decoded (subframes 1-3 for GPS, pages 1-5 for Galileo)

Returns

• GNSSDecoderState: Updated decoder state with newly decoded data

Example

state = GPSL1DecoderState(1)  # PRN 1
state = decode(state, UInt8(0b10110010), 8)

See Also

• GNSSDecoderState: The state structure being updated
• is_sat_healthy: Check if satellite health is good after decoding

reset_decoder_state(
    state::GNSSDecoderState{<:GNSSDecoder.GPSL1Data}
) -> GNSSDecoderState{GNSSDecoder.GPSL1Data, C, CA, GNSSDecoder.UInt320} where {C<:GNSSDecoder.AbstractGNSSConstants, CA<:GNSSDecoder.AbstractGNSSCache}

Reset the GPS L1 decoder state after a signal loss or reacquisition.

Clears the bit buffers and time-of-week (TOW) field while preserving other decoded ephemeris and clock data in raw_data. This allows faster recovery after brief signal outages without requiring a full re-decode of all subframes.

Arguments

• state::GNSSDecoderState{<:GPSL1Data}: Current GPS L1 decoder state

Returns

• GNSSDecoderState{<:GPSL1Data}: Reset decoder state with cleared buffers

Example

# After detecting signal loss
state = reset_decoder_state(state)
# Continue decoding with preserved ephemeris
state = decode(state, new_bits, num_bits)

See Also

• GPSL1DecoderState: Create a fresh decoder state
• decode: Continue decoding after reset

reset_decoder_state(
    state::GNSSDecoderState{<:GNSSDecoder.GalileoE1BData}
) -> GNSSDecoderState{GNSSDecoder.GalileoE1BData, C, CA, GNSSDecoder.UInt288} where {C<:GNSSDecoder.AbstractGNSSConstants, CA<:GNSSDecoder.AbstractGNSSCache}

Reset the Galileo E1B decoder state after a signal loss or reacquisition.

Clears the bit buffers and time-of-week (TOW) field while preserving other decoded ephemeris and clock data in raw_data. This allows faster recovery after brief signal outages without requiring a full re-decode of all pages.

Arguments

• state::GNSSDecoderState{<:GalileoE1BData}: Current Galileo E1B decoder state

Returns

• GNSSDecoderState{<:GalileoE1BData}: Reset decoder state with cleared buffers

Example

# After detecting signal loss
state = reset_decoder_state(state)
# Continue decoding with preserved ephemeris
state = decode(state, new_bits, num_bits)

See Also

• GalileoE1BDecoderState: Create a fresh decoder state
• decode: Continue decoding after reset

is_sat_healthy(
    state::GNSSDecoderState{<:GNSSDecoder.GPSL1Data}
) -> Bool

Check if the GPS satellite is healthy and usable for positioning.

Examines the 6-bit satellite health field (svhealth) from subframe 1. A satellite is considered healthy only if all health bits are zero ("000000").

Arguments

• state::GNSSDecoderState{<:GPSL1Data}: GPS L1 decoder state with decoded data

Returns

• Bool: true if satellite health status indicates normal operation

Example

state = GPSL1DecoderState(1)
state = decode(state, bits, num_bits)
if is_sat_healthy(state)
    # Safe to use for positioning
end

See Also

• GPSL1DecoderState: Create decoder state
• decode: Decode navigation data

is_sat_healthy(
    state::GNSSDecoderState{<:GNSSDecoder.GalileoE1BData}
) -> Bool

Check if the Galileo satellite is healthy and usable for positioning.

Examines both the signal health status (signal_health_e1b) and data validity status (data_validity_status_e1b) from page type 5. A satellite is considered healthy only if both conditions are met:

• Signal health is signal_ok
• Data validity is navigation_data_valid

Arguments

• state::GNSSDecoderState{<:GalileoE1BData}: Galileo E1B decoder state with decoded data

Returns

• Bool: true if satellite health and data validity indicate normal operation

Example

state = GalileoE1BDecoderState(1)
state = decode(state, bits, num_bits)
if is_sat_healthy(state)
    # Safe to use for positioning
end

See Also

• GalileoE1BDecoderState: Create decoder state
• decode: Decode navigation data

GPSL1Constants

WGS 84 constants and LNAV message structure parameters for GPS L1 C/A signal decoding.

The physical constants are defined in IS-GPS-200 (Interface Specification) and are used for computing satellite positions and clock corrections from broadcast ephemeris data.

Fields

• syncro_sequence_length::Int: Length of synchronization sequence in bits (300 bits = 10 words × 30 bits)
• preamble::UInt8: TLM word preamble pattern (10001011 binary, 0x8B)
• preamble_length::Int: Length of preamble in bits (8)
• word_length::Int: Length of each LNAV word in bits (30)
• PI::Float64: Mathematical constant π = 3.1415926535898 (IS-GPS-200 Table 20-IV)
• Ω_dot_e::Float64: WGS 84 Earth rotation rate = 7.2921151467×10⁻⁵ rad/s
• c::Float64: Speed of light = 2.99792458×10⁸ m/s
• μ::Float64: WGS 84 Earth gravitational parameter = 3.986005×10¹⁴ m³/s²
• F::Float64: Relativistic correction constant = -4.442807633×10⁻¹⁰ s/√m

Reference

IS-GPS-200N, Section 20.3.3 and Table 20-IV

GPSL1Data

Decoded GPS L1 C/A LNAV navigation message data.

Contains ephemeris, clock correction, and satellite health parameters decoded from subframes 1, 2, and 3 of the GPS LNAV message. All parameters conform to IS-GPS-200N.

Telemetry and Handover Word (TLM/HOW) Fields

• last_subframe_id::Int: ID of the last decoded subframe (1-5)
• integrity_status_flag::Bool: LNAV data integrity status (0=OK, 1=bad)
• TOW::Int64: Time of Week at message transmission (seconds, 0-604784)
• alert_flag::Bool: URA may be worse than indicated (0=OK, 1=alert)
• anti_spoof_flag::Bool: Anti-spoofing mode (0=off, 1=on)

Subframe 1 - Clock Correction Parameters

• trans_week::Int64: GPS week number (modulo 1024)
• codeonl2::Int64: Code on L2 channel (0=invalid, 1=P-code, 2=C/A-code, 3=invalid)
• ura::Float64: User Range Accuracy (meters), derived from URA index
• svhealth::String: 6-bit satellite health status ("000000" = healthy)
• IODC::String: Issue of Data, Clock (10-bit binary string)
• l2pcode::Bool: L2 P-code data flag (1=LNAV OFF on P-code)
• T_GD::Float64: L1-L2 group delay correction (seconds)
• t_0c::Int64: Clock reference time (seconds)
• a_f0::Float64: Clock bias correction coefficient (seconds)
• a_f1::Float64: Clock drift correction coefficient (s/s)
• a_f2::Float64: Clock drift rate correction coefficient (s/s²)

Subframe 2 - Ephemeris Parameters (Part 1)

• IODE_Sub_2::String: Issue of Data, Ephemeris from subframe 2 (8-bit binary string)
• C_rs::Float64: Sine harmonic correction to orbit radius (meters)
• Δn::Float64: Mean motion difference from computed value (semi-circles/s)
• M_0::Float64: Mean anomaly at reference time (semi-circles)
• C_uc::Float64: Cosine harmonic correction to argument of latitude (rad)
• e::Float64: Eccentricity (dimensionless, range 0-0.03)
• C_us::Float64: Sine harmonic correction to argument of latitude (rad)
• sqrt_A::Float64: Square root of semi-major axis (√m)
• t_0e::Int64: Ephemeris reference time (seconds)
• fit_interval::Bool: Curve fit interval flag (0=4h, 1=>4h)
• AODO::Int64: Age of Data Offset for NMCT (seconds)

Subframe 3 - Ephemeris Parameters (Part 2)

• C_ic::Float64: Cosine harmonic correction to inclination (rad)
• Ω_0::Float64: Longitude of ascending node at weekly epoch (semi-circles)
• C_is::Float64: Sine harmonic correction to inclination (rad)
• i_0::Float64: Inclination angle at reference time (semi-circles)
• C_rc::Float64: Cosine harmonic correction to orbit radius (meters)
• ω::Float64: Argument of perigee (semi-circles)
• Ω_dot::Float64: Rate of right ascension (semi-circles/s)
• IODE_Sub_3::String: Issue of Data, Ephemeris from subframe 3 (8-bit binary string)
• i_dot::Float64: Rate of inclination angle (semi-circles/s)

Reference

IS-GPS-200N, Tables 20-I, 20-II, 20-III, Sections 20.3.3.3-20.3.3.4

GalileoE1BConstants

GTRF constants and I/NAV message structure parameters for Galileo E1B signal decoding.

The physical constants are defined in the Galileo OS SIS ICD (Open Service Signal-In-Space Interface Control Document) and are used for computing satellite positions and clock corrections from broadcast ephemeris data.

Fields

• syncro_sequence_length::Int: Length of synchronization sequence in bits (250 bits per page)
• preamble::UInt16: Page synchronization pattern (0101100000 binary)
• preamble_length::Int: Length of preamble in bits (10)
• PI::Float64: Mathematical constant π = 3.1415926535898 (Galileo OS SIS ICD Table 68)
• Ω_dot_e::Float64: Mean angular velocity of the Earth = 7.2921151467×10⁻⁵ rad/s
• c::Float64: Speed of light = 2.99792458×10⁸ m/s
• μ::Float64: Geocentric gravitational constant = 3.986004418×10¹⁴ m³/s²
• F::Float64: Relativistic correction constant = -4.442807309×10⁻¹⁰ s/√m

Reference

Galileo OS SIS ICD, Issue 2.2, Table 68

GalileoE1BData

Decoded Galileo E1B I/NAV navigation message data.

Contains ephemeris, clock correction, signal health, and group delay parameters decoded from word types 1-5 of the Galileo I/NAV message. All parameters conform to the Galileo OS SIS ICD.

Galileo System Time (GST) Fields

• WN::Int64: Week Number (0-4095)
• TOW::Int64: Time of Week at message transmission (seconds, 0-604799)

Ephemeris Parameters (Word Types 1-3)

• t_0e::Float64: Ephemeris reference time (seconds)
• M_0::Float64: Mean anomaly at reference time (semi-circles)
• e::Float64: Eccentricity (dimensionless)
• sqrt_A::Float64: Square root of semi-major axis (√m)
• Ω_0::Float64: Longitude of ascending node at weekly epoch (semi-circles)
• i_0::Float64: Inclination angle at reference time (semi-circles)
• ω::Float64: Argument of perigee (semi-circles)
• i_dot::Float64: Rate of change of inclination angle (semi-circles/s)
• Ω_dot::Float64: Rate of change of right ascension (semi-circles/s)
• Δn::Float64: Mean motion difference from computed value (semi-circles/s)
• C_uc::Float64: Cosine harmonic correction to argument of latitude (rad)
• C_us::Float64: Sine harmonic correction to argument of latitude (rad)
• C_rc::Float64: Cosine harmonic correction to orbit radius (meters)
• C_rs::Float64: Sine harmonic correction to orbit radius (meters)
• C_ic::Float64: Cosine harmonic correction to inclination (rad)
• C_is::Float64: Sine harmonic correction to inclination (rad)

Clock Correction Parameters (Word Type 4)

• t_0c::Float64: Clock correction reference time (seconds)
• a_f0::Float64: SV clock bias correction coefficient (seconds)
• a_f1::Float64: SV clock drift correction coefficient (s/s)
• a_f2::Float64: SV clock drift rate correction coefficient (s/s²)

Issue of Data (Word Types 1-4)

• IOD_nav1::UInt: Issue of Data from word type 1 (10-bit)
• IOD_nav2::UInt: Issue of Data from word type 2 (10-bit)
• IOD_nav3::UInt: Issue of Data from word type 3 (10-bit)
• IOD_nav4::UInt: Issue of Data from word type 4 (10-bit)
• num_pages_after_last_TOW::Int: Pages decoded since last TOW update
• num_bits_after_valid_syncro_sequence_after_last_TOW::Int: Bits since last TOW sync

Signal Health and Data Validity (Word Type 5)

• signal_health_e1b::SignalHealth: E1-B/C signal health status (0=OK, 1=out of service, 2=in test, 3=will be out of service)
• signal_health_e5b::SignalHealth: E5b signal health status
• data_validity_status_e1b::DataValidityStatus: E1-B data validity (0=valid, 1=working without guarantee)
• data_validity_status_e5b::DataValidityStatus: E5b data validity

Broadcast Group Delay (Word Type 5)

• broadcast_group_delay_e1_e5a::Float64: E1-E5a group delay correction (seconds)
• broadcast_group_delay_e1_e5b::Float64: E1-E5b group delay correction (seconds)

Reference

Galileo OS SIS ICD, Issue 2.2, Tables 42-46, 67, 70, 72

SignalHealth

Galileo signal health status enumeration.

Indicates the operational status of a Galileo signal component as broadcast in word type 5.

Values

• signal_ok: Signal is operating normally (value 0)
• signal_out_of_service: Signal is out of service (value 1)
• signal_will_be_out_of_service: Signal is in Extended Operations Mode (value 2)
• signal_component_currently_in_test: Signal component is currently in test (value 3)

Reference

Galileo OS SIS ICD, Issue 2.2, Table 84

DataValidityStatus

Galileo navigation data validity status enumeration.

Indicates whether the broadcast navigation data should be trusted for positioning.

Values

• navigation_data_valid: Navigation data is valid (value 0)
• working_without_guarantee: Navigation data is working without guarantee (value 1)

Reference

Galileo OS SIS ICD, Issue 2.2, Table 81