API Reference

AbstractGNSS{C}

Abstract supertype for all GNSS system types.

Concrete subtypes include GPSL1, GPSL5, and GalileoE1B. The type parameter C represents the code matrix type.

GPSL1{C} <: AbstractGNSS{C}

GPS L1 C/A signal type.

GPS L1 uses BPSK (LOC) modulation with a 1023-chip C/A code at 1.023 Mcps, transmitted on the L1 carrier frequency of 1575.42 MHz.

Example

gpsl1 = GPSL1()
get_code_length(gpsl1)  # 1023

GPSL5{C} <: AbstractGNSS{C}

GPS L5 signal type.

GPS L5 uses BPSK (LOC) modulation with a 10230-chip code at 10.23 Mcps and a 10-bit Neuman-Hofman secondary code, transmitted on the L5 carrier frequency of 1176.45 MHz.

Example

gpsl5 = GPSL5()
get_code_length(gpsl5)           # 10230
get_secondary_code_length(gpsl5) # 10

GalileoE1B{C} <: AbstractGNSS{C}

Galileo E1B signal type.

Galileo E1B uses CBOC(6,1,1/11) modulation with a 4092 chip code at 1.023 Mcps, transmitted on the E1 carrier frequency of 1575.42 MHz.

LOC()

Legacy/BPSK modulation (no subcarrier).

Used for GPS L1 C/A and GPS L5 signals.

BOCsin(m, n)

Sine-phased Binary Offset Carrier modulation.

BOC(m,n) uses a subcarrier frequency of m * 1.023 MHz and a code rate of n * 1.023 Mcps.

Arguments

• m: Subcarrier frequency multiplier (must be ≥ 1)
• n: Code rate multiplier (must be ≥ 1)

Example

boc11 = BOCsin(1, 1)  # BOC(1,1)

BOCcos(m, n)

Cosine-phased Binary Offset Carrier modulation.

BOC(m,n) uses a subcarrier frequency of m * 1.023 MHz and a code rate of n * 1.023 Mcps.

Arguments

• m: Subcarrier frequency multiplier (must be ≥ 1)
• n: Code rate multiplier (must be ≥ 1)

Example

boc11 = BOCcos(1, 1)  # BOC(1,1) with cosine phase

CBOC(boc1, boc2, boc1_power)

Composite Binary Offset Carrier modulation.

CBOC combines two BOC modulations with specified power distribution. Used for Galileo E1B signals as CBOC(6,1,1/11).

Arguments

• boc1: First BOC component
• boc2: Second BOC component
• boc1_power: Power fraction allocated to first BOC (0 < power < 1)

Example

cboc = CBOC(BOCsin(1, 1), BOCsin(6, 1), 10/11)  # CBOC(6,1,1/11)

gen_code(num_samples, gnss, prn, sampling_frequency)
gen_code(
    num_samples,
    gnss,
    prn,
    sampling_frequency,
    code_frequency
)
gen_code(
    num_samples,
    gnss,
    prn,
    sampling_frequency,
    code_frequency,
    start_phase
)
gen_code(
    num_samples,
    gnss,
    prn,
    sampling_frequency,
    code_frequency,
    start_phase,
    start_index
)

Generate a sampled code signal for a given PRN.

Allocates and returns a new buffer containing the spreading code sampled at the specified sampling frequency. For in-place operation, use gen_code!.

Arguments

• num_samples: Number of samples to generate
• gnss: GNSS system instance (e.g., GPSL1(), GPSL5(), GalileoE1B())
• prn: PRN number of the satellite
• sampling_frequency: Sampling frequency (must be larger than code frequency)
• code_frequency: Code chipping rate (default: system's nominal code frequency)
• start_phase: Initial code phase in chips (default: 0.0)
• start_index: Index offset (default: 0)

Returns

• Vector: Sampled code signal

Examples

julia> using Unitful: MHz
julia> sampled_code = gen_code(4000, GPSL1(), 1, 4MHz)
julia> length(sampled_code)
4000

gen_code!(sampled_code, gnss, prn, sampling_frequency)
gen_code!(
    sampled_code,
    gnss,
    prn,
    sampling_frequency,
    code_frequency
)
gen_code!(
    sampled_code,
    gnss,
    prn,
    sampling_frequency,
    code_frequency,
    start_phase
)
gen_code!(
    sampled_code,
    gnss,
    prn,
    sampling_frequency,
    code_frequency,
    start_phase,
    start_index_shift
)
gen_code!(
    sampled_code,
    gnss,
    prn,
    sampling_frequency,
    code_frequency,
    start_phase,
    start_index_shift,
    maximum_expected_sampling_frequency
)
gen_code!(
    sampled_code,
    gnss,
    prn,
    sampling_frequency,
    code_frequency,
    start_phase,
    start_index_shift,
    maximum_expected_sampling_frequency,
    maximum_expected_doppler
)
gen_code!(
    sampled_code,
    gnss,
    prn,
    sampling_frequency,
    code_frequency,
    start_phase,
    start_index_shift,
    maximum_expected_sampling_frequency,
    maximum_expected_doppler,
    PHASET
)

Generate the code signal in-place for a given PRN.

This is a highly optimized function for generating sampled spreading codes at arbitrary sampling rates. It uses fixed-point arithmetic and minimizes memory access by exploiting the fact that consecutive samples often map to the same code chip. The algorithm avoids per-sample floating-point operations and modulo calculations, making it suitable for real-time GNSS signal processing applications.

Samples the spreading code at the specified sampling frequency and stores the result in the provided buffer. Includes subcarrier modulation for BOC-type signals.

Arguments

• sampled_code: Pre-allocated output buffer
• gnss: GNSS system instance (e.g., GPSL1(), GPSL5(), GalileoE1B())
• prn: PRN number of the satellite
• sampling_frequency: Sampling frequency (must be larger than code frequency)
• code_frequency: Code chipping rate (default: system's nominal code frequency)
• start_phase: Initial code phase in chips (default: 0.0)
• start_index_shift: Index offset for the output buffer (default: 0)
• maximum_expected_sampling_frequency: Maximum expected sampling frequency for optimization
• maximum_expected_doppler: Maximum expected Doppler frequency (default: 8000 Hz)
• PHASET: Integer type for phase calculations (default: Int32)

Returns

• The modified sampled_code buffer

Examples

julia> using Unitful: MHz
julia> buffer = zeros(Int16, 4000)
julia> gen_code!(buffer, GPSL1(), 1, 4MHz)

get_code(system, phase, prn)

Get the code value at a given phase for a specific PRN.

Returns the spreading code value (including subcarrier modulation for BOC signals) at the specified code phase. The phase is automatically wrapped to the code length.

Arguments

• system: A GNSS system instance (e.g., GPSL1(), GPSL5(), GalileoE1B())
• phase: Code phase in chips
• prn: PRN number of the satellite

Returns

• Code value (typically Int8 for BPSK, Float32 for CBOC)

Examples

julia> get_code(GPSL1(), 0.0, 1)
1
julia> get_code(GPSL1(), 1200.3, 1)
-1
julia> get_code.(GPSL1(), 0:1022, 1)  # Full code period

get_code(modulation, system, phase, prn)

Get code value for BOC-modulated signals at a given phase.

Internal method that handles BOC modulation (sine or cosine phased).

get_code(modulation, system, phase, prn)

Get code value for LOC (BPSK) signals at a given phase.

Internal method that handles legacy/BPSK modulation without subcarrier.

get_code_unsafe(system, phase, prn)

Get the code value at a given phase without bounds checking.

This is a faster version of get_code that skips the modulo operation. The phase must be within [0, code_length * secondary_code_length).

Arguments

• system: A GNSS system instance
• phase: Code phase in chips (must be within valid range)
• prn: PRN number of the satellite

Returns

• Code value at the given phase

Examples

julia> get_code_unsafe(GPSL1(), 500.0, 1)

get_code_unsafe(modulation, system, phase, prn)

Get code value for BOC signals without bounds checking.

Internal method for BOC modulation without phase wrapping.

get_code_unsafe(modulation, system, phase, prn)

Get code value for LOC (BPSK) signals without bounds checking.

Internal method for BPSK modulation without phase wrapping.

get_codes(gnss)

Get the full code matrix for a GNSS system.

Returns the codes as a matrix where each column represents a PRN.

Arguments

• gnss: A GNSS system instance (e.g., GPSL1(), GPSL5(), GalileoE1B())

Returns

• Matrix: Code matrix of size (code_length, num_prns)

Examples

julia> codes = get_codes(GPSL1())
julia> size(codes)
(1023, 37)

get_code_length(gpsl1)

Get the code length for GPS L1.

Returns

• Int: 1023 chips

Examples

julia> get_code_length(GPSL1())
1023

get_code_length(gpsl5)

Get the code length for GPS L5.

Returns

• Int: 10230 chips

Examples

julia> get_code_length(GPSL5())
10230

get_code_length(galileo_e1b)

Get the code length for Galileo E1B.

Returns

• Int: 4092 chips

Examples

julia> get_code_length(GalileoE1B())
4092

get_secondary_code_length(gnss)

Get the length of the secondary code.

Arguments

• gnss: A GNSS system instance

Returns

• Int: Secondary code length (1 if no secondary code)

Examples

julia> get_secondary_code_length(GPSL1())
1
julia> get_secondary_code_length(GPSL5())
10

get_secondary_code(gpsl1)

Get the secondary code for GPS L1.

GPS L1 has no secondary code, so this returns 1.

Returns

• Int: 1 (no secondary code)

Examples

julia> get_secondary_code(GPSL1())
1

get_secondary_code(galileo_e1b)

Get the secondary code for Galileo E1B.

Galileo E1B has no secondary code, so this returns 1.

Returns

• Int: 1 (no secondary code)

Examples

julia> get_secondary_code(GalileoE1B())
1

get_secondary_code(gnss, phase)

Get the secondary code value at a given phase.

Arguments

• gnss: A GNSS system instance
• phase: Code phase in chips

Returns

• Secondary code value at the given phase

Examples

julia> get_secondary_code(GPSL5(), 10230.0)  # Start of second code period
1

get_secondary_code(gnss, code, phase)

Get secondary code value when code is a single integer (no secondary code).

Returns the code value unchanged.

get_secondary_code(gnss, code, phase)

Get secondary code value at phase when code is a tuple (has secondary code).

Computes the secondary code index from the phase and returns the corresponding value.

get_center_frequency(gpsl1)

Get the center (carrier) frequency for GPS L1.

Returns

• Frequency: 1575.42 MHz

Examples

julia> get_center_frequency(GPSL1())
1575420000 Hz

get_center_frequency(gpsl5)

Get the center (carrier) frequency for GPS L5.

Returns

• Frequency: 1176.45 MHz

Examples

julia> get_center_frequency(GPSL5())
1176450000 Hz

get_center_frequency(galileo_e1b)

Get the center (carrier) frequency for Galileo E1B.

Returns

• Frequency: 1575.42 MHz

Examples

julia> get_center_frequency(GalileoE1B())
1575420000 Hz

get_code_frequency(gpsl1)

Get the code chipping rate for GPS L1.

Returns

• Frequency: 1.023 MHz

Examples

julia> get_code_frequency(GPSL1())
1023000 Hz

get_code_frequency(gpsl5)

Get the code chipping rate for GPS L5.

Returns

• Frequency: 10.23 MHz

Examples

julia> get_code_frequency(GPSL5())
10230000 Hz

get_code_frequency(galileo_e1b)

Get the code chipping rate for Galileo E1B.

Returns

• Frequency: 1.023 MHz

Examples

julia> get_code_frequency(GalileoE1B())
1023000 Hz

get_data_frequency(gpsl1)

Get the data bit rate for GPS L1.

Returns

• Frequency: 50 Hz

Examples

julia> get_data_frequency(GPSL1())
50 Hz

get_data_frequency(gpsl5)

Get the data bit rate for GPS L5.

Returns

• Frequency: 100 Hz

Examples

julia> get_data_frequency(GPSL5())
100 Hz

get_data_frequency(galileo_e1b)

Get the data bit rate for Galileo E1B.

Returns

• Frequency: 250 Hz

Examples

julia> get_data_frequency(GalileoE1B())
250 Hz

get_code_center_frequency_ratio(gnss)

Get the ratio of code frequency to center frequency.

This ratio is used to compute the code Doppler from the carrier Doppler.

Arguments

• gnss: A GNSS system instance

Returns

• Float64: The code-to-center frequency ratio

Examples

julia> get_code_center_frequency_ratio(GPSL1())
0.0006493506493506494

get_modulation(s)

Get the modulation type for a GNSS system.

Arguments

• system: A GNSS system instance or type

Returns

• Modulation: The modulation type (LOC, BOCsin, BOCcos, or CBOC)

Examples

julia> get_modulation(GPSL1())
LOC()
julia> get_modulation(GalileoE1B())
CBOC{BOCsin{Int64, Int64}, BOCsin{Int64, Int64}}(BOCsin{Int64, Int64}(1, 1), BOCsin{Int64, Int64}(6, 1), 0.90909094f0)

get_system_string(s)

Get the system name as a string.

Arguments

• system: A GNSS system instance

Returns

• String: System identifier string

Examples

julia> get_system_string(GPSL1())
"GPSL1"

min_bits_for_code_length(gnss)

Get the minimum number of bits needed to represent the code length.

Calculates the number of bits required to represent the full code length, including secondary code if present.

Arguments

• gnss: A GNSS system instance

Returns

• Int: Number of bits needed

Examples

julia> min_bits_for_code_length(GPSL1())
10
julia> min_bits_for_code_length(GPSL5())
17

get_code_type(system)

Get the element type for code values of a GNSS system.

Returns the numeric type used to represent code values. For BPSK (LOC) signals, this is typically Int16. For CBOC signals, this is a floating-point type.

Arguments

• system: A GNSS system instance

Returns

• Type: The element type for code values

Examples

julia> get_code_type(GPSL1())
Int16
julia> get_code_type(GalileoE1B())
Float32

get_code_spectrum(system, f)

Get the spectral power density of a GNSS signal at a given frequency.

Computes the power spectral density based on the system's modulation type.

Arguments

• system: A GNSS system instance
• f: Baseband frequency at which to evaluate the spectrum

Returns

• Spectral power density value

Examples

julia> using Unitful: kHz
julia> get_code_spectrum(GPSL1(), 0kHz)
9.775171065493646e-7

get_code_spectrum_BPSK(fc, f)

Calculate the spectral power density of a BPSK modulated signal.

Computes the power spectral density at baseband frequency f for a BPSK signal with chip rate fc.

Arguments

• fc: Code chip rate
• f: Baseband frequency at which to evaluate the spectrum

Returns

• Spectral power density value

Examples

julia> using Unitful: MHz, kHz
julia> get_code_spectrum_BPSK(1.023MHz, 0kHz)
9.775171065493646e-7

get_code_spectrum_BOCsin(fc, fs, f)

Calculate the spectral power density of a sine-phased BOC modulated signal.

Computes the power spectral density at baseband frequency f for a BOC(sin) signal with chip rate fc and subcarrier frequency fs.

Arguments

• fc: Code chip rate
• fs: Subcarrier frequency
• f: Baseband frequency at which to evaluate the spectrum

Returns

• Spectral power density value

get_code_spectrum_BOCcos(fc, fs, f)

Calculate the spectral power density of a cosine-phased BOC modulated signal.

Computes the power spectral density at baseband frequency f for a BOC(cos) signal with chip rate fc and subcarrier frequency fs.

Arguments

• fc: Code chip rate
• fs: Subcarrier frequency
• f: Baseband frequency at which to evaluate the spectrum

Returns

• Spectral power density value

read_in_codes(type, filename, num_prns, code_length)

Read codes from a binary file.

Reads codes encoded in the specified type from a file. The code length must be provided by code_length and the number of PRNs by num_prns.

Arguments

• type: The data type of the codes (e.g., Int8)
• filename: Path to the binary file containing the codes
• num_prns: Number of PRN codes in the file
• code_length: Length of each code sequence

Returns

• Matrix{type}: A matrix of size (code_length, num_prns) containing the codes

Examples

julia> read_in_codes(Int8, "/data/gpsl1codes.bin", 32, 1023)