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Acquisition.jl

GNSS signal acquisition using the FM-DBZP (Frequency-domain Modified Double Block Zero Padding) algorithm.

Acquisition.jl is part of the JuliaGNSS ecosystem and works with GNSSSignals.jl for signal definitions.

Installation

using Pkg
Pkg.add("Acquisition")

Quick Start

using Acquisition, GNSSSignals
import Unitful: Hz

system = GPSL1()
(; signal, sampling_freq, interm_freq) = generate_test_signal(system, 1)

# Acquire GPS L1 C/A signals for PRNs 1–32
results = acquire(system, signal, sampling_freq, 1:32; interm_freq)

# Reuse a pre-computed plan for repeated acquisitions
plan = plan_acquire(system, sampling_freq, 1:32)
results = acquire!(plan, signal, 1:32; interm_freq)
Pick a fast sampling frequency

Acquisition performance depends strongly on the prime factorization of samples_per_code. The commonly-cited 16.368 MHz GPS L1 rate is ~3× slower than the nearby 16.384 MHz because of a radix-31 inner FFT. See Sampling Frequency and FFT Performance for the rule of thumb and a table of measured timings.

Algorithm Overview

This library implements the FM-DBZP algorithm from Heckler & Garrison (2009), which performs simultaneous correlation across all code phases and Doppler bins using a two-dimensional FFT structure.

The signal segment of length N = num_coherently_integrated_code_periods × samples_per_code is divided into num_blocks equal sub-blocks. A row-wise inverse FFT performs circular correlation against each PRN sub-block, filling a 2D coherent integration matrix (num_doppler_bins × samples_per_code). A column-wise FFT then resolves the Doppler dimension, producing a power surface that is peak-searched for acquisition.

Features

  • FM-DBZP algorithm: Joint code-phase and Doppler search via 2-D FFT structure
  • Pre-computed plans: Reuse FFT plans and buffers across acquisitions with plan_acquire
  • Multi-threaded: PRNs processed in parallel — start Julia with -t N to use N threads
  • Non-coherent integration: Accumulate power across multiple signal segments to improve sensitivity at low CN0
  • Data bit handling: Bit-edge search and sign-combination search for coherent integration spanning multiple data bits
  • Sub-sample interpolation: Parabolic interpolation for Doppler and code-phase refinement below grid resolution
  • Plotting support: Visualise acquisition results with Plots.jl

Contents