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Add Octave tooling to load, plot and simulate f_error dump scans
load_f_error_dump/find_f_error_scans/plot_f_error_scan (utils/matlab/libs) read and visualize the per-bin CSV written by the tracking f_error_dump diagnostic, and plot_all_f_error_scans (utils/matlab) batches plot_f_error_scan over every scan in a dump, optionally saving PNGs. f_error_sim (utils/matlab/libs) is a self-contained Monte Carlo simulation of the same bin-scan/CN0-estimator logic, useful for sizing f_error_step_num/f_error_accumulation/f_error_doppler_step without a live capture.
This commit is contained in:
joebre
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% f_error_sim.m
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%
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% Octave Monte Carlo simulation of the tracking "frequency error reduction"
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% state (state 5) implemented in dll_pll_veml_tracking.cc: right after
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% pull-in, a passive scan tests f_error_step_num Doppler bins centered on the
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% pull-in Doppler estimate, spaced f_error_doppler_step Hz apart
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% (bin 0 -> +0, then alternating +step, -step, +2*step, -2*step, ...,
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% matching dll_pll_veml_tracking::f_error_bin_multiplier()). Each bin is
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% incoherently accumulated for f_error_accumulation code periods (|Prompt|^2
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% summed), and the bin with the highest accumulated power is kept as the
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% corrected Doppler.
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%
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% This script reproduces that exact bin geometry and accumulation logic on
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% simulated noisy correlator samples, for a given C/N0 and initial (pull-in)
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% frequency error, fixed to the Galileo E1 code period (Td = 4 ms). It also
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% reproduces the CN0 M2M4 estimator (lock_detectors.cc::cn0_m2m4_estimator)
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% applied to the winning bin's raw samples, matching the receiver's own
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% "Frequency error reduction: CN0 ..." diagnostic line.
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%
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% Usage:
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% f_error_sim() % all defaults
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% f_error_sim(CN0_dBHz, f_error_step_num, f_error_accumulation, ...
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% f_error_doppler_step, f_error_init_Hz, n_trials, seed)
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%
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% f_error_sim(35, 9, 20, 62.5, 150) % typical EVK1029 fer.conf-like case
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% f_error_sim(30, 5, 10, 125, -300, 5000, 2)
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%
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% What it prints:
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% - the bin table (index, multiplier, Doppler tested, noiseless sinc loss)
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% - Monte Carlo statistics: residual Doppler error after the scan, bin
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% "capture" probability (did it pick the bin closest to the true
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% frequency?), and CN0 estimate bias/spread on the winning bin
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%
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% What it plots:
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% 1) One example trial's per-bin accumulated power vs. Doppler tested,
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% with the true frequency marked -- the same data the receiver now logs
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% in its "bin Doppler [Hz]" / "bin correlation power" diagnostic vectors.
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% 2) Histogram of the residual Doppler error left after the scan, over all
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% Monte Carlo trials.
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% -------------------------------------------------------------------------
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%
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% GNSS-SDR is a Global Navigation Satellite System software-defined receiver.
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% This file is part of GNSS-SDR.
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%
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% SPDX-FileCopyrightText: Joel Brenner, 2026. joel.brenner(at)saphyrion.ch
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% SPDX-License-Identifier: GPL-3.0-or-later
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%
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% -------------------------------------------------------------------------
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function f_error_sim(CN0_dBHz, f_error_step_num, f_error_accumulation, f_error_doppler_step, f_error_init_Hz, n_trials, seed)
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%% ------------------------- PARAMETERS ----------------------------------
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if nargin < 1 || isempty(CN0_dBHz), CN0_dBHz = 35; end % [dB-Hz]
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if nargin < 2 || isempty(f_error_step_num), f_error_step_num = 9; end % number of Doppler bins
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if nargin < 3 || isempty(f_error_accumulation), f_error_accumulation = 20; end % incoherent accum. per bin [code periods]
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if nargin < 4 || isempty(f_error_doppler_step), f_error_doppler_step = 62.5; end % [Hz] bin spacing
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if nargin < 5 || isempty(f_error_init_Hz), f_error_init_Hz = 150; end % [Hz] true residual Doppler at pull-in
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if nargin < 6 || isempty(n_trials), n_trials = 2000; end % Monte Carlo trial count
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if nargin < 7 || isempty(seed), seed = 1; end % RNG seed, [] = random
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%% ------------------------------------------------------------------------
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if ~isempty(seed)
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rand('state', seed);
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randn('state', seed);
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end
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Td = 4e-3; % Galileo E1 code period [s] -- fixed per this script's scope
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% mirror Dll_Pll_Conf::SetFromConfiguration(): f_error_step_num must be odd
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% (a center bin plus a symmetric number of +/- steps); round up if even.
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f_error_step_num = max(1, round(f_error_step_num));
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if mod(f_error_step_num, 2) == 0
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f_error_step_num = f_error_step_num + 1;
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printf('note: f_error_step_num rounded up to %d (must be odd)\n', f_error_step_num);
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end
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num_bins = f_error_step_num;
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% bin 0 -> 0; then alternating outward: +1, -1, +2, -2, +3, -3, ...
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% (matches dll_pll_veml_tracking::f_error_bin_multiplier(), 0-based bin_index)
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bin_mult = zeros(1, num_bins);
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for idx = 1:num_bins
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bin_index = idx - 1;
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if bin_index == 0
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bin_mult(idx) = 0;
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else
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half_steps = floor((bin_index + 1) / 2);
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if mod(bin_index, 2) == 1
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bin_mult(idx) = half_steps;
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else
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bin_mult(idx) = -half_steps;
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end
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end
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end
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bin_doppler_offset = bin_mult * f_error_doppler_step; % [Hz], relative to pull-in estimate
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bin_residual_error = f_error_init_Hz - bin_doppler_offset; % [Hz], true - tested, per bin
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sinc0 = @(x) (x == 0) * 1 + (x ~= 0) .* (sin(x + (x == 0)) ./ (x + (x == 0)));
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A = sqrt(2 * 10^(CN0_dBHz / 10) * Td); % correlator amplitude; SNR = 2*(C/N0)*Td, unit-variance complex noise per branch
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printf('--- f_error_sim: CN0=%.1f dB-Hz, f_error_step_num=%d, f_error_accumulation=%d, f_error_doppler_step=%.2f Hz, f_error_init=%.1f Hz, Td=%.1f ms (Galileo E1) ---\n', ...
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CN0_dBHz, num_bins, f_error_accumulation, f_error_doppler_step, f_error_init_Hz, Td * 1e3);
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% noiseless per-bin loss, for the printed table
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theta_bins = pi * bin_residual_error * Td;
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bin_loss_dB = 20 * log10(abs(sinc0(theta_bins)) + eps);
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printf('\n bin mult Doppler[Hz] residual[Hz] sinc loss[dB]\n');
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[~, ideal_bin] = min(abs(bin_residual_error));
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for idx = 1:num_bins
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marker = '';
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if idx == ideal_bin, marker = ' <- closest to truth'; end
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printf(' %2d %+3d %8.2f %8.2f %6.2f%s\n', ...
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idx - 1, bin_mult(idx), bin_doppler_offset(idx), bin_residual_error(idx), bin_loss_dB(idx), marker);
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end
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%% --------------------------- Monte Carlo ---------------------------------
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winning_bin = zeros(1, n_trials);
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residual_after = zeros(1, n_trials);
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cn0_est_dBHz = zeros(1, n_trials);
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example_power = []; % saved from trial 1, for plotting
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for t = 1:n_trials
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bin_power = zeros(1, num_bins);
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bin_samples = cell(1, num_bins);
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for b = 1:num_bins
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theta = pi * bin_residual_error(b) * Td;
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amp = A * sinc0(theta);
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k = (1:f_error_accumulation).';
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phase = (2 * k - 1) * theta; % midpoint-sampling phase ramp, one full 2*theta per epoch
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samples = amp * exp(1j * phase) + (randn(f_error_accumulation, 1) + 1j * randn(f_error_accumulation, 1));
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bin_power(b) = sum(abs(samples) .^ 2);
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bin_samples{b} = samples;
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end
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[~, best_bin] = max(bin_power);
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winning_bin(t) = best_bin;
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residual_after(t) = f_error_init_Hz - bin_doppler_offset(best_bin);
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cn0_est_dBHz(t) = cn0_m2m4(bin_samples{best_bin}, Td);
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if t == 1
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example_power = bin_power;
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end
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end
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capture_prob = mean(winning_bin == ideal_bin);
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printf('\nMonte Carlo results (%d trials):\n', n_trials);
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printf(' Residual Doppler error after scan: mean=%.2f Hz, std=%.2f Hz, RMSE=%.2f Hz (initial error was %.1f Hz)\n', ...
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mean(residual_after), std(residual_after), sqrt(mean(residual_after .^ 2)), f_error_init_Hz);
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printf(' Bin-capture probability (picked bin closest to truth, bin %d): %.1f%%\n', ideal_bin - 1, 100 * capture_prob);
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printf(' CN0 estimate on winning bin: mean=%.2f dB-Hz, std=%.2f dB-Hz (true CN0=%.1f dB-Hz)\n', ...
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mean(cn0_est_dBHz), std(cn0_est_dBHz), CN0_dBHz);
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%% ------------------------------ Plots -------------------------------------
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figure('Name', 'Frequency error reduction: example bin scan');
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bar(bin_doppler_offset, example_power);
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hold on;
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yl = ylim();
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plot([f_error_init_Hz, f_error_init_Hz], yl, 'r--', 'LineWidth', 1.5);
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hold off;
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xlabel('Doppler tested [Hz]');
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ylabel('Accumulated |Prompt|^2 power');
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title(sprintf('Example bin scan (trial 1) -- true error = %.1f Hz', f_error_init_Hz));
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legend('bin power', 'true frequency', 'Location', 'northeast');
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grid on;
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figure('Name', 'Frequency error reduction: residual error distribution');
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hist(residual_after, min(40, max(10, round(n_trials / 50))));
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xlabel('Residual Doppler error after scan [Hz]');
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ylabel('Trial count');
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title(sprintf('Residual error after %d-bin scan (initial error = %.1f Hz)', num_bins, f_error_init_Hz));
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grid on;
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end
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function cn0_dBHz = cn0_m2m4(prompt_samples, coh_integration_time_s)
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% Octave port of lock_detectors.cc::cn0_m2m4_estimator(), applied to a
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% column vector of complex Prompt samples, for exact parity with the
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% receiver's own state-5 CN0 diagnostic.
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n = numel(prompt_samples);
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if n == 0 || coh_integration_time_s == 0
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cn0_dBHz = -100;
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return;
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end
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Psig = mean(abs(real(prompt_samples)));
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Psig = Psig^2;
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p2 = abs(prompt_samples) .^ 2;
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m2 = mean(p2);
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m4 = mean(p2 .^ 2);
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aux = sqrt(2 * m2^2 - m4);
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if isnan(aux)
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denominator = m2 - Psig;
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if denominator == 0
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cn0_dBHz = -100;
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return;
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end
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SNR_aux = Psig / denominator;
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else
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denominator = m2 - aux;
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if denominator == 0
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cn0_dBHz = -100;
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return;
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end
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SNR_aux = aux / denominator;
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end
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if SNR_aux <= 0
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cn0_dBHz = -100;
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return;
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end
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cn0_dBHz = 10 * log10(SNR_aux) - 10 * log10(coh_integration_time_s);
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end
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@@ -0,0 +1,29 @@
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% find_f_error_scans.m
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%
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% Returns the indices into a scans struct array (as returned by
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% load_f_error_dump) matching a given PRN, optionally restricted to a
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% specific channel.
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%
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% Usage:
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% idxs = find_f_error_scans(scans, 13); % all scans for PRN 13, any channel
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% idxs = find_f_error_scans(scans, 13, 2); % PRN 13 on channel 2 only
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%
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% See also: load_f_error_dump, plot_f_error_scan
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% -------------------------------------------------------------------------
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%
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% GNSS-SDR is a Global Navigation Satellite System software-defined receiver.
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% This file is part of GNSS-SDR.
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%
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% SPDX-FileCopyrightText: Joel Brenner, 2026. joel.brenner(at)saphyrion.ch
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% SPDX-License-Identifier: GPL-3.0-or-later
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%
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% -------------------------------------------------------------------------
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function idxs = find_f_error_scans(scans, prn, channel)
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mask = [scans.prn] == prn;
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if nargin >= 3 && ~isempty(channel)
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mask = mask & ([scans.channel] == channel);
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end
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idxs = find(mask);
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end
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@@ -0,0 +1,78 @@
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% load_f_error_dump.m
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%
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% Loads the CSV written by dll_pll_veml_tracking's state-5 (frequency error
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% reduction) diagnostic -- see Dll_Pll_Conf::f_error_dump_filename -- into an
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% Octave struct array, one element per scan (one satellite's pass through
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% state 5). Each row of the CSV is one Doppler bin; this groups rows by
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% scan_id.
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%
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% CSV columns (header row is skipped):
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% scan_id, prn, system_char, channel, cn0_dBHz, selected_doppler_hz,
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% selected_bin, bin_index, doppler_hz, power
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%
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% Usage:
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% scans = load_f_error_dump(); % default: ./f_error_dump.csv
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% scans = load_f_error_dump('/path/to/dump.csv');
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% load_f_error_dump(); % no output arg: also prints a summary table
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%
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% Each scans(i) has fields:
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% scan_id, prn, system_char, channel, cn0_dBHz, selected_doppler_hz, selected_bin,
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% doppler_hz (row vector, increasing Doppler order), power (row vector, same order)
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%
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% See also: find_f_error_scans, plot_f_error_scan
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% -------------------------------------------------------------------------
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%
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% GNSS-SDR is a Global Navigation Satellite System software-defined receiver.
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% This file is part of GNSS-SDR.
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%
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% SPDX-FileCopyrightText: Joel Brenner, 2026. joel.brenner(at)saphyrion.ch
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% SPDX-License-Identifier: GPL-3.0-or-later
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%
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% -------------------------------------------------------------------------
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function scans = load_f_error_dump(filename)
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if nargin < 1 || isempty(filename)
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filename = 'f_error_dump.csv';
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end
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raw = csvread(filename, 1, 0); % skip header row
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if isempty(raw)
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error('load_f_error_dump: no data rows found in %s', filename);
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end
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scan_id_col = raw(:, 1);
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unique_ids = unique(scan_id_col);
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n = numel(unique_ids);
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scans = struct('scan_id', {}, 'prn', {}, 'system_char', {}, 'channel', {}, 'cn0_dBHz', {}, ...
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'selected_doppler_hz', {}, 'selected_bin', {}, ...
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'doppler_hz', {}, 'power', {});
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for i = 1:n
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rows = raw(scan_id_col == unique_ids(i), :);
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[~, order] = sort(rows(:, 8)); % bin_index, defensive (writer already emits increasing Doppler order)
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rows = rows(order, :);
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scans(i).scan_id = rows(1, 1);
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scans(i).prn = rows(1, 2);
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scans(i).system_char = rows(1, 3);
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scans(i).channel = rows(1, 4);
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scans(i).cn0_dBHz = rows(1, 5);
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scans(i).selected_doppler_hz = rows(1, 6);
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scans(i).selected_bin = rows(1, 7);
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scans(i).doppler_hz = rows(:, 9)';
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scans(i).power = rows(:, 10)';
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end
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if nargout == 0
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printf('%6s %5s %4s %9s %14s %8s %6s\n', 'scan', 'PRN', 'ch', 'CN0[dBHz]', 'selDoppler[Hz]', 'nBins', '');
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for i = 1:n
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printf('%6d %5d %4d %9.2f %14.2f %8d\n', scans(i).scan_id, scans(i).prn, scans(i).channel, ...
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scans(i).cn0_dBHz, scans(i).selected_doppler_hz, numel(scans(i).doppler_hz));
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end
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printf('\n%d scans loaded from %s\n', n, filename);
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printf('PRNs present: %s\n', mat2str(unique([scans.prn])));
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clear scans; % avoid echoing the struct array to the console when called as a script
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end
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end
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@@ -0,0 +1,59 @@
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% plot_f_error_scan.m
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%
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% Bar-plots one state-5 frequency-error-reduction scan (as loaded by
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% load_f_error_dump), with the selected/winning Doppler marked. Optionally
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% overlays the theoretical sinc(pi*Delta_f*Td)^2 envelope (normalized to the
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% scan's own peak) for comparison, if the coherent integration time Td [s] is
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% given -- e.g. Td=0.004 for Galileo E1, Td=0.001 for GPS L1 C/A.
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%
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% Usage:
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% scans = load_f_error_dump();
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% plot_f_error_scan(scans, 5); % plot scans(5)
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% plot_f_error_scan(scans, 5, 0.004); % + theoretical Galileo E1 sinc^2 overlay
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%
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% See also: load_f_error_dump, find_f_error_scans
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% -------------------------------------------------------------------------
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%
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% GNSS-SDR is a Global Navigation Satellite System software-defined receiver.
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% This file is part of GNSS-SDR.
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%
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% SPDX-FileCopyrightText: Joel Brenner, 2026. joel.brenner(at)saphyrion.ch
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% SPDX-License-Identifier: GPL-3.0-or-later
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%
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% -------------------------------------------------------------------------
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function plot_f_error_scan(scans, idx, Td)
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if idx < 1 || idx > numel(scans)
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error('plot_f_error_scan: idx %d out of range (1..%d)', idx, numel(scans));
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end
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s = scans(idx);
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figure();
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bar(s.doppler_hz, s.power);
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hold on;
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if nargin >= 3 && ~isempty(Td)
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% theoretical envelope centered on the selected (winning) Doppler, since that's
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% this scan's best estimate of the true residual frequency
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theta = pi * (s.doppler_hz - s.selected_doppler_hz) * Td;
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sinc0 = @(x) (x == 0) * 1 + (x ~= 0) .* (sin(x + (x == 0)) ./ (x + (x == 0)));
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envelope = (sinc0(theta) .^ 2) * max(s.power);
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plot(s.doppler_hz, envelope, 'k--', 'LineWidth', 1.3);
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end
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yl = ylim();
|
||||
plot([s.selected_doppler_hz, s.selected_doppler_hz], yl, 'r--', 'LineWidth', 1.5);
|
||||
hold off;
|
||||
|
||||
xlabel('Doppler tested [Hz]');
|
||||
ylabel('Accumulated correlation power');
|
||||
if nargin >= 3 && ~isempty(Td)
|
||||
legend('bin power', 'theoretical sinc^2 (centered on selected)', 'selected Doppler', 'Location', 'northeast');
|
||||
else
|
||||
legend('bin power', 'selected Doppler', 'Location', 'northeast');
|
||||
end
|
||||
title(sprintf('PRN%d ch%d scan %d: CN0=%.1f dB-Hz, selected=%.1f Hz (bin %d/%d)', ...
|
||||
s.prn, s.channel, s.scan_id, s.cn0_dBHz, s.selected_doppler_hz, s.selected_bin, numel(s.doppler_hz) - 1));
|
||||
grid on;
|
||||
end
|
||||
@@ -0,0 +1,68 @@
|
||||
% plot_all_f_error_scans.m
|
||||
%
|
||||
% Bar-plots every scan in a scans struct array (as returned by
|
||||
% load_f_error_dump), one figure per scan -- a batch wrapper around
|
||||
% plot_f_error_scan. Optionally restrict to a subset of scans (e.g. from
|
||||
% find_f_error_scans) and/or save each figure to disk instead of leaving a
|
||||
% window open per scan (recommended once there are more than a handful).
|
||||
%
|
||||
% Usage:
|
||||
% scans = load_f_error_dump();
|
||||
% plot_all_f_error_scans(scans); % every scan, one window each
|
||||
% plot_all_f_error_scans(scans, 0.004); % + theoretical sinc^2 overlay (Galileo E1 Td)
|
||||
% plot_all_f_error_scans(scans, 0.004, find_f_error_scans(scans, 13)); % only PRN 13's scans
|
||||
% plot_all_f_error_scans(scans, 0.004, [], 'plots'); % save PNGs into ./plots/ instead of opening windows
|
||||
%
|
||||
% See also: load_f_error_dump, find_f_error_scans, plot_f_error_scan
|
||||
|
||||
% -------------------------------------------------------------------------
|
||||
%
|
||||
% GNSS-SDR is a Global Navigation Satellite System software-defined receiver.
|
||||
% This file is part of GNSS-SDR.
|
||||
%
|
||||
% SPDX-FileCopyrightText: Joel Brenner, 2026. joel.brenner(at)saphyrion.ch
|
||||
% SPDX-License-Identifier: GPL-3.0-or-later
|
||||
%
|
||||
% -------------------------------------------------------------------------
|
||||
|
||||
function plot_all_f_error_scans(scans, Td, idxs, save_dir)
|
||||
if ~exist('load_f_error_dump.m', 'file')
|
||||
addpath('./libs')
|
||||
end
|
||||
if nargin < 2
|
||||
Td = [];
|
||||
end
|
||||
if nargin < 3 || isempty(idxs)
|
||||
idxs = 1:numel(scans);
|
||||
end
|
||||
if nargin < 4
|
||||
save_dir = '';
|
||||
end
|
||||
|
||||
if ~isempty(save_dir)
|
||||
% note: do NOT set DefaultFigureVisible='off' here -- combined with an
|
||||
% invisible figure, saveas()/print() falls back to the fltk renderer,
|
||||
% which then fails without a real X display. Leaving figures nominally
|
||||
% visible (but headlessly rendered via gnuplot) is what actually works.
|
||||
graphics_toolkit('gnuplot');
|
||||
if ~exist(save_dir, 'dir')
|
||||
mkdir(save_dir);
|
||||
end
|
||||
end
|
||||
|
||||
for idx = idxs
|
||||
s = scans(idx);
|
||||
plot_f_error_scan(scans, idx, Td);
|
||||
|
||||
if ~isempty(save_dir)
|
||||
fname = fullfile(save_dir, sprintf('scan%04d_prn%d_ch%d.png', s.scan_id, s.prn, s.channel));
|
||||
saveas(gcf(), fname);
|
||||
close(gcf());
|
||||
end
|
||||
end
|
||||
|
||||
if ~isempty(save_dir)
|
||||
set(0, 'DefaultFigureVisible', 'on');
|
||||
printf('Saved %d plots to %s\n', numel(idxs), save_dir);
|
||||
end
|
||||
end
|
||||
Reference in New Issue
Block a user