Underwater Acoustic Channel Toolbox — Channel Estimation Scripts

with Signal Processing Toolbox™ or with the signal and statistics packages.

This MATLAB®/Octave toolbox estimates underwater acoustic channels from single-carrier recordings and visualizes the results.

Please report bugs and suggest enhancements by creating a new issue. We welcome your feedback.

Quick start

Run main.m in MATLAB or Octave. The script generates a BPSK signal, passes it through a synthetic multipath channel with Doppler, estimates the time-varying impulse response, and plots the results.

Functions

Function	Description
est.m	Adaptive channel estimation with LMS, RLS, or SFTF, and optional delay tracking via a second-order PLL.
plots.m	Visualization of the estimated channel: time-varying IR, Doppler-delay scattering function, delay-angle (broadband beamforming), multipath intensity profile, PLL phase, and estimation parameters.

Output format

The estimator produces two structs that are saved alongside the channel data:

params — physical parameters of the channel.

Field	Description
fs_delay	Sampling rate in the delay domain [Hz]
fs_time	Sampling rate along the time axis [Hz]
fc	Center frequency [Hz]

meta — estimation metadata.

Field	Description
description	Free-text description of the experiment
nsd	Samples per symbol in the delay domain
nst	Samples per symbol in the time domain
Fs	Sample rate of the received signal
K_1, K_2	Anti-causal and causal filter lengths [symbols]
fc	Center frequency [Hz]
element_spacing	Array element spacing [m]
vertical	true if vertical array
delay_tracking	true if delay tracking is enabled
limit	Lower dB limit for plotting
optim	Optimizer (1: LMS, 2: RLS, 3: SFTF)
mu	LMS step size (when optim == 1)
lambda	Forgetting factor (when optim == 2 or 3)
Kf_1, Kf_2	PLL loop filter coefficients
nslr	Delay tracking rate (when delay_tracking == true)
codename	Short identifier for the channel

The .mat file contains h_hat, either theta_hat or phi_hat (depending on the tracking mode), params, meta, and version.

Plotting

plots.m returns a struct of figure handles. Saving is left to the caller.

% After estimation:
figs = plots(h_hat, theta_hat, params, meta);

% With standalone subplot figures:
figs = plots(h_hat, theta_hat, params, meta, true);

% Export:
exportgraphics(figs.main, "channel.pdf", "Resolution", 300);
exportgraphics(figs.ir, "channel_ir.pdf", "Resolution", 300);

To plot a previously saved channel:

channel = load('yellow_2.mat');
if isfield(channel, 'phi_hat')
  phase = channel.phi_hat;
else
  phase = channel.theta_hat;
end
figs = plots(channel.h_hat, phase, channel.params, channel.meta);

The returned struct figs may contain the following fields:

Field	Description
main	2×3 summary figure
ir	Time-varying impulse response
doppler	Doppler-delay scattering function
delay_angle	Delay-angle plot (vertical arrays with M ≥ 13)
mip	Multipath intensity profile
pll	PLL phase trajectory

License

The license is available in the LICENSE file within this repository.

© 2025-2026, Underwater Acoustic Channels Group.