Convolutional Neural Network (CNN) have been widely used in image
classification. Over the years, they have also benefited from various
enhancements and they are now considered as state of the art techniques for
image like data. However, when they are used for regression to estimate some
function value from images, fewer recommendations are available. In this study,
a novel CNN regression model is proposed. It combines convolutional neural
layers to extract high level features representations from images with a soft
labelling technique. More specifically, as the deep regression task is
challenging, the idea is to account for some uncertainty in the targets that
are seen as distributions around their mean. The estimations are carried out by
the model in the form of distributions. Building from earlier work, a specific
histogram loss function based on the Kullback-Leibler (KL) divergence is
applied during training. The model takes advantage of the CNN feature
representation and is able to carry out estimation from multi-channel input
images. To assess and illustrate the technique, the model is applied to Global
Navigation Satellite System (GNSS) multi-path estimation where multi-path
signal parameters have to be estimated from correlator output images from the I
and Q channels. The multi-path signal delay, magnitude, Doppler shift frequency
and phase parameters are estimated from synthetically generated datasets of
satellite signals. Experiments are conducted under various receiving conditions
and various input images resolutions to test the estimation performances
quality and robustness. The results show that the proposed soft labelling CNN
technique using distributional loss outperforms classical CNN regression under
all conditions. Furthermore, the extra learning performance achieved by the
model allows the reduction of input image resolution from 80x80 down to 40x40
or sometimes 20x20.