Title: Efficient Dense Labeling of Human Activity Sequences from Wearables using Fully Convolutional Networks,
Abstract: Recognizing human activities in a sequence is a challenging area of research
in ubiquitous computing. Most approaches use a fixed size sliding window over
consecutive samples to extract features---either handcrafted or learned
features---and predict a single label for all samples in the window. Two key
problems emanate from this approach: i) the samples in one window may not
always share the same label. Consequently, using one label for all samples
within a window inevitably lead to loss of information; ii) the testing phase
is constrained by the window size selected during training while the best
window size is difficult to tune in practice. We propose an efficient algorithm
that can predict the label of each sample, which we call dense labeling, in a
sequence of human activities of arbitrary length using a fully convolutional
network. In particular, our approach overcomes the problems posed by the
sliding window step. Additionally, our algorithm learns both the features and
classifier automatically. We release a new daily activity dataset based on a
wearable sensor with hospitalized patients. We conduct extensive experiments
and demonstrate that our proposed approach is able to outperform the
state-of-the-arts in terms of classification and label misalignment measures on
three challenging datasets: Opportunity, Hand Gesture, and our new dataset.