Step Counting with Attention-based LSTM

Abstract

Physical activity is recognized as an essential component of overall health. One measure of physical activity, the step count, is well known as a predictor of long-term morbidity and mortality. Step Counting (SC) is the automated counting of the number of steps an individual takes over a specified period of time and space. Due to the ubiquity of smartphones and smartwatches, most current SC approaches rely on the built-in accelerometer sensors on these devices. The sensor signals are analyzed as multivariate time series, and the number of steps is calculated through a variety of approaches, such as time-domain, frequency-domain, machine-learning, and deep-learning approaches. Most of the existing approaches rely on dividing the input signal into windows, detecting steps in each window, and summing the detected steps. However, these approaches require the determination of multiple parameters, including the window size. Furthermore, most of the existing deep-learning SC approaches require ground-truth labels for every single step, which can be arduous and time-consuming to annotate. To circumvent these requirements, we present a novel SC approach utilizing many-to-one attention-based LSTM. With the proposed LSTM network, SC is solved as a regression problem, taking the entire sensor signal as input and the step count as the output. The analysis shows that the attention-based LSTM automatically learned the pattern of steps even in the absence of ground-truth labels. The experimental results on three publicly available SC datasets demonstrate that the proposed method successfully counts the number of steps with low values of mean absolute error and high values of SC accuracy.