Feature extraction from smartphone inertial signals for human activity segmentation

This paper proposes the adaptation of well-known strategies successfully used in speech processing: Mel Frequency Cepstral Coefficients (MFCCs) and Perceptual Linear Prediction (PLP) coefficients. Additionally characteristics like RASTA filtering or delta coefficients are also considered and evaluated for inertial signal processing. These adaptations have been incorporated into a Human Activity Recognition and Segmentation (HARS) system based on Hidden Markov Models (HMMs) for recognizing and segmenting six different physical activities: walking, walking-upstairs, walking-downstairs, sitting, standing and lying. All experiments have been done using a publicly available dataset named UCI Human Activity Recognition Using Smartphones, which includes several sessions with physical activity sequences from 30 volunteers. This dataset has been randomly divided into six subsets for performing a six-fold cross validation procedure. For every experiment, average values from the six-fold cross-validation procedure are shown. The results presented in this paper overcome significantly baseline error rates, constituting a relevant contribution in the field. Adapted MFCC and PLP coefficients improve human activity recognition and segmentation accuracies while reducing feature vector size considerably. RASTA-filtering and delta coefficients contribute significantly to reduce the segmentation error rate obtaining the best results: an Activity Segmentation Error Rate lower than 0.5%. (C) 2015 Elsevier B.V. All rights reserved.