Walking Recognition in Mobile Devices.

Presently, smartphones are used more and more for purposes that have nothing to do withphone calls or simple data transfers. One example is the recognition of human activity, which isrelevant information for many applications in the domains of medical diagnosis, elderly assistance,indoor localization, and navigation. The information captured by the inertial sensors of the phone(accelerometer, gyroscope, and magnetometer) can be analyzed to determine the activity performedby the person who is carrying the device, in particular in the activity of walking. Nevertheless,the development of a standalone application able to detect the walking activity starting only fromthe data provided by these inertial sensors is a complex task. This complexity lies in the hardwaredisparity, noise on data, and mostly the many movements that the smartphone can experience andwhich have nothing to do with the physical displacement of the owner. In this work, we exploreand compare several approaches for identifying the walking activity. We categorize them into twomain groups: the first one uses features extracted from the inertial data, whereas the second oneanalyzes the characteristic shape of the time series made up of the sensors readings. Due to the lackof public datasets of inertial data from smartphones for the recognition of human activity underno constraints, we collected data from 77 different people who were not connected to this research.Using this dataset, which we published online, we performed an extensive experimental validationand comparison of our proposals.

Robust Step Counting for Inertial Navigation with Mobile Phones.

Mobile phones are increasingly used for purposes that have nothing to do with phone calls or simple data transfers, and one such use is indoor inertial navigation. Nevertheless, the development of a standalone application able to detect the displacement of the user starting only from the data provided by the most common inertial sensors in the mobile phones (accelerometer, gyroscope and magnetometer), is a complex task. This complexity lies in the hardware disparity, noise on data, and mostly the many movements that the mobile phone can experience and which have nothing to do with the physical displacement of the owner. In our case, we describe a proposal, which, after using quaternions and a Kalman filter to project the sensors readings into an Earth Centered inertial reference system, combines a classic Peak-valley detector with an ensemble of SVMs (Support Vector Machines) and a standard deviation based classifier. Our proposal is able to identify and filter out those segments of signal that do not correspond to the behavior of "walking", and thus achieve a robust detection of the physical displacement and counting of steps. We have performed an extensive experimental validation of our proposal using a dataset with 140 records obtained from 75 different people who were not connected to this research.