Beyond Where to How: A Machine Learning Approach for Sensing Mobility Contexts Using Smartphone Sensors

This paper presents the results of research on the use of smartphone sensors (namely, GPS and accelerometers), geospatial information (points of interest, such as bus stops and train stations) and machine learning (ML) to sense mobility contexts. Our goal is to develop techniques to continuously and automatically detect a smartphone user’s mobility activities, including walking, running, driving and using a bus or train, in real-time or near-real-time (<5 s). We investigated a wide range of supervised learning techniques for classification, including decision trees (DT), support vector machines (SVM), naive Bayes classifiers (NB), Bayesian networks (BN), logistic regression (LR), artificial neural networks (ANN) and several instance-based classifiers (KStar, LWLand IBk). Applying ten-fold cross-validation, the best performers in terms of correct classification rate (i.e., recall) were DT (96.5%), BN (90.9%), LWL (95.5%) and KStar (95.6%). In particular, the DT-algorithm RandomForest exhibited the best overall performance. After a feature selection process for a subset of algorithms, the performance was improved slightly. Furthermore, after tuning the parameters of RandomForest, performance improved to above 97.5%. Lastly, we measured the computational complexity of the classifiers, in terms of central processing unit (CPU) time needed for classification, to provide a rough comparison between the algorithms in terms of battery usage requirements. As a result, the classifiers can be ranked from lowest to highest complexity (i.e., computational cost) as follows: SVM, ANN, LR, BN, DT, NB, IBk, LWL and KStar. The instance-based classifiers take considerably more computational time than the non-instance-based classifiers, whereas the slowest non-instance-based classifier (NB) required about five-times the amount of CPU time as the fastest classifier (SVM). The above results suggest that DT algorithms are excellent candidates for detecting mobility contexts in smartphones, both in terms of performance and computational complexity

A method for ice-aware maritime route optimization

We present a method for ice-aware maritime route optimization. Our aim is to increase the safety and efficiency of maritime transport under icy conditions. The proposed method is based on the A algorithm, developed by Hart et al. It uses a model of maritime navigation, consisting of (1) a sea spatial model, (2) ship maneuverability model, (3) sea ice model, and (4) ship performance model. The sea ice model, which provides a snapshot of the sea ice conditions, is based on previous work by the Finnish Meteorological Institute. The ship performance model, based on previous work by Kotovirta et al., estimates ship transit speed as a function of ice conditions and ship design parameters. The main novelties in this paper are the application of the A algorithm to maritime route optimization and development of an associated cost function that takes into account ice conditions and available icebreaker assistance. We present preliminary results based on the method, using the Baltic Sea as a case study. Generated routes are compared with historical routes under the same ice conditions. Areas of future work and needed enhancements are briefly discusse