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Classifying falls using out-of-distribution detection in human activity recognition
KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Software and Computer systems, SCS. Qamcom Research and Technology, Stockholm, Sweden.ORCID iD: 0000-0001-6780-7755
KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Software and Computer systems, SCS. Qamcom Research and Technology, Stockholm, Sweden.ORCID iD: 0000-0003-4984-029X
KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Software and Computer systems, SCS.ORCID iD: 0000-0003-4516-7317
2023 (English)In: AI Communications, ISSN 0921-7126, E-ISSN 1875-8452, Vol. 36, no 4, p. 251-267Article in journal (Refereed) Published
Abstract [en]

As the research community focuses on improving the reliability of deep learning, identifying out-of-distribution (OOD) data has become crucial. Detecting OOD inputs during test/prediction allows the model to account for discriminative features unknown to the model. This capability increases the model's reliability since this model provides a class prediction solely at incoming data similar to the training one. Although OOD detection is well-established in computer vision, it is relatively unexplored in other areas, like time series-based human activity recognition (HAR). Since uncertainty has been a critical driver for OOD in vision-based models, the same component has proven effective in time-series applications. In this work, we propose an ensemble-based temporal learning framework to address the OOD detection problem in HAR with time-series data. First, we define different types of OOD for HAR that arise from realistic scenarios. Then we apply our ensemble-based temporal learning framework incorporating uncertainty to detect OODs for the defined HAR workloads. This particular formulation also allows a novel approach to fall detection. We train our model on non-fall activities and detect falls as OOD. Our method shows state-of-The-Art performance in a fall detection task using much lesser data. Furthermore, the ensemble framework outperformed the traditional deep-learning method (our baseline) on the OOD detection task across all the other chosen datasets.

Place, publisher, year, edition, pages
IOS Press , 2023. Vol. 36, no 4, p. 251-267
Keywords [en]
deep learning, human activity recognition, Out-of-distribution detection, time-series classification, uncertainty estimation
National Category
Computer Sciences Bioinformatics (Computational Biology)
Identifiers
URN: urn:nbn:se:kth:diva-339522DOI: 10.3233/AIC-220205ISI: 001087274200001Scopus ID: 2-s2.0-85175210057OAI: oai:DiVA.org:kth-339522DiVA, id: diva2:1811849
Note

QC 20231114

Available from: 2023-11-14 Created: 2023-11-14 Last updated: 2024-04-11Bibliographically approved
In thesis
1. Towards Trustworthy Machine Learning For Human Activity Recognition
Open this publication in new window or tab >>Towards Trustworthy Machine Learning For Human Activity Recognition
2024 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Human Activity Recognition presents a multifaceted challenge, encompassing the complexity of human activities, the diversity of sensors used, and the imperative to safeguard user data privacy. Recent advancements in machine learning, deep learning, and sensor technology have opened up new possibilities for human activity recognition. Wearable sensor-based human activity recognition involves collecting time-series data from various sensors, capturing intricate aspects of human activities. The focus of the above activity recognition problem is classifying human activities from the time-series data. Hence, this time-series classification problem demands efficient utilization of temporal properties. Moreover, while accurate prediction is crucial in human activity recognition, the reliability of predictions often goes unnoticed. Ensuring that predictions are reliable involves addressing two issues: calibrating miscalibrated predictions that fail to accurately represent the true likelihood of the data and addressing the challenges around uncertain predictions. Modern deep learning models, used extensively in human activity recognition, often struggle with the above issues. In addition to reliability concerns, machine learning algorithms employed in Human Activity Recognition are also plagued by privacy issues stemming from the utilization of sensitive activity data during model training. While existing techniques such as federated learning can provide some degree of privacy protection in these scenarios, they tend to adhere to a uniform concept of privacy and lack quantifiable privacy metrics that can be effectively conveyed to users and customized to cater to their individual privacy preferences. Hence, in the thesis, we identify the challenges around the effective use of temporal data, reliability, and privacy issues of machine learning models used for wearable sensor-based human activity recognition. To tackle these challenges, we put forth novel solutions, striving to enhance the overall performance and trustworthiness of machine learning models employed in human activity recognition.

Firstly, to improve classification performance, we propose a new temporal ensembling framework that uses data temporality effectively. The framework accommodates various window sizes for time-series data and trains an ensemble of deep-learning models based on that. It enhances classification accuracy and preserves temporal information.

Secondly, we address reliability through calibration and uncertainty estimation. The aforementioned temporal ensembling framework is used for calibration and uncertainty estimation. It provides well-calibrated predictions for human activity recognition and detects out-of-distribution activities, an important task of uncertainty estimation. Furthermore, we apply these methods to real-world scenarios, enhancing the reliability of human activity recognition models.

Thirdly, to address the privacy concern, we introduce a differentially private framework for time-series human activity recognition, quantifying privacy. Additionally, we develop a collaborative federated learning framework, allowing users to define their privacy preferences, advancing privacy preservation in human activity recognition.

These contributions address major challenges and promote improved classification, reliability, and privacy preservation in human activity recognition. It helps us to move towards trustworthy machine learning in human activity recognition, facilitating their usage in realistic and practical scenarios.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2024. p. xii, 56
Series
TRITA-EECS-AVL ; 2024:12
National Category
Computer Sciences
Research subject
Computer Science; Information and Communication Technology
Identifiers
urn:nbn:se:kth:diva-343130 (URN)978-91-8040-826-4 (ISBN)
Public defence
2024-03-06, https://kth-se.zoom.us/j/63687967257, Sal C, Kistagången 16, Kista, Stockholm, 13:00 (English)
Opponent
Supervisors
Funder
EU, Horizon 2020, 813162
Note

QC 20240207

Available from: 2024-02-07 Created: 2024-02-07 Last updated: 2024-02-29Bibliographically approved

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Roy, DebadityaKomini, VangjushGirdzijauskas, Sarunas

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