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  • 1.
    Luan, Siyu
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Towards safe and efficient application of deep neural networks in resource-constrained real-time embedded systems2023Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    We consider real-time safety-critical systems that feature closed-loop interactions between the embedded computing system and the physical environment with a sense-compute-actuate feedback loop. Deep Learning (DL) with Deep Neural Networks (DNNs) has achieved success in many application domains, but there are still significant challenges in its application in real-time safety-critical systems that require high levels of safety certification under significant hardware resource constraints. This thesis considers the following overarching research goal: How to achieve safe and efficient application of DNNs in resource-constrained Real-Time Embedded (RTE) systems in the context of safety-critical application domains such as Autonomous Driving? Towards reaching that goal, this thesis presents a set of algorithms and techniques that aim to address three Research Questions (RQs): RQ1: How to achieve accurate and efficient Out-of-Distribution (OOD) detection for DNNs in RTE systems? RQ2: How to predict the performance of DNNs under continuous distribution shifts? RQ3: How to achieve efficient inference of Deep Reinforcement Learning (DRL) agents in RTE systems?

    For RQ1, we present a framework for OOD detection based on outlier detection in one or more hidden layers of a DNN with either Isolation Forest (IF) or Local Outlier Factor (LOF). We also perform a comprehensive and systematic benchmark study of multiple well-known OOD detection algorithms in terms of both accuracy and execution time on different hardware platforms, in order to provide a useful reference for the practical deployment of OOD detection algorithms in RTE systems. For RQ2, we present a framework for predicting the performance of DNNs for end-to-end Autonomous Driving under continuous distribution shifts with two approaches: using an Autoencoder that attempts to reconstruct the input image; and applying Anomaly Detection algorithms to the hidden layer(s) of the DNN. For RQ3, we present a framework for model compression of the policy network of a DRL agent for deployment in RTE systems by leveraging the relevance scores computed by Layer-wise Relevance Propagation (LRP) to rank and prune the convolutional filters, combined with fine-tuning using policy distillation.

    The algorithms and techniques developed in this thesis have been evaluated on standard datasets and benchmarks. To summarize our findings, we have developed novel OOD detection algorithms with high accuracy and efficiency; identified OOD detection algorithms with relatively high accuracy and low execution times through benchmarking; developed a framework for DNN performance prediction under continuous distribution shifts, and identified most effective Anomaly Detection algorithms for use in the framework; developed a framework for model compression of DRL agents that is effective in reducing model size and inference time for deployment in RTE systems. The research results are expected to assist system designers in the task of safe and efficient application of DNNs in resource-constrained RTE systems.

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  • 2.
    Luan, Siyu
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Gu, Zonghua
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Freidovich, Leonid B.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik. Department of Information Technologies and AI, Sirius University of Science and Technology, Sochi, Russian Federation.
    Jiang, Lili
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för datavetenskap.
    Zhao, Qingling
    College of Computer Science and Technology, Nanjing University of Science and Technology, Nanjing, China.
    Out-of-Distribution Detection for Deep Neural Networks with Isolation Forest and Local Outlier Factor2021Inngår i: IEEE Access, E-ISSN 2169-3536, Vol. 9, s. 132980-132989Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Deep Neural Networks (DNNs) are extensively deployed in today's safety-critical autonomous systems thanks to their excellent performance. However, they are known to make mistakes unpredictably, e.g., a DNN may misclassify an object if it is used for perception, or issue unsafe control commands if it is used for planning and control. One common cause for such unpredictable mistakes is Out-of-Distribution (OOD) input samples, i.e., samples that fall outside of the distribution of the training dataset. We present a framework for OOD detection based on outlier detection in one or more hidden layers of a DNN with a runtime monitor based on either Isolation Forest (IF) or Local Outlier Factor (LOF). Performance evaluation indicates that LOF is a promising method in terms of both the Machine Learning metrics of precision, recall, F1 score and accuracy, as well as computational efficiency during testing.

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  • 3.
    Luan, Siyu
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Gu, Zonghua
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Saremi, Amin
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Freidovich, Leonid B.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Jiang, Lili
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för datavetenskap.
    Wan, Shaohua
    Shenzhen Institute for Advanced Study, University of Electronic Science and Technology of China, Shenzhen, China.
    Timing performance benchmarking of out-of-distribution detection algorithms2023Inngår i: Journal of Signal Processing Systems, ISSN 1939-8018, E-ISSN 1939-8115, Vol. 95, nr 12, s. 1355-1370Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In an open world with a long-tail distribution of input samples, Deep Neural Networks (DNNs) may make unpredictable mistakes for Out-of-Distribution (OOD) inputs at test time, despite high levels of accuracy obtained during model training. OOD detection can be an effective runtime assurance mechanism for safe deployment of machine learning algorithms in safety–critical applications such as medical imaging and autonomous driving. A large number of OOD detection algorithms have been proposed in recent years, with a wide range of performance metrics in terms of accuracy and execution time. For real-time safety–critical applications, e.g., autonomous driving, timing performance is of great importance in addition to accuracy. We perform a comprehensive and systematic benchmark study of multiple OOD detection algorithms in terms of both accuracy and execution time on different hardware platforms, including a powerful workstation and a resource-constrained embedded device, equipped with both CPU and GPU. We also profile and analyze the internal details of each algorithm to identify the performance bottlenecks and potential for GPU acceleration. This paper aims to provide a useful reference for the practical deployment of OOD detection algorithms for real-time safety–critical applications.

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  • 4.
    Luan, Siyu
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Gu, Zonghua
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Wan, Shaohua
    Shenzhen Institute for Advanced Study, University of Electronic Science and Technology of China, Shenzhen, China.
    Efficient performance prediction of end-to-end autonomous driving under continuous distribution shifts based on anomaly detection2023Inngår i: Journal of Signal Processing Systems, ISSN 1939-8018, E-ISSN 1939-8115, Vol. 95, nr 12, s. 1455-1468Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A Deep Neural Network (DNN)’s prediction may be unreliable outside of its training distribution despite high levels of accuracy obtained during model training. The DNN may experience different degrees of accuracy degradation for different levels of distribution shifts, hence it is important to predict its performance (accuracy) under distribution shifts. In this paper, we consider the end-to-end approach to autonomous driving of using a DNN to map from an input image to the control action such as the steering angle. For each input image with possible perturbations that cause distribution shifts, we design a Performance Prediction Module to compute its anomaly score, and use it to predict the DNN’s expected prediction error, i.e., its expected deviation from the ground truth (optimal) control action, which is not available after deployment. If the expected prediction error is too large, then the DNN’s prediction may no longer be trusted, and remedial actions should be taken to ensure safety. We consider different methods for computing the anomaly score for the input image, including using the reconstruction error of an Autoencoder, or applying an Anomaly Detection algorithm to a hidden layer of the DNN. We present performance evaluation of the different methods in terms of both prediction accuracy and execution time on different hardware platforms, in order to provide a useful reference for the designer to choose among the different methods.

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  • 5.
    Luan, Siyu
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Gu, Zonghua
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Xu, Rui
    School of Computer Science and Engineering, Nanjing University of Science and Technology, Nanjing, China.
    Zhao, Qingling
    School of Computer Science and Engineering, Nanjing University of Science and Technology, Nanjing, China.
    Chen, Gang
    School of Computer Science and Engineering, Sun Yat-sen University, Guangzhou, China.
    LRP-based network pruning and policy distillation of robust and non-robust DRL agents for embedded systems2023Inngår i: Concurrency and Computation, ISSN 1532-0626, E-ISSN 1532-0634, Vol. 35, nr 19, artikkel-id e7351Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Reinforcement learning (RL) is an effective approach to developing control policies by maximizing the agent's reward. Deep reinforcement learning uses deep neural networks (DNNs) for function approximation in RL, and has achieved tremendous success in recent years. Large DNNs often incur significant memory size and computational overheads, which may impede their deployment into resource-constrained embedded systems. For deployment of a trained RL agent on embedded systems, it is necessary to compress the policy network of the RL agent to improve its memory and computation efficiency. In this article, we perform model compression of the policy network of an RL agent by leveraging the relevance scores computed by layer-wise relevance propagation (LRP), a technique for Explainable AI (XAI), to rank and prune the convolutional filters in the policy network, combined with fine-tuning with policy distillation. Performance evaluation based on several Atari games indicates that our proposed approach is effective in reducing model size and inference time of RL agents. We also consider robust RL agents trained with RADIAL-RL versus standard RL agents, and show that a robust RL agent can achieve better performance (higher average reward) after pruning than a standard RL agent for different attack strengths and pruning rates.

    Fulltekst (pdf)
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  • 6.
    Xu, Rui
    et al.
    Nanjing University of Science and Technology, School of Computer Science and Engineering, Nanjing, China.
    Luan, Siyu
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Gu, Zonghua
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Zhao, Qingling
    Nanjing University of Science and Technology, School of Computer Science and Engineering, Nanjing, China.
    Chen, Gang
    Sun Yat-sen University, School of Computer Science and Engineering, Guangzhou, China.
    LRP-based Policy Pruning and Distillation of Reinforcement Learning Agents for Embedded Systems2022Inngår i: 2022 IEEE 25th International Symposium on Real-Time Distributed Computing, ISORC 2022, Institute of Electrical and Electronics Engineers (IEEE), 2022Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Reinforcement Learning (RL) is an effective approach to developing control policies by maximizing the agent's reward. Deep Reinforcement Learning (DRL) uses Deep Neural Networks (DNNs) for function approximation in RL, and has achieved tremendous success in recent years. Large DNNs often incur significant memory size and computational overheads, which greatly impedes their deployment into resource-constrained embedded systems. For deployment of a trained RL agent on embedded systems, it is necessary to compress the Policy Network of the RL agent to improve its memory and computation efficiency. In this paper, we perform model compression of the Policy Network of an RL agent by leveraging the relevance scores computed by Layer-wise Relevance Propagation (LRP), a technique for Explainable AI (XAI), to rank and prune the convolutional filters in the Policy Network, combined with fine-Tuning with Policy Distillation. Performance evaluation based on several Atari games indicates that our proposed approach is effective in reducing model size and inference time of RL agents.

  • 7.
    Zhao, Qingling
    et al.
    The PCA Lab, School of Computer Science and Engineering, Nanjing University of Science and Technology, Systems for High-Dimensional Information of Ministry of Education, Jiangsu Key Lab of Image and Video Understanding for Social Security, Jiangsu, Nanjing, China.
    Chen, Mingqiang
    The PCA Lab, School of Computer Science and Engineering, Nanjing University of Science and Technology, Systems for High-Dimensional Information of Ministry of Education, Jiangsu Key Lab of Image and Video Understanding for Social Security, Jiangsu, Nanjing, China.
    Gu, Zonghua
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Luan, Siyu
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Zeng, Haibo
    Department of Electrical and Computer Engineering, Virginia Tech, VA, Blacksburg, United States.
    Chakrabory, Samarjit
    Department of Computer Science, University of North Carolina, NC, Chapel Hill, United States.
    CAN bus intrusion detection based on auxiliary classifier GAN and out-of-distribution detection2022Inngår i: ACM Transactions on Embedded Computing Systems, ISSN 1539-9087, E-ISSN 1558-3465, Vol. 21, nr 4, artikkel-id 45Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Controller Area Network (CAN) is a ubiquitous bus protocol present in the Electrical/Electronic (E/E) systems of almost all vehicles. It is vulnerable to a range of attacks once the attacker gains access to the bus through the vehicle's attack surface. We address the problem of Intrusion Detection on the CAN bus and present a series of methods based on two classifiers trained with Auxiliary Classifier Generative Adversarial Network (ACGAN) to detect and assign fine-grained labels to Known Attacks and also detect the Unknown Attack class in a dataset containing a mixture of (Normal + Known Attacks + Unknown Attack) messages. The most effective method is a cascaded two-stage classification architecture, with the multi-class Auxiliary Classifier in the first stage for classification of Normal and Known Attacks, passing Out-of-Distribution (OOD) samples to the binary Real-Fake Classifier in the second stage for detection of the Unknown Attack class. Performance evaluation demonstrates that our method achieves both high classification accuracy and low runtime overhead, making it suitable for deployment in the resource-constrained in-vehicle environment.

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