ODHD: one-class brain-inspired hyperdimensional computing for outlier detection

Outlier detection is a classical and important technique that has been used in different application domains such as medical diagnosis and Internet-of-Things. Recently, machine learning-based outlier detection algorithms, such as one-class support vector machine (OCSVM), isolation forest and autoencoder, have demonstrated promising results in outlier detection. In this paper, we take a radical departure from these classical learning methods and propose ODHD, an outlier detection method based on hyperdimensional computing (HDC). In ODHD, the outlier detection process is based on a P-U learning structure, in which we train a one-class HV based on inlier samples. This HV represents the abstraction information of all inlier samples; hence, any (testing) sample whose corresponding HV is dissimilar from this HV will be considered as an outlier. We perform an extensive evaluation using six datasets across different application domains and compare ODHD with multiple baseline methods including OCSVM, isolation forest, and autoencoder using three metrics including accuracy, F1 score and ROC-AUC. Experimental results show that ODHD outperforms all the baseline methods on every dataset for every metric. Moreover, we perform a design space exploration for ODHD to illustrate the tradeoff between performance and efficiency. The promising results presented in this paper provide a viable option and alternative to traditional learning algorithms for outlier detection.