I. Introduction
Our global population is entering an aging stage, and the number and proportion of older people in almost every country in the world are fast increasing. By 2050, the number of people aged 60 will reach 2.1 billion [1]. As they grow older, many of them are likely to suffer from some geriatric diseases, such as dementia or Alzheimer’s, which will make them more challenging to live independently [2]. Due to the shortage of caregivers and the imperfection of available healthcare infrastructure, many studies have begun to establish the assisted living system to help monitor activities of daily living (ADLs) [3], [4]. Especially, human activity recognition (HAR) is a vital research area that focuses on identifying human actions based on the information obtained from various kinds of sensors used for activity monitoring [5].