## 2 Literature Review  
### Smart Home for the Elderly  
The market maturity and popularity of smart homes are still low [26], and the aging adoption trend of the smart home industry is not obvious [27]. However, there is no doubt that a smart home would have a prosperous future and provide an effective solution for the global challenges of an aging society [28]. At present, many developed countries are already exploring the application of smart homes in dealing with the aging challenges, such as the United States, the United Kingdom, France, Italy, Japan, South Korea, etc. [29]. Many projects are in progress, with funding from international organizations and local governments. In the United States, the \"Aging in place\" project at the University of Missouri in Colombia focuses on offering elderly long-term healthcare services in the home environment due to their choices [30]. Another project at MIT, called \"The house of the future\", conducts qualitative and quantitative studies on the relationship of the elderly group with their living environment factors and builds a user model based on updating the machine learning data set [31]. Moreover, there is a smart home system called \"ACHE\" in boulder, which aims to optimize the usage of energy resources by realizing intelligent control of temperature, heating, and lighting with respecting the lifestyle and habits of its residents [32]. What is more, \"GatorTech Smart House\" in Florida, developed by [PERSON] et al., equipped the home components including entrance door, bathroom, floor, mailbox, etc. with sensors and actuators and connected them into the online platform to try to provide a comfortable and safe home environment for the elderly [33]. In Europe, Gloucester's Smart House project funding by the UK government aims to help the elderly suffering from dementia. The majority of items in the house are under continuous monitoring via sensors [34]. Another project called \"The ENABLE\" also focuses on the subject with moderate dementia and provide assistive technology to improve their quality of life [35; 36]. Moreover, \"CarerNet\", a project in the UK, proposes the concept of \"hospital at home\" and deploys telemedicine service for older adults, including emergency response, community health information, real-time monitoring, etc. [37]. In Netherland, a smart home system has been built to learn residents habits and make decisions by itself according to the subjects' behavior pattern and daily routine and it can also measure the daily physiological signs such as blood pressure, blood sugar, mean arterial pressure, arrhythmia, lung capacity, body weight, body temperature, and body fat. The main purpose of this project is to promote the communication of seniors, caregivers, and service providers [38; 39]. In some Asian countries, like Japan, smart homes usually apply assistive technologies to create a smart and comfortable environment for older adults to live at home and improve their quality of life. There are 13 smart home examples called \"Welfare Techno-Houses (WTH)\" built by The Japanese Ministry of International Trade and Industry [40; 41]. In Tokyo, [PERSON] et al. have developed a system based on resident vital physical signs analysis including breathing, heart rate, body motion, etc. to monitor the sleeping status of seniors [42]. In Nara, [PERSON] et al. have designed a monitoring system to provide elderly physical data and daily life information for rehabilitation therapists [43]. Moreover, a smart home, designed by Dr. [PERSON] in Osaka, inserts 167 sensors in a home environment, including home appliances like refrigerator, TV set, rice cooker, air conditioning, and home furniture to detect the elderly's activities and realize intelligent adjustment and control [44]. The discussion above is a part of typical smart home examples, and there are still plenty of other projects and research. However, to sum up, the majority of existing projects and research are mainly concentrated in the following five aspects. First, home automation.