1. Telecommunication Engineering Institute, Beijing Polytechnic, Beijing 100176, China (Corresponding author), e-mail: malei235@126.com, https://orcid.org/0000-0001-8816-4621
2. Mechanical and Electrical Engineering Institute, Beijing Polytechnic, Beijing 100176, China
3. China Population and Development Research Center, No. 12 Dahuisi Rd., Haidian District, Beijing 100081, China