  Recently, ambient backscatter communications has been introduced as a
cutting-edge technology which enables smart devices to communicate by utilizing
ambient radio frequency (RF) signals without requiring active RF transmission.
This technology is especially effective in addressing communication and energy
efficiency problems for low-power communications systems such as sensor
networks. It is expected to realize numerous Internet-of-Things (IoT)
applications. Therefore, this paper aims to provide a contemporary and
comprehensive literature review on fundamentals, applications, challenges, and
research efforts/progress of ambient backscatter communications. In particular,
we first present fundamentals of backscatter communications and briefly review
bistatic backscatter communications systems. Then, the general architecture,
advantages, and solutions to address existing issues and limitations of ambient
backscatter communications systems are discussed. Additionally, emerging
applications of ambient backscatter communications are highlighted. Finally, we
outline some open issues and future research directions.
