I. Introduction
The Internet of Things (IoT) has drawn great interests in both academic and industrial areas. IoT is supposed to enable ubiquitous connectivity among billions of physical objects, such as vehicles, mobile phones, sensors, etc. [1], [2]. IoT greatly promotes the gathering and exchanging of information, which is believed to bring a huge boost in productivity and act as a cornerstone in the future intelligent society. In recent years, the large-scale application of IoT is achieved with the rapid development of wireless communication technology, cloud computing, integrated circuits, etc. [3].