  Mobile devices supporting the "Internet of Things" (IoT), often have limited
capabilities in computation, battery energy, and storage space, especially to
support resource-intensive applications involving virtual reality (VR),
augmented reality (AR), multimedia delivery and artificial intelligence (AI),
which could require broad bandwidth, low response latency and large
computational power. Edge cloud or edge computing is an emerging topic and
technology that can tackle the deficiency of the currently centralized-only
cloud computing model and move the computation and storage resource closer to
the devices in support of the above-mentioned applications. To make this
happen, efficient coordination mechanisms and "offloading" algorithms are
needed to allow the mobile devices and the edge cloud to work together
smoothly. In this survey paper, we investigate the key issues, methods, and
various state-of-the-art efforts related to the offloading problem. We adopt a
new characterizing model to study the whole process of offloading from mobile
devices to the edge cloud. Through comprehensive discussions, we aim to draw an
overall "big picture" on the existing efforts and research directions. Our
study also indicates that the offloading algorithms in edge cloud have
demonstrated profound potentials for future technology and application
development.
