  With the development of next-generation wireless networks, the Internet of
Things (IoT) is evolving towards the intelligent IoT (iIoT), where intelligent
applications usually have stringent delay and jitter requirements. In order to
provide low-latency services to heterogeneous users in the emerging iIoT,
multi-tier computing was proposed by effectively combining edge computing and
fog computing. More specifically, multi-tier computing systems compensate for
cloud computing through task offloading and dispersing computing tasks to
multi-tier nodes along the continuum from the cloud to things. In this paper,
we investigate key techniques and directions for wireless communications and
resource allocation approaches to enable task offloading in multi-tier
computing systems. A multi-tier computing model, with its main functionality
and optimization methods, is presented in details. We hope that this paper will
serve as a valuable reference and guide to the theoretical, algorithmic, and
systematic opportunities of multi-tier computing towards next-generation
wireless networks.
