  By pushing computation, cache, and network control to the edge, mobile edge
computing (MEC) is expected to play a leading role in fifth generation (5G) and
future sixth generation (6G). Nevertheless, facing ubiquitous fast-growing
computational demands, it is impossible for a single MEC paradigm to
effectively support high-quality intelligent services at end user equipments
(UEs). To address this issue, we propose an air-ground collaborative MEC
(AGC-MEC) architecture in this article. The proposed AGC-MEC integrates all
potentially available MEC servers within air and ground in the envisioned 6G,
by a variety of collaborative ways to provide computation services at their
best for UEs. Firstly, we introduce the AGC-MEC architecture and elaborate
three typical use cases. Then, we discuss four main challenges in the AGC-MEC
as well as their potential solutions. Next, we conduct a case study of
collaborative service placement for AGC-MEC to validate the effectiveness of
the proposed collaborative service placement strategy. Finally, we highlight
several potential research directions of the AGC-MEC.
