  Mobile edge computing provides users with a cloud environment close to the
edge of the wireless network, supporting the computing intensive applications
that have low latency requirements. The combination of offloading with the
wireless communication brings new challenges. This paper investigates the
service caching problem during the long-term service offloading in the
user-centric wireless network. To meet the time-varying service demands of a
typical user, a cooperative service caching strategy in the unit of the base
station (BS) cluster is proposed. We formulate the caching problem as a
time-averaged completion delay minimization problem and transform it into
time-decoupled instantaneous problems with a virtual caching cost queue at
first. Then we propose a distributed algorithm which is based on the
consensus-sharing alternating direction method of multipliers to solve each
instantaneous problem. The simulations validate that the proposed online
distributed service caching algorithm can achieve the optimal time-averaged
completion delay of offloading tasks with the smallest caching cost in the unit
of a BS cluster.
