  More and more scholars focus on mobile edge computing (MEC) technology,
because the strong storage and computing capabilities of MEC servers can reduce
the long transmission delay, bandwidth waste, energy consumption, and privacy
leaks in the data transmission process. In this paper, we study the cache
placement problem to determine how to cache videos and which videos to be
cached in a mobile edge computing system. First, we derive the video request
probability by taking into account video popularity, user preference and the
characteristic of video representations. Second, based on the acquired request
probability, we formulate a cache placement problem with the objective to
maximize the cache hit ratio subject to the storage capacity constraints.
Finally, in order to solve the formulated problem, we transform it into a
grouping knapsack problem and develop a dynamic programming algorithm to obtain
the optimal caching strategy. Simulation results show that the proposed
algorithm can greatly improve the cache hit ratio.
