Evolution say 5G base station architecture, we have to mention the CU and DU separate things. 
CU stands Centralized Unit, is the concentration unit;
DU stands for Distributed Unit, that is, the distribution unit.
Why CU and DU to be separated?
CU and CU separated in the end what are the benefits?
Now 5G base station deployments are based on CU and DU separation architecture do?
First, why CU and DU to be separated?
Let's look at the architecture and 4G wireless access network part 5G any different: 
As can be seen from the figure, the base station is divided into an internal 4G BBU, RRU and the antenna several modules, each base station has a set of the BBU, and by BBU directly connected to the core network.
By the age 5G, the original merged into AAUs RRU and the antenna, and the BBU is split into the CU and DU, DU has a set of each station, then multiple sites with common centralized management of a CU.
It can be seen in the architecture and 2G / 3G infrastructure 5G exactly the same way!