UDN is the key technology for 5 G. 5 G UDN also make 5 G satisfy the future 1 000 times traf? c growth. With the deployment of a large number of low-power stations

the interference and frequent switching problems caused by the smaller distance between stations have affected the user experience. And these large number of low-power station needs a lot of transmission resources. This paper focuses on the key technologies to solve these problems: virtual cell

dual connection

CoMP

wireless backhaul. This paper also has discussed the way of network architecture of 5 G UND.