Introduction
To provide true 5G service to users, 5G cells will be deployed with full coverage and UE (User Equipment) will be able to connect to 5G network everywhere. However, in the early stage of 5G services, the 5G cells will be partially deployed and there will be 5G coverage holes. The initial 5G commercial service will be launched from early 2019, but the initial investment for 5G service will be limited because of a lack of 5G UE. So, the 5G network needs to be interworked with the existing LTE network. The interworking solution can provide seamless service to users. This white paper introduces the solutions for 4G-5G interworking and compares the solutions in terms of performance, the features and the migration to a true 5G service network.