Finally, techniques for interworking and integrating the 5G system with other RATs will be developed.
By taking advantage of multiple RATs, the 5G system will be able to take advantage of the unique characteristics of each RAT and improve the practicality of the system as a whole.
For instance, the 4G system is used for exchanging the control messages to maintain the connection, to perform handover, and to provide real-time services such as VoLTE.
The technology operating in mmWave unlicensed frequency band would support the gigabit data rate service.
Multiple mmWave cells can be overlaid on top of the underlying 4G macro cells, as shown in Figure 18.