5G Stuff: Cell topology and CN-RAN connection in 5G NR

Like in earlier cellular technologies, 5G is also assumed to support the following cell layouts

 - Homogeneous, where all cells provide similar coverage and these can be macro or small cells

 - Heterogeneous, where cells can be of different sizes and may be overlapped, like macro and small cells

Depends on the operator requirements, one of the above can be used while deploying 5G NR along with LTE.

As one option, both LTE and 5G NR cells are over-laid and co-located to provide the same coverage. In this case, all cells are in homogeneous layout and the eNodeBs co-located.

In another case, due to LTE co-existence various combinations are to be considered:
     
        - both LTE and 5G NR cells co-located and overlaid
        - both LTE and 5G NR cells non co-located and overlaid

For ex: when LTE is used to serve as macro, 5G NR can be used as small.

If needed, 5G NR is used to serve as macro and LTE can be used as small.

Depends on the deployment scenarios following CN-RAN connections are possible

1. NR gNB as master node and is connected  to NextGen Core
         - Standalone NR gNB deployment
         - NR gNB (macro cell) is also connected to eLTE eNB (small cell and only User plane is connected to NextGen Core) to support Data flow aggregation
         - NR gNB (macro cell) is also connected to another NR gNB (small cell and only User plane is connected to NextGen Core) to support Data flow aggregation

2. eNB as master node and connected to EPC
         - LTE eNB (macro cell) is also connected to NR gNB (small cell and only User plane is connected to EPC) to support Data flow aggregation

3. LTE eNB as master node and is connected to NextGen Core
         - Standalone eLTE eNB is connected to NextGen Core
         - LTE eNB (macro cell) is also connected to NR gNB (small cell and only User plane is connected to NextGen Core) to support Data flow aggregation

4. Mobility between 5G NR and LTE system
        - eLTE eNB is connected to EPC and 5G NR gNB is interfaced to NextGenCore. Here EPC and NextGen Core may be connected (For Further Study - FFS?)
        - eLTE eNB and NR gNB are connected to NextGen Core

5. WLAN integration
        - WLAN interworking with NR via NextGen Core

        - WLAN aggregation with NR via NextGen Core

        

More details can be found in 3GPP TR38.804 V14.0, 4.1.2/4.1.3