The overall Architecture of 5G RAN or NG-RAN (next generation radio access technology network) is similar to LTE Architecture. However some changes and improvements are introduced.   This article contains the following points:

• 5G RAN architecture and interfaces
• gNB functions
• 5G RAN Split

 

5G RAN architecture and interfaces

  As in each technology standard generation for broadband cellular networks, The Base stations is the main node in the Radio access network. In 5G networks base stations are called as gNBs (Next Generation Node B) to distinguish them from eNBs utilized in LTE.  Another noticeable change is that MME in LTE is replaced by AMF (Access & Mobility Management Functio) and S-GW is replaced by UPF (User Plane Function)  interfaces.    5G is operating currently in two modes, which are non-standalone and standalone mode of operation. For non-standalone operation specification defined the extension for S1 and X2 interfaces whereas for standalone operation new interfaces are defined as following:

• Xn as the Interface between gNBs 
• NG as the Interface between RAN and Core Network 

 

gNB Functions

 

 Similarly to eNBs in LTE, gNBs are network access points that provide coverage for user devices. Some of gNBs functions are:    

• Radio Resource Management (RRM) which includes sub-functions such as radio bearer control, radio admission control, connection mobility control, allocation of resources to UEs in uplink and downlink directions (i.e. scheduling), measurements, and measurement reporting configuration
• Transmission of downlink data toward the UEs and reception of uplink data from the UEs 
• Security functions such as encryption and integrity protection of transferred data 
• Routing and ensuring QoS for user data and control information sent toward the 5GC
• Connection management including connection setup, release, and mobility 
• Broadcasting of system information
• Locating UEs in the radio network by sending paging messages 

   

5G RAN Split

  One of the major changes in the new NG-RAN architecture comparing with the legacy generation is the gNB internal structure split into two parts which are:  

• CU (Central Unit)
• DU (Distributed Unit)

    Central Unit (gNB-CU): a logical node hosting RRC, SDAP and PDCP protocols of the gNB or RRC and PDCP protocols of the en-gNB. it includes the  en-gNB functions like Transfer of user data, Mobility control, Radio access network sharing, Session Management .The gNB-CU  controls the operation of DUs over front-haul and terminates the F1 interface connected with the gNB-DU.   Distributed Unit (gNB-DU): a logical node hosting RLC, MAC and PHY layers of the gNB or en-gNB, and its operation is partly controlled by gNB-CU. It includes a subset of the gNB functions, depending on the functional split option  One gNB-DU supports one or multiple cells. One cell is supported by only one gNB-DU. The gNB-DU terminates the F1 interface connected with the gNB-CU.