5G NR Split Bearer: Functions and Concepts Explained

This page explains the basics of 5G NR Split Bearer. It also covers the functions of split bearers in 5G NR and LTE systems when operating in DC (Dual Connectivity) mode.

Before we dive into split bearers, let’s clarify some key terms related to Dual Connectivity (DC).

• DC (Dual Connectivity): A technology that achieves wider bandwidths by connecting a user device (UE) to two base stations in a master/secondary setup. This allows the UE to transmit and receive data using multiple component carriers (CCs) supported by both base stations. In essence, it’s like having two connections to the network at the same time!

• Base Station: A radio transceiver that serves as the access point for wireless communication. In LTE, the base station is known as an eNB, while in 5G NR (New Radio), it’s called a gNB.

• Carrier: A radio signal that’s modulated to carry information. Think of it as the “frequency lane” on which data travels.

• Split Bearer: In DC, a bearer (a logical connection for data transfer) that is transmitted and received via both the master and secondary base stations. This allows for increased throughput and redundancy.

• MN (Master Node): In DC, the base station that establishes the initial RRC (Radio Resource Control) connection with the UE. In LTE-NR DC, this could be either the LTE base station (eNB) or the NR base station (gNB).

• MCG (Master Cell Group): The set of serving cells controlled by the Master Node.

• SCG (Secondary Cell Group): The set of serving cells controlled by the Secondary Node.

• CN (Core Network): The central part of the mobile network that handles functions like authentication, mobility management, and connecting to the internet.

• UE (User Equipment): The mobile device, such as a smartphone or tablet, used by the end user.

• SN (Secondary Node): The base station that provides additional radio resources to the UE in DC mode, under the control of the Master Node.

• C-Plane (Control Plane): The part of the network that carries signaling information, such as commands and control messages.

• U-Plane (User Plane): The part of the network that carries the actual user data, like voice calls, video streams, and web browsing traffic.

LTE NR DC Split Bearers

• LTE DC (Release 12) specifies MCG Split Bearer to achieve high throughput. In this setup, the Master Node (MN) acts as the splitting point. Downlink data from the Core Network (CN) destined for the UE can be transferred in two ways:

  1. Directly through the MN’s carrier.
  2. Initially transmitted to the Secondary Node (SN) via the X2 interface, and then transmitted to the UE via the SN’s carrier. The X2 interface is a direct connection between the eNB and gNB, allowing for fast data transfer.

• In SCG Split Bearer, the user data splitting point is configured at the SN. This means the Secondary Node is responsible for deciding how to split and route the data to the UE.

References

• 3GPP standards for 5G NR (New Radio) 38 series