Sign in Subscribe

rrc 5g nr

Last updated on 

RRC (Radio Resource Control) is a layer in the 3GPP architecture that handles the control plane signaling between the User Equipment (UE) and the Radio Access Network (RAN), which in 5G is referred to as NR (New Radio).

Let's delve into RRC in the context of 5G NR:

1. RRC States in 5G NR:

RRC in 5G NR has various states, just like in LTE. These states determine the kind of operations the UE can perform.

  • RRC_IDLE: In this state, the UE is not connected to the network. It periodically monitors for any paging messages to see if it needs to go to a connected state.
  • RRC_CONNECTED: This is the state where the UE is connected to the network. Within this state, there are various sub-states like:
    • RRC_CONNECTED_INACTIVE: UE is connected but not actively transmitting/receiving data.
    • RRC_CONNECTED_ACTIVE: UE is actively sending/receiving data.

2. RRC Connection Establishment:

When the UE wants to establish an RRC connection with the network, it goes through the following steps:

  • Random Access Procedure: The UE initiates a random access procedure to get the network's attention.
  • RRC Connection Request: After the random access, the UE sends an RRC connection request to the network.
  • RRC Connection Setup: The network responds with an RRC connection setup message.
  • RRC Connection Reconfiguration: Further configuration may be needed after the connection is established, like adding more bearers or changing the radio resources.

3. RRC Messaging:

RRC messages are used for various purposes, such as:

  • Mobility Management: Handling handovers between cells, cell reselection, etc.
  • Connection Management: Setting up, maintaining, and releasing the RRC connection.
  • Security Control: Initiating security procedures like ciphering and integrity protection.
  • Resource Allocation: Allocating resources for data transfer.

4. RRC Signaling Radio Bearers (SRB):

SRBs are used to carry RRC messages. In 5G NR, there are mainly two types:

  • SRB0: Used for initial RRC connection establishment.
  • SRB1: Used for RRC connection re-establishment, mobility procedures, etc.

5. RRC 5G NR Enhancements:

With 5G NR, there are several enhancements to the RRC layer:

  • Flexible Slot-based Design: 5G NR introduces flexible slot-based designs for efficient resource utilization.
  • Support for Multiple Numerologies: 5G NR supports multiple numerologies, allowing for more flexible subcarrier spacing and hence better support for various services.
  • Enhanced Mobility Support: Better support for high-speed mobility scenarios, like in vehicular communications.