Deploying 5G introduces both similarities and key differences compared to LTE protocols. The typical OSI layers and 5G New Radio (NR) protocols on the air interface are particularly relevant for Stand-alone (SA) Architecture. So, now let us see what sets 5G NR protocols apart along with Reliable Best wireless site survey software, site survey tools for wireless networks & Indoor cellular coverage walk testing tool and Reliable LTE RF drive test tools in telecom & RF drive test software in telecom in detail.
In the Control Plane stack for NR, no changes have been made compared to LTE. However, the User Plane stack for NR introduces the Service Data Adaption Protocol (SDAP) layer on top of the Packet Data Convergence Protocol (PDCP). SDAP manages QoS Flow and Bearer mapping, marking QoS Flow IDs for downlink (DL) and uplink (UL) packets.
Enhanced Layer 2 Data Flow
In Layer 2, 5G NR supports multiple IP flows within a single Radio Bearer. A new MAC PDU format enables MAC/PHY parallel processing, an improvement over LTE’s MAC PDU format, which does not facilitate this parallel processing. Despite these improvements, Carrier Aggregation in NR remains unchanged from LTE, except for the addition of the SDAP layer. Channel Access control and System information are specific to the Stand-alone option.
NR Principles for Access
NG-RAN in 5G supports various overload and access control functions such as RACH back-off, RRC Connection Reject, RRC Connection Release, and UE-based access barring mechanisms. A unified access-barring mechanism for NR addresses all use cases and scenarios that E-UTRA managed with specialized tools. Each access attempt falls into one of the Access Categories specified in 3GPP TS 22.261. In the RRC_IDLE state, the UE NAS informs RRC of the access category, and the Connection Request includes data to help the gNB decide whether to reject the request.
Improved System Information Delivery in NR
In 5G NR, only a minimal set of System Information Blocks (SIBs) is broadcast, similar to the Master Information Block (MIB) and SIB1. Additional SIBs can be requested by the UE via on-demand broadcast or dedicated signalling.
Mobility States and Characteristics
In RRC_IDLE, 5G NR employs the 3GPP PLMN Selection principle. The cell selection process includes both initial and stored cell selection, akin to LTE. In cell reselection, intra-frequency selection is based on cell ranking, while inter-frequency selection is based on absolute priorities. The serving cell can provide a Neighbour Cell List (NCL) or blacklist. Cell reselection is speed-dependent and service-based.
RRC_INACTIVE State
In RRC_INACTIVE, the UE remains in CM-CONNECTED mode, using cell reselection. The last serving gNB retains the UE context, allowing the UE to move freely within the RNA without updating the gNB. The gNB pages the UE within the RNA, prompting the UE to initiate the RNA update procedure upon an RNA change.
RRC_CONNECTED State
Network-controlled mobility applies to UEs with two types of mobility: cell-level mobility using RRC signalling (e.g., handovers) and beam-level mobility, which does not require explicit RRC signalling and is managed at lower layers. For intra-NR, “make-before-break handover” is used without involving the 5G core. UE measurements and reporting for Radio Resource Management (RRM) include beam measurements.
Random Access Procedure
Several events can trigger the random-access procedure, including initial access from RRC_IDLE, RRC Connection Re-establishment, handover, transition from RRC_INACTIVE, requests for other SIBs, and DL or UL data arrival during RRC_CONNECTED when UL synchronization is not maintained.
In contention-based random access, the UE sends a random-access preamble, to which the gNB responds with a random-access response.
NG-RAN QoS Concept
NG-RAN maps packets from different PDU sessions to different DRBs, ensuring at least one default DRB for each session. NG-RAN is responsible for mapping multiple QoS flows to a DRB within each PDU session, with uplink QoS flow to DRB mapping supported by reflective QoS (mirroring downlink marking) or explicit RAN configuration.
Voice Support in NR
While the initial focus was on Non-Stand Alone (NSA) mode, voice support via NR is particularly relevant for 5G Stand Alone (SA) mode. In NSA architecture, IMS voice/VoLTE operates on LTE radio without changes compared to LTE-only option 1. As operators migrate to option 2 for commercial 5G deployments, end-to-end IMS voice support over the 5G core and NR will be defined for SA mode, inheriting functions like SPS from LTE.
Public Warning Services (PWS)
Different SIBs are defined for ETWS primary and secondary notifications, and CMAS notifications. Paging informs UEs about ETWS and CMAS indications, with UEs monitoring these indications during their paging occasions in RRC_IDLE and RRC_INACTIVE states. UEs also monitor indications during any paging occasion in RRC_CONNECTED.
Emergency Calls
From 3GPP Release 15, 5G NR supports emergency calls, essential due to regulatory requirements like those from the FCC in the USA (50m accuracy) and cell ID requirements in the EU.
Enhanced/Precise Positioning in Release 16
Release 15 supports positioning to meet regulatory requirements for emergency calls. Release 16 adds precise positioning via RTK correction information and SIB/multicast/dedicated provisioning. Network-based positioning for NR relies on smaller cells and massive MIMO with beamforming.
New Principles for UE Capabilities
UE capabilities no longer rely on categories, with the network calculating the maximum supported data rate based on capabilities and formulas. Data rates may be signalled for UEs unable to support the maximum data rate. LTE optimizations for acquiring band combination information have been introduced to reduce capability signalling. A temporary capability restriction request can be sent by the UE to signal limited availability of some capabilities, controlled by the network.
NR URLLC Support
Ultra-Reliable Low-Latency Communications (URLLC) support in NR is crucial for minimizing delays while ensuring high service reliability. In NR, RLC retransmission (ARQ) is not assumed, meeting strict latency requirements for URLLC applications. Packet duplication applies in multi-connectivity and carrier aggregation scenarios. PDCP-level packet duplication, configured via RRC, can be used for both SRB and DRBs. Also read similar articles from here.
