3GPP Release 15 - RAN Features

3GPP Release 15 — Detailed Technical Analysis Across RAN Working Groups

3GPP Release 15, finalized in June 2018, marks the first commercial standardization of 5G New Radio (NR). It laid the foundation for 5G networks through Standalone (SA) and Non-Standalone (NSA) modes, introducing a service-based, virtualized core network and new physical-layer technologies for enhanced capacity, latency, and flexibility. Below is a detailed breakdown of RAN1–RAN5 contributions, along with technical insights, implementation aspects, and practical use cases.

RAN1 — Physical Layer Innovations

Focus: Waveform, numerology, multiple access, MIMO, and reference signals.

1. Flexible Numerology and Frame Structure

• Introduced scalable subcarrier spacing:  to support varied latency and frequency ranges (FR1 and FR2).

• Enables both low-latency (<1 ms TTI) and high-throughput applications.

• Implementation: Baseband processing dynamically adapts FFT size and cyclic prefix per numerology.

• Use case: Low-latency industrial control (30 kHz) vs. high-bandwidth mmWave eMBB links (120 kHz).

2. Massive MIMO and Beamforming

• Introduced full-support for 3D beamforming and flexible antenna port mapping (up to 64 TRx elements).

• CSI-RS based channel estimation for user-specific beam management.

• Example: 64T64R gNB arrays form dynamic UE-specific beams, improving spectral efficiency in dense deployments.

3. OFDM-Based Duplexing and Resource Allocation

• Supports both TDD and FDD with unified slot structure.

• Mini-slot transmission (2–7 OFDM symbols) enables immediate data scheduling, key for URLLC.

• Implementation: gNB scheduler dynamically preempts ongoing DL transmissions for URLLC bursts.

4. Reference Signals and Synchronization

• Introduced new signals: SS/PBCH blocks, CSI-RS, PTRS, and SRS.

• SS/PBCH provides initial synchronization and beam discovery.

• CSI-RS used for beam refinement and mobility tracking.

5. Channel Coding Evolution

• LDPC for data channels, replacing Turbo codes for eMBB throughput efficiency.

• Polar codes introduced for control channels (PDCCH, PUCCH) due to short block length performance.

• Use case: High-reliability control signaling in variable data-rate environments.

RAN2 — Radio Interface Protocols (MAC, RLC, PDCP, RRC)

Focus: Radio interface architecture, scheduling, RRC states, bearer setup, and signaling optimization.

1. Dual Connectivity (DC)

• Introduced Master and Secondary gNB architecture, where UE splits traffic between LTE and NR (NSA mode).

• Use case: Enhanced throughput during early 5G rollouts before pure 5G cores (EPC-based EN-DC).

2. RRC_INACTIVE State

• Introduced a new UE state to minimize signaling overhead while maintaining low latency resume.

• Implementation: UE stores RRC context, enabling fast connect (~10 ms) for sporadic traffic.

• Use case: IoT sensors with periodic small data bursts.

3. QoS Flow-Based Architecture

• PDCP restructured into QoS Flow IDs, aligning with 5GC architecture.

• Implementation: Each PDU Session routes through SDAP mapping QoS flows to DRBs.

• Use case: Video streaming with dynamic bitrate adaptation.

4. Header Compression & Security

• Adopted RoHCv2 optimization and enhanced ciphering to reduce control plane overhead.

5. Mobility and Handover Enhancements

• Defined unified inter-RAT handover signaling across LTE–NR (NSA) and NR–NR (SA) networks.

RAN3 — Evolved NG Interface Architecture & Dual Connectivity

Focus: F1, Xn, and NG interface definitions; management of gNB-CU/DU and interoperability.

1. gNB Split Architecture (CU/DU)

• Logical separation between Centralized Unit (CU) and Distributed Unit (DU).

• Implementation: F1-C (control) and F1-U (user) interfaces designed with flexible fronthaul transport.

• Use case: Cloud-RAN and multi-vendor interoperability.

2. NG Interface with 5GC

• Introduced NG-C (control plane) and NG-U (user plane) interfaces, replacing S1 in LTE.

• Supports service-based 5G Core functions via AMF/SMF.

3. EN-DC Architecture

• Defined Xn and S1* signaling for interoperability between eNB and gNB.

• Enables smooth LTE anchor operation during early 5G deployments.

4. Session Continuity and Network Slicing

• Incorporated procedures for inter-slice mobility using QoS continuity.

• Example: A device seamlessly switches between slices (eMBB → URLLC) based on latency demand.

RAN4 — RF and Spectrum Aspects

Focus: Band definition, power levels, spectrum aggregation, and coexistence.

1. New Frequency Ranges (FR1 and FR2)

• FR1: 410 MHz – 7.125 GHz

• FR2: 24.25 – 52.6 GHz (mmWave)

• Implementation: Device RF front-end modular design supports dual range using switchable LNA chains.

2. Bandwidth and Carrier Aggregation

• Defined up to 400 MHz channel bandwidth in FR2.

• Aggregated carriers combine NR and LTE for hybrid deployments.

3. Power Class and EIRP Calibration

• Established UE classes for mmWave devices; introduced stringent EVM and ACLR parameters.

• Use case: Small cells and CPEs using beam-steering for 5G FWA.

4. Coexistence and Emission Control

• Defined spectrum masks ensuring coexistence across multiple RATs.

• Enables NR sharing with LTE or NR-U in unlicensed bands.

5. RF Performance and Reference Sensitivity

• Enhanced base station sensitivity modeling for Massive MIMO arrays.

• Introduced beam-based power control to manage per-beam EIRP.

RAN5 — Device Testing and Conformance

Focus: Conformance, signaling, and UE performance testing procedures.

1. Test Specifications Alignment

• Introduced TS 38.521 / 38.533 / 38.141 for NR UE and base station RF and protocol conformance.

2. OTA (Over-The-Air) Test Framework

• Introduced Anechoic Chamber testing models for mmWave devices, considering beam control and dynamic radiation patterns.

• Example: 5G smartphone characterization with phased-array beam switching validation.

3. End-to-End Signaling Verification

• Verified interoperability of RRC/PDCP/PHY layers, critical for early NSA integrations.

4. Performance Benchmarks

• Defined KPIs for latency, throughput, and reference sensitivity in realistic propagation environments.

Summary of Features in 3GPP Release 15 per RAN WGs

Use Case Mapping by Feature Category

Feature	Technology Layer	Example Use Case
Massive MIMO & Beamforming	RAN1	Stadium coverage with multi-user beam control
RRC_INACTIVE State	RAN2	Smart sensors with low-power on-demand connectivity
gNB-CU/DU Split	RAN3	Cloud RAN architecture deployment
Carrier Aggregation	RAN4	5G-NSA combining LTE@Sub-6GHz + NR@mmWave
OTA Beam Testing	RAN5	Smartphone mmWave certification in labs

Summary

Release 15 forms the bedrock of 5G Phase 1, defining the NR physical layer, new radio protocols, flexible architecture, and RF/conformance aspects. It enables key 5G services — eMBB, URLLC, and mMTC — across a unified architecture supporting both NSA and SA modes. Future releases (Rel-16 onward) expand on these foundations with V2X, sidelink enhancements, and native AI/ML-driven optimizations.

References

1. https://www.etsi.org/deliver/etsi_ts/138200_138299/138201/15.00.00_60/ts_138201v150000p.pdf

2. https://www.etsi.org/deliver/etsi_ts/138300_138399/138300/15.15.00_60/ts_138300v151500p.pdf

3. https://www.telit.com/blog/whats-in-3gpp-release-15-5g-standard-lte-improvement/

4. https://www.techplayon.com/3gpp-release-15/