Key Technical Points of 5G Radio Group (RAN4) in Release 18

Release 18 defines the RF performance of 5G-Advanced bands/devices within the RAN working group. RAN4's main work includes:

I. Band/Device RF (Performance) Characteristics: FR1 < 5MHz dedicated spectrum FRMCS migrated from GSM-R.

•  Operating Principle: Coexistence with GSM-R's n100 (1900MHz, 3-5MHz bandwidth) specified ACS/SEM; reduced bandwidth and adjusted power levels for narrowband operation; RRM requirements ensure interference to traditional railways is less than 1%.
•  Progress: European railways lacked NR spectrum during the migration from GSM-R, and the 5MHz minimum bandwidth limitation prevented coexistence. Results: Actual coexistence tests (m28+n100) showed zero interference.

II. RedCap Evolution (positioning via frequency hopping PRS/SRS).

• Operating Principle: The UE with reduced bandwidth (20MHz) uses frequency hopping PRS within a total bandwidth of 100MHz; gNB coordinates the frequency hopping mode; the UE reports the time of arrival (ToA) for each hop, achieving centimeter-level accuracy.
• Progress: Due to the narrow bandwidth, Rel-17 RedCap positioning accuracy is limited to within 10 meters.
• Implementation Results: Positioning accuracy for wearable devices/industrial sensors is less than 1 meter.

III. NTN, Sidelink & ITS include NTN (above 10 GHz), Sidelink, and ITS (Intelligent Transportation Systems) radio frequencies;

• Operating Principle: Ka-band (17-31 GHz) NTN radio frequencies require ±50 kHz Doppler tolerance and 1000 ms propagation delay. UE power level 3 and beam compatibility are mandatory. The channel model includes atmospheric attenuation and rain attenuation.
• Progress: Rel-17 NTN is limited to L/S bands; millimeter-wave satellites are subject to propagation obstruction.
• Implementation Goal: 30 GHz geostationary orbit (GEO) satellite coverage, suitable for backhaul/Internet of Things (IoT).

IV. L1/L2 Mobility, XR KPI RRM includes RRM for L1/L2 mobility and XR KPIs. RRM.

• Operating Principle: RRM specifications for L1-RSRP measurement (delay <2ms) and L2 handover execution (delay <5ms). Interference requirements during multi-TRP operations (ICIC coordination).
• Progress: Lack of RRM specifications for L1/L2 mobility; 30% measurement failure rate under high load.
• Implementation Results: Standardized performance targets for device certification.

V. Smart Repeater Channel Model.

• Operating Principle: Simulates new channel models for base stations, propagation between smart repeaters and UEs, including real reflections, shadows, and Doppler effects. These models capture enhanced beamforming and relay capabilities of smart repeaters in complex urban and indoor scenarios.
• Progress: Existing channel models cannot accurately capture the behavior of smart repeaters, leading to poor design and testing results. The new model accurately predicts performance and validates repeater-assisted coverage extension and capacity enhancement technologies, helping implementers optimize deployment and operation.

VI. RAN4 Application Areas

• Rail Transit Communication (n100) 3-5MHz (for FRMCS coexistence).
• Wearable devices (RedCap centimeter-level positioning).
• Millimeter-wave fixed wireless access (FWA) (71GHz RF specification).

VII. Achievements

• RF Design: UE power level <5MHz (reduced bandwidth filter); test model includes Doppler effect at NTN >10GHz.
• Application Examples: FRMCS verification in the n28 band; gNB/UE meets ACS/SEM limits when operating in parallel with GSM-R at 3MHz NR.