Key Technical Points of 5G Radio Group (RAN5) in Rel-18

RAN5 is the User Equipment (UE) Conformance Test Group. Its goal is to establish UE conformance test specifications on the radio interface based on 3GPP core specifications, covering 2G, 3G, 4G, 5G, and future technologies. The test specifications established in Rel-18 include:

I. AI/ML Model and Mobile IAB Conformance (Testing)

• Working Principle: TTCN-3 test cases verify MT handover (no-service UE disconnection), NCGI reallocation timing (<50ms), and topology change signaling. Simulates multi-layer backhaul link trees.
• Problem Solving: Lack of standardized test framework; operators' refusal to deploy mobile IAB.
• Result: The first Anritsu/Keysight test suites were certified (December 2024).

II. XR QoE KPI, L1/L2 Mobility (Testing)

• Working Principle: Test cases simulate 6DoF motion patterns, measuring attitude prediction accuracy (<2cm), rendering latency (<20ms), and motion sickness probability. Verify multi-sensor QoS prioritization under congestion conditions.
• Problem Solved: Lack of standardized XR KPIs; inconsistent performance metrics claimed by vendors. Result: Universal pass/fail criteria for XR certification.

III. NTN/RedCap Positioning, FRMCS Radio Frequency (Test)

• Operating Principle: Channel simulator simulates 1500km geosynchronous delay, ±30kHz Doppler shift. RedCap testing verifies 20MHz bandwidth positioning (accuracy <1 meter); FRMCS verifies coexistence of ACS/SEM and GSM-R in 3MHz bandwidth.
• Problem Solved: Lack of testing infrastructure for new vertical industries/devices. Result: First batch of NTN-certified smartphones, RedCap wearables (Q1 2025).

IV. MBS Inactive State, Time Flexibility Verification

• Operating Principle: Verify inactive UEs joining/leaving MBS sessions without RRC conversion. Test HARQ merging (multicast + unicast), group key processing, and session inter-cell mobility.
• Issue resolved: Rel-17MBS testing only covered the RRC_CONNECTED state. Result: Battery-optimized multicast has been validated for stadiums/IoT.

V. RAN5 Test Applications

• Vendor Certification (Anritsu/TTCN-3 AI CSI Test Kit).
• Carrier IoT (Mobile IAB Topology Testing).

VI. RAN5 Test Practice

• Test Platform: Updated TS 38.523/38.533 to support L1 mobility (e.g., CHO triggering on L1-RSRP).
• Example: Mobile IAB test case uses the Spirent emulator to verify that no serving UE drops during MT handover.