# 3 GPP Evolution from 5G to 6G: A 10-Year Retrospective
## 5 3 GPP Release 18: Dawn of 5G-Advanced
### Enhancements to Existing Features  
The MIMO evolution in Release 18 focused on enhancing performance to address deficiencies in signaling latency, overheads, spectral efficiency, and coverage. Key improvements included multi-TRP support, enhanced codebooks, and expanded spatial multiplexing capabilities. Multi-TRP support extended the unified TCI framework to allow simultaneous communication with multiple TRPs, optimizing beam indication and timing advance adjustments. The enhancements facilitated efficient resource allocation and dynamic TRP switching. Enhanced codebooks supported an increased number of ports,  
Figure 4: An illustration of 5G NTN architecture. coherent joint transmission, and dynamic TRP selection. This improved multi-user MIMO performance, especially for high/medium-speed scenarios. For spatial multiplexing, enhanced DMRS configurations doubled the number of orthogonal ports for both uplink and downlink, increasing multi-user MIMO scheduling capacity. Uplink capabilities supported up to eight transmission layers with advanced codebook and non-codebook options for high-end UEs, e.g., customer premises equipment and industrial devices. In Release 18, further NR coverage enhancements built on Release-17 efforts to address remaining coverage challenges for bottleneck channels, introducing improvements in PRACH coverage and dynamic waveform switching, among others. PRACH coverage enhancements included support for repetitions in the four-step RACH procedure, enabling UEs to dynamically adjust repetition numbers based on synchronization signal block (SSB) reference-signal-received power thresholds. Dynamic waveform switching between DFT-s-OFDM and CP-OFDM was enabled, allowing networks to optimize waveforms dynamically for coverage or capacity without requiring RRC reconfiguration. NR mobility enhancements in Release 19 focused on reducing latency, enhancing reliability, and optimizing inter-cell and DC transitions. Key advancements included layer 1/layer2 triggered mobility (LTM) with low-latency procedures, selective activation of cell groups in NR-DC, and CHO enhancements. Figure 5 provides an illustration which compares LTM to conventional layer 3-based mobility. Furthermore, new Release-17 configurations enabled RACH-less mobility, early timing acquisition, and efficient cell reselection using idle/inactive mode measurement results. Enhanced CHO mechanisms supported simultaneous primary cell (PCell) and primary secondary cell (PSCell) evaluation. Release 18 introduced further advancements in NR sidelink, enhancing its applications for V2X communication. Among the key enhancements was the introduction of CA in the ITS spectrum. Packet duplication ensured robust transmissions across aggregated carriers, benefiting both in-coverage and out-of-coverage UEs. NR sidelink was also extended to operate in unlicensed spectrum bands. Advanced channel access mechanisms were adopted, along with multi-channel access procedures. These advancements facilitated reliable communication in the unlicensed spectrum while maintaining compatibility with existing sidelink operations. Release 18 also addressed LTE-NR sidelink coexistence in the 5.9 GHz spectrum, enabling dynamic resource-sharing between LTE and NR sidelink. Figure 5: An illustration of layer 3 based mobility vs. LTM. Relay capabilities were enhanced to extend connectivity and service continuity. Single-hop UE-to-UE and UE-to-network relay support expanded coverage for out-of-coverage scenarios. Multi-path relay functionality enabled UEs to communicate simultaneously over direct and indirect paths. Another major enhancement area in Release 18 was NR positioning, introducing new features for sidelink positioning. The work also introduced carrier phase positioning for centimeter-level precision, utilizing carrier phase measurements for both downlink and uplink methods. Further enhancements addressed RedCap UEs, incorporating frequency hopping for wider bandwidth measurements.