# 3 GPP Evolution from 5G to 6G: A 10-Year Retrospective
## 5 3 GPP Release 18: Dawn of 5G-Advanced
### New Features  
The NR network energy savings enhancements introduced in Release 18 aimed to reduce environmental impact and operational costs by optimizing energy consumption in 5G networks [68]. Key features included CSI enhancements for spatial and power domain adaptations, cell discontinuous transmission (DTX)/DRX mechanisms enabling periodic active and inactive periods for gNB, and SSB-less SCell operation for inter-band CA [69]. A barring mechanism was introduced to prevent legacy UEs from camping on cells using energy-saving techniques. Inter-node beam activation facilitated selective SSB beam switching and enhanced paging optimized beam usage for stationary UEs, improving network energy efficiency. XR enhancements in Release 18 focused on improving awareness, power saving, and capacity to better support XR services [70]. For XR awareness, the enhancements included improved uplink scheduling through additional buffer size tables, delay status reports, and uplink assistance information (e.g., jitter, burst arrival, and periodicity) reporting per QoS flow. For power saving, gNBs can configure DRX cycles aligned with video frame rates (e.g., 30, 60 frames per second) and enable configured grants without monitoring uplink retransmissions [71]. For capacity, enhancements included multiple configured grant PUSCH transmission occasions within a single period and signaling unused configured grant PUSCH occasions via uplink control information. The protocol data unit (PDU) set based discard mechanisms that enabled efficient packet handling, discarding redundant PDUs when no longer needed. In congestion scenarios, PDU importance can dictate discard prioritization, with shorter discard timers for lower-priority service data units. The Release-18 work on AI/ML for NG-RAN enhanced data collection and signaling within NG-RAN to support AI/ML-based functions, including network energy saving, load balancing, and mobility optimization [72; 73]. It introduced signaling procedures for data exchange, enabling AI/ML model training and inference in either NG-RAN nodes or operation, administration, and management (OAM) systems. For energy saving, AI/ML optimized cell/node activation to reduce consumption, utilizing an \"energy cost\" metric. Load balancing leveraged AI/ML predictions and feedback to distribute traffic efficiently across cells. Mobility optimization improved handover success by using UE trajectory predictions and measuring trajectory feedback. In-device coexistence enhancements address internal interference within UEs between a 3 GPP RAT and other RATs, like WiFi, Bluetooth, and ultra-wideband (UWB) [74]. The Release-18 work introduced frequency division multiplexing (FDM), time division multiplexing (TDM), and autonomous denial solutions to mitigate interference between NR and other RATs within UEs. The FDM solution allowed UEs to report affected NR frequencies. The TDM solution enabled UEs to propose preferred active durations and cycles for affected frequencies, optimizing scheduling to minimize conflicts. The autonomous denial solution allowed UEs to selectively deny uplink transmissions within limits. Release 18 enhanced NR support for uncrewed aerial vehicles (UAVs), building on previous LTE-based solutions [75; 76]. These enhancements addressed UAV-specific requirements, such as low latency for control, high data rates for multimedia, and interference management to protect terrestrial networks. Key features included altitude reporting,altitude-dependent event triggers for interference reporting, and improved flight path reporting with dynamic updates. NR also introduced 'broadcast remote identification' and 'detect and avoid' using sidelink, aerial-specific out-of-band emission compliance, and subscription-based aerial UE identification. Air-to-ground (ATG) networks enabled in-flight connectivity using ground-based cell towers to communicate with ATG terminals mounted on aircraft [77]. The Release-18 work focused on adjacent channel coexistence, RF requirements, and RRM for ATG deployment.