# 3 GPP Evolution from 5G to 6G: A 10-Year Retrospective
## 3 3 GPP Release 16: First 5G Upgrade
### New Features  
The industrial IoT emerged as a key vertical supported by Release 16 [43]. Expanding on Release 15's capabilities, Release 16 introduced mechanisms to achieve URLLC for factory automation, energy distribution, and remote industrial applications [44]. Features like uplink preemption allowed higher-priority transmissions to override lower-priority ones in real-time, optimizing latency-sensitive operations. Enhanced collision resolution techniques improved resource efficiency by intelligently handling conflicts between multiple uplink transmissions, ensuring the seamless integration of diverse traffic flows. Time-sensitive networking (TSN) was a notable addition for industrial use cases, providing precise synchronization and the prioritization of traffic flows. These enhancements collectively enabled NR to meet the demands of industrial automation, ensuring reliability and efficiency for mission-critical applications.  
Another significant advancement was NR's capability to operate in the unlicensed spectrum, building on the legacy of LTE's licensed assisted access (LAA) [45]. Unlike LTE-LAA, Release 16 enabled standalone operation in unlicensed bands, including the newly allocated 6 GHz spectrum. This functionality enhanced deployment flexibility and increased data rates, using mechanisms such as listen-before-talk (LBT) to ensure harmonious coexistence with other wireless technologies [46].  
Intelligent transportation system (ITS) and V2X communication also benefited from Release 16's innovations [47; 48]. With sidelink communication as a core component, Release 16 NR supported unicast, groupcast, and broadcast transmissions tailored to ITS applications [49; 50]. These enhancements addressed advanced use cases such as vehicle platooning, cooperative lane merging, and remote driving. The integration of robust QoS frameworks ensured that these applications operate reliably under diverse conditions.  
Accurate positioning capabilities are increasingly essential, especially for indoor applications and emergency services [51]. Figure 3 provides an illustration of the 5G NR positioning framework, where LTE positioning protocol (LPP) is used between UE and location management function (LMF) and NR positioning protocol A (NRPPa) is used between NG-RAN node and LMF [52]. Release 16 introduced advanced positioning methods that complemented traditional global navigation satellite systems (GNSS) [53]. The new positioning reference signal (PRS) allowed for improved time-of-arrival estimation, enabling precise positioning, even in challenging environments. Uplink-based positioning enhancements leveraged extended sounding reference signal (SRS) and beamforming to increase accuracy and range.  
Release 16 introduced IAB, which allows nodes to serve as both access points and backhaul units [54]. This feature enabled 5G NR to use wireless backhaul as an alternative to traditional fiber links, simplifying the deployment of small cells in dense urban areas and temporary event settings. Operating efficiently in TDD mode and leveraging  
Figure 3: An illustration of 5G NR positioning framework.  
mmWave bands, IAB facilitates both in-band and out-of-band operations to optimize network architecture and performance [55; 56].  
Lastly, following a comprehensive study on non-orthogonal multiple access (NOMA) [57], 3 GPP conducted minimal normative work on the 2-step random access channel (RACH). The 2-step RACH procedure consists of two steps: in message A, the UE transmits a preamble combined with its initial uplink data in a single transmission and in message B, the gNB responds with a combined random-access response and contention resolution message, which includes information about resource allocation and acknowledgment of the UE's request [58]. Though 2-step RACH has the potential of latency reduction, it is faced with implementation complexity.