## 6 Mobile Networks
### Evolution Toward 6G  
Currently, with 5G commercial networks already being deployed, both industry and academia are already starting to work on the definitions and capabilities to be offered by 6 GS. The major 6G Flagship project [129], coordinated by the University of Oulu, has already been launched. Its primary goals revolve around the work on key 6G technology enablers, the deployment of the nationwide testbed, the trialing of demanding verticalapplications, and the pioneering development of the 6 GS vision based on the recent market and technological trends. The early concepts envision the process of evolution from 5G to 6G as a transition from \"connected things\" to \"connected intelligence\" due to the deep integration of AI in the network, accompanied by global connectivity and support for larger numbers of devices. The expected key capabilities of 6G include [130]:  
* _Increased performance_--Operation in a higher-frequency spectrum in sub-THz (cf. Figure 1) and potentially THz bands, together with enhancements of the resource scheduling mechanisms, will enable the provisioning of data rates of up to 1 Tbps [131] to network users. Moreover, due to the projected technological improvements, 6 GS will target latencies below 1 ms in CP and below 0.1 ms in UP [131], exceptional reliability (frame error rate below \(10^{-9}\)), and 10\(\times\) higher spectrum efficiency than in 5 GS (capacity growth) [132]. * _Ubiquitous availability_--6 GS is envisioned to support worldwide service availability by tight integration with NTN (satellite systems, airborne platforms, etc.) and support for nomadic cells. The currently ongoing standardization efforts regarding the integration of 5 GS with NTN systems (focus on architectural design and coverage and availability extension) are considered to be the initial step in unleashing the full potential of the unified terrestrial and satellite ecosystem [133]. * _Robust communication_--Highly flexible, coherent, and ultra-reliable services will be facilitated by a newly redesigned CN that will be built according to \"software-only\" paradigms. The new approach will contribute to the aspects of network scalability and mobility support by adapting cloud-native service state sharing and migration. * _Heterogeneity of infrastructure owners_--The improved security and trust mechanisms with support for deterministic QoS and governance in multi-administrated environments are expected to facilitate network deployments on multiple administrative domains. This will allow for capitalizing on the cloud and edge infrastructure providers, leveraging the availability of network services. * _Sustainability_--By exploiting AI-driven optimization techniques and reducing network overhead, the reduction of the carbon footprint of mobile networks both on the network side and the UE side is planned. * _Ultra-precise positioning_--Due to the operation in higher THz bands, 6G-based localization techniques will enable finer spatial and temporal resolution. Moreover, it is expected that RAN nodes will support ultra-massive MIMO that can also contribute to finer angular resolution in Angle of Arrival (AoA) localization methods. Altogether, a precision of 1 cm in 3D is targeted as an ultimate goal. * _Support for a very large number of devices_--The adoption of advanced RAN mechanisms, such as massive MIMO, as well as complete RAN reorganization toward cell-free networks, is expected to allow a supporting device density of up to 100/m\({}^{3}\)[134]. Moreover, solutions that support low-energy or battery-free IoT devices are planned to be incorporated such as Intelligent Reflective Surface (IRS)--a massive number of reflecting elements that allow for the achievement of high passive beamforming gains [135]. * _Advanced cognitive insight_--The adoption of AI-based mechanisms, enhanced localization, and sensing will allow for more accurate predictions regarding UEs and network events.