In this section we briefly outline the key drivers for the Campus Network evolution towards 6G.
3.4.1 Nomadic 5G networks
We have illustrated before, that there is a growing demand for nomadic networks. However, the deployment of nomadic, autonomous 5G networks, with variable time constraints at diverse locations, raises several challenges. First, frequencies used for the ad-hoc deployment will have to be allocated on-demand and potentially only for a short time. Schemes like dynamic frequency allocation or continuous spectrum trading need to reach maturity, to reliably enable use cases such as 5G networks for construction sites, or autonomous nomadic networks for first responders. In particular, the latter raises additional challenges: the unpredictable radio propagation characteristics of the target environment, which may be circumvented by supporting a variety of nomadic antenna systems ranging from traditional telescope antenna poll deployments up to tethered drones acting as flying base stations being close to the end users thus reducing radio attenuation. Especially drones yield to the research aspect of building 5G campus networks utilizing non-terrestrial network elements for hosting elements of the network core, radio units, or just acting as backhaul connectivity. Thus, nomadic 5G networks will evolve and merge with non-terrestrial network (NTN) architectures. All those aspects are addressed by ongoing lighthouse research projects of FOKUS [43
3.4.3 Evolution towards 6G
Nowadays, 6G is hyped and politically motivated to stipulate digital sovereignty for future telecommunication systems. From a technological perspective, future developments will rather be an evolution of 5G, which is also driven through innovations enabled by the flexible network architectures of 5G campus networks. Use cases driving 6G and the underlying technology, as looked at by current 6G light house projects, underline this [45
As such, the 6G evolution will be driven by private campus networks; their geographically limited extension will make them a key candidate for utilizing micro-cellular infrastructures as provided by THz spectrum. Also, they will push and benefit from novel agile software architectures natively incorporating AI and ML for network optimization, operation, and even dynamic autonomous deployments [48
]. With that, campus networks drive the revolutionary evolution towards beyond 5G and 6G networks, and thereby push the sustainability and network resilience goals as recently outlined by the German government [7
There is no doubt, that campus networks are considered internationally as innovation drivers for 5G towards 6G, as they provide a means to implement innovative features needed by different verticals. Many white papers published in the last 2–3 years, which use synonymous terms, like private/mobile/enterprise networks or non-public networks, provide evidence for this trend. It is worth looking at the major innovation spots addressed by 5G campus network research and development projects and to compare these with current 6G research topics as listed in Table 3
. Note that this table is not aiming for completeness but meant only to highlight important trends.
Comparison of 5G campus networks research and potential 6G innovations
THz and Optical Wireless
Positioning and Sensing
Holistic/scheduled network management
The drivers for higher frequencies are spectrum shortages in lower spectra around the globe and increased capacity requirements. When it comes to the 5G spectrum, we have witnessed the rise of mmWave [50
] in recent years and current campus frequencies in 26 GHz are also becoming available in this context [12
In 6G we can observe that (sub)terahertz spectrum is considered a key architectural driver and enabler for new features, such as joint communications and sensing [51
]. Another promising type of wireless communication is based on visible light spectrum. While promising high data rates, THz and visible light communication (VLC) are particularly promising for indoor and privacy aware controlled environments such as campus networks.
Joint communication and sensing
The ability to combine telecommunications with sensing capabilities to simultaneously exchange information and observe the environment has seen increased interest in research towards future wireless networks. Localization and positioning, for example, are key capabilities in industrial 5G use cases and we can witness a high demand for appropriate solutions in automation and intra-logistics campus networks [52
As mentioned above, 6G terahertz research is specifically going beyond positioning and extending towards utilizing the 6G RAN as a sensor. The resulting information can be collected and aggregated to create digital twins of networks and their environment, giving rise to new opportunities for management of radio resources and localization and positioning of end devices. Campus networks can make use of these added features for improvements in regards to surveillance and operational safety.
Software-based network principles have been all around us for two decades and 5G is the first real global implementation of a softwarized mobile wireless network. The 3GPP SBA provided the opportunity for cloud-native and micro service type implementations of the core network architecture. In the future telecommunications networks like the 6G mobile network will have to further evolve this software-based approach to incorporate modern development techniques such as DevOps and CI/CD. The components of networks will be constantly updated, fixed and improved as vendors continuously develop them. This trend will require vendors and operators to embrace open source software and communities, as they play a key role in this environment.
Network Function Virtualization (NFV) has been introduced with 3G and 4G already for IP Multimedia Subsystem (IMS) and Evolved Packet Core (EPC), driven by the exploitation of cloud computing principles. In addition to the rise of edge computing, in order to combine the cloud computing benefits with local requirements for privacy and low latency communications, NFV has become a key design principle for 5G [16
] and also provides scalability and redundancy.
As virtualization technology has evolved in the recent years, so-called cloud native software design principles emerged. From virtual machines to containers and serverless computing as well as function as a service (FaaS), service design needs to consider the virtualization of the infrastructure, to fully take advantage of it. Micro services are examples of the resulting architectures. The 6G network has to continue in this direction to reach the point of infrastructure-less networking. Particularly 6G campus networks should be able to operate in diverse deployment scenarios, which may include infrastructure-less segments or complete networks.
Disaggregation and aggregation
Although we have already witnessed the disaggregation of the key core network functionalities in 3GPP Rel. 16 with the introduction of the SBA [19
], it was mainly the rise of ORAN and the more generalized Open RAN concept three years ago, which sparked the global trend towards open and customizable 5G networks, in which operators of network infrastructures will have the freedom to choose their network components from different vendors and aggregate and particularly disaggregate their network functions in a plug and play mode. Obviously, this requires the proper identification of an appropriate functional split and corresponding industry wide standards for the interfaces identified [16
Whereas the Open RAN concept was invented by global network operators with the intent of lowering the costs of 4G/5G wide area networks through increased competition, nowadays the concept is considered key for building up economically highly customized campus networks and also to drive innovations in 5G [7
While it will probably take quite some time to establish an open network ecosystem based on Open RAN and to adopt these principles in existing networks, the concept in principle is guiding the way 6G architectures will look like. In particular we assume a higher degree of “RAN-Core” convergence in which former authentication, QoS and mobility management functionalities of the core network might be partially integrated as x/rApps in an Open RAN Radio Intelligent Controller (RIC), or functionalities of the Open RAN might be integrated in an extended core network architecture. Therefore, the 6G architecture is considered as a highly modular and agile system, which the authors refer to as “organic” [54
The automation of network management has a long tradition, since the use of expert systems has been considered to assist the human operator some 30–40 years ago. The rise and corresponding hype around artificial intelligence (AI) and machine learning (ML) has led to the concept of zero touch management. In principle, AI/ML have traditionally been utilized for fault/performance/security management and network optimization. More recently, it has been considered to let them take an active part in network control, e.g., the real time RIC within Open RAN or the Network Data Analytics Function (NWDAF) within the SBA [19
There is no doubt, that the operators of campus networks in particular, would benefit from these solutions, as they might lack the operational experience. But, we also have to acknowledge the additional reliability, availability, and resilience requirements of campus networks [55
Early 6G architectures propose supporting AI/ML “by design”, thus representing integral ingredients of future 6G networks. The idea of AI native networks includes intelligence as a service as well as AI/ML based or assisted management and orchestration [56
Universal access through NTN
Universal access to mobile networks is considered an important societal value and a key design requirement for 6G. However, the deployment of 5G in areas outside the city centres and industrial hubs is not economical. Even the adoption of higher frequencies offers only limited coverage areas and the implied costs of building up the radio towers would be significant. NTNs have emerged as a potential solution for remote access and backhaul of mobile networks. Therefore, the integration of satellite networks and 5G has been an international research topic for many years and the European Space Agency (esa) has launched a number of research projects which also stimulated corresponding 3GPP study items [59
]. Thus, remotely located and even nomadic 5G campus networks can be connected with the greater Internet or enterprise networks. Lower, medium and geostationary orbit (LEO, MEO and GEO) Satellites and high-altitude platforms (HAPS) are being developed to provide direct network access to 5G devices [60
]. These NTN technologies are considered a key pillar for the 6G architecture definition [61