Increasing capacity demands in emerging wireless technologies are expected to be met by network densification and spectrum bands open to multiple technologies. These will, in turn, increase the level of interference and also result in more complex inter-technology interactions, which will need to be managed through spectrum sharing mechanisms. Consequently, novel spectrum sharing mechanisms should be designed to allow spectrum access for multiple technologies, while efficiently utilizing the spectrum resources overall. Importantly, it is not trivial to design such efficient mechanisms, not only due to technical aspects, but also due to regulatory and business model constraints. In this survey we address spectrum sharing mechanisms for wireless inter-technology coexistence by means of a technology circle that incorporates in a unified, system-level view the technical and non-technical aspects. We thus systematically explore the spectrum sharing design space consisting of parameters at different layers. Using this framework, we present a literature review on inter-technology coexistence with a focus on wireless technologies with equal spectrum access rights, i.e. (i) primary/primary, (ii) secondary/secondary, and (iii) technologies operating in a spectrum commons. Moreover, we reflect on our literature review to identify possible spectrum sharing design solutions and performance evaluation approaches useful for future coexistence cases. Finally, we discuss spectrum sharing design challenges and suggest future research directions.

The 6th generation of wireless mobile networks is emerging as a paradigm shifting successor to unifying the experience across the physical, digital, and human worlds, pushing boundaries on performance in capacity, throughput, latency, scalability, flexibility, and reliability, while prominently addressing new major factors, including sustainability, security and privacy, as well as digital inclusion. Many research institutions and initiatives worldwide have started investigations to make 6G a reality by approximately 2030. In Germany, federal funding from the German Ministry of Education and Research (BMBF) supports a large-scale 6G initiative, with its lighthouse project, called 6G-ANNA. The core aim of this project is to develop the key aspects of a holistic, sustainable, secure, and resilient 6G system design that will simplify and improve the interaction between humans, digital assets, and the physical environment. This paper shares the vision of the project’s main technical working areas and advances, spanning topics from radio access, integration of multiple networks, as well as automation and simplification in networking to new applications and testbed scenarios, including real-time digital twins and extended reality. The industrial impact and relevance of standardization makes 6G-ANNA uniquely positioned to lead and realize the vision of next-generation wireless mobile network technologies, systems, and applications.

Satellite networks are expected to support global connectivity via future 3GPP non-terrestrial networks (NTNs), as well as private non-geostationary satellite orbit (NGSO) constellations, e.g. OneWeb, SpaceX, and Amazon’s Kuiper. In both 3GPP and private NGSO networks, handling mobility is critical, due to the intrinsic continuous movement of the satellites. In this paper we select three representative inter-satellite handover (HO) strategies and we study their impact on the achievable space-to-ground link performance in emerging NGSO constellations. With (i) Closest Satellite HO a ground station always connects to the closest satellite, with (ii) Max Visibility HO a ground station connects and remains connected to the satellite with the maximum visibility time, until this satellite stops being visible, while with (iii) CINR-based HO a ground station is handed over to the closest satellite if the carrier-to-interference-and-noise ratio (CINR) decreases by 3 dB below a maximum reference level. The first two HO strategies achieve the upper and lower bounds of the satellite-to-ground link performance based on the constellation geometry, while the third one is representative of HO mechanisms triggered by signal strength measurements. We consider five private constellations with different characteristics, some of which have already been launched. The goal is to determine the most suitable HO strategy for each constellation and our results show that this depends on the constellation type, i.e. low earth orbit (LEO), medium earth orbit (MEO) and highly elliptical orbit (HEO), and design. For large LEO constellations with thousands of satellites like SpaceX and Kuiper, CINR-based HO is recommended, since it achieves a good tradeoff among the spectral efficiency, propagation delay and handover rate, while the Doppler shift is in any case high. For smaller LEO constellations with hundreds of satellites like OneWeb, Closest Satellite HO is preferred due to the highest spectral efficiency and lowest propagation delay, while the handover overhead is similar for all strategies. For MEO and HEO constellations with tens to a few hundreds of satellites like Mangata and Pleiades, Closest Satellite HO is best. This achieves the highest spectral efficiency, lowest delay and sometimes a low Doppler shift, while the handover rate is in any case low. Finally, CINR-based HO is recommended in seldom cases of strong inter-constellation interference. Overall, the results suggest that the inter-satellite HO strategy should be adjusted to the constellation specifics, where e.g. adaptive handover selection algorithms could be employed for constellations that are enhanced in time by adding new satellites and orbit types.

Proponents of deploying LTE in the 5 GHz band for providing additional cellular network capacity have claimed that LTE would be a better neighbour to Wi-Fi in the unlicensed band, than Wi-Fi is to itself. On the other side of the debate, the Wi-Fi community has objected that LTE would be highly detrimental to Wi-Fi network performance. However, there is a lack of transparent and systematic engineering evidence supporting the contradicting claims of the two camps, which is essential for ascertaining whether regulatory intervention is in fact required to protect the Wi-Fi incumbent from the new LTE entrant. To this end, we present a comprehensive coexistence study of Wi-Fi and LTE-in-unlicensed, surveying a large parameter space of coexistence mechanisms and a range of representative network densities and deployment scenarios. Our results show that, typically, harmonious coexistence between Wi-Fi and LTE is ensured by the large number of 5 GHz channels. For the worst-case scenario of forced co-channel operation, LTE is sometimes a better neighbour to Wi-Fi-when effective node density is low-but sometimes worse-when density is high. We find that distributed interference coordination is only necessary to prevent a “tragedy of the commons” in regimes where interference is very likely. We also show that in practice it does not make a difference to the incumbent what kind of coexistence mechanism is added to LTE-in-unlicensed, as long as one is in place. We therefore conclude that LTE is neither friend nor foe to Wi-Fi in the unlicensed bands in general. We submit that the systematic engineering analysis exemplified by our case study is a best-practice approach for supporting evidence-based rulemaking by the regulator.

We study whether realistic fifth-generation (5G) mm-wave cellular networks would cause harmful out-of-band interference to weather satellites sensing in the 23.8 GHz band. We estimate uplink and downlink interference from a single interferer and a network of interferers in New York City, using real three-dimensional (3D) building data and realistic antenna patterns. We perform detailed ray-tracing propagation simulations, for locations of the MetOp-B weather satellite and its scanning orientations and ground interferer antenna orientations for representative urban cell sites. In addition to the ITU-R threshold of –136 dBm/200 MHz, we propose an alternative set of harmful interference thresholds directly related to the sensitivity of the satellite sensor. Our results show that the 3GPP power leakage limits are sufficient to ensure that interference from a single 5G device is not harmful if considering the ITU-R threshold, but not if the weather prediction software can tolerate only very low interference levels. Importantly, aggregate interference resulting in practice from a 5G network with realistic network densities is often harmful, even considering the least conservative ITU-R threshold. Overall, our comprehensive coexistence study thus strongly suggests that additional engineering and/or regulatory solutions will be necessary to protect weather satellite passive sensing from mm-wave cellular network interference.

Interference evaluation is crucial when deciding whether and how wireless technologies should operate. In this paper, we demonstrate the benefit of risk-informed interference assessment to aid spectrum regulators in making decisions, and to readily convey engineering insight. We apply, for the first time, risk assessment to an open question of inter-technology spectrum sharing, i.e., a Wi-Fi/LTE coexistence study in the unlicensed band, and we demonstrate that this method comprehensively quantifies the interference impact. We perform simulations with our newly publicly available tool and we consider throughput degradation and fairness as example metrics to assess the risk for different network densities, numbers of channels, and deployments. The risk assessment study shows that no regulatory intervention is needed to ensure harmonious technical Wi-Fi/LTE coexistence: for the typically large number of channels available in the 5 GHz band, the risk for Wi-Fi from LTE is negligible. As an engineering insight, Wi-Fi coexists better with itself in dense deployments, but better with LTE in sparse deployments. Also, both main LTE-in-unlicensed variants coexist well with Wi-Fi in general. For LTE intra-technology inter-operator coexistence, both variants typically coexist well in the 5 GHz band, but for dense deployments, implementing listen-before-talk causes less interference.