This white paper explores the road to implementing broadband connectivity in future 6G wireless systems. Different categories of use cases are considered, from extreme capacity with peak data rates up to 1~Tbps, to raising the typical data rates by orders-of-magnitude, to support broadband connectivity at railway speeds up to 1000 km/h. To achieve these goals, not only the terrestrial networks will be evolved but they will also be integrated with satellite networks, all facilitating autonomous systems and various interconnected structures.
We believe that several categories of enablers at the infrastructure, spectrum, and protocol/algorithmic levels are required to realize the intended broadband connectivity goals in 6G. At the infrastructure level, we consider ultra-massive MIMO technology (possibly implemented using holographic radio), intelligent reflecting surfaces, user-centric and scalable cell-free networking, integrated access and backhaul, and integrated space and terrestrial networks. At the spectrum level, the network must seamlessly utilize sub-6 GHz bands for coverage and spatial multiplexing of many devices, while higher bands will be used for pushing the peak rates of point-to-point links. The latter path will lead to THz communications complemented by visible light communications in specific scenarios. At the protocol/algorithmic level, the enablers include improved coding, modulation, and waveforms to achieve lower latencies, higher reliability, and reduced complexity.
Different options will be needed to optimally support different use cases. The resource efficiency can be further improved by using various combinations of full-duplex radios, interference management based on rate-splitting, machine-learning-based optimization, coded caching, and broadcasting. Finally, the three levels of enablers must be utilized not only to deliver better broadband services in urban areas, but full-coverage broadband connectivity must also be one of the key outcomes of 6G.
- There will be ultra massive MIMO realized with fully digital arrays and holographic radio to create a spatially continuous electromagnetic aperture to enable ultra-high density, and pixelated ultra-high resolution spatial multiplexing.
- We expect user-centric and scalable cell-free networking to enable the densification of network infrastructure with access points (APs) in 6G.
- We see that THz communications will provide high capacity point to point links complementing the wide area coverage at lower frequencies.
- We also believe that intelligent reflecting surfaces (IRS) will be integrated to wireless systems to create a smart, programmable, and controllable wireless propagation environment, which brings new degrees of freedom to the optimization of wireless networks, in addition to the traditional transceiver design.
List of Contributors
- Nandana Rajatheva, Centre for Wireless Communications, University of Oulu, Finland
- Italo Atzeni, Centre for Wireless Communications, University of Oulu, Finland
- Emil Björnson, Department of Electrical Engineering (ISY), Linköping University, Sweden
- Andre Bourdoux, IMEC, Belgium
- Stefano Buzzi, Department of Electrical and Information Engineering, University of Cassino and Southern Latium, Italy
- Jean-Baptiste Dore, CEA-Leti, France
- Serhat Erkucuk, Department of Electrical and Electronics Engineering, Kadir Has University, Turkey
- Manuel Fuentes, Institute of Telecommunications and Multimedia Applications, Universitat Politecnica de Valencia, Spain
- Ke Guan, State Key Laboratory of Rail Traffic Control and Safety, Beijing Jiaotong University, and Beijing Engineering Research Center of High-speed Railway Broadband Mobile Communications, China
- Yuzhou Hu, Algorithm Department, ZTE Corporation, China
- Xiaojing Huang, School of Electrical and Data Engineering, Faculty of Engineering and Information Technology, University of Technology Sydney, Australia
- Jari Hulkkonen, Nokia Bell Labs, Finland
- Josep Miquel Jornet, Department of Electrical and Computer Engineering, Institute for the Wireless Internet of Things, Northeastern University, USA
- Marcos Katz, Centre for Wireless Communications, University of Oulu, Finland
- Rickard Nilsson, Department of Computer Science, Electrical and Space Engineering, Luleå University of Technology, Sweden
- Erdal Panayirci, Department of Electrical and Electronics Engineering, Kadir Has University, Turkey
- Khaled Rabie, Department of Engineering, Manchester Metropolitan University, UK
- Nuwanthika Rajapaksha, Centre for Wireless Communications, University of Oulu, Finland
- MohammadJavad Salehi, Centre for Wireless Communications, University of Oulu, Finland
- Hadi Sarieddeen, Division of Computer, Electrical and Mathematical Sciences and Engineering, King Abdullah University of Science and Technology, Saudi Arabia
- Shahriar Shahabuddin, Mobile Networks, Nokia, Oulu, Finland
- Tommy Svensson, Department of Electrical Engineering, Chalmers University of Technology, Sweden
- Oskari Tervo, Nokia Bell Labs, Finland
- Antti Tölli, Centre for Wireless Communications, University of Oulu, Finland
- Qingqing Wu, State Key Laboratory of Internet of Things for Smart City and Department of Electrical and Computer Engineering, University of Macau, Macau, China
- Wen Xu, Huawei Technologies, Germany