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WIreLess LOWband communications: massive and ultra-reliable access

Periodic Reporting for period 4 - WILLOW (WIreLess LOWband communications: massive and ultra-reliable access)

Période du rapport: 2019-10-01 au 2020-03-31

Cellular wireless systems from 2G to today’s 4G have been continuously evolving towards offering broadband connectivity to the users. While the trend of reaching even higher rates will continue in the fifth generation of wireless systems, there is a common consensus that 5G will not only be “4G, but faster“, but it will offer new modes of connectivity to a massive number of simple devices and/or support extremely reliable connections. WILLOW was a precursor to this consensus, as its research plan was proposed back in 2014, when the notions of massive and ultra-reliable communication were in their infancy.

It is very rewarding to see that this plan has become one of the central elements on the global research agenda for wireless communications in relation to 5G systems and beyond. Namely, since 2014 Massive machine-type communications (mMTC) and Ultra-reliable and low-latency communications (URLLC) became two of the three pillars of 5G and the main arguments for the digital revolution brought by 5G and the other emerging wireless systems. Figure 1 was originally part of the WILLOW proposal and it turned into one of the most recognizable graphs that describes the operation of 5G systems. The prevalence of these research topics is seen in the surge of special issues, workshops, and papers dedicated to massive and-or ultra-reliable wireless communications for Internet of Things (IoT). It can thus be confidently stated that WILLOW made a major contribution to the worldwide research agenda on wireless communications. This is seen through the more than 80 publications that came out of the project, some of which already have a large number of citations.

The objective of WILLOW has been to investigate the fundamental wireless schemes and protocols for massive and ultra-reliable lowband connectivity, now widely known as IoT connectivity. The avaliability of IoT connectivity for massive number of devices, as well as support for IoT connections with ultra-high reliability, will introduce disruptive changes in the vertical sectors: energy, transportation, industrial production, health, etc. For example, once ultra-reliable wireless connections are available, the notion of a robot changes from a single physical entity to a distributed group of modules that are wirelessly collaborating towards performing the robotic function. This paradigm fits in the emerging concept of Industry 4.0 taht consists of smart interconnected production facilities.

5G is quickly becoming the foundational digital technology in the world and WILLOW made pioneering contributions to the two novel aspects of 5G, massive and ultra-reliable IoT, which is an indicator for a large potential impact on the society.
The results from WILLOW made a major contribution to the worldwide research agenda on wireless communications. This is seen through the more than 80 publications that came out of the project, some of which already have a large number of citations. The PI gave 20 keynotes at various conferences and workshops and lectured at several international schools on wireless communications and 5G.

Among the achievements of the WILLOW project, here is the list of five most important:

1. The research in WILLOW has uncovered the fundamental principles of communication protocols with short data packets, which are essential in IoT connectivity. This research has been based on the following observation: When the data size carried by the packet becomes small and comparable to the size of the control information, one must model the transmission cost of control information. This is illustrated on Figure 2.

2. The main motivation behind ultra-reliable wireless is to provide wireless links that can be as reliable as, e.g. cables. The research in the project has led to the identification of system blocks and principles for building ultra-reliable wireless systems. This includes the statistical machine learning framework for ultra-reliability by noting that the wireless system should at first learn the environment (distances, propagation features, blockages) in order to be able to guarantee that e.g. a link can operate 99.999% of the time. Another important concept is multi-connectivity, also called interface diversity – how to use multiple interfaces (cellular, WiFi, etc.) available on a device in order to ensure highly reliable delivery of information.

3. The research in the project has created the first communication-theoretic model for characterizing how the heterogeneous wireless services in 5G, including massive and ultra-reliable communication, should share the same spectrum. This can be tackled mostly in a heuristic way within the other research and the 5G standardization process, while WILLOW provided a theoretical basis for devising different schemes for spectrum allocation and sharing.

4. The research in WILLOW has led to the conclusion that blockchain can fundamentally change the assumptions we have about the traffic and the operation of massive IoT systems. Namely, massive IoT systems have been designed by assuming that they will be dominated by uplink traffic, that is, transmissions from an IoT device to the network. The use of blockchains over in massive IoT systems in order to support trustful transactions from the IoT devices leads to a more symmetric traffic, since an IoT device also needs to receive information related to the blockchains and distributed ledgers. We have shown this shift in the traffic analytically and in an experimental setup. The consequence of these conclusions can be that only some IoT standards, capable to support symmetric traffic, will survive over a long term.

5. Massive MIMO is a key emerging wireless technology, originally intended for supporting broadband communication and one of the cornerstones of the 5G radio architecture. We have shown what are the benefits and challenges of using massive MIMO to support IoT connectivity.
In summary, WILLOW succeeded in offering a comprehensive analysis in the uncharted area, introducing new models and techniques for supporting these communication modes. The results and publications from WILLOW inspired a number of academic and industrial researchers towards building technology for 5G and beyond-5G wireless systems.