Cloud Wireless Networks: An Information Theoretic Framework

Periodic Reporting for period 5 - CloudRadioNet (Cloud Wireless Networks: An Information Theoretic Framework)

Berichtszeitraum: 2023-01-01 bis 2023-06-30

This research project has been focused on the development of novel information theoretic
concepts and techniques and their usage, as to identify the ultimate communications
limits and potential of different cloud radio access networks (C-RAN) and fog radio
access networks (F-RAN) structures, in which the central signal processing is
migrated from the radio units to the cloud (remote central units), via
fronthaul/backhaul infrastructure links. Moreover, it was directed also, to introduce and
study the optimal or close to optimal strategies for those systems that are to be
motivated by the developed theory. We focus on wireless networks, having future
cellular technology in mind, but the basic tools and approaches to be built and
researched are relevant to other communications networks as well. Cloud
communication networks motivate novel information theoretic views, and
perspectives which put in center backhaul/fronthaul connections deviating thus
considerably from standard theoretical studies of communications links and
networks, which is applied to this domain. Further, our research demonstrates
intimate connections of C-RAN to distributed information bottleneck, which are used
in some insightful theoretical analyses of communications systems. The theoretical
understanding which results from this research will facilitate the design and
implementation of efficient, robust and reliable communications techniques, the
demand for which is steadily increasing. The change of paradigms from 'how to do' to
'what to do' due to the available advanced technologies turns the information
theoretic understanding to a leading practical tool, guiding the constriction of
advanced communications networks.

Our achievements addressing these basic theoretical questions, account for:
* Information Theoretic perspective of up and down link C-RAN: New technologies, concepts and information theoretic characterization.
* Fog radio access networks: an information theoretic view.
* Network information theoretic view:
- Cooperative networks: The impact of cooperation on performance enhancement, as measured via an information theoretic approach has been examined for useful network models. models and understanding the theoretical impact of number of cooperation rounds.
- Physical layer secrecy over cooperative and C-RAN networks.
- Central aspects of (ultra) reliability and latency in networks.
* Information theoretic bottleneck views of C-RAN networks and beyond.
* Networks, processing, systems aspects and practical implications:
* An Information-estimation view of communications networks, accounting for the impact of cognition and cooperation, broadcast approach strategies, feedback and aspects and practical constraints.
* Impact of learning on Ultra-Reliable Communication.

To conclude, our achievements, as reflected in the dozens of published and presented work, at the best journals in the field and at top international professional gatherings has addressed all the planned aspects, and way beyond.

Our research achievement so far addresses a wide spectrum of C-RAN and F-RAN related aspects, and the achievements as specified are not only of primary theoretical importance, but do carry practical implications. Here we detail in short (space limitations): the central direct achievements, which account for a wide scope of information theoretic analysis of C-RAN, F-RAN and its network components, as well as relevant information theoretic concepts as is reflected by the 65 published JOURNAL papers and way over a hundred of papers presented in the top tier worldwide conferences, and lectures at top tier academic universities in Europe, US and other places.
These studies reflect our work and results and their wide-scope worldwide dissemination and explorations (s is reflected by citations of these works).

All our studies are focused on the development of novel information theoretic concepts and techniques and their usage, as to identify the ultimate
communications limits and potential of different C-RAN and F-RAN structures.

Specifically, our work has contributed significantly to the basic theoretical questions, we have posed, and here we name the central elements of our studies:

*Information Theoretic perspective of up and down link C-RAN:

*F-RAN radio access networks: an information theoretic view of cooperative networks:
The impact of cooperation on performance enhancement, as measured via an information theoretic approach, examined for a variety of C-RAN, F-RAN and network related problems.

* Physical layer secrecy over cooperative and C-RAN networks

* An Information-estimation view of communications networks, accounting for the impact of cognition and cooperation and feedback.

* Information theoretic bottleneck views of C-RAN networks, and basic connections to advanced information theoretic network concepts, including double-sided information bottleneck.

* Impact of network and communications structure and demands, such as (Device-to-Device communications), Ultra Reliable Low Latency (URLLC), Reconfigurable Intelligent Surfaces based systems, Delay constrains, Congestion, and Signaling constraints.

* Impact of learning on ultra-reliable communication with differential quality of service.

We will further details the major theoretical achievements which carry also strong practical implications in the next section, and associate those with some central publications that have appeared in the top class international relevant journals.

Our general research view accounts for the fact that in such C-RAN, F-RAN based networks information theoretic separation concepts are no more optimal, even if each component is based on state-of-the art theoretical results. Our theoretical view and results so far reflect novel insights, analysis and techniques, which can be of use in general networks as communication viewed via the information-theoretic paradigm. Thus, isolating simple basic components of the network is essentially sub-optimal. Our achievements in this research project, incorporates, in a unified way, under the general cover of information theory: Multi-terminal distributed networks; Basic and timely concepts of distributed coding and communications; Network communications and primarily noisy network coding, index coding, as associated with interference alignment and caching; Signal processing addressing directly the impact of distributed channel state information; A variety of fundamental concepts in optimization and random matrix theories. One of the major concepts we pursue in our research, which has direct practical implications is robust (oblivious) processing at the radio (relay) units, where it is guaranteed to perform well in general and in this sense our approach reflects universal features, which is not dependent on the communications/coding strategy used by the user equipment. We have demonstrated that our theoretical concepts of oblivious cloud radio access connect to a variety of "information bottleneck" (used in deep and machine learning) problems. These are of fundamental importance and demonstrate interdisciplinary features. This path provides a natural theoretical framework directed towards better understanding of the potential and limitations of cloud based networks, which form basic components of future wireless technology (as cell-less systems) and the theoretical results that are provided account also for practical and technological constraints and demands. Recently, we have addressed also the impact of feedback on CRAN communications, as well as enriched the information-bottleneck framework examined. Further aspects of learning are studied in the framework of ultra-reliable communications. The reported theoretical results provide the grounds for future studies, which may carry also an impact on future wireless technology.

UpLink (Multiple Access) MIMO Cloud Radio Access Network.

DownLink (Broadcast) MIMO Cloud Radio Access Network.

Cell-Less wireless system: Cells are Replaced by Radio-Units.

Periodic Reporting for period 5 - CloudRadioNet (Cloud Wireless Networks: An Information Theoretic Framework)

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