Community Research and Development Information Service - CORDIS


CloudRadioNet Report Summary

Project ID: 694630
Funded under: H2020-EU.1.1.

Periodic Reporting for period 1 - CloudRadioNet (Cloud Wireless Networks: An Information Theoretic Framework)

Reporting period: 2016-07-01 to 2017-12-31

Summary of the context and overall objectives of the project

This research project is 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) 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 is 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.

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.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

Our research achievement so far address a wide spectrum of C-RAN related aspects, and the achievements as specified are not only of primary theoretical importance, but do carry practical implications.

S.-H. Park, O. Simeone and S. Shamai Shitz, “Time-Asynchronous Robust Cooperative Transmission for the Downlink of C-RAN,” IEEE Signal Processing Letters, Vol. 23, No. 10, October 2016. Abstract— This letter studies the robust design of downlink precoding for cloud radio access network (C-RAN) in the presence of asynchronism among remote radio heads (RRHs). Specifically, a C-RAN downlink system is considered in which nonideal fronthaul links connecting two RRHs to a baseband unit (BBU) may cause a time offset, as well as a phase offset, between the transmissions of the two RRHs. The offsets are apriori not known to the BBU. With the aim of counteracting the unknown time offset, a robust precod- ing scheme is considered that is based on the idea of correlating the signal transmitted by one RRH with a number of delayed versions of the signal transmitted by the other RRH. For this transmission strategy, the problem of maximizing the worst-case minimum rate is tackled while satisfying per-RRH transmit power constraints. Numerical results are reported that verify the advantages of the proposed robust scheme as compared to the conventional nonro- bust design criteria as well as noncooperative transmission.

S.-H. Park, O. Simeone and S. Shamai Shitz, “Joint Optimization of Cloud and Edge Processing for Fog Radio Access Networks,” IEEE Trans. on Wireless Communications, vol. 15, no. 11, pp. 7621-7632, 2016. Abstract— This paper studies the joint design of cloud and edge processing for the downlink of a fog radio access net- work (F-RAN). In an F-RAN, as in cloud-RAN (C-RAN), a baseband processing unit (BBU) can perform joint baseband processing on behalf of the remote radio heads (RRHs) that are connected to the BBU by means of the fronthaul links. In addition to the minimal functionalities of conventional RRHs in C-RAN, the RRHs in an F-RAN may be equipped with local caches, in which frequently requested contents can be stored, as well as with baseband processing capabilities. They are hence referred to as enhanced RRH (eRRH). This paper focuses on the design of the delivery phase for an arbitrary pre- fetching strategy used to populate the caches of the eRRHs. Two fronthauling modes are considered, namely, a hard-transfer mode, whereby non-cached files are communicated over the fronthaul links to a subset of eRRHs, and a soft-transfer mode, whereby the fronthaul links are used to convey quantized baseband signals as in a C-RAN. Unlike the hard-transfer mode in which baseband processing is traditionally carried out only at the eRRHs, the soft-transfer mode enables both centralized precoding at the BBU and local precoding at the eRRHs based on the cached contents, by means of a novel superposition coding approach. To attain the advantages of both approaches, a hybrid design of soft- and hard-transfer modes is also proposed. The problem of maximizing the delivery rate is tackled under fronthaul capacity and per- eRRH power constraints. Numerical results are provided to compare the performance of hard- and soft-transfer fronthauling modes, as well as of the hybrid scheme, for different baseline prefetching strategies.

Y. Sun, R. Duan, Y. Liang, A. Khisti and S. Shamai (Shitz), “Capacity Characterization for State-Dependent Gaussian Channel With a Helper,” IEEE Transactions on Information Theory, vol. 62, no. 12, December 2016, Page(s):7123-7134.
— The state-dependent point-to-point Gaussian channel with a helper is first studied, in which a transmitter communicates with a receiver via a state-corrupted channel.
The state is not known

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Our general research view accounts for the fact that in such C-RAN based networks information theoretic separation concepts are no more optimal, even if each component is based on state-of-the art theoretical results.
Thus, isolating simple basic components of the network is essentially suboptimal.
Our view 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 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.
This path provides a natural theoretical framework directed towards better understanding of the potential and limitation of cloud networks on one hand and paves the way to innovative universal communications design principles on the other.
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