In recent years, the cellular networking domain has witnessed significant advancements, from the development and widespread rollout of the fifth generation (5G) cellular networks, to more recent efforts towards defining the requirements and enabling technologies for the sixth generation (6G) cellular networks. These advancements are mainly triggered by the increasing demands in terms of bandwidth, availability, reliability, and communication delay. In fact, more and more users of mobile broadband are expected to be connected to the network, continuously downloading and uploading content, requiring pervasive connectivity to remote services and applications.

Traditionally, cellular networks have been designed based on centralized architectures. More recently, an emerging class of distributed applications and use cases, requiring direct communication between devices in proximity of each other, triggered the cellular networking domain towards its first paradigm shift, enabling Proximity Services (ProSe) based device- to-device (D2D) communication capabilities. Current 3rd Generation Partnership Project (3GPP) specifications consider two D2D communication scenarios: (i) direct 1-hop Sidelink (SL) communication between two neighboring User Equipment (UEs), and (ii) 2-hop Sidelink (SL) communication between a UE and the core network using another UE as a relay. However, 5G (and beyond) networks are expected to also support scenarios and verticals for which low-latency multi-hop (more than 2 hops) D2D communication is essential, such as public safety (i.e., disaster scenarios when the cellular infrastructure is unavailable), railway virtual coupling (i.e., platoons of trains), smart factories and farming, and others. In order to support such use cases, several challenges must be addressed, such as off-network distributed resource allocation with bounded delay and strong reliability constraints, and joint scheduling and relaying mechanisms compatible with existing 3GPP specifications.

The Cellular Ad Hoc Networking for Decentralized IoT Architectures (CANDI) project will fill this gap by developing multi- hop sidelink communications. The project will build on existing D2D specifications and standards and leverage recent cellular innovations, as well as wireless ad hoc network concepts, in order to enable multi-hop UE-to-UE relaying for next- generation decentralized cellular networks.