Relaying in full-duplex radio communication systems

Abstract

As explained in many chapters of this book, relaying in principle means indirect data transmission from a source node to a destination node via intermediate relay nodes (RNs), e.g., not so unlike repeaters, gap-fillers, or signal boosters do in old-fashioned wireless systems. On the other hand, the field of information theory has addressed many classical questions related to the performance of idealistic relay links. Relay transceivers in these original research areas conventionally operate in a full-duplex (FD) mode, while later studies on cooperative communication deemed it impossible to begin with and focused almost invariably on half-duplex (HD) relaying. However, modern relay transceivers such as those assumed in the context of this chapter are much more advanced than simple analog amplifiers in terms of their processing capabilities so that, e.g., they can be made robust to interference. Time has thus become right for us to return to the origins of relaying by promoting FD operation as a practical and highly efficient design choice whose technical difficulties can be now overcome. With this background, this chapter provides an overview of essential aspects to be considered when introducing FD operation into relaying systems. Two particular contributions are central for this development, namely introducing transmit power control for FD relaying and comparing the performance of FD relay links to that of their HD counterparts. The main focus herein is on infrastructure relaying although the considered systems have their relatives with cable-connected distributed antennas and mobile relays instead. Thus, the considered relay transceivers are fixed nodes and belong to infrastructure deployed by a network operator. This scope choice differs from earlier mainstream literature which is inclined toward ad hoc mobile relaying by user terminals. When discussing cellular systems, the link elements may be referred to as a base station (BS), a RN, and a user equipment (UE). The BS and RNs form a “backhaul link” while UEs are always connected to a “service link”. There is typically only one relay per each group of destinations (except for special hand-over situations) while backhaul links may involve multihop relaying. Furthermore, the study is formulated in an implicit context to concern a single subcarrier within orthogonal frequency-division multiplexing (OFDM) transmission.