Abstract
Integrated access and backhaul (IAB) network consists of base station (BS), relay nodes (RNs), and user-equipments (UEs), where BS and RNs exchange UE data via wireless in-band backhaul while sharing the same frequency-time resources with access links. In this paper, a flexible time-division-duplex (TDD)-based IAB network is considered where RNs and BS are assigned to distinct uplink (UL) or downlink (DL) transmission modes to mitigate conventional half-duplex (HD) loss at RNs. An iterative beamformer design is proposed to manage the resulting cross-channel interference and to allocate wireless backhaul and access resources jointly over two consecutive data delivery intervals required for communications between the BS and UEs through HD RNs. Dynamic traffic behavior is handled via weighted queue minimization objective, and user-specific UL/DL queues are also introduced at RNs to guarantee reliable end-to-end data delivery. Bi-directional forward-backward training via spatially precoded over-the-air pilot signaling is employed to allow decentralized beamformer design across all the nodes. A novel user allocation method is proposed to assign UEs to BS or RNs based only on long-term channel statistics and some practical IAB limitations. The numerical examples illustrate the superior system performance of the considered flexible IAB in comparison to the conventional HD relaying system.
Highlights
Small cell deployment has been recognized as a key research direction to fulfill ever-growing traffic demand in the next-generation cellular systems [1]–[3]
Self-backhauling or integrated access and backhaul (IAB) network consists of three components, which have been coined as IAB-donor, IAB-nodes (i.e., relay nodes (RNs)), and
We further propose a novel centralized approach to assign users into respective base stations (BS) or RN by using path gain information and concerning potential practical constraints that are unique to IAB systems, such as limited spatial degrees of freedom in the BS-RN channel due to the line-of-sight (LOS) deployment and significant UL-to-DL interference of the nearby UE pairs
Summary
Small cell deployment has been recognized as a key research direction to fulfill ever-growing traffic demand in the next-generation cellular systems [1]–[3] Connecting these small-cell base stations (BS) to the core network using optical fiber can be onerous and costly [4]. Current developments of millimeter-wave (mm-Wave) communication have enabled the possibility to use high-speed wireless backhaul for densified small-cell networks, which can be more cost-effective, flexible, and easier to be deployed [5]. We refer to these networks as integrated access and backhaul (IAB) systems or self-backhaul systems. IAB systems have received significant attention in the 3GPP new radio (NR) specifications [6], [7]
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