# An Integrated Access and Backhaul Approach to Sustainable Dense Small Cell Network Planning
## 1 Introduction  
Integrated Access and Backhaul (IAB), an enhancement of long-term evolution (LTE) relay technology, was ushered in by the 3 rd Generation Partnership Project (3 GPP) in release-15 [1]. This innovation primarily addresses the challenges associated with the deployment costs of wired backhaul links and the extension of network coverage. In contrast to traditional base stations, IAB is operative in both the sub-6 GHz and the above 6 GHz spectrum [2]. It capitalizes on massive beamforming and the utilization of millimeter wave (mmWave), therefore facilitating the provision of backhaul with cost-effective bandwidth [3]. Figure 1 shows the architecture of an IAB network defined by 3 GPP release-16 [4]. The network nodes in an IAB network are either IAB-donors or IAB nodes. The IAB donors connect to the core network with fiber and can provide wireless access services to mobile users as well as wireless backhaul to IAB nodes. The IAB nodes provide wireless access service to mobile users and wireless backhaul traffic to other IAB nodes as well. The IAB network introduces one or more wireless backhaul IAB nodes on the basis of the 5G New Radio (NR) network architecture, and the user equipment is able to access the network via intermediary nodes that facilitate extended connectivity. Furthermore, an IAB nodeis designed to use the same basic infrastructure to provide wireless access and backhaul service for UEs and other IAB nodes, respectively, which means that the IAB nodes can be deployed densely and more flexibly. Therefore, these kinds of 'plug and play' design nodes are a more sustainable way of network planning to extend the coverage of the network. Since they avoid the need for large cabling and infrastructure intrusions, such as in road digging, their environmental footprint is greatly decreased. The durability and flexibility with which network designs may be updated to respond to increasing demands highlight the adaptability of IAB networks, ensuring that they remain a sustainable alternative for dynamic urban environments and changing connectivity needs. In the realm of network planning, IAB networks have emerged as a pivotal strategy to enhance the density of mobile networks without the accompanying cost of fiber deployment. Within this ambit, ref. [5] showcases how using a standardized wireless technology for both access and backhaul (like the 5G New Radio standard) can offer flexibility in operation and compatibility across different IAB manufacturers. Their study highlights the merits of IAB, such as marked improvements in UE rates and its significance during incremental fiber deployments. While the authors present evidence for increased UE rates, they largely ignore the potential latency and spectrum shortage inherent in wireless backhaul. Taking a leap from there, ref. [6] highlights the ability of IAB networks to manage resources both centrally and distributively, proposing a coordinated parallel resource allocation scheme (CPReal) to seamlessly handle both bursty and non-bursty traffic. Exploring the technical details, ref. [7] investigates the challenges faced by full duplex-enabled IAB networks, especially concerning self-interference at millimeter wave (mmWave) frequencies. Although insightful, the study somewhat neglects the multifaceted interference sources and their cumulative impacts on network performance. In the quest for optimal deployment, ref. [8] highlights the importance of the densification of wireless networks and how mmWave small cells can aid in addressing increasing wireless demands, advocating for the adaptability of IAB networks in resource allocation. Ref. [9] proposed a  
Figure 1: Integrated access and backhaul (IAB) architecture. The central unit (CU) in the IAB donor connects to the core network, while its distributed unit (DU) and the DU in the IAB nodes serve UEs and the other nodes. Mobile terminals (MTs) link with the DU of a parent node or donor.