# An Integrated Access and Backhaul Approach to Sustainable Dense Small Cell Network Planning
## 2 System Model  
We consider an IAB network consisting of IAB nodes and donors, operating in the 60 GHz license-exempt frequency band. The system is designed to achieve fiber-like data rates, reaching up to 1 Gbit/s. We specifically focus on a city-based deployment, incorporating a wireless mesh network, as illustrated in Figure 2.  
The candidate sites for IAB node deployment include urban infrastructures, such as lamp-posts and bus-stops. These locations are selected in a way to facilitate line-of-sight (LoS) transmission for user access whenever possible. Our design faces several challenges, particularly in identifying optimal installation locations for each of the IAB nodes while minimizing the total number of nodes. While potential multi-hop scenarios pose some limitations, this is further compounded by the need to ensure that the data transfer rates are consistently served.  
To guide our discussion, we outline the following key assumptions governing the system model:  
Figure 2: A sample mmWave integrated access and backhaul (IAB) network model with directional antenna.  
* **All nodes/donors are unified:** We introduce this assumption to streamline the network design and analytical processes. Each node and donor is characterized by a uniform access and backhaul radius. An area is considered covered if it lies within the access radius of a deployed node or donor. Similarly, a node is deemed serviceable by a donor if it is located within the donor's backhaul radius. This consistency and standardiation, together with the requirement that all nodes and donors are at the same height, eliminates deviations that may muddy network performance evaluations, allowing us to focus on optimising deployment sites.
* **LoS transmission is consistently maintained:** Operating in the 60 GHz band necessitates a focus on ensuring LoS connections, owing to the millimeter-wave (mmWave) characteristics, which are highly susceptible to blockages and attenuation. Consequently, the consistent maintenance of LoS transmissions is integral to attaining optimal data throughput and network performance. The nodes are, therefore, positioned to facilitate LoS, ensuring that the inherent propagation characteristics of the 60 GHz frequency are maximized to deliver robust connectivity.  
To facilitate analysis, we assume that a certain number of donors pre-exist within an area, which is composed of one or more plane rectangular zones (an example is shown in Figure 3). Therefore, the core of our work is to deploy a finite number of nodes within potential locations to ensure that both access and backhaul requirements are adequately met.  
Figure 3: The grid indicates the area waiting to be covered and the location of deployment: solid red markers represent donors connected to the core network, red outlined markers denote deployed nodes, and white markers indicate potential node positions that remain undeployed. The green areas highlight the access coverage facilitated by the deployed nodes and donors, while the blue regions indicate the extent of backhaul coverage.  
In our model, we aim to deploy IAB donors and nodes at designated candidate locations. Here, the candidate location of a node is symbolized as \(j\), while \(i\) represents the exact coordinates where a donor is situated. Our primary objective is to determine the optimal deployment locations of the IAB nodes and, at the same time, to minimize the number of deployed nodes. We further define the communication model, ensuring that the power received at each grid center fulfills or surpasses a predefined signal-to-noise ratio (SNR) threshold, \(SNR_{0}\). This requirement ensures that users (on the access side) are guaranteed to be provided with their necessary data rate service.