## 1 Introduction
### Contributions  
This initial investigation considers a PSC scenario setup in an urban environment with fixed MBS and mobile UABSs constituting an AG-HetNet infrastructure operating in the LTE band class 14 frequency [2]. Each base station in the AG-HetNet model proposed in Section 2 is integrated with three-dimensional (3D) beamforming (3 DBF). In specifics, the macro base stations (MBSs) can use inter-cell interference coordination (ICIC) techniques defined in 3 GPP Release-10/11 and UABSs can utilize cell range expansion bias (CRE) defined in 3 GPP Release-8 to offload ground user equipment (GUE) from MBSs. Within the defined AG-HetNet, a mock emergency scenario is simulated by randomly eliminating several fixed MBSs and the GUEs clustering at locations irrespective of cellular coverage and infrastructure as shown in Figure 1. During or in the aftermath of an emergency, the UABS are deployed on a fixed hexagonal grid to restore damaged infrastructure and relieve the network congestion on the terrestrial networks. Subsequently, to evaluate the performance of this AG-HetNet, we consider _coverage probability_ and _fifth percentile SE_ (5 pSE) as the key performance indicators (KPIs). To maximize these two KPIs of the wireless network, we optimize the ICIC and CRE network parameters using a brute-force technique while mitigating intercell interference. Our specific contributions and comparison with the existing literature are summarized in Table 1. To summarize the key contributions of this article,  
* We first define a framework for the AG-HetNet public safety network that considers a real-life disaster event, such as hurricanes or earthquakes, and the potential impact on public safety infrastructure and real-time users. * To accurately study the signal reliability and performance improvement for the PSC in the disaster-struck, public safety network, the system model considers several key aspects, such as the CRE, ICIC, and 3 DBF defined in various 3 GPP releases. * In the disaster-struck, public safety network, we evaluate and analyze the performance of AG-HetNet for different ICIC schemes and different numbers of UABS deployments. Figure 1: An illustration of a PSC scenario with fixed MBS, mobile UABSs, and clustered GUEs constitute the air–ground HetNet infrastructure. The MBS can use various inter-cell interference coordination techniques defined in LTE-Advanced. The UABSs can utilize range expansion bias to offload GUEs from MBS. The rest of this paper is organized to define AG-HetNet, the wireless network parameters, and the performance evaluation in various sections. In Section 2, an LTE-Advanced AG-HetNet system is defined, where each base station is integrated with 3 DBF and the determined KPIs are expressed as a function of network parameters. The UABS fixed deployment scheme and ICIC network parameter optimization using a brute-force technique are described in Section 3. Whereas in Section 4, via extensive computer-based simulations, we analyze and compare the defined KPIs of the AG-HetNet for various ICIC techniques and clustering distributions of GUE. Finally, the last section provides concluding remarks. Table 2 lists the notations and symbols used throughout the paper.