# Dynamic Repositioning of Aerial Base Stations for Enhanced User Experience in 5G and Beyond  
[PERSON]  
1 Department of Computer Science, UET Mardan, Chasadda Road, Mardan 23200, Pakistan; [EMAIL_ADDRESS] (S.U.R.); [EMAIL_ADDRESS] (M.U.)1 Department of Computer Science, UET Mardan, Chasadda Road, Mardan 23200, Pakistan; shams@utemardan.  
targets, a variety of advanced techniques are being employed, including massive MIMO (Multiple-Input, Multiple-Output), millimeter Wave, and ultra-dense deployment (UDD) of small cells [2].  
UDD involves the deployment of many closely spaced base stations which incurs tremendous capital expenditure (CAPEX) and operational expenditure (OPEX); therefore, it is important to maximize the utilization of UDD resources. However, due to user mobility and activities, user density changes all the time [3]. For example, user density around shopping areas is higher on weekends and in the evening compared to weekdays and work hours, respectively; in the evening time, user density around parks is higher compared to work hours; during sports events, density around sports venues is drastically higher; and during rallies and protests, user density constantly changes. Such fluctuations in user density result in some parts of the network being overloaded, whereas other parts are under-utilized if the deployment is fixed. Therefore, it is highly desirable, on the part of service providers, to be able to adjust the deployment, i.e., location, of small cells according to user density, which can be achieved by mounting the small cells onto unmanned aerial vehicles (UAVs), which we will call Aerial Base Stations (ABSs), as shown in Figure 1. The use of such an ABS-based network offers an attractive solution to the problem of network under-utilization due to varying user density and provides the service provider with a significant reduction in CAPEX and OPEX.  
In the deployment of an ABS-based network, an immediate problem that arises is the optimal placement of the ABSs based on the user density distribution. Since UDNs are aimed at increasing capacity while ensuring the best user experience, such as providing higher data rates anywhere, therefore, for enhanced spectral efficiency, the received power and signal-to-interference ratio (SIR) should be higher. In this work, we study the problem of the optimal placement of ABSs at a subset of candidate locations that maximizes the total received power and the total SIR. A candidate position is a location where an ABS can be deployed and perched on a platform while it is deployed there. The deployed ABS can receive power at that location; so, when an ABS reaches its deployed candidate location, it does not need to hover. Furthermore, it means that there is no risk of a UAV or small cell running out of energy while it is operating at a candidate location. To the best of our knowledge, no other work has studied the problem of the optimal placement of ABSs at a set of discrete candidate locations as described above.  
The main contributions of this work are as follows:  
* This paper proposes a novel idea of potential candidate positions, a subset of which will be chosen for the placement of ABSs based on user density.  
Figure 1: Aerial Base Station-based ultra-dense mobile network.  
* This paper formulates the problem of optimal ABS placement at a subset of the candidate positions to maximize received power and SIR.
* This paper develops solutions for the formulated problems to determine the optimal placement of ABSs.  
The rest of the paper is organized as follows. Section 2 gives a brief overview of related works. Section 3 describes the system model. In Section 4, the problem is formulated, whereas in Section 5, a solution for the problem is modeled in MATLAB. Section 6 discusses the simulation results and Section 7 draws some conclusions from this work.