# NFV/SDN as an Enabler for Dynamic Placement Method of mmWave Embedded UAV Access Base Stations
## 1 Introduction
Furthermore, the miniaturization of devices is an important issue for UAVs, and the use of frequencies with shorter wavelengths such as millimeter-wave is more advantageous in this respect. Regardless of several disadvantages when using these higher frequency bands, e.g., limited coverage, such issues have been overcome by introducing a high-directivity beamforming technique together with a fast-beam switching mechanism. For these reasons, nowadays, millimeter-wave is even being introduced into 5G cellular networks [13] and its employment for UAV applications is also being discussed by 3 GPP and other organizations [14]. Different from conventional works, this paper therefore studies the placement of access UAV networks employing broadband millimeter-wave. As mentioned above, in the millimeter-wave band, the effects of distance attenuation and blocking are significant, so UAV placement concerning the user distribution becomes an important issue. However, there has been little study of the deployment of UAV networks in the millimeter-wave band. The following is a partial list of references that discussed UAV deployment in millimeter-wave bands. In [15], the goal was to maximize the number of users that can be covered, with convolutional neural networks used to increase computational efficiency. In [16], an algorithm to solve the placement problem to achieve the required SINR (Signal-to-Interference-and-Noise Ratio) for all users was considered. In [17], the placement problem of UAVs was considered to maximize the total data rate provided to the user. In this paper, we consider the placement problem with a different objective from these references, i.e., to improve the overall user rate's cumulative distribution function (CDF), as will be shown in Section 4. In addition, in the conventional literature, the distribution of users is assumed to be uniform. However, in the real environment of mobile communication, users are not uniformly distributed, but rather non-uniformly distributed. Since the maximum number of users accommodated by a single base station is limited to attain a target desired user rate, whether the user distribution is uniform or biasedly non-uniform is a significant factor when considering the problem of UAV base station placement. For these reasons, in this paper, we propose a new approach to non-uniform user distribution in the millimeter-wave band. Specifically, the placement of millimeter-wave band UAV networks with various user distributions will be investigated. In summary, this paper deals with the problem of deploying access UAVs to increase the downlink data rate provided to stationary users distributed non-uniformly on the ground. UAV base stations are dynamically deployed, unlike ground base stations, and the spacing between UAV base stations is irregular, so there can be various situations of coverage overlap. Therefore, interference from other UAV base stations is a major problem. For this reason, after studying the placement method, this paper furthermore introduces an interference reduction method called Fractional Frequency Reuse (FFR) to overcome the severe interference issue. Various control protocols for UAVs for different purposes including security/surveillance have been studied by other researchers, e.g., [18] is thus outside the scope of this paper. In this paper, we will focus only on the communication network aspect rather than control protocols of UAVs. Numerical analyses are conducted in Section 4 to confirm the effectiveness of our proposed method, in terms of not only average user rate but outage user rate. This paper extends from the authors' previous work in [19], where additional comparison results against a conventional microwave-band system are included in Section 4. Our numerical results further reveal that the proposed method's performance in the millimeter-wave band is superior to that in the conventional microwave band. Thus, this paper makes an unparalleled academic contribution to the field.