# Performance Assessment and Comparison of Deployment Options for 5G Millimeter Wave Systems
###### Abstract  
The roll-outs of fifth-generation (5G) New Radio (NR) systems operating in the millimeter-wave (mmWave) frequency band are essential for satisfying IMT-2020 requirements set forth by ITU-R in terms of the data rate at the access interface. To overcome mmWave-specific propagation phenomena, a number of radio access network densification options have been proposed, including a conventional base station (BS) as well as integrated access and backhaul (IAB) with terrestrial and aerial IAB nodes. The aim of this paper is to qualitatively and quantitatively compare the proposed deployments using coverage, spectral efficiency and BS density as the main metrics of interest. To this end, we develop a model capturing the specifics of various deployment options. Our numerical results demonstrate that, while the implementation of terrestrial relaying nodes potentially improves coverage and spectral efficiency, aerial relays provide the highest coverage, three times that of a direct link connection, and also significantly reduce the required BS density. The main benefit is provided by the link between the BS and the aerial relay. However, gains are highly dependent on a number of elements in antenna arrays and targeted outage probability. The use  
deployments as there should always be line-of-sight (LoS) conditions between IAB donors and IAB nodes or between two IAB nodes [15]. Subsequently, in Release 17 [16], where the architecture has been further refined, the use of mobile IAB nodes that might be installed in cars or unmanned aerial vehicles (UAV) is proposed. The use of UAVs has recently been shown to be very useful as network access points at high altitude, enabling efficient avoidance of blockage by large static objects, such as buildings. In spite of different types of deployment options for 5G mmWave NR systems, including conventional BS-based and terrestrial [17] or mobile IAB systems, to the best of the authors' knowledge, there has been no detailed assessment as to which provides the best performance for these systems under different environmental conditions. On the one hand, the use of UAV-mounted IAB nodes brings high blockage tolerance at the expense of additional operational expenditures (OPEX) for the network operators and longer propagation paths [18]. On the other hand, in some deployment conditions, such as suburbs and rural areas, terrestrial, and even conventional, BS-based roll-outs might be sufficient. In our paper, we qualitatively and quantitatively characterize different types of 5G mmWave NR deployment options, including (i) conventional BS-based systems, (ii) terrestrial IAB systems, and (iii) aerial IAB systems. Similarly, terrestrial coverage was studied in [19]; however, the study focused on transmission power impact to coverage, whereas we consider antenna arrays and outage probability as parameters and also give a comparison against aerial IABs. We account for specific mmWave propagation conditions, including blockage by small dynamic and large static objects. The main metrics of interest are coverage and spectral efficiency. The rest of the paper is organized as follows: In Section 2, we introduce our system model, describe the considered scenarios of direct connection and the terrestrial and aerial relays, and introduce blockage models according to the 3 GPP standard [8]. In this section, we also describe the main metrics of interest. Here, similarly to [20], we focus on an analysis of spectral efficiency and coverage. Then, in Section 3, we establish coverage and spectral efficiency metrics for the considered deployment options. The numerical results are presented in Section 4. We show that the main benefit is achieved for the link from BS to UAV, giving three times the coverage of direct connection. In addition, we highlight the drawbacks of using aerial relays, since it is necessary to increase the number of antenna elements on the relay in order to reduce outage probability.