Mohammad Mahdi Azari

Joint Sum-Rate and Power Gain Analysis of an Aerial Base Station

The use of unmanned aerial vehicles (UAVs) as aerial base stations (ABSs) is a promising approach to meet extreme data rate, coverage or power saving requirements in future wireless networks. However, the potential benefits that an ABS can provide depend strongly on its altitude, which affects the fading statistics of its transmissions. In this paper, we propose an altitude dependent performance model that allows to analyze both power and sum-rate capacity gain of the ABS. In contrast to the existing literature, we take into account the height-dependent small-scale fading and path loss exponent in order to provide a complete characterization of the air-to-ground communication links. Our results show that there is an optimal altitude range, representing a trade-off between sum-rate and transmit power gains. Within that optimal range, the height of the ABS can be adapted to optimize for rate or power respectively. The derivations are based on the outage probability of the network, which is studied as function of altitude as well.

Ultra Reliable UAV Communication Using Altitude and Cooperation Diversity

The use of unmanned aerial vehicles (UAVs) serving as aerial base stations is expected to become predominant in the next decade. However, in order, for this technology, to unfold its full potential, it is necessary to develop a fundamental understanding of the distinctive features of air-to-ground (A2G) links. As a contribution in this direction, this paper proposes a generic framework for the analysis and optimization of the A2G systems. In contrast to the existing literature, this framework incorporates both height-dependent path loss exponent and small-scale fading, and unifies a widely used ground-to-ground channel model with that of A2G for the analysis of large-scale wireless networks. We derive analytical expressions for the optimal UAV height that minimizes the outage probability of an arbitrary A2G link. Moreover, our framework allows us to derive a height-dependent closed-form expression for the outage probability of an A2G cooperative communication network. Our results suggest that the optimal location of the UAVs with respect to the ground nodes does not change by the inclusion of ground relays. This enables interesting insights about the deployment of future A2G networks, as the system reliability could be adjusted dynamically by adding relaying nodes without requiring changes in the position of the corresponding UAVs. Finally, to optimize the network for multiple destinations, we derive an optimum altitude of the UAV for maximum coverage region by guaranteeing a minimum outage performance over the region.

Optimal UAV Positioning for Terrestrial-Aerial Communication in Presence of Fading

Aerial communication platforms have been recently recognized as an effective solution to provide wireless access to terrestrial users, which promise to increase reliability and throughput thanks to their superior coverage capabilities. In this paper, we explore the impact of the height of an Unmanned Aerial Vehicle (UAV) on the area over which it can provide wireless service. We investigate the problem by characterizing the coverage area for a target outage probability, showing that for the case of Rician fading there exist a unique optimum height that maximizes the coverage area. The optimum UAV height guarantees a beneficial trade-off between path loss and fading, which vary as function of distance and the elevation angle with respect to the ground terminals. Moreover, a closed-form approximated solution is provided, which is valid for any functional dependency between the elevation angle and the Rician factor.

Coverage and Power Gain of Aerial Versus Terrestrial Base Stations

Aerial stations have been recently recognized as an attractive alternative to provide wireless services to terrestrial users thanks to their superior coverage capability. In this paper, the coverage and power gain that can be achieved by a drone with respect to a terrestrial base station are studied. We address the problem by characterizing the coverage area based on the network outage probability, taking into account the height depending fading and path loss exponent that characterize air-to-ground wireless links. Results show that there exist a unique optimal altitude that provides the largest coverage and power gain, which strikes a fine balance between the path loss, due to the higher altitude, and a reduced influence of the multipath scattering. While numerical evaluations show that even at low altitudes the network gains up to 4x coverage or 20 dB power, the gain achieved at optimal altitude can be higher

Using mobility for increasing the energy efficiency of multihop communications

Mobile robots equipped with cameras and sensors produce large amounts of data, which needs to be transferred energy-efficiently due to battery limitations. While most literature focuses on heterogeneous ad-hoc sensor networks, we use controlled robot mobility to reduce the energy cost per successfully transferred bit over a multihop link. In particular, we analyze the trade-off between hopping and movement cost. Our main conclusion is that, according to the parameters of the network, either the most efficient solution for large link distances is single hop with mobility or multiple hops without mobility. Interestingly, a combination of both do not provide important energy savings.