On the Deployment Problem in Cell-Free UAV Networks

Abstract

Cell-free (CF) structures are expected to be a game changer for beyond-5G wireless networks. With every user potentially communicating with every base station, cooperation at a central processing point is poised to provide much higher spectral efficiencies. At the same time, the growing interest in unmanned aerial vehicles (UAVs) makes CF-UAV networks an appealing scenario. This paper investigates the uplink of a CF network where UAVs serve as flying base stations. The optimization of the UAV locations is shown to markedly increase the minimum local-average signal-to-interference-plus-noise ratio, which in turn increases the spectral efficiency. The improvements are associated to pilot contamination and to geometry.

Cell-Free UAV Networks: Asymptotic Analysis and Deployment Optimization

“…The channel coherence is larger than that of ground networks because aerial settings exhibit higher coherence bandwidths; this, in turn, enables channel estimation with low pilot contamination. Henceforth, contamination is thereby neglected, and readers interested in results that include it are referred to [1]. Unless otherwise specified, and, consistently with the neglect of contamination, we consider a higher value of τ ; precisely, τ = 200 for a 3.2% pilot overhead.…”

“…The derivatives of γ k,m and r i,m w.r.t. x m , can be found in [1] and the derivatives w.r.t. y m can be obtained similarly, altogether completing (36).…”

“…Therefore, affordable techniques should be investigated. A potential alternative is simulated annealing [1]. However, the exploration in simulated annealing is limited to only one possible direction.…”

“…The calculation of the derivatives for each term is straightforward, involving only polynomial terms that depend on g i,m and γ i,m , whose derivatives are derived in (69) and [1], respectively. After some algebra, the derivative of each interfering…”

“…This work was supported in part by NSF Award CCF-1815339, by ERC grant 694975, by the ICREA Academia program, and by the Fractus Chair on Tech Transfer and 6G. Part of this work was presented at the 2021 IEEE Globecom Conf [1]…”