Caching to the Sky: Performance Analysis of Cache-Assisted CoMP for Cellular-Connected UAVs

Abstract

Providing connectivity to aerial users, such as cellular-connected unmanned aerial vehicles (UAVs) or flying taxis, is a key challenge for tomorrow's cellular systems. In this paper, the use of coordinated multi-point (CoMP) transmission along with caching for providing seamless connectivity to aerial users is investigated. In particular, a network of clustered cache-enabled small base stations (SBSs) serving aerial users is considered in which a requested content by an aerial user is cooperatively transmitted from collaborative ground SBSs. For this network, a novel upper bound expression on the coverage probability is derived as a function of the system parameters. The effects of various system parameters such as collaboration distance and content availability on the achievable performance are then investigated. Results reveal that, when the antennas of the SBSs are tilted downwards, the coverage probability of a high-altitude aerial user is upper bounded by that of a ground user regardless of the transmission scheme. Moreover, it is shown that for a low signal-to-interference-ratio (SIR) threshold, CoMP transmission improves the coverage probability for aerial users from 10% to 70% under a collaboration distance of 200 m.

Toward a Connected Sky: Performance of Beamforming With Down-Tilted Antennas for Ground and UAV User Co-Existence

“…For the large-scale fading, the channel between BS i and the AU includes LoS and NLoS components, which are considered separately along with their probabilities of occurrence [11]. For small-scale fading, we adopt a Nakagami-mv model for the channel between each single antenna and the AU, as done in [9], [11], [12], with the following probability distribution function (PDF):…”

“…The main merit of this representation, i.e., P v c|r = e T Mv 1, is that it leads to valuable system insights. For example, the impact of the shape parameter Mv = M mv on the intended channel gain hiK ∼ Γ(M mv, η/mv), which is typically related to the antenna size and the Nakagami fading parameter mv, is clearly illustrated by this finite sum representation (9). Although it is not tractable to obtain closed-form expressions for t k (the entries populating T Mv ), special cases of interest, e.g., LoS or NLoS communications, can lead to closed-form expressions, following [18].…”

“…In [8], through system simulations, the authors evaluated the performance of the downlink of AUs when supported by either a traditional cellular network, or Ramy a massive multiple-input multiple-output (MIMO)-enabled network with zero-forcing beamforming (ZFBF). In [9], the authors showed that cooperative transmission significantly improves the coverage probability for high-altitude AUs. However, while the works in [5], [7], [9], and [10] have analyzed the performance of cellular-connected UAVs, their approaches can not be used to effectively improve the performance of AUs while enhancing spectral efficiency (SE) by spatial multiplexing.…”

“…In [9], the authors showed that cooperative transmission significantly improves the coverage probability for high-altitude AUs. However, while the works in [5], [7], [9], and [10] have analyzed the performance of cellular-connected UAVs, their approaches can not be used to effectively improve the performance of AUs while enhancing spectral efficiency (SE) by spatial multiplexing. Also, even though the work in [8] has proposed MIMO beamforming for an AU co-existing with multiple GUs, this work provides no analytical characterization of the performance of AUs or the impact of the antennas' down-tilt angles.…”

Cooperative Transmission and Probabilistic Caching for Clustered D2D Networks

“…The analysis of wireless caching networks that underlies a physical interference model, is commonly conducted by means of stochastic point processes. For instance, modeling device locations as a Poisson point process (PPP) is a widely adopted approach in the wireless caching area [5], [6]. However, while the PPP model is tractable, a realistic model for D2D caching networks needs to capture the Ramy This publication has emanated from research conducted with the financial support of Science Foundation Ireland (SFI) and is co-funded under the European Regional Development Fund under Grant Number 13/RC/2077.…”