Link Budget Analysis for Reconfigurable Smart Surfaces in Aerial Platforms

Abstract

Non-terrestrial networks, including Unmanned Aerial Vehicles (UAVs), High Altitude Platform Station (HAPS) nodes and Low Earth Orbiting (LEO) satellites, are expected to have a pivotal role in sixth-generation wireless networks. With inherent features such as flexible placement, wide footprints, and preferred channel conditions, they can tackle several challenges faced by current terrestrial networks. However, their successful and widespread adoption relies on energy-efficient on-board communication systems. In this context, the integration of Reconfigurable Smart Surfaces (RSS) into aerial platforms is envisioned as a key enabler of energy-efficient and cost-effective aerial platform deployments. RSS consist of low-cost reflectors capable of smartly directing signals in a nearly passive way. In this paper, we investigate the link budget of RSS-assisted communications for two RSS reflection paradigms discussed in the literature, namely "specular" and "scattering" paradigms. Specifically, we analyze the characteristics of RSS-equipped aerial platforms and compare their communication performance with that of RSS-assisted terrestrial networks using standardized channel models. In addition, we derive the optimal aerial platform placements for both reflection paradigms. Our results provide important insights for the design of RSS-assisted communications. For instance, given that a HAPS has a large area for RSS, it provides superior link budget performance in most studied scenarios. In contrast, the limited RSS area on UAVs and the large propagation loss in LEO satellite communications make them unfavorable candidates for supporting terrestrial users. Finally, the optimal location of an RSS-equipped platform may depend on the platform's altitude, coverage footprint, and type of environment.

RIS Meets Aerodynamic HAPS: A Multi-Objective Optimization Approach

“…These parameters are inline with the specifications of one of the well-known aerodynamic HAPS, HAWK30, [7], [22]. The terrestrial Tx and Rx coordinates in the scale of km are (x T , y T , z T ) = (−5, 0, 20) and (x R , y R , z R ) = (5,0,20), respectively. The planar antenna gain of RIS element (p, q) to S can be considered as g S p,q θ S p,q (t) , φ S p,q (t) = 4π λ 2 c d x d y cos θ S p,q (t) for θ S p,q (t) ∈ 0, π 2 and zero otherwise, [13].…”

“…Non-terrestrial RIS (NT-RIS) is an intelligent intermediate reflection layer, where RIS is mounted on a non-terrestrial platform to connect the unconnected terrestrial infrastructures. Extensive research has been conducted to address the benefits of adopting NT-RIS in wireless networks, see [2]- [5] and the references therein. In practical cases, high altitude platform station (HAPS)-RIS is one of the promising candidates to be exploited for NT-RIS compared to other non-terrestrial platforms such as satellite-RIS and unmanned aerial vehicle (UAV)-RIS, [4], [5].…”

“…Extensive research has been conducted to address the benefits of adopting NT-RIS in wireless networks, see [2]- [5] and the references therein. In practical cases, high altitude platform station (HAPS)-RIS is one of the promising candidates to be exploited for NT-RIS compared to other non-terrestrial platforms such as satellite-RIS and unmanned aerial vehicle (UAV)-RIS, [4], [5]. HAPS operates at much higher altitude which leads to establishing line of sight (LoS) dominated connection and a much wider coverage area compared to UAV.…”

“…The investigation of HAPS-RIS communications is still in its infancy. The existing literature on this topic is mostly focused on aerostatic HAPS-RIS, [4], [5], [8], [9], while the aerodynamic HAPS-RIS is left as an open research topic. The necessity of research on this direction has been emphasised in [10].…”