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Abstract—This paper addresses the concept of optical transport network based on high altitude platforms (HAPs) flying in lower stratosphere and equipped with optical communications payload. The stratospheric transport network is formed of optical links between HAPs and optical backhaul uplinks and downlinks between HAPs and ground stations (GSs) hosting gateways to the backbone network. In order to consider limitations of free space optics (FSO) for the dimensioning of stratospheric optical transport network (OTN), we investigate the physical layer aspects for a DWDM based optical interplatform link (IPL). Taking into account the physical constraints imposed by FSO, we estimate the number of wavelengths required for full interconnectivity without wavelength conversions. We are using an analytical approach for bus and full mesh regular topologies, and a numerical approach for circumcircled star, ring and star regular topologies. We also evaluate the performance of a representative network with irregular topology using different routing and wavelength assignment algorithms. We show that the number of wavelengths needed to achieve full interconnectivity strongly depends on the physical topology of the network, and that adaptive routing yields better overall performance of the network compared to fixed and fixed alternate routing. The analysis also shows that resources in realistic network topologies tend to be used very inefficiently, which could be improved by traffic engineering solutions or wavelength conversions.
Mohorčič et al. (Tue,) studied this question.