Wavelength requirements in optical transport networks based on high-altitude platforms

The concept of optical transport network based on high altitude platforms (HAPs) is addressed in this paper. The 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. Taking into account the physical constraints imposed by free space optics (FSO) we analyze the number of wavelengths required for full interconnectivity without wavelength conversions in two regular topologies and determine 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.