Network Architectures Exploiting Multiple HAP Constellations for Load Balancing

This paper addresses network architectures in a constellation of high altitude platforms (HAPs) with overlapping coverage areas, focusing on the additional network elements/functionalities required to make use of load balancing mechanisms. According to the location within the network and the complexity of additional equipment/ functionality the paper proposes two different architectures. In the case of the basic utilisation of multiple HAPs a new equipment/functionality is installed only at the user premises, supporting load balancing only for the connections initialised from the HAP user network to the Internet (i.e. the outbound connections). In the case of advanced utilisation of multiple HAPs a new equipment/functionality is needed both at the user premises and in the HAP network, thus supporting load balancing in both directions. For the performance evaluation of load balancing mechanisms we built a simulation model supporting typical applications such as e-mail, file transfer, web browsing and IP telephony. Simulation results confirm that in the case of traffic load close to the congestion load balancing mechanism significantly improves the performance of selected reference applications. In order to asses the feasibility of the proposed network architectures in a multiple HAP system, and to confirm that carefully designed and pointed directional user antennas allow establishment of multiple access links for load balancing and to improve resilience of the network, we also investigate HAP visibility distribution across the coverage area for a single HAP system and a system comprising 4 HAPs. Key-Words: High Altitude Platforms, network architectures, load balancing, multiple HAP constellation