Performance and energy efficiency of hybrid ARQ over ground-HAP links

In HAP systems, the on-board power is a limited resource and each HAP-based communication system should use it as effectively as possible. In this paper we address the issue of the energy efficiency of a HAP-based communication system at link layer. An analytical formulation is carried out in order to investigate the trade-off between performance and energy consumption of different error recovery mechanisms, namely, pure-ARQ and type II hybrid ARQ protocols. The results are then used to optimize physical layer parameters, such as the transmission power. A Multicarrier Code Division Multiple Access based air interface is considered. After the definitions of energy efficiency of link level error control schemes, the optimum value of the transmission power in terms of energy efficiency will be computed.