Stochastic modelling of multi-layer HAP-LEO systems in 6G for energy saving: An analytical approach

In the current era of communication systems, the next-generation technology known as sixth generation (6G) is anticipated to extensively utilize space-air-terrestrial networks (SAT). High altitude platforms (HAPs) and low earth orbit (LEO) satellites are essential components of SAT network. The presented study proposes an architecture which concentrates on energy saving of HAP in the SAT network. Further, a stochastic model has been proposed which considers three energy saving states of HAP; power saving, standby, and sleep states. It has been assumed that in these states, the energy consumption of HAP is very low or zero. Whenever, there is an arrival of a packet in the system, HAP will start providing service immediately and the whole system will be in active state. The analysis of the stochastic model has been carried out using Markov process (MP) and semi-Markov process (SMP). The system has been analysed in steady-state for both the MP and SMP to obtain the steady-state probabilities. Through the numerical results, the effective contribution of energy saving states in enhancing the energy saving of HAP system has been provided and a comparison for the MP and SMP case has been described in detail. To verify the accuracy of the presented model, a discrete-event simulation approach is employed.