Energy Efficient Network Coding HARQ Transmission Scheme for S-IoT

Satellite-based Internet of Things (S-IoT) is suggested to meet the emergency applications and services of ubiquitous terrestrial IoT user equipments (UEs) in the future IoT. Since the limited power constraints of the satellite and the IoT UEs, it is a vital challenging to design an energy efficient transmission scheme, which can reduce the number of retransmission rounds while offer high throughput. In this article, we combine the network coding and hybrid automatic repeat request (HARQ) to propose a network coding HARQ (NC HARQ) transmission scheme for typical S-IoT scenarios, i.e., the multiple unicast downlink transmission and network coding bidirectional relaying scenarios. We derive the theoretical expressions for the metrics of system performance, including the average number of transmission rounds, the system throughput and the energy efficiency (EE). Specifically, our derivations are completed in two methods, i.e., the mutual information cumulation method and the matrix exponential (ME) distribution method. Based on the above analytical results, we formulate and solve the maximum EE optimization problem to obtain the optimal maximum transmission rounds in two typical communication scenarios. Simulations are provided to validate our analytical results, and confirm the improvement of our proposed NC HARQ scheme.