LoRa Energy-Delay-Tradeoff Hybrid MAC Protocol for LEO Satellite IoT Networks

Due to the nature of global coverage, low Earth orbit (LEO) satellite-based Internet of Things (IoT) networks have become one of the hotspots in the field of IoT. Long range (LoRa) is the main technical standard in the terrestrial network for the IoT use cases with the characteristics of low power consumption, wide area coverage, and so on. In this article, to meet the challenge of delay and power consumption requirement for diverse applications, we propose a hybrid medium access control (MAC) protocol for LoRa satellite-based IoT networks. Based on the Markov chain model and LEO satellite channel characteristics, we derive a closed-form expression of delay and power consumption for LEO satellite with transparent forwarding and regenerative forwarding, respectively. On this basis, we formulate an optimization problem that trades off delay and power consumption, to optimize the timer and number of windows parameters of the proposed hybrid MAC protocol. To solve this multiobjective optimization problem, we also design a joint support vector machine (SVM) and Nondominated Sorting Genetic Algorithm-II (NSGA-II) method to get the parameters. NSGA-II is employed to solve complex multiobjective optimization problems; meanwhile, the SVM is used to reduce the algorithmic time complexity of NSGA-II. Simulation results show that compared with the traditional long-range wide area network (LoRaWAN), the proposed hybrid MAC protocol can effectively reduce terminal power consumption under the constraint of service delay.