Abstract. The sensor data collection satellite (SDCS) system, as a part of the Internet of Things (IoT), enables data transmission in areas without Internet and mobile communication coverage. A novel technology named LoRa for Low power wide area network (LPWAN) enables energy-efficient communication over long distances, which can meet the requirement of energy-constraint in SDCS system. However, the LoRaWAN as the MAC protocol of LoRa has the problem of initial channel allocation and power selection if directly used in SDCS system. In this paper, we propose a SA-LoRaWAN protocol for power adaptation based on position information of sensors and satellite, and sensors can dynamically access channel according to the packet buffer size. We use OPNET to model SDCS system based on SA-LoRaWAN protocol, and the simulation results demonstrate that the proposed protocol can reduce the energy consumption and improve the packet delivery rate.

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The main limitation of the development of underwater wireless electromagnetic communication is severe attenuation introduced by the seawater characteristics of high permittivity and high conductivity. Fortunately, in previous studies, it was found through experiments that the loss between two underwater antennas near seawater surface or seabed is much smaller than the higher order severe attenuation for the line of sight (LOS) path in seawater. But no one has given reasonable explanation for this phenomenon. To solve this problem, we investigate the propagation mechanism of this phenomenon theoretically. The main component of seabed-rock-layer is basalt, an alternative seabed-rock-layer communication channel model based on evanescent wave generated by the total reflection on the seabed-rock-layer surface is proposed in this paper. Then we analyze the performance of this model according to Goos-Hanchen (GH) Shift of evanescent wave. Simulation results show that the path loss in this model is about 1/20 of that in seawater and the propagation velocity can be increased 20 times. Proposed technology is expected to become an important part of underwater high speed and reliable communication.

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