Analysis And Research Of Downlink Communication Based On LoRa Receiving Window Mechanism

With the diversification of IoT scenarios,traditional short-distance low-power technologies have been unable to meet the needs of applications.LoRa technology has emerged as a long-distance low-power technology and is widely used in various IoT scenarios.However,in order to meet the characteristics of low power consumption,LoRa technology has limited ability to support downlink data services.Therefore,for IOT applications with more downlink data,such as vehicle monitoring in parking lots,smart buildings and energy management,LoRa technology needs to have corresponding mechanisms to ensure the effectiveness of communication.This paper combines the different receiving window mechanisms in the end-device Class A/B/C mode introduced in the LoRaWAN protocol,and designs the strategy of dynamic switching between modes.It also analyzes the problems existing in each mode and the corresponding improvement measures.The downlink reliability of the LoRa network reduces the power consumption of the end-device.The main work of this paper is as follows:(1)The end-device energy consumption model and network energy consumption model are established according to the different modes defined for the end-device in LoRaWAN protocol.According to the requirements of downlink traff-ic and end-device energy consumption,an active switching strategy based on end-device adaptation and a passive switching strategy based on server commands are designed to form a complete mode switching strategy.(2)Aiming at the problem that a large number of end-devices simultaneously transmit the frames to be acknowledged in Class A mode,causing a downlink conflict,a corresponding conflict model is established.This paper proposes a strategy of broadcasting ACK collision avoidance,which can reduce the probability of downlink ACK collision by confirming multiple end-devices at one time.(3)Aiming at the problem of how to select the optimal number of preset receiving window(PingSlot)in Class B mode,the end-to-end delay model from server to end-device and the unit energy consumption model of end-device are established,and the relationship between time delay,energy consumption and the number of PingSlot is given.The cost function is designed according to the derived relationship to select the optimal number of PingSlots at different downlink data generation rates.(4)In the actual LoRa network,the mode switching strategy and broadcasting ACK strategy are implemented.The accuracy of downlink energy consumption model,conflict model and delay model is verified,and the improvement effect of mode switching strategy and broadcast ACK strategy on downlink performance is analyzed quantitatively.According to the test results of theoretical analysis and practical LoRa network,end-device mode switching strategy,broadcast ACK collision avoidance strategy and optimal PingSlot calculation method can effectively improve the packet loss and collision and ductility,and save energy to the maximum extent while ensuring the downlink performance.