Research And Implementation Of Bulk Data Dissemination In LoRa Networks

As a promising low-power wide-area network communication technology,LoRa has been adopted by many Io T applications with the feature of low transmission power,long transmission distance and robust to interference.In these applications,data dissemination is a building block for requirements such as fixing software bugs and modifying end-device functionality.The data dissemination protocol in LoRa WAN has two problems: high power consumption and the use of high-complexity encoding method.Due to different network topologies and unique parameter(spreading factors)in the LoRa physical layer,classical data dissemination protocols in wireless sensor networks cannot be directly integrated into LoRa WAN.Therefore,the thesis proposes a low-power and reliable data dissemination protocol DAU(Divide And Upgrade)suitable for LoRa WAN networks.Based on LoRa’s unique physical layer parameter spreading factor,the DAU protocol divides end devices into several groups.Each group performs data dissemination separately.Different groups use different spreading factors to receive data from the gateway.Grouping can prevent that all end devices switch to the largest spreading factor for communication,thereby reducing power consumption.Before broadcasting data,the gateway needs to perform the handshake with the end devices participating in the data dissemination of this group,that is,to send metadata related to data dissemination to end devices.The DAU protocol proposes a beacon-based fast handshake mechanism.The gateway periodically broadcasts a beacon to synchronize the time of the end devices,so that they can open the listening window to receive data from the gateway at the same time.The bitmap contained in the beacon is used to help the end device determine whether it participates in the upcoming data dissemination process.In order to ensure reliability,the end device needs to send NACK to inform the gateway of its missing data.To deal with the problem that NACKs sent by multiple devices at the same time collide at the gateway,the DAU protocol proposes a NACK detection method based on the channel activity detection mechanism.The gateway performs channel activity detection in the logical channel determined by the spreading factor and frequency to determine whether there is a NACK.The gateway does not need to demodulate the NACK,thus avoiding the collision problem.After detecting NACK,the gateway broadcasts the encoded data packet through a lightweight encoding strategy to reduce the number of retransmissions.Experimental results show that the DAU protocol can effectively reduce the energy consumption of end devices during data dissemination.In addition,the DAU protocol can effectively reduce decoding overhead while ensuring reliability.