Research Of Access And Network Communication Methods MQTT Based For IOT Devices

The Internet of Things is a platform that is used for connecting and exchanging information between things or between people and things.In recent years,it has become an important research for countries to compete in the information industry.MQTT is a Client Server publish/subscribe messaging transport protocol.It is light weight,open,simple,and designed so as to be easy to implement.These characteristics make it as a potential standard communication protocol in the Internet of Things system.This subject originates from the project of “Intelligent Lighting Control System's Research and Application Demonstration Based on IoT Technology” in the lab where the author was studying.In this paper,a series of researches are carried out to solve the problems in Io T system engineering applications,such as on the network access and the cloud platform access for devices,and the communication methods under many complex relationships between devices.The main work of this article is summarized as follows:(1)Aiming at the problem of network access of Wi-Fi devices in IoT system,a method of using UDP multicast to transfer the name and password of wireless network access point is proposed.Based on the analysis of the 802.11 data frame format,the method that use the data frame length and the destination MAC address in the frame header of the 802.11 data frame to encode the configuration information is proposed.The device is set to work in listening mode to capture 802.11 data packet and parse the information of wireless network access point.(2)For the requirement of devices access to cloud platform,the cloud platform access procedures and verification methods for terminal devices have been formulated to ensure the legal and secure access of devices.The devices access the RESTful API interface provided by the cloud platform through the HTTP protocol for authentication,and establishes communication with the MQTT server according to the verification results.(3)Aiming at the complex communication relationships among devices in the IoT system,and considering the questions that use the publish/subscribe methods which are based on topic to realize the communication between devices have some problems,the method for quickly and easily establishing a communication relationship between devices is proposed by establishing a topic mapping table.The method can realize the decoupling of the communication relationship between devices,and can ensure the flexible modification when the coupling relationships are changed.(4)The development of the terminal equipment was completed.The design of the hardware part with the STM32F429VIT6 as the main controller and the EMW1062 as the Wi-Fi communication module was determined.On this basis,the hardware design of the power supply circuit and the Wi-Fi communication circuit was completed.On the software part,the implementation of service programs such as device network access,cloud platform access,and MQTT communication has been completed with the transplanting of FreeRTOS real-time operating system and the LWIP network protocol stack.After completing the research and design of the system,a system test platform was set up to test various functions such as Wi-Fi access of IoT terminal devices,communication with cloud platform,and communication between devices.The results show that the Wi-Fi access configuration technology studied in this thesis can achieve the network access of the devices conveniently and effectively.The terminal device communication method based on MQTT that is proposed in this paper can realize the communication between devices reliably and flexibly.This methods can meet the communication needs of the Io T system.