Reaserch On The Communication Technology Of Attitude And Heading Reference System Based On LwIP

In recent years,with the application of the attitude and heading reference system more and more widely,the mid-high-end attitude and heading reference system plays an important role in different scenarios and the performance of real-time computing speed,attitude data accuracy and so on has been continuously improved.The traditional attitude and heading reference system is based upon serial communication.Due to the limitation of serial communication(transmission speed,transmission distance,etc.),the attitude and heading reference system cannot guarantee the timely transmission of realtime attitude data in all fields.Therefore,this thesis proposes the design of the attitude and heading reference system based upon ethernet communication.While improving transmission mode,the author considered the limitation that LwIP protocol stack itself is not designed for a specific embedded environment.Then put forward further modification of the protocol stack.This thesis mainly completed the following tasks:(1)This thesis put forward the design plan of the attitude and heading reference system based on the LwIP protocol stack and set up STM32F4 as the microcontroller of hardware platform,which transplants the LwIP protocol stack and designs attitude fusion algorithm(Kalman filter algorithm and Madgwick algorithm),thus realizing the real-time transmission function of attitude data through ethernet communication.Firstly,the composition of the lw IP protocol stack and related communication mechanism are introduced.And the part of the mechanism which is not suitable for the application of heading and attitude reference system is analyzed;Then proposes an improved plan and carries out simulation verification for the inapplicability;Next,in the building part of software and hardware platform of the attitude and heading reference system,three-axis accelerometer,three-axis gyroscope,three-axis magnetic sensor and the chip selection and hardware circuit design of Ethernet chip are studied.Meanwhile,the software platform is built;Finally,the feasibility of the improved scheme is verified by actual test.(2)This thesis presented an improved scheme for the limitation in the application of LwIP protocol stack.Firstly,the optimal choice of cwnd initial window is verified by NS2 software simulation.Through formula derivation and NS2 simulation data analysis of multiple bandwidth delay product networks,the initial value of the original slow start algorithm is changed from 1*MSS to 3*MSS;secondly,congestion avoidance algorithm is improved,and an improved scheme of reasonably choosing cwnd value according to the system retransmission times is proposed,thus solving the problem that traditional algorithm would re-enter the slow start algorithm once the packet is lost,and the feasibility of the improved scheme was verified by NS2 simulation;next,the data transfer flow of LwIP protocol stack is optimized,which simplify the flow of data transmission within the LwIP protocol stack,thus improving the efficiency of data transmission;finally,the clipping to the protocol stack itself is proposed to reduce the usage of useless protocols to the memory resource of the microcontroller.(3)The improved scheme is verified by measurement.By Wireshark analysis of the measured data,the results of the test show that the improved scheme can effectively improve the throughput stability of the system data;the feasibility of the optimization scheme of the data transmission flow is verified by the actual data of the data increase in the time series of Wireshark and Stevens.The results show that the data transmission is improved effectively;finally,the LwIP clipping and the stability of system functions are tested.After a comprehensive analysis of the data,it shows that the improved LwIP protocol stack can maintain more stable network throughput while occupying less memory,and the system can run steadily for a long time.