Design And Implementation Of A Data Link Layer Protocol For HF Communication System

HF communication,also known as High-frequency(HF)communication,uses a frequency range of 3-30 MHz.Due to its sky-wave transmission characteristics,it occupies an unreplaceable position in the communications field for other means of communication.The research content of this thesis comes from scientific research project "HF dual-frequency intelligent transceiver verification system".The design goal of this project is to realize a "HF frequency selection and communication system" with functions such as short-wave automatic frequency selection,link establishment,data transmission and link protection.Based on the existing foundation of the laboratory,the data link layer protocol of the system is studied in this thesis.The data transmission,frequency update,and link protection functions in that protocol are designed and implemented.The main work and content of this thesis are as follows:1.Combining with the project requirements,in order to improve the throughput of data transmission under the premise of guaranteeing reliability,a dual-frequency data transmission protocol is designed based on the analysis of the single-frequency data transmission method,and the dual-frequency time-sharing transmission mode in that protocol is implemented in this thesis.A file breakpoint retransmission function is Designed and implemented;an initial rate adaptation method,a loop buffer mechanism,and an adaptive rate changing method are redesigned and implemented.2.The time-varying characteristics of the HF channel will cause the optimal frequency changed.After the link is established,in order to adapt the operating frequency of this system to this change,based on the analysis of the HF adaptive technology,a frequency update protocol that updates the operating frequency of the system is designed and implemented in this thesis,the protocol is designed in the combination of prediction and detection.3.In order to prevent malicious monitoring and interference from outside,a link protection protocol of the system is designed and implemented in this thesis.Based on the study of the standard encryption method of Data Encryption Standard(DES),a 24-bit electronic codebook(ECB)mode encryption algorithm is designed,the algorithm realizes the concealment of data information without affecting the normal communication of the system.Through algorithm tests and system tests indicated that,the encryption algorithm can achieve the goal of completely encrypting data,increasing the security of the system,and will not affect the normal communication of the system.4.After all the hardware and software of the entire system was completed,the joint tests were conducted indoor and outdoor.HF radio stations and channel simulation equipment which developed by laboratory is used for Indoor experiments,and outdoor circuit test sites and HF channel equipment are provided by Project commissioner.Through testing and analysis,the validity of dual-frequency data transmission,adaptive rate changing,file breakpoint retransmission and frequency update is verified.At present,the scientific research project of the laboratory has reached the requirements of the Project commissioner and entered the project delivery phase.