Design Of Data Link Layer Protocol For New HF Frequency Selection Communication Terminal

As a way to achieve long-distance communication without relying on infrastructure and relay equipment,HF communication has always played an irreplaceable role in the field of wireless communication.The research content of this paper is derived from the scientific research project "Development of New HF Frequency Selection Communication Terminal".The purpose of the research is to further improve link establishment efficiency,data transmission throughput,and data transmission security.The research method is to design and implement the data link layer protocol of the new HF frequency selection communication terminal based on the existing hardware equipment and some application software.The main contents of this paper are as follows: 1.Introduce the working state of the existing short-wave frequency selective communication terminal and the relationship between each working state.The existing hardware components and software framework of the HF frequency selection communication terminal are given.The automatic link establishment module and data transmission module which need to be improved,and the link protection module which need to be added are explained in the software structure.2.In order to improve the efficiency of link establishment,a time-sharing automatic link establishment protocol for data link layer is designed.Through the establishment of the ray transmission loss prediction model,the selection of the best working frequency set in different time periods is realized.The time-sharing synchronous scanning technology of each station is designed,so that the new HF frequency selection communication terminal can work on different optimal frequency sets all the time.Two automatic link establishment methods based on time-sharing synchronous scanning are designed.3.In accordance with the needs of users,in order to maximize the data transmission throughput under the premise of ensuring reliability,this paper designs a dual-frequency scanning data transmission protocol.The file preprocessing function for unified file format is designed,and the mechanism of circular buffer is designed for the transmission of large files.The data reliability transmission protocol is designed by using Cyclic Redundancy Check,selective retransmission and other methods.Through the theoretical research on diversity technology,a dual-frequency scanning data transmission protocol for time-division transmission on two frequencies is designed.4.In order to prevent malicious interception and attack of data during transmission,this paper designs a link protection protocol at the data link layer.The basic requirements of the new HF frequency selection communication terminal for link protection are analyzed.The RC4 stream encryption algorithm is chosen as the core algorithm of the link protection protocol.With the purpose of resisting active password cracking and passive retransmission attack,the key consisting of information such as time domain and frequency domain are designed.The link protection protocol that meets the practical application is designed.In the indoor test platform and the outdoor actual line test platform,the completed data link layer software is tested.The correctness and efficiency of the time-sharing automatic link establishment protocol,dual-frequency scanning data transmission protocol and link protection protocol are verified.