| With the rapid development of today's communication technology,shortwave communication,an ancient and traditional communication method,has not been eliminated,on the contrary,it has attracted more and more attention from researchers at home and abroad.Compared with other communication methods,shortwave communication has the characteristics of long communication distance,strong anti-destroy ability,flexible use,and low communication cost,which makes it play an irreplaceable role in the communication field.With the growth of communication services and the diversification of communication application scenarios,the existing text and picture data transmission methods of the system and the reliability of link establishment cannot meet the needs of users.Based on the scientific research project "Development of New Shortwave Operation Service Terminals",a shortwave communication system data link layer protocol including real-time vocoding,new link establishment,and new detection frequency change has been designed and implemented.The main tasks completed are as follows:1.Describes the overall design framework of the system.The working status and physical layer waveform of the system are introduced in detail,and the hardware composition and software structure of the new shortwave communication system are given;2.For the purpose of efficient and real-time communication,the vocoding speech-to-digital transmission protocol is designed and implemented.In view of the problem that the transmission delay is too long and affects the user's communication experience,the synchronization header of the vocoding speech waveform is sent in advance,which effectively reduces the transmission delay.According to the characteristics of network port transmission and vocoding compression technology,the data preprocessing function of vocoding is designed to solve the problem of voice distortion;in order to meet the requirements of real-time transmission of vocoding,the data transmission process of realtime voice transmission is designed.3.During the link establishment process,the reliability of the data unit is critical to the performance of the link establishment function.A new burst waveform with better performance is adopted,and the data unit is redesigned;due to the change of the data unit,the link building protocol will also be changed accordingly;without affecting the normal function,the original The link establishment protocol was studied,and the good design ideas were extracted,and a new type of link establishment protocol was designed for the purpose of improving the reliability of link establishment.4.The time synchronization protocol must be simple and efficient,and must also consider the specific conditions of the two stations.In this regard,the time synchronization function is split into two functions: synchronization training and synchronization.Synchronous training uses the way of sending PDUs in whole seconds,which streamlines the original protocol process and improves the synchronization efficiency.Synchronization is suitable for time synchronization when communicating between two fixed locations.5.In order to improve the effectiveness and success rate of detection frequency update,a new detection frequency update protocol is designed.The selection of the self-use frequency group in the detection frequency is particularly important to the success of the frequency change.The original self-use frequency group and the frequency group to be detected are combined to design a more reasonable self-use frequency group selection scheme.During the link establishment phase of the detection frequency,a "dual-channel scanning reception" function was designed to improve the success rate of detection frequency.6.By building an indoor test platform and an outdoor actual line test platform,the realized functions were tested,and the test results were statistically analyzed to verify the correctness of the protocols such as real-time vocoding,new link establishment,and new detection frequency update. |
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