Research And Implementation On Key Technologies Of Hybrid Hopping Spread Spectrum Communication System

Hybrid frequency hopping spread spectrum technology is a communication technology that combines direct sequence spread spectrum and frequency hopping spread spectrum.Because of its stronger anti-jamming and safety,it has been widely used in the field of aerospace TT&C.With the development of electronic countermeasure technology,the indicator of hybrid hopping spread spectrum communication system is constantly updated.At present,the spread spectrum code with a high bit rate and long period and the carrier with high hop rate,large bandwidth,and multiple frequency points have become the new indicator of the hybrid hopping spread spectrum system.At present,the spread spectrum code with a high bit rate and long period and the high-quality frequency hopping carrier with the fast hop,large bandwidth,and multiple frequency points have become the new indicators of the hybrid hopping spread spectrum system.The update of the indicators has significantly improved the system performance but also increased the difficulty of the system design.The method of using a single-channel direct digital synthesis(DDS)to generate a high-quality frequency hopping carrier will occupy a lot of hardware resources,which will limit the design of other parts of the system and affects the performance of the system.The difference between the system uplink clock and downlink clock will produce errors,and these errors will show the characteristics of fast change and large fluctuation due to the high dynamic characteristics of the system signal.The use of the previous tracking synchronization technology to compensate for such high dynamic errors is easy to produce the phenomenon of loop lock loss,and leading to the failure of the system synchronization.In this paper,the overall structure of the system is designed,and two solutions to the above two problems are studied.The results are simulated by MATLAB tools and Model Sim tools,and the system is realized by FPGA.The main research contents of this paper are as follows:1.According to the current hybrid hopping spread spectrum communication system indicators,the overall system is designed,the basic structure and implementation process of each part are described,and simulation experiments are carried out on each part through simulation tools.2.To solve this problem that the generation of high-quality frequency hopping carriers will take up a lot of hardware resources,a bidirectional multi-channel structure of the fast frequency hopping carrier generation method is developed.In this method,a high-quality frequency hopping carrier is generated by parallel DDS,and the two-way frequency hopping algorithm is combined with the high frequency IF carrier generated by the DAC module to realize the bidirectional frequency hopping with IF carrier frequency as the central frequency point.The results are analyzed by Modelsim tool,Matlab tool,and upper computer interface.The results show that this method can effectively reduce the consumption of system hardware resources based on ensuring the quality of the original frequency hopping carrier.Compared with one-way frequency hopping,the Block memory bits resources of the system can be saved by 53%,leaving space for the design of other parts of the system.3.To solve this problem that the compensation speed of the traditional feedback loop cannot keep up with the synchronization failure caused by the error change speed of the current hybrid hopping spread spectrum communication system,a hybrid hopping spread spectrum signal tracking synchronization method based on coordinate rotation digital computer(CORDIC)algorithm is developed.In this method,the carrier synchronization error and timing synchronization error are mapped to the phase,and the error is compensated by two-dimensional rotation.According to the BPSK modulation property,the optimal rotation position and compensation error are determined to realize the system synchronization.Through the analysis of the simulation results,it is proved that this method can effectively compensate the timing synchronization error and carrier synchronization error of the system under the condition of the system frequency hopping rate of 20000 hops per second and the frequency hopping bandwidth of 327.52 MHz.Compared with the traditional feedback loop compensation technology,the performance of this method has obvious advantages.