Design Of A Broadband Code-hopping Communication System And FPGA Implementation Of The Baseband

The security of direct sequence spread spectrum communication system is not a secret communication with the development of electronic countermeasure.In order to improve the security of direct sequence spread spectrum communication system,the code hopping technology is introduced.Based on the original direct spread sequence(DSSS)system,the code hopping technique adds a time-hopping spread spectrum code with the hopping pattern,which can effectively increase the anti-interception and security of the system.In this paper,the code hopping system is studied.A broadband code hopping communication system is designed and the baseband is implemented by FPGA.1.The selection of pseudorandom sequence is completed,and a method of generating balanced Gold sequence in real time is designed.Compared with the usual method of generating balanced Gold sequences the proposed method only need to store the optimal pairs of Gold sequences by adding judgment modules,and the number of spread spectrum codes in the code hopping system is greatly increased.2.The baseband of the transmitter is designed and implemented by FPGA,including the basic clock module,framing module,code hopping generation module,spread spectrum module,scrambling module and baseband modulation module.The length of the synchronous head is 16384 and the length of the spread spectrum code is 2048.The information transmission rate is 19.53 kbps.The correctness of the design is verified.3.The PMF-FFT algorithm used in the capture terminal is improved,and the length of shift register is reduced when the receiver performs correlation operation on the synchronous head by adopting the method of twice spread spectrum.The complexity of hardware implementation is reduced while the acquisition quality is guaranteed.The narrowband interference suppression module is added,and the narrowband interference suppression is realized by improving the windowing algorithm.The simulation results show that the module has a good effect on narrowband interference suppression.4.The baseband of the receiving terminal is designed and implemented by FPGA,which is mainly composed of carrier tracking module,code tracking module,descrambling solution and decision module,and the correctness of the scheme design is verified.