Research On Key Techniques Of Shortwave FH/GMSK Communication

Gaussian minimal shift keying is one of the modern modulate technique with high efficiency, eminent utilization of the spectrum resource, and strong anti-multipath and anti-fading ability. Because of small radiation beyond band wide and noncoherent demodulation ability, GMSK has been wildly applied in the wireless system.Combining GMSK with shortwave frequency-hopping system in this thesis has two purposes: first, implementing high-speed data transmitting system with GMSK; second, enhancing the anti-interference ability of the whole system with frequency-hopping technique.At the first part of this thesis, we introduce the frequency-hopping communication system and give a math model of shortwave slow frequency-hopping system with GMSK technique. Second, we research the simulation and implementation of the GMSK modulator and also give its structure in FPGA using the method of restoring orthogonal waveform. Then, we give the 1 bit differential demodulation simulation result based on Viterbi algorithm. The experimental simulation result indicated that the bit error rata of 1 bit differential demodulation based on Viterbi algorithm can satisfy the requirement of the shortwave communication system, thus we interpret the feasibility of using GMSK in shortwave system. Finally, we study the synchronized technology in the frequency-hopping system and mainly introduce frequency-hopping pattern synchronization. This thesis uses synchronization of the head frame to realize the frequency-hopping pattern synchronization. In this part, we combing the catch and trace method in one cycle, and give the implementation of PN synchronization cycle structure in FPGA.