Research On Technique Of Modulation And Demodulation With Gaussian Minimum Shift Keying (GMSK) In Shortwave Frequency-Hopping System

The advantages of strong anti-interference, random address selection make shortwave frequency-hopping (FH) communication have a wide application in the areas of military. Modem FH communication system need transmit a mass of data, traditional modulations are no longer suitable for high-speed data transmitting in FH system due to low spectrum efficiency. Therefore, it has a practical significance to develop some fit methods of modulation with high spectrum efficiency for shortwave FH communication system.With the advantages of good spectrum utilization and power efficiency as well as noncoherent demodulation can be employed, GMSK (Gaussian Minimum Shift Keying) has been widely applied in the wireless system. It will be introduced for shortwave FH to implement high-speed data transmitting in this paper. Firstly, based on some digital modulation techniques used in shortwave FH system, main research is made on the principle, the method of generation and demodulation, characteristic of GMSK signal. Secondly, the design of the GMSK modulation based on the technique of DDS (Direct Digital Synthesis) has provided; the model of shortwave SFH/GMSK system is built in this paper. According to the feature of shortwave channel, a noncoherent demodulation methods based on the Viterbi algorithm is fouced on studing, and differential phase detection scheme based on the Viterbi algorithm is presented. Finally, the performance of this demodulation method under various conditions such as AWGN and Rayeigh fading are analysed by computer simulation.The simulation results show that the bit error rate of the differential phase detection scheme based on the Viterbi algorithm basically meet the requirement of shortwave communication. Forthermore, it is feasible to introduce the GMSK into the shortwave communication.