| The advantages of strong anti-interference, random address selection make slow frequency-hopping (SFH) communication have a wide application in the areas of military and mobile communication. Modern 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.The combination of costant envelope and high spectral efficiency makes the Gaussian minimum-shift keying(GMSK) modulation scheme highly popular in the wireless system. It will be introduced for shortwave SFH to implement high-speed data transmitting in this paper.Firstly, based on some digital modulation techniques used in shortwave SFH system, main research is made on the principle, the method of generation and demodulation, characteristic of GMSK signal.Secondly, the model of shortwave SFH/GMSK system is built in the Simulink. It is known that B_bT_b makes the modulation scheme even more bandwidth-efficient at the price of increased intersymbol interference(ISI) and Viterbi algorithm can be used to improve the performance in the presence of ISI,so two noncoherent demodulation methods based on the Viterbi algorithm is fouced on studing, and differential phase detection(DPD) scheme and limiter discriminator detection(LDD) scheme based on the Viterbi algorithm is presented.Finally, the performance of this demodulation method under various conditions such as Gaussian channel and Rayeigh fading are analysed by computer simulation. |
PDF Full Text Request