Designing a Differential Frequency Hopping System with Hop Variable Frequency Transition Function

Differential frequency hopping (DFH) was introduced as a new technology for reliable high data rate transmission in high frequency (HF) bands. Since modulation, coding and frequency hopping are combined together with frequency transition function (FTF) in DFH system. However, it was shown by recent researchers that an intelligent eavesdropper may threat the security of the system by finding FTF and sending jamming signal toward authorized receivers. The root of this drawback is the poor 2-dimensional (2D) continuity of DFH sequence generated by constant FTF. In this paper, we propose a simple DFH system with hop variable FTF controlled by a synchronized scrambler and descrambler between receiver and transmitter. The 2D continuity performance of generated DFH patterns between constant FTF and hop variable FTF are tested and compared. Theoretical analysis and simulation results show that the DFH code generator which combines G with PN sequence increases security of DFH system without decreasing the SER performance.