Research On Modulation & Demodulation And Speech Coding In Frequency-hopping Radio

In order to keep information transfer accurate and up-to-date under conditions of combat and disaster relief, Frequency-hopping Radio becomes more and more important. As the existence of enemy jamming on the battlefield and the variation of the natural environment of disaster area, Frequency-hopping Radio should transfer voice with enough performance against bit errors and compatible with Civilian equipment. So a suitable speech coding should be selected and higher requirements for modulation and demodulation scheme must be met.Firstly, the Hardware platform is described, and the GMSK is proved to be superior in the high frequency roll-off areas and the spectrum efficiency through comparison of the FSK, MSK and GMSK schemes. As a conclusion it is feasible of GMSK modulation to apply in Frequency-hopping communication system. Secondly, a GMSK modulation algorithm based on DDS&DSP and a 2-bit differential demodulation algorithm based on DSP are proposed. In order to enable Frequency-hopping Radio to be compatible with FM, achieve real-time communication with Civilian equipment in the special period, an FM modulation algorithm based on DDS&DSP is also presented. The correctness of the algorithm is verified by non-coherent demodulation. Finally, we make an intensive study of the CVSD Speech Coding, and it needs to optimize the various encoding parameters with feasible method under the condition of Fixed-point DSP. The output SNR meets the technical requirements after using the CVSD Speech Coding with optimized parameters in the voice transmission system.