Research On Highly Accurate Speed-Measuring For DS-FFH/MSK TT&C

Hybrid spread-spectrum TT&C had the features such as low signal to noise ratio, and large Doppler frequency shift (S-band carrier Doppler frequency up to±150 KHz and above). Compared with the ordinary hybrid spread spectrum communication systems, hybrid spread-spectrum TT&C needed to take the task of measuring the speed and the distance. In deep space measurement tasks, the weak signal, space transport time would be extended, if the coherent measurement was carried out, the relay satellite would be needed for the coherent transmission, which will undoubtedly increase the design difficulties of the relay satellite transponder. In this situation, the study of non-coherent high-precision Doppler speed measurement methods is becoming increasingly important. This article was intended primarily for the studies and simulations of the DS-FFH/MSK hybrid spread-spectrum TT&C under the low signal to noise ratio and large Doppler frequency shift measurement environments, the main point was about the Doppler frequency's high accurate measuring of speed measurement.First, based on the research and analysis of Doppler frequency speed measurement principles, DS-FFH/MSK hybrid spread-spectrum TT&C, and the low signal to noise ratio, large Doppler frequency shift the system had to face was analyzed. With the SystemVue software, the simulation platform was built, by carrying out the simulation and analysis of direct spread (DS), Fast FH (FFH) module, and MSK modulation demodulation module, it was known that the designed module could work normally and meet requirements.Secondly, a detailed analysis of Fast FH (FFH) time phase distortion which caused the signal to noise ratio was made, the corresponding expression was derived, and the different parameters of the synthesizer under different frequency were listed out. On this basis, the signal to noise ratio losses of released signal influenced by the phase Shivering was clear, the simulation results were given as well as its detailed analysis, and the method of how to suppress the influences to the speed measurement caused by the FFH phase distortion was also summed up, finished all the above work without increasing the system overhead.Finally, analyzed the situation of with the presence of large Doppler frequency shift and without the presence of large Doppler frequency shift, the different effects; analyzed direct spread (DS) second dimension search algorithm which based on the FFT Doppler frequency movement, pointed out its limitations is:in frequency domain influenced by the symbol jump, range attenuation and frequency points offset will happen. The method of Doppler frequency movement speed measurement based on FFT was designed:by increased I,Q two road signals calculation amount, the signal which not affected by the symbol jump was made, work on the signal by FFT, sought the Doppler frequency estimated value by peak points, completed the speed measurement; as to the several key issues, such as code phase transition, signal length, FFT spectrum losses, were analyzed in details and the improved methods were also given, the simulation results and measurement accuracy could be achieved were given in details. Simulation results showed that this method could effectively solved the problems happened in low signal to noise ratio and large Doppler shift conditions, the question of DS-FFH/MSK hybrid spread-spectrum TT&C Signal's Doppler frequency measurement could be solved, and the accuracy wasΔν= 0.11m/s.