Study On Synchronization Technology Under Low Signal-to-noise And Large Dynamic

In the face of the harsh and complex communication environment in deep space exploration, how to realize signal synchronization under low SNR and high dynamic is an important problem which must be faced in the deep space communication system. Low signal to noise ratio often leads to communication interruptions in deep space communication, which brings the reestablishment process of communication link. During the process receivers need to complete signal synchronization including multiple unknown modulation parameters’ estimation. But the demodulation process in Low signal to noise ratio is hard to realize quickly. However, the high dynamic condition makes parameters to be estimated change heavily in short-time,which makes the reestablishment process more difficult. Either of the two bad communication conditions has rigorous requirements to synchronization technology. And the two communication conditions have contradicting influence to synchronization system. Thus it is hard to realize synchronization with both conditions.The proposition of efficient encoding makes it possible to improve the performance of synchronization system in low signal to noise ratio environment. Synchronization technology aided by decoding information is the development direction of synchronization technology under bad environment in future. In this paper, taking deep space exploration as research background, taking Mars landing process in deep space communication as an application example, we select the code-aided synchronization algorithm as the basic way to study the received signal synchronization in view of the low signal-to-noise ratio and large dynamic communication conditions. In this paper through the analysis of low SNR and high dynamic application requirements and their effects on the received signal, the synchronization process is divided into three parts: carrier synchronization, timing synchronization, frame synchronization.In the carrier synchronization part, this paper divides carrier synchronization into two parts: coarse synchronization and fine synchronization process. This paper not only proposes an improved frequency shift average periodogram algorithm, but also designs twice estimation process to realize coarse synchronization. During fine synchronization process, the paper makes use of coded aided Costas loop to realize signal fine estimation under low signal to noise ratio.In bit synchronization part, this paper also divdes the process into two parts to make sure the estimation of bit bias in the range of all the symbol period. In this paper, the bit bias is first limited to half a symbol period range using partitioned search mode. Then code aided interative time synchronization algorithm is used to estimate the left time bias.In frame synchronization part, this paper introduces two code aided frame synchronization algorithm, and makes comparison between the algorithms by simulations. Finally, the hard decision frame synchronization is chose to frame offset estimation, considering algorithm performance and realization complexity.All the parts’ algorithm performace can reach communication system’s demand, making sure bit error rate lower than 310?when 0/ 2bE N ?dB.