Snr Estimation In Deep Space Communications And Timing Synchronization Technology Research

In communication systems, the knowledge of the signal to noise ratio (SNR) isusually needed to be known beforehand for many signal processing modules andalgorithms in order to get the best system performance, such as power control, decodingand adaptive modulation etc. And it’s also a key issue in communication systems thatthe receiver can accurately sample signals for the sake of reducing inter symbolsinterference (ISI) and lowering bit error rate (BER). At present, there are manyalgorithms about the estimation of the SNR and the timing synchronization, and themethods based maximum likelihood (ML) estimation and the exceptation maximum(EM) parameter estimation will be discussed in this thesis，which could be combinedwith the posteriori probability information from the decoder to estimate the parametersiteratively. And these methods based on Code Aid(CA), not only have higher estimationaccuracy, but also can be adapt to the low SNR circumstance.One of the characteristics of deep-space communication is long distancetransmission, causing the extreme low SNR at the receiver. Therefore, it’s greatimportant to research the SNR estimation algorithm and timing synchronization schemefor the receiver which has the requirements of high sensitivity in low SNR environment.For the SNR estimation algorithm and timing synchronization scheme, the mainresearch content and the innovations in this thesis are introduced as follows:The first part, the SNR estimation method of DA and NDA based on the MLalgorithm will be introduced respectively, then focus on the SNR estimation methodbased on ML algorithm and EM theory, then combine with the decoding softinformation to update the iterative process of SNR estimation in the coding system.Finally, in accordance with the channel environment of the deep space communication,the ML-DA of the pilot sequence could be jointed with the code aided estimation of theSNR to estimate the SNR, which has achieved better performance at low BER.The second part mainly studies the timing synchronization scheme based the EMtheory, which makes use of the interpolation method to obtain the approximatelyoptimal sampling point and then combines with the probability information from the decoder. Finally, a timing synchronization scheme jointing the cycle-slip detection isproposed, which could be applied to the deep space communication and solve theincidental cycle-slip phenomenon while estimating the sampling error,and be tested bythe simulation.