The Research On Performance Of Wavelet Thresholding Extracting Weak Signal In Deep Space Transmission Link

Since the beginning of twenty-first century, the deep space exploration as oneof the three major space activities plays an increasingly important role in theexploration of space resources in the universe space. But because of the extremelylong distance of the communication link, the received signal strength is very low.And at the same time, with the development of the deep space communication, thetransmission rate of precious science of remote sensing and telemetry data shouldbe as high as possible, which results in the received signal-to-noise-ratio beinglower than the receiver’s decoding threshold. And low SNR can not guarante highspeed and reliable transmission.Long distance transmission and high transfer rates cause low SNR, and on theone hand, in order to solve the problem of low SNR, we can use many methods toimprove the energy per bit of the received signal, such as increase the transmitpower to enhance the energy of the received signal or increase the antenna size toimprove the link gain. However, increasing the power of deep space communicationtransmission data or antenna size will bring a great price. So by increasing theenergy of received signal to improve the SNR of received signal is not desirable incurrent level of technological development and in short-term. On the other hand, wecan improve SNR by processing weak signal at algorithm level, and this method canreduce the impact of noise in the signal in short term and at a lower cost to achievea given rapid transmission of deep space remote sensing and telemetry data.Considering a variety of weak signal extraction algorithm, in which the weak signalcan be gathered in a number of sparse coefficients by wavelet transfom, and theenerge of noise will spread to all of the coefficients. So we can set a threshold, andthe coefficients which are lower than the threshold will be set to zero. Afterprocessing the signal, it will be able to subtracte noise from the weak signal, whichis very conductive to the extraction of weak signal of the deep spacecommunication.First this paper gives a brief introduction to the basic throry of wavelettransform, and then it gives a detail analysis of the feasibility of the waveletthresholding method to extract weak signal. And it comes to the conclusion that thethresholding method can extract weak signal on certain conditions. Then it give thedeep space communication relay link model which is suitable for current China·sdevelopment status. And then the method of deep space link power budget is given;After that it gives the selection method of relevant parameters in the waveletthresholding and it apply the parameters to deep space communication. The results show that the wavelet thresholding can effectively improve the carrier-to-noise-ratio,And taking into account the weak signal extraction engineering, the waveletthresholding method has been simplified, and then this paper compares theperformance between the simplified wavelet thresholding and the waveletthresholding method. And it comes to the conclusion that the performance of thewavelet thresholding is also as good as wavelet thresholding method. At last, thispaper gives hardware implementation of wavelet thresholding in detail. And itanalysis the power and resources of the hardware. This paper comes to theconclusion that the wavelet thresholding method can meet the weighth and powerrequirements of deep space communications well.