The Application Analysis And Research Of GMSK Modulation System In Deep-Space

Deep-space communication has the characteristics of long communicationdistance, big transmission delay, and complex communication environment, and itscommunication channel is a typical band-limited and non-linear channel.With theincreasing traffic and the scarcity of spectrum resources, all of this promote theresearch and development of high-bandwidth efficiency and power-efficientmodulation technology.GMSK modulation has the characteristics of constant envelope,continuous phase,fast spectrum decay and the narrow frequency band of modulatedwave and so on.On the other hand, GMSK has a high bandwidth and power utilization,and it can effectively reduce adjacent channel interference, improve the efficiency ofnon-linear power amplifier,it is suitable for deep-space communication very much dueto these characteristics.In this paper,we mainly study GMSK continuous phase modulation techniqueadapt to deep-space communications.At first, deep-space communication channelcharacteristics and communication link have been studied, and the paper sums up thedeep-space communication with the characteristics of the long communicationdistance, the big signal propagation delay, the low receiver signal to noise ratio,introduce the concept of the GMSK signal, state representation, the phasecharacteristics, the grid state diagram as well as the modulator implementation.Then,this paper focuses on the research of coherent demodulation algorithm ofGMSK signal, and analysis the complexity of the Viterbi algorithm in chart form onthe basis of introducing maximum likelihood sequential detection principle detailedly.Studies show that the complexity of the Viterbi algorithm relate with the correlationlength L of the GMSK signal modulation.Therefore, according to the characteristicsof larger calculation and the high complexity of the MLSD algorithm, thedemodulation algorithm of the Laurent optimal detection and Laurent sub-optimaldetection of the GMSK signals been got by introducing Laurent algorithm and the Malgorithm, under the premise of considering the complexity and demodulationperformance, Laurent optimal detection combining with the M algorithm of theGMSK signal is described in this paper, the proposed new joint algorithm make Malgorithm taking the place of Viterbi algorithm, it can reduce the number of gridsearch, and simplify the GMSK coherent receiver from the aspect of the number ofmatched filter and each symbol calculation amount.The performance of the corresponding coherent demodulation algorithm is derived by computersimulation,and the indicators of the BER performance and complexity of overallsystem is studied.Finally, the application of wavelet denoising in GMSK communication system isdescribed in this paper, we study the selection of threshold rules, the wavelet function,wavelet decomposition level and so on detailly, a receiver for GMSK communicationsystem based on wavelet pretreatment program is presented, and it has been found thatthe scheme is feasible through the computer simulation.