Research Of Satellite-based AIS Receiver Based On USRP B210

The satellite-based AIS receiver is faced with many challenges,such as large transmission delay,serious collision of messages,low SNR and large Doppler frequency offset and so on.According to above challenges,this thesis mainly studies the key technology of satellite-based AIS receiver,and proposes a new design scheme of satellite-based AIS receiver.The system is established in universal software radio platform,and its performance is tested with experimental instruments.The main work of this thesis is as follows:(1)The key technology of satellite-based AIS receiver is studied,A new design scheme of satellite-based AIS receiver is presented.USRP and GNU Radio are used as hardware and software platform of AIS system.The basic principle of each signal processing algorithm is analyzed in detail,and its simulation results are given.In particular,traditional frequency estimation algorithm based on FFT can not satisfy the need of satellite-based AIS systems,and an improved self correlation-FFT algorithm is proposed.Improved algorithm is obtained on basis of frequency offset estimation algorithm based on FFT and sign of frequency offset,and it enlarges the frequency offset estimation range and realizes the large Doppler frequency offset estimation.The simulation results show that range of frequency offset estimation is extended and estimation accuracy is high.(2)The realization and passed test of satellite-based AIS receiver.The RF signal is received and converted into base-band by USRP.Then,base-band signal is transmitted to computer via USB cable for parameter estimation,demodulation and other signal processing.The modules,implementing algorithm of processing signal,are constructed by C++ and the system is constructed so that the signals transmitted to the computer can be correctly processed in GNU Radio.(3)The performance of satellite-based AIS system is tested by simulating signal.Test results show that system can solve time-slot conflict to a certain extent and accurately estimate the large Doppler frequency offset.At the same time,in order to capture and process signal in real time and accurately,it is necessary to accurately find tarting point of a time slot in order to divide data stream into time slots.Therefore,based on principle of time tag,a time slot partition algorithm based on time stamp is proposed.Time slot of first sampling point of received signal is judged by obtaining time information,and starting point of next slot is found accurately.Test results show,algorithm can accurately find starting point of a time slot,so that data stream can be accurately partitioned and system can process signals in real time and correctly.