Researches On Signal Acquisition And Tracking Method In BDS

The global navigation satellite system(GNSS),such as GPS,Galileo,Beidou System(BDS)of China,etc.,is playing a great role in navigation and communication in all domain,which particularly means a lot in the future development of civil aviation industry.It is a promising trend.However along with this trend,the traditional modulation methods cannot meet the increasing needs facing the frequency band congestion.Thus,the Binary Offset Carrier(BOC)modulation method,which is able to shift and share the frequency band,has been proposed.But meanwhile this method brings a new problem since it changes the traditional signal characteristics,making the signal receiving and processing process much more difficult.Compared with traditional modulation methods,the BOC modulation induces a multi-peak phenomenon,producing side peaks whose amplitudes are very close to the main peak,causing ambiguity during signal acquisition and tracking process.This paper analyzes the basic theory of the BOC modulation,introduces its generation,acquisition and tracking program in order to find a breakthrough point of the BOC signal process algorithm.Combining the characteristics of Beidou signals and the parameters of BOC modulation,some simulations of the existing algorithm are made and analyzed to find their advantages and disadvantages.After that,some general features are concluded: the auto-correlation functions(ACF)of BOC signals are symmetrical and periodical;the ACFs of the original BPSK signals could be approximately regarded as an envelope of them,etc..According to these features,this paper proposes an unambiguous acquisition scheme for all kinds of BOC signals by constituting a synthesis supplemental correlation function(SSCF)to eliminate side peaks while keep the single narrow main peak of the BOC ACF.By applying this scheme,the ambiguity problem caused by BOC modulation is well solved.Finally,it is compared with other methods especially with the BPSK-like method.